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75 results on '"Gogineni, S."'

1. Antarctic Bedmap data: Findable, Accessible, Interoperable, and Reusable (FAIR) sharing of 60 years of ice bed, surface, and thickness data

Author

Frémand, A. C., Fretwell, P., Bodart, J. A., Pritchard, H. D., Aitken, A., Bamber, J. L., Bell, R., Bianchi, C., Bingham, R. G., Blankenship, D. D., Casassa, G., Catania, G., Christianson, K., Conway, H., Corr, H. F. J., Cui, X., Damaske, D., Damm, V., Drews, R., Eagles, G., Eisen, O., Eisermann, H., Ferraccioli, F., Field, E., Forsberg, R., Franke, S., Fujita, S., Gim, Y., Goel, V., Gogineni, S. P., Greenbaum, J., Hills, B., Hindmarsh, R. C. A., Hoffman, A. O., Holmlund, P., Holschuh, N., Holt, J. W., Horlings, A. N., Humbert, A., Jacobel, R. W., Jansen, D., Jenkins, A., Jokat, W., Jordan, T., King, E., Kohler, J., Krabill, W., Kusk Gillespie, M., Langley, K., Lee, J., Leitchenkov, G., Leuschen, C., Luyendyk, B., MacGregor, J., MacKie, E., Matsuoka, K., Morlighem, M., Mouginot, J., Nitsche, F. O., Nogi, Y., Nost, O. A., Paden, J., Pattyn, F., Popov, S. V., Rignot, E., Rippin, D. M., Rivera, A., Roberts, J., Ross, N., Ruppel, A., Schroeder, D. M., Siegert, M. J., Smith, A. M., Steinhage, D., Studinger, M., Sun, B., Tabacco, I., Tinto, K., Urbini, S., Vaughan, D., Welch, B. C., Wilson, D. S., Young, D. A., Zirizzotti, A., Frémand, A. C., Fretwell, P., Bodart, J. A., Pritchard, H. D., Aitken, A., Bamber, J. L., Bell, R., Bianchi, C., Bingham, R. G., Blankenship, D. D., Casassa, G., Catania, G., Christianson, K., Conway, H., Corr, H. F. J., Cui, X., Damaske, D., Damm, V., Drews, R., Eagles, G., Eisen, O., Eisermann, H., Ferraccioli, F., Field, E., Forsberg, R., Franke, S., Fujita, S., Gim, Y., Goel, V., Gogineni, S. P., Greenbaum, J., Hills, B., Hindmarsh, R. C. A., Hoffman, A. O., Holmlund, P., Holschuh, N., Holt, J. W., Horlings, A. N., Humbert, A., Jacobel, R. W., Jansen, D., Jenkins, A., Jokat, W., Jordan, T., King, E., Kohler, J., Krabill, W., Kusk Gillespie, M., Langley, K., Lee, J., Leitchenkov, G., Leuschen, C., Luyendyk, B., MacGregor, J., MacKie, E., Matsuoka, K., Morlighem, M., Mouginot, J., Nitsche, F. O., Nogi, Y., Nost, O. A., Paden, J., Pattyn, F., Popov, S. V., Rignot, E., Rippin, D. M., Rivera, A., Roberts, J., Ross, N., Ruppel, A., Schroeder, D. M., Siegert, M. J., Smith, A. M., Steinhage, D., Studinger, M., Sun, B., Tabacco, I., Tinto, K., Urbini, S., Vaughan, D., Welch, B. C., Wilson, D. S., Young, D. A., and Zirizzotti, A.

Abstract

One of the key components of this research has been the mapping of Antarctic bed topography and ice thickness parameters that are crucial for modelling ice flow and hence for predicting future ice loss and the ensuing sea level rise. Supported by the Scientific Committee on Antarctic Research (SCAR), the Bedmap3 Action Group aims not only to produce new gridded maps of ice thickness and bed topography for the international scientific community, but also to standardize and make available all the geophysical survey data points used in producing the Bedmap gridded products. Here, we document the survey data used in the latest iteration, Bedmap3, incorporating and adding to all of the datasets previously used for Bedmap1 and Bedmap2, including ice bed, surface and thickness point data from all Antarctic geophysical campaigns since the 1950s. More specifically, we describe the processes used to standardize and make these and future surveys and gridded datasets accessible under the Findable, Accessible, Interoperable, and Reusable (FAIR) data principles. With the goals of making the gridding process reproducible and allowing scientists to re-use the data freely for their own analysis, we introduce the new SCAR Bedmap Data Portal (https://bedmap.scar.org, last access: 1 March 2023) created to provide unprecedented open access to these important datasets through a web-map interface. We believe that this data release will be a valuable asset to Antarctic research and will greatly extend the life cycle of the data held within it. Data are available from the UK Polar Data Centre: https://data.bas.ac.uk (last access: 5 May 2023​​​​​​​). See the Data availability section for the complete list of datasets.

Published
2023

2. Holocene deceleration of the Greenland Ice Sheet.

Author

MacGregor, Joseph A, MacGregor, Joseph A, Colgan, William T, Fahnestock, Mark A, Morlighem, Mathieu, Catania, Ginny A, Paden, John D, Gogineni, S Prasad, MacGregor, Joseph A, MacGregor, Joseph A, Colgan, William T, Fahnestock, Mark A, Morlighem, Mathieu, Catania, Ginny A, Paden, John D, and Gogineni, S Prasad

Abstract

Recent peripheral thinning of the Greenland Ice Sheet is partly offset by interior thickening and is overprinted on its poorly constrained Holocene evolution. On the basis of the ice sheet's radiostratigraphy, ice flow in its interior is slower now than the average speed over the past nine millennia. Generally higher Holocene accumulation rates relative to modern estimates can only partially explain this millennial-scale deceleration. The ice sheet's dynamic response to the decreasing proportion of softer ice from the last glacial period and the deglacial collapse of the ice bridge across Nares Strait also contributed to this pattern. Thus, recent interior thickening of the Greenland Ice Sheet is partly an ongoing dynamic response to the last deglaciation that is large enough to affect interpretation of its mass balance from altimetry.

Published
2016

3. A synthesis of the basal thermal state of the Greenland Ice Sheet.

Author

MacGregor, Joseph A, MacGregor, Joseph A, Fahnestock, Mark A, Catania, Ginny A, Aschwanden, Andy, Clow, Gary D, Colgan, William T, Gogineni, S Prasad, Morlighem, Mathieu, Nowicki, Sophie MJ, Paden, John D, Price, Stephen F, Seroussi, Hélène, MacGregor, Joseph A, MacGregor, Joseph A, Fahnestock, Mark A, Catania, Ginny A, Aschwanden, Andy, Clow, Gary D, Colgan, William T, Gogineni, S Prasad, Morlighem, Mathieu, Nowicki, Sophie MJ, Paden, John D, Price, Stephen F, and Seroussi, Hélène

Abstract

The basal thermal state of an ice sheet (frozen or thawed) is an important control upon its evolution, dynamics and response to external forcings. However, this state can only be observed directly within sparse boreholes or inferred conclusively from the presence of subglacial lakes. Here we synthesize spatially extensive inferences of the basal thermal state of the Greenland Ice Sheet to better constrain this state. Existing inferences include outputs from the eight thermomechanical ice-flow models included in the SeaRISE effort. New remote-sensing inferences of the basal thermal state are derived from Holocene radiostratigraphy, modern surface velocity and MODIS imagery. Both thermomechanical modeling and remote inferences generally agree that the Northeast Greenland Ice Stream and large portions of the southwestern ice-drainage systems are thawed at the bed, whereas the bed beneath the central ice divides, particularly their west-facing slopes, is frozen. Elsewhere, there is poor agreement regarding the basal thermal state. Both models and remote inferences rarely represent the borehole-observed basal thermal state accurately near NorthGRIP and DYE-3. This synthesis identifies a large portion of the Greenland Ice Sheet (about one third by area) where additional observations would most improve knowledge of its overall basal thermal state.

Published
2016

4. Holocene deceleration of the Greenland Ice Sheet.

Author

MacGregor, Joseph A, MacGregor, Joseph A, Colgan, William T, Fahnestock, Mark A, Morlighem, Mathieu, Catania, Ginny A, Paden, John D, Gogineni, S Prasad, MacGregor, Joseph A, MacGregor, Joseph A, Colgan, William T, Fahnestock, Mark A, Morlighem, Mathieu, Catania, Ginny A, Paden, John D, and Gogineni, S Prasad

Abstract

Recent peripheral thinning of the Greenland Ice Sheet is partly offset by interior thickening and is overprinted on its poorly constrained Holocene evolution. On the basis of the ice sheet's radiostratigraphy, ice flow in its interior is slower now than the average speed over the past nine millennia. Generally higher Holocene accumulation rates relative to modern estimates can only partially explain this millennial-scale deceleration. The ice sheet's dynamic response to the decreasing proportion of softer ice from the last glacial period and the deglacial collapse of the ice bridge across Nares Strait also contributed to this pattern. Thus, recent interior thickening of the Greenland Ice Sheet is partly an ongoing dynamic response to the last deglaciation that is large enough to affect interpretation of its mass balance from altimetry.

Published
2016

5. A synthesis of the basal thermal state of the Greenland Ice Sheet.

Author

MacGregor, Joseph A, MacGregor, Joseph A, Fahnestock, Mark A, Catania, Ginny A, Aschwanden, Andy, Clow, Gary D, Colgan, William T, Gogineni, S Prasad, Morlighem, Mathieu, Nowicki, Sophie MJ, Paden, John D, Price, Stephen F, Seroussi, Hélène, MacGregor, Joseph A, MacGregor, Joseph A, Fahnestock, Mark A, Catania, Ginny A, Aschwanden, Andy, Clow, Gary D, Colgan, William T, Gogineni, S Prasad, Morlighem, Mathieu, Nowicki, Sophie MJ, Paden, John D, Price, Stephen F, and Seroussi, Hélène

Abstract

The basal thermal state of an ice sheet (frozen or thawed) is an important control upon its evolution, dynamics and response to external forcings. However, this state can only be observed directly within sparse boreholes or inferred conclusively from the presence of subglacial lakes. Here we synthesize spatially extensive inferences of the basal thermal state of the Greenland Ice Sheet to better constrain this state. Existing inferences include outputs from the eight thermomechanical ice-flow models included in the SeaRISE effort. New remote-sensing inferences of the basal thermal state are derived from Holocene radiostratigraphy, modern surface velocity and MODIS imagery. Both thermomechanical modeling and remote inferences generally agree that the Northeast Greenland Ice Stream and large portions of the southwestern ice-drainage systems are thawed at the bed, whereas the bed beneath the central ice divides, particularly their west-facing slopes, is frozen. Elsewhere, there is poor agreement regarding the basal thermal state. Both models and remote inferences rarely represent the borehole-observed basal thermal state accurately near NorthGRIP and DYE-3. This synthesis identifies a large portion of the Greenland Ice Sheet (about one third by area) where additional observations would most improve knowledge of its overall basal thermal state.

Published
2016

6. Antarctic firn compaction rates from repeat-track airborne radar data: I. Methods

Author

Medley, B., Ligtenberg, S. R. M., Joughin, I., van den Broeke, M. R., Gogineni, S., Nowicki, S., Medley, B., Ligtenberg, S. R. M., Joughin, I., van den Broeke, M. R., Gogineni, S., and Nowicki, S.

Abstract

While measurements of ice-sheet surface elevation change are increasingly used to assess mass change, the processes that control the elevation fluctuations not related to ice-flow dynamics (e.g. firn compaction and accumulation) remain difficult to measure. Here we use radar data from the Thwaites Glacier (West Antarctica) catchment to measure the rate of thickness change between horizons of constant age over different time intervals: 2009–10, 2010–11 and 2009–11. The average compaction rate to ~25 m depth is 0.33 m a–1, with largest compaction rates near the surface. Our measurements indicate that the accumulation rate controls much of the spatio-temporal variations in the compaction rate while the role of temperature is unclear due to a lack of measurements. Based on a semi-empirical, steady-state densification model, we find that surveying older firn horizons minimizes the potential bias resulting from the variable depth of the constant age horizon. Our results suggest that the spatiotemporal variations in the firn compaction rate are an important consideration when converting surface elevation change to ice mass change. Compaction rates varied by up to 0.12 m a–1 over distances <6 km and were on average >20% larger during the 2010–11 interval than during 2009–10.

Published
2015

7. Radiostratigraphy and age structure of the Greenland Ice Sheet.

Author

MacGregor, Joseph A, MacGregor, Joseph A, Fahnestock, Mark A, Catania, Ginny A, Paden, John D, Prasad Gogineni, S, Young, S Keith, Rybarski, Susan C, Mabrey, Alexandria N, Wagman, Benjamin M, Morlighem, Mathieu, MacGregor, Joseph A, MacGregor, Joseph A, Fahnestock, Mark A, Catania, Ginny A, Paden, John D, Prasad Gogineni, S, Young, S Keith, Rybarski, Susan C, Mabrey, Alexandria N, Wagman, Benjamin M, and Morlighem, Mathieu

Abstract

Several decades of ice-penetrating radar surveys of the Greenland and Antarctic ice sheets have observed numerous widespread internal reflections. Analysis of this radiostratigraphy has produced valuable insights into ice sheet dynamics and motivates additional mapping of these reflections. Here we present a comprehensive deep radiostratigraphy of the Greenland Ice Sheet from airborne deep ice-penetrating radar data collected over Greenland by The University of Kansas between 1993 and 2013. To map this radiostratigraphy efficiently, we developed new techniques for predicting reflection slope from the phase recorded by coherent radars. When integrated along track, these slope fields predict the radiostratigraphy and simplify semiautomatic reflection tracing. Core-intersecting reflections were dated using synchronized depth-age relationships for six deep ice cores. Additional reflections were dated by matching reflections between transects and by extending reflection-inferred depth-age relationships using the local effective vertical strain rate. The oldest reflections, dating to the Eemian period, are found mostly in the northern part of the ice sheet. Within the onset regions of several fast-flowing outlet glaciers and ice streams, reflections typically do not conform to the bed topography. Disrupted radiostratigraphy is also observed in a region north of the Northeast Greenland Ice Stream that is not presently flowing rapidly. Dated reflections are used to generate a gridded age volume for most of the ice sheet and also to determine the depths of key climate transitions that were not observed directly. This radiostratigraphy provides a new constraint on the dynamics and history of the Greenland Ice Sheet.Key pointsPhase information predicts reflection slope and simplifies reflection tracingReflections can be dated away from ice cores using a simple ice flow modelRadiostratigraphy is often disrupted near the onset of fast ice flow.

Published
2015

8. Radiostratigraphy and age structure of the Greenland Ice Sheet

Author

Macgregor, JA, Macgregor, JA, Fahnestock, MA, Catania, GA, Paden, JD, Prasad Gogineni, S, Young, SK, Rybarski, SC, Mabrey, AN, Wagman, BM, Morlighem, M, Macgregor, JA, Macgregor, JA, Fahnestock, MA, Catania, GA, Paden, JD, Prasad Gogineni, S, Young, SK, Rybarski, SC, Mabrey, AN, Wagman, BM, and Morlighem, M

Abstract

©2015. The Authors. Several decades of ice-penetrating radar surveys of the Greenland and Antarctic ice sheets have observed numerous widespread internal reflections. Analysis of this radiostratigraphy has produced valuable insights into ice sheet dynamics and motivates additional mapping of these reflections. Here we present a comprehensive deep radiostratigraphy of the Greenland Ice Sheet from airborne deep ice-penetrating radar data collected over Greenland by The University of Kansas between 1993 and 2013. To map this radiostratigraphy efficiently, we developed new techniques for predicting reflection slope from the phase recorded by coherent radars. When integrated along track, these slope fields predict the radiostratigraphy and simplify semiautomatic reflection tracing. Core-intersecting reflections were dated using synchronized depth-age relationships for six deep ice cores. Additional reflections were dated by matching reflections between transects and by extending reflection-inferred depth-age relationships using the local effective vertical strain rate. The oldest reflections, dating to the Eemian period, are found mostly in the northern part of the ice sheet. Within the onset regions of several fast-flowing outlet glaciers and ice streams, reflections typically do not conform to the bed topography. Disrupted radiostratigraphy is also observed in a region north of the Northeast Greenland Ice Stream that is not presently flowing rapidly. Dated reflections are used to generate a gridded age volume for most of the ice sheet and also to determine the depths of key climate transitions that were not observed directly. This radiostratigraphy provides a new constraint on the dynamics and history of the Greenland Ice Sheet.

Published
2015

9. Antarctic firn compaction rates from repeat-track airborne radar data: I. Methods

Author

Sub Dynamics Meteorology, Marine and Atmospheric Research, Medley, B., Ligtenberg, S. R. M., Joughin, I., van den Broeke, M. R., Gogineni, S., Nowicki, S., Sub Dynamics Meteorology, Marine and Atmospheric Research, Medley, B., Ligtenberg, S. R. M., Joughin, I., van den Broeke, M. R., Gogineni, S., and Nowicki, S.

Published
2015

10. Ultra-Wideband Radars for Measurements over Land and Sea Ice

Author

Hale, Richard, Miller, Heinrich, Gogineni, S., Yan, J.-B., Rodriguez-Morales, F., Leuschen, C., Wang, Z., Paden, John, Gomez-Garcia, D, Binder, Tobias, Steinhage, Daniel, Gehrmann, Martin, Braaten, David, Hale, Richard, Miller, Heinrich, Gogineni, S., Yan, J.-B., Rodriguez-Morales, F., Leuschen, C., Wang, Z., Paden, John, Gomez-Garcia, D, Binder, Tobias, Steinhage, Daniel, Gehrmann, Martin, and Braaten, David

Abstract

We developed two ultra-wideband (UWB) radars for measurements over ice sheets in Greenland and Antarctica, and sea ice. One of the UWB radars operates over the frequency range of 150-600 MHz with a large cross-track 24-element array. It is designed to sound ice, image ice-bed interface and map internal layers with fine resolution. The 24-element-array consists of three 8-element sub-arrays. One of these sub-arrays is mounted under the fuselage and the other two are mounted under the wings of BT-67 aircraft. The measured inflight VSWR is less than 2 over the entire operating range. The fuselage sub- array is used both for transmission and reception, and wing-mounted sub-arrays are used for reception. The transmitter consists of 8-channel digital waveform generator to synthesize chirped pulses of selectable pulse width and duration. It also consists of driver and power amplifiers to increase the power level to about 1 kW and a fast transmit/receive switch that can handle more than 1 kW of peak power. Each receiver consists of a limiter, switches, low-noise and driver amplifiers, and filters to shape and amplify received signals to the level required for digitization. The digital sub-section consists of timing and control sub-system, and 24-A/D converters to digitize received signals at a rate of 1.6 GHz. The radar performance is evaluated using a delay line to simulate returns from about 2 km thick ice and the loop sensitivity is more than 215 dB. The other UWB microwave radar operates over the frequency range of 2-18 GHz in the Frequency-modulated Continuous Wave (FM-CW) mode. It is designed to sound more than 100 cm snow over sea ice and map internal layers to a depth about 25-40 m in polar firn and ice. We operated the microwave radar over snow-covered sea ice and mapped snow as thin as 5 cm and as thick as 60 cm. With an early version of the radar we mapped internal layers to a depth of 45 m with fine resolution in West Antarctica. We will discuss design considera

Published
2015

11. Radiostratigraphy and age structure of the Greenland Ice Sheet

Author

Macgregor, JA, Macgregor, JA, Fahnestock, MA, Catania, GA, Paden, JD, Prasad Gogineni, S, Young, SK, Rybarski, SC, Mabrey, AN, Wagman, BM, Morlighem, M, Macgregor, JA, Macgregor, JA, Fahnestock, MA, Catania, GA, Paden, JD, Prasad Gogineni, S, Young, SK, Rybarski, SC, Mabrey, AN, Wagman, BM, and Morlighem, M

Abstract

©2015. The Authors. Several decades of ice-penetrating radar surveys of the Greenland and Antarctic ice sheets have observed numerous widespread internal reflections. Analysis of this radiostratigraphy has produced valuable insights into ice sheet dynamics and motivates additional mapping of these reflections. Here we present a comprehensive deep radiostratigraphy of the Greenland Ice Sheet from airborne deep ice-penetrating radar data collected over Greenland by The University of Kansas between 1993 and 2013. To map this radiostratigraphy efficiently, we developed new techniques for predicting reflection slope from the phase recorded by coherent radars. When integrated along track, these slope fields predict the radiostratigraphy and simplify semiautomatic reflection tracing. Core-intersecting reflections were dated using synchronized depth-age relationships for six deep ice cores. Additional reflections were dated by matching reflections between transects and by extending reflection-inferred depth-age relationships using the local effective vertical strain rate. The oldest reflections, dating to the Eemian period, are found mostly in the northern part of the ice sheet. Within the onset regions of several fast-flowing outlet glaciers and ice streams, reflections typically do not conform to the bed topography. Disrupted radiostratigraphy is also observed in a region north of the Northeast Greenland Ice Stream that is not presently flowing rapidly. Dated reflections are used to generate a gridded age volume for most of the ice sheet and also to determine the depths of key climate transitions that were not observed directly. This radiostratigraphy provides a new constraint on the dynamics and history of the Greenland Ice Sheet.

Published
2015

12. Radiostratigraphy and age structure of the Greenland Ice Sheet.

Author

MacGregor, Joseph A, MacGregor, Joseph A, Fahnestock, Mark A, Catania, Ginny A, Paden, John D, Prasad Gogineni, S, Young, S Keith, Rybarski, Susan C, Mabrey, Alexandria N, Wagman, Benjamin M, Morlighem, Mathieu, MacGregor, Joseph A, MacGregor, Joseph A, Fahnestock, Mark A, Catania, Ginny A, Paden, John D, Prasad Gogineni, S, Young, S Keith, Rybarski, Susan C, Mabrey, Alexandria N, Wagman, Benjamin M, and Morlighem, Mathieu

Abstract

Several decades of ice-penetrating radar surveys of the Greenland and Antarctic ice sheets have observed numerous widespread internal reflections. Analysis of this radiostratigraphy has produced valuable insights into ice sheet dynamics and motivates additional mapping of these reflections. Here we present a comprehensive deep radiostratigraphy of the Greenland Ice Sheet from airborne deep ice-penetrating radar data collected over Greenland by The University of Kansas between 1993 and 2013. To map this radiostratigraphy efficiently, we developed new techniques for predicting reflection slope from the phase recorded by coherent radars. When integrated along track, these slope fields predict the radiostratigraphy and simplify semiautomatic reflection tracing. Core-intersecting reflections were dated using synchronized depth-age relationships for six deep ice cores. Additional reflections were dated by matching reflections between transects and by extending reflection-inferred depth-age relationships using the local effective vertical strain rate. The oldest reflections, dating to the Eemian period, are found mostly in the northern part of the ice sheet. Within the onset regions of several fast-flowing outlet glaciers and ice streams, reflections typically do not conform to the bed topography. Disrupted radiostratigraphy is also observed in a region north of the Northeast Greenland Ice Stream that is not presently flowing rapidly. Dated reflections are used to generate a gridded age volume for most of the ice sheet and also to determine the depths of key climate transitions that were not observed directly. This radiostratigraphy provides a new constraint on the dynamics and history of the Greenland Ice Sheet.Key pointsPhase information predicts reflection slope and simplifies reflection tracingReflections can be dated away from ice cores using a simple ice flow modelRadiostratigraphy is often disrupted near the onset of fast ice flow.

Published
2015

13. Antarctic firn compaction rates from repeat-track airborne radar data: I. Methods

Author

Sub Dynamics Meteorology, Marine and Atmospheric Research, Medley, B., Ligtenberg, S. R. M., Joughin, I., van den Broeke, M. R., Gogineni, S., Nowicki, S., Sub Dynamics Meteorology, Marine and Atmospheric Research, Medley, B., Ligtenberg, S. R. M., Joughin, I., van den Broeke, M. R., Gogineni, S., and Nowicki, S.

Published
2015

14. Ultra-Wideband Radars for Measurements over Land and Sea Ice

Author

Hale, Richard, Miller, Heinrich, Gogineni, S., Yan, J.-B., Rodriguez-Morales, F., Leuschen, C., Wang, Z., Paden, John, Gomez-Garcia, D, Binder, Tobias, Steinhage, Daniel, Gehrmann, Martin, Braaten, David, Hale, Richard, Miller, Heinrich, Gogineni, S., Yan, J.-B., Rodriguez-Morales, F., Leuschen, C., Wang, Z., Paden, John, Gomez-Garcia, D, Binder, Tobias, Steinhage, Daniel, Gehrmann, Martin, and Braaten, David

Abstract

We developed two ultra-wideband (UWB) radars for measurements over ice sheets in Greenland and Antarctica, and sea ice. One of the UWB radars operates over the frequency range of 150-600 MHz with a large cross-track 24-element array. It is designed to sound ice, image ice-bed interface and map internal layers with fine resolution. The 24-element-array consists of three 8-element sub-arrays. One of these sub-arrays is mounted under the fuselage and the other two are mounted under the wings of BT-67 aircraft. The measured inflight VSWR is less than 2 over the entire operating range. The fuselage sub- array is used both for transmission and reception, and wing-mounted sub-arrays are used for reception. The transmitter consists of 8-channel digital waveform generator to synthesize chirped pulses of selectable pulse width and duration. It also consists of driver and power amplifiers to increase the power level to about 1 kW and a fast transmit/receive switch that can handle more than 1 kW of peak power. Each receiver consists of a limiter, switches, low-noise and driver amplifiers, and filters to shape and amplify received signals to the level required for digitization. The digital sub-section consists of timing and control sub-system, and 24-A/D converters to digitize received signals at a rate of 1.6 GHz. The radar performance is evaluated using a delay line to simulate returns from about 2 km thick ice and the loop sensitivity is more than 215 dB. The other UWB microwave radar operates over the frequency range of 2-18 GHz in the Frequency-modulated Continuous Wave (FM-CW) mode. It is designed to sound more than 100 cm snow over sea ice and map internal layers to a depth about 25-40 m in polar firn and ice. We operated the microwave radar over snow-covered sea ice and mapped snow as thin as 5 cm and as thick as 60 cm. With an early version of the radar we mapped internal layers to a depth of 45 m with fine resolution in West Antarctica. We will discuss design considera

Published
2015

15. Antarctic firn compaction rates from repeat-track airborne radar data: I. Methods

Author

Sub Dynamics Meteorology, Marine and Atmospheric Research, Medley, B., Ligtenberg, S. R. M., Joughin, I., van den Broeke, M. R., Gogineni, S., Nowicki, S., Sub Dynamics Meteorology, Marine and Atmospheric Research, Medley, B., Ligtenberg, S. R. M., Joughin, I., van den Broeke, M. R., Gogineni, S., and Nowicki, S.

Published
2015

16. Constraining the recent mass balance of pine island and thwaites glaciers, west antarctica, with airborne observations of snow accumulation

Author

Medley, B., Joughin, I., Smith, B. E., Das, S. B., Steig, E. J., Conway, H., Gogineni, S., Lewis, C., Criscitiello, A. S., McConnell, J. R., Van Den Broeke, M. R., Lenaerts, J. T M, Bromwich, D. H., Nicolas, J. P., Leuschen, C., Medley, B., Joughin, I., Smith, B. E., Das, S. B., Steig, E. J., Conway, H., Gogineni, S., Lewis, C., Criscitiello, A. S., McConnell, J. R., Van Den Broeke, M. R., Lenaerts, J. T M, Bromwich, D. H., Nicolas, J. P., and Leuschen, C.

Abstract

In Antarctica, uncertainties in mass input and output translate directly into uncertainty in glacier mass balance and thus in sea level impact. While remotely sensed observations of ice velocity and thickness over the major outlet glaciers have improved our understanding of ice loss to the ocean, snow accumulation over the vast Antarctic interior remains largely unmeasured. Here, we show that an airborne radar system, combined with ice-core glaciochemical analysis, provide the means necessary to measure the accumulation rate at the catchment-scale along the Amundsen Sea coast of West Antarctica. We used along-track radar-derived accumulation to generate a 1985-2009 average accumulation grid that resolves moderate- to large-scale features (>25 km) over the Pine Island-Thwaites glacier drainage system. Comparisons with estimates from atmospheric models and gridded climatologies generally show our results as having less accumulation in the lower-elevation coastal zone but greater accumulation in the interior. Ice discharge, measured over discrete time intervals between 1994 and 2012, combined with our catchment-wide accumulation rates provide an 18-year mass balance history for the sector. While Thwaites Glacier lost the most ice in the mid-1990s, Pine Island Glacier's losses increased substantially by 2006, overtaking Thwaites as the largest regional contributor to sea-level rise. The trend of increasing discharge for both glaciers, however, appears to have leveled off since 2008.

Published
2014

17. Constraining the recent mass balance of pine island and thwaites glaciers, west antarctica, with airborne observations of snow accumulation

Author

Sub Dynamics Meteorology, Marine and Atmospheric Research, Medley, B., Joughin, I., Smith, B. E., Das, S. B., Steig, E. J., Conway, H., Gogineni, S., Lewis, C., Criscitiello, A. S., McConnell, J. R., Van Den Broeke, M. R., Lenaerts, J. T M, Bromwich, D. H., Nicolas, J. P., Leuschen, C., Sub Dynamics Meteorology, Marine and Atmospheric Research, Medley, B., Joughin, I., Smith, B. E., Das, S. B., Steig, E. J., Conway, H., Gogineni, S., Lewis, C., Criscitiello, A. S., McConnell, J. R., Van Den Broeke, M. R., Lenaerts, J. T M, Bromwich, D. H., Nicolas, J. P., and Leuschen, C.

Published
2014

18. Constraining the recent mass balance of Pine Island and Thwaites glaciers, West Antarctica, with airborne observations of snow accumulation

Author

Medley, Brooke, Joughin, Ian, Smith, B. E., Das, Sarah B., Steig, Eric J., Conway, Howard, Gogineni, S., Lewis, Cameron, Criscitiello, Alison S., McConnell, Joseph R., van den Broeke, Michiel R., Lenaerts, Jan T. M., Bromwich, D. H., Nicolas, J. P., Leuschen, C., Medley, Brooke, Joughin, Ian, Smith, B. E., Das, Sarah B., Steig, Eric J., Conway, Howard, Gogineni, S., Lewis, Cameron, Criscitiello, Alison S., McConnell, Joseph R., van den Broeke, Michiel R., Lenaerts, Jan T. M., Bromwich, D. H., Nicolas, J. P., and Leuschen, C.

Abstract

In Antarctica, uncertainties in mass input and output translate directly into uncertainty in glacier mass balance and thus in sea level impact. While remotely sensed observations of ice velocity and thickness over the major outlet glaciers have improved our understanding of ice loss to the ocean, snow accumulation over the vast Antarctic interior remains largely unmeasured. Here, we show that an airborne radar system, combined with ice-core glaciochemical analysis, provide the means necessary to measure the accumulation rate at the catchment-scale along the Amundsen Sea coast of West Antarctica. We used along-track radar-derived accumulation to generate a 1985–2009 average accumulation grid that resolves moderate- to large-scale features (>25 km) over the Pine Island–Thwaites glacier drainage system. Comparisons with estimates from atmospheric models and gridded climatologies generally show our results as having less accumulation in the lower-elevation coastal zone but greater accumulation in the interior. Ice discharge, measured over discrete time intervals between 1994 and 2012, combined with our catchment-wide accumulation rates provide an 18-year mass balance history for the sector. While Thwaites Glacier lost the most ice in the mid-1990s, Pine Island Glacier's losses increased substantially by 2006, overtaking Thwaites as the largest regional contributor to sea-level rise. The trend of increasing discharge for both glaciers, however, appears to have leveled off since 2008.

Published
2014

19. Isochronous information in a Greenland ice sheet radio-echo sounding dataset

Author

Sime, Louise C., Karlsson, Nanna B., Paden, John D., Gogineni, S. Prasad, Sime, Louise C., Karlsson, Nanna B., Paden, John D., and Gogineni, S. Prasad

Abstract

The evaluation of ice sheet models is one of the pressing problems in the study of ice sheets dynamics. Here we examine the question of how much isochronous information is contained within the publicly available CReSIS Greenland airborne radio-echo soundings dataset. We identify regions containing isochronous reflectors using ARESP algorithms [Sime et al., 2011]. We find that isochronous reflectors are present within 36% of the CReSIS RES englacial data by location, and 41% by total number of data. Between 1000 and 3000 m in depth, isochronous reflectors are present along more than 50% of the dataset flight path. Lower volumes of cold glacial period ice also correspond with more isochronous reflectors. We find good agreement between ARESP and continuity index [Karlsson et al., 2012] results, providing confidence in these findings. Ice structure datasets, based on data identified here, will be of use in evaluating ice sheet simulations and the assessment of past rates of snow accumulation.

Published
2014

20. Constraining the recent mass balance of Pine Island and Thwaites glaciers, West Antarctica, with airborne observations of snow accumulation

Author

Medley, Brooke, Joughin, Ian, Smith, B. E., Das, Sarah B., Steig, Eric J., Conway, Howard, Gogineni, S., Lewis, Cameron, Criscitiello, Alison S., McConnell, Joseph R., van den Broeke, Michiel R., Lenaerts, Jan T. M., Bromwich, D. H., Nicolas, J. P., Leuschen, C., Medley, Brooke, Joughin, Ian, Smith, B. E., Das, Sarah B., Steig, Eric J., Conway, Howard, Gogineni, S., Lewis, Cameron, Criscitiello, Alison S., McConnell, Joseph R., van den Broeke, Michiel R., Lenaerts, Jan T. M., Bromwich, D. H., Nicolas, J. P., and Leuschen, C.

Abstract

© The Author(s), 2014. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Cryosphere 8 (2014): 1375-1392, doi:10.5194/tc-8-1375-2014., In Antarctica, uncertainties in mass input and output translate directly into uncertainty in glacier mass balance and thus in sea level impact. While remotely sensed observations of ice velocity and thickness over the major outlet glaciers have improved our understanding of ice loss to the ocean, snow accumulation over the vast Antarctic interior remains largely unmeasured. Here, we show that an airborne radar system, combined with ice-core glaciochemical analysis, provide the means necessary to measure the accumulation rate at the catchment-scale along the Amundsen Sea coast of West Antarctica. We used along-track radar-derived accumulation to generate a 1985–2009 average accumulation grid that resolves moderate- to large-scale features (>25 km) over the Pine Island–Thwaites glacier drainage system. Comparisons with estimates from atmospheric models and gridded climatologies generally show our results as having less accumulation in the lower-elevation coastal zone but greater accumulation in the interior. Ice discharge, measured over discrete time intervals between 1994 and 2012, combined with our catchment-wide accumulation rates provide an 18-year mass balance history for the sector. While Thwaites Glacier lost the most ice in the mid-1990s, Pine Island Glacier's losses increased substantially by 2006, overtaking Thwaites as the largest regional contributor to sea-level rise. The trend of increasing discharge for both glaciers, however, appears to have leveled off since 2008., This research was supported at UW by NSF OPP grants ANT-0631973 (B Medley, I. Joughin, E. J. Steig, and H. Conway) and ANT-0424589 (B. Medley and I. Joughin). Work at WHOI was supported by NSF OPP grant ANT-0632031 and NASA grant NNX10AP09G (S. B. Das and A. S. Criscitiello). D. H. Bromwich and J. P. Nicolas were supported by NASA grant NN12XAI29G and NSF grant ANT-1049089.

Published
2014

21. Constraining the recent mass balance of pine island and thwaites glaciers, west antarctica, with airborne observations of snow accumulation

Author

Sub Dynamics Meteorology, Marine and Atmospheric Research, Medley, B., Joughin, I., Smith, B. E., Das, S. B., Steig, E. J., Conway, H., Gogineni, S., Lewis, C., Criscitiello, A. S., McConnell, J. R., Van Den Broeke, M. R., Lenaerts, J. T M, Bromwich, D. H., Nicolas, J. P., Leuschen, C., Sub Dynamics Meteorology, Marine and Atmospheric Research, Medley, B., Joughin, I., Smith, B. E., Das, S. B., Steig, E. J., Conway, H., Gogineni, S., Lewis, C., Criscitiello, A. S., McConnell, J. R., Van Den Broeke, M. R., Lenaerts, J. T M, Bromwich, D. H., Nicolas, J. P., and Leuschen, C.

Published
2014

22. Constraining the recent mass balance of pine island and thwaites glaciers, west antarctica, with airborne observations of snow accumulation

Author

Sub Dynamics Meteorology, Marine and Atmospheric Research, Medley, B., Joughin, I., Smith, B. E., Das, S. B., Steig, E. J., Conway, H., Gogineni, S., Lewis, C., Criscitiello, A. S., McConnell, J. R., Van Den Broeke, M. R., Lenaerts, J. T M, Bromwich, D. H., Nicolas, J. P., Leuschen, C., Sub Dynamics Meteorology, Marine and Atmospheric Research, Medley, B., Joughin, I., Smith, B. E., Das, S. B., Steig, E. J., Conway, H., Gogineni, S., Lewis, C., Criscitiello, A. S., McConnell, J. R., Van Den Broeke, M. R., Lenaerts, J. T M, Bromwich, D. H., Nicolas, J. P., and Leuschen, C.

Published
2014

23. Isochronous information in a Greenland ice sheet radio-echo sounding dataset

Author

Sime, Louise C., Karlsson, Nanna B., Paden, John D., Gogineni, S. Prasad, Sime, Louise C., Karlsson, Nanna B., Paden, John D., and Gogineni, S. Prasad

Abstract

The evaluation of ice sheet models is one of the pressing problems in the study of ice sheets dynamics. Here we examine the question of how much isochronous information is contained within the publicly available CReSIS Greenland airborne radio-echo soundings dataset. We identify regions containing isochronous reflectors using ARESP algorithms [Sime et al., 2011]. We find that isochronous reflectors are present within 36% of the CReSIS RES englacial data by location, and 41% by total number of data. Between 1000 and 3000 m in depth, isochronous reflectors are present along more than 50% of the dataset flight path. Lower volumes of cold glacial period ice also correspond with more isochronous reflectors. We find good agreement between ARESP and continuity index [Karlsson et al., 2012] results, providing confidence in these findings. Ice structure datasets, based on data identified here, will be of use in evaluating ice sheet simulations and the assessment of past rates of snow accumulation.

Published
2014

25. Advanced Multifrequency Radar Instrumentation for Polar Research

Author

Rodriguez-Morales, F., Gogineni, S., Leuschen, C.J., Paden, J.D., Li, J., Lewis, C.C., Panzer, B., Gomez-Garcia Alvestegui, D., Patel, A., Byers, K., Crowe, R., Hale, R.D., Panton, Christian, Rodriguez-Morales, F., Gogineni, S., Leuschen, C.J., Paden, J.D., Li, J., Lewis, C.C., Panzer, B., Gomez-Garcia Alvestegui, D., Patel, A., Byers, K., Crowe, R., Hale, R.D., and Panton, Christian

Published
2014

26. Advanced Multifrequency Radar Instrumentation for Polar Research

Author

Rodriguez-Morales, F., Gogineni, S., Leuschen, C.J., Paden, J.D., Li, J., Lewis, C.C., Panzer, B., Gomez-Garcia Alvestegui, D., Patel, A., Byers, K., Crowe, R., Hale, R.D., Panton, Christian, Rodriguez-Morales, F., Gogineni, S., Leuschen, C.J., Paden, J.D., Li, J., Lewis, C.C., Panzer, B., Gomez-Garcia Alvestegui, D., Patel, A., Byers, K., Crowe, R., Hale, R.D., and Panton, Christian

Published
2014

28. Airborne-radar and ice-core observations of annual snow accumulation over Thwaites Glacier, West Antarctica confirm the spatiotemporal variability of global and regional atmospheric models

Author

Medley, B., Joughin, I., Das, S.B., Steig, E. J., Conway, H., Gogineni, S., Criscitiello, A.S., McConnell, J.R., Smith, B.E., van den Broeke, M.R., Lenaerts, J.T.M., Bromwich, D.H., Nicolas, J.P., Medley, B., Joughin, I., Das, S.B., Steig, E. J., Conway, H., Gogineni, S., Criscitiello, A.S., McConnell, J.R., Smith, B.E., van den Broeke, M.R., Lenaerts, J.T.M., Bromwich, D.H., and Nicolas, J.P.

Abstract

We use an airborne-radar method, verified with ice-core accumulation records, to determine the spatiotemporal variations of snow accumulation over Thwaites Glacier, West Antarctica between 1980 and 2009. We also present a regional evaluation of modeled accumulation in Antarctica. Comparisons between radar-derived measurements and model outputs show that three global models capture the interannual variability well (r > 0.9), but a high-resolution regional model (RACMO2) has better absolute accuracy and captures the observed spatial variability (r = 0.86). Neither the measured nor modeled accumulation records over Thwaites Glacier show any trend since 1980. Although an increase in accumulation may potentially accompany the observed warming in the region, the projected trend is too small to detect over the 30 year record.

Published
2013

29. Eemian interglacial reconstructed from a Greenland folded ice core

Author

Dahl-Jensen, D., Albert, M. R., Aldahan, Ala, Azuma, N., Balslev-Clausen, D., Baumgartner, M., Berggren, Ann-Marie, Bigler, M., Binder, T., Blunier, T., Bourgeois, J. C., Brook, E. J., Buchardt, S. L., Buizert, C., Capron, E., Chappellaz, J., Chung, J., Clausen, H. B., Cvijanovic, I., Davies, S. M., Ditlevsen, P., Eicher, O., Fischer, H., Fisher, D. A., Fleet, L. G., Gfeller, G., Gkinis, V., Gogineni, S., Goto-Azuma, K., Grinsted, A., Gudlaugsdottir, H., Guillevic, M., Hansen, S. B., Hansson, M., Hirabayashi, M., Hong, S., Hur, S. D., Huybrechts, P., Hvidberg, C. S., Iizuka, Y., Jenk, T., Johnsen, S. J., Jones, T. R., Jouzel, J., Karlsson, N. B., Kawamura, K., Keegan, K., Kettner, E., Kipfstuhl, S., Kjaer, H. A., Koutnik, M., Kuramoto, T., Koehler, P., Laepple, T., Landais, A., Langen, P. L., Larsen, L. B., Leuenberger, D., Leuenberger, M., Leuschen, C., Li, J., Lipenkov, V., Martinerie, P., Maselli, O. J., Masson-Delmotte, V., McConnell, J. R., Miller, H., Mini, O., Miyamoto, A., Montagnat-Rentier, M., Mulvaney, R., Muscheler, R., Orsi, A. J., Paden, J., Panton, C., Pattyn, F., Petit, J. -R, Pol, K., Popp, T., Possnert, Göran, Prie, F., Prokopiou, M., Quiquet, A., Rasmussen, S. O., Raynaud, D., Ren, J., Reutenauer, C., Ritz, C., Rockmann, T., Rosen, J. L., Rubino, M., Rybak, O., Samyn, D., Sapart, C. J., Schilt, A., Schmidt, A. M. Z., Schwander, J., Schuepbach, S., Seierstad, I., Severinghaus, J. P., Sheldon, S., Simonsen, S. B., Sjolte, J., Solgaard, A. M., Sowers, T., Sperlich, P., Steen-Larsen, H. C., Steffen, K., Steffensen, J. P., Steinhage, D., Stocker, T. F., Stowasser, C., Sturevik, A. S., Sturges, W. T., Sveinbjornsdottir, A., Svensson, A., Tison, J. -L, Uetake, J., Vallelonga, P., van de Wal, R. S. W., van der Wel, G., Vaughn, B. H., Vinther, B., Waddington, E., Wegner, A., Weikusat, I., White, J. W. C., Wilhelms, F., Winstrup, M., Witrant, E., Wolff, E. W., Xiao, C., Zheng, J., Dahl-Jensen, D., Albert, M. R., Aldahan, Ala, Azuma, N., Balslev-Clausen, D., Baumgartner, M., Berggren, Ann-Marie, Bigler, M., Binder, T., Blunier, T., Bourgeois, J. C., Brook, E. J., Buchardt, S. L., Buizert, C., Capron, E., Chappellaz, J., Chung, J., Clausen, H. B., Cvijanovic, I., Davies, S. M., Ditlevsen, P., Eicher, O., Fischer, H., Fisher, D. A., Fleet, L. G., Gfeller, G., Gkinis, V., Gogineni, S., Goto-Azuma, K., Grinsted, A., Gudlaugsdottir, H., Guillevic, M., Hansen, S. B., Hansson, M., Hirabayashi, M., Hong, S., Hur, S. D., Huybrechts, P., Hvidberg, C. S., Iizuka, Y., Jenk, T., Johnsen, S. J., Jones, T. R., Jouzel, J., Karlsson, N. B., Kawamura, K., Keegan, K., Kettner, E., Kipfstuhl, S., Kjaer, H. A., Koutnik, M., Kuramoto, T., Koehler, P., Laepple, T., Landais, A., Langen, P. L., Larsen, L. B., Leuenberger, D., Leuenberger, M., Leuschen, C., Li, J., Lipenkov, V., Martinerie, P., Maselli, O. J., Masson-Delmotte, V., McConnell, J. R., Miller, H., Mini, O., Miyamoto, A., Montagnat-Rentier, M., Mulvaney, R., Muscheler, R., Orsi, A. J., Paden, J., Panton, C., Pattyn, F., Petit, J. -R, Pol, K., Popp, T., Possnert, Göran, Prie, F., Prokopiou, M., Quiquet, A., Rasmussen, S. O., Raynaud, D., Ren, J., Reutenauer, C., Ritz, C., Rockmann, T., Rosen, J. L., Rubino, M., Rybak, O., Samyn, D., Sapart, C. J., Schilt, A., Schmidt, A. M. Z., Schwander, J., Schuepbach, S., Seierstad, I., Severinghaus, J. P., Sheldon, S., Simonsen, S. B., Sjolte, J., Solgaard, A. M., Sowers, T., Sperlich, P., Steen-Larsen, H. C., Steffen, K., Steffensen, J. P., Steinhage, D., Stocker, T. F., Stowasser, C., Sturevik, A. S., Sturges, W. T., Sveinbjornsdottir, A., Svensson, A., Tison, J. -L, Uetake, J., Vallelonga, P., van de Wal, R. S. W., van der Wel, G., Vaughn, B. H., Vinther, B., Waddington, E., Wegner, A., Weikusat, I., White, J. W. C., Wilhelms, F., Winstrup, M., Witrant, E., Wolff, E. W., Xiao, C., and Zheng, J.

Abstract

Efforts to extract a Greenland ice core with a complete record of the Eemian interglacial (130,000 to 115,000 years ago) have until now been unsuccessful. The response of the Greenland ice sheet to the warmer-than-present climate of the Eemian has thus remained unclear. Here we present the new North Greenland Eemian Ice Drilling ('NEEM') ice core and show only a modest ice-sheet response to the strong warming in the early Eemian. We reconstructed the Eemian record from folded ice using globally homogeneous parameters known from dated Greenland and Antarctic ice-core records. On the basis of water stable isotopes, NEEM surface temperatures after the onset of the Eemian (126,000 years ago) peaked at 8 +/- 4 degrees Celsius above the mean of the past millennium, followed by a gradual cooling that was probably driven by the decreasing summer insolation. Between 128,000 and 122,000 years ago, the thickness of the northwest Greenland ice sheet decreased by 400 +/- 250 metres, reaching surface elevations 122,000 years ago of 130 +/- 300 metres lower than the present. Extensive surface melt occurred at the NEEM site during the Eemian, a phenomenon witnessed when melt layers formed again at NEEM during the exceptional heat of July 2012. With additional warming, surface melt might become more common in the future.

Published
2013
Full Text
View/download PDF

30. A new bed elevation dataset for Greenland

Author

Bamber, J. L, Bamber, J. L, Griggs, J. A, Hurkmans, R. T. W. L, Dowdeswell, J. A, Gogineni, S. P, Howat, I., Mouginot, J., Paden, J., Palmer, S., Rignot, E., Steinhage, D., Bamber, J. L, Bamber, J. L, Griggs, J. A, Hurkmans, R. T. W. L, Dowdeswell, J. A, Gogineni, S. P, Howat, I., Mouginot, J., Paden, J., Palmer, S., Rignot, E., and Steinhage, D.

Published
2013

31. Eemian interglacial reconstructed from a Greenland folded ice core

Author

Dahl-Jensen, D., Albert, M. R., Aldahan, A., Azuma, N., Balslev-Clausen, D., Baumgartner, M., Berggren, A. -M, Bigler, M., Binder, T., Blunier, T., Bourgeois, J. C., Brook, E. J., Buchardt, S. L., Buizert, C., Capron, E., Chappellaz, J., Chung, J., Clausen, H. B., Cvijanovic, I., Davies, S. M., Ditlevsen, P., Eicher, O., Fischer, H., Fisher, D. A., Fleet, L. G., Gfeller, G., Gkinis, V., Gogineni, S., Goto-Azuma, K., Grinsted, A., Gudlaugsdottir, H., Guillevic, M., Hansen, S. B., Hansson, Margareta, Hirabayashi, M., Hong, S., Hur, S. D., Huybrechts, P., Hvidberg, C. S., Iizuka, Yoshinori, Jenk, T., Johnsen, S. J., Jones, T. R., Jouzel, J., Karlsson, N. B., Kawamura, K., Keegan, K., Kettner, E., Kipfstuhl, S., Kjaer, H. A., Koutnik, M., Kuramoto, T., Koehler, P., Laepple, T., Landais, A., Langen, P. L., Larsen, L. B., Leuenberger, D., Leuenberger, M., Leuschen, C., Li, J., Lipenkov, V., Martinerie, P., Maselli, O. J., Masson-Delmotte, V., McConnell, J. R., Miller, H., Mini, O., Miyamoto, A., Montagnat-Rentier, M., Mulvaney, R., Muscheler, R., Orsi, A. J., Paden, J., Panton, C., Pattyn, F., Petit, J. -R, Pol, K., Popp, T., Possnert, G., Prie, F., Prokopiou, M., Quiquet, A., Rasmussen, S. O., Raynaud, D., Ren, J., Reutenauer, C., Ritz, C., Rockmann, T., Rosen, J. L., Rubino, M., Rybak, O., Samyn, D., Sapart, C. J., Schilt, A., Schmidt, A. M. Z., Schwander, J., Schuepbach, S., Seierstad, I., Severinghaus, J. P., Sheldon, S., Simonsen, S. B., Sjolte, J., Solgaard, A. M., Sowers, T., Sperlich, P., Steen-Larsen, H. C., Steffen, K., Steffensen, J. P., Steinhage, D., Stocker, T. F., Stowasser, C., Sturevik, A. S., Sturges, W. T., Sveinbjornsdottir, A., Svensson, A., Tison, J. -L, Uetake, J., Vallelonga, P., van de Wal, R. S. W., van der Wel, G., Vaughn, B. H., Vinther, B., Waddington, E., Wegner, A., Weikusat, I., White, J. W. C., Wilhelms, F., Winstrup, M., Witrant, E., Wolff, E. W., Xiao, C., Zheng, J., Dahl-Jensen, D., Albert, M. R., Aldahan, A., Azuma, N., Balslev-Clausen, D., Baumgartner, M., Berggren, A. -M, Bigler, M., Binder, T., Blunier, T., Bourgeois, J. C., Brook, E. J., Buchardt, S. L., Buizert, C., Capron, E., Chappellaz, J., Chung, J., Clausen, H. B., Cvijanovic, I., Davies, S. M., Ditlevsen, P., Eicher, O., Fischer, H., Fisher, D. A., Fleet, L. G., Gfeller, G., Gkinis, V., Gogineni, S., Goto-Azuma, K., Grinsted, A., Gudlaugsdottir, H., Guillevic, M., Hansen, S. B., Hansson, Margareta, Hirabayashi, M., Hong, S., Hur, S. D., Huybrechts, P., Hvidberg, C. S., Iizuka, Yoshinori, Jenk, T., Johnsen, S. J., Jones, T. R., Jouzel, J., Karlsson, N. B., Kawamura, K., Keegan, K., Kettner, E., Kipfstuhl, S., Kjaer, H. A., Koutnik, M., Kuramoto, T., Koehler, P., Laepple, T., Landais, A., Langen, P. L., Larsen, L. B., Leuenberger, D., Leuenberger, M., Leuschen, C., Li, J., Lipenkov, V., Martinerie, P., Maselli, O. J., Masson-Delmotte, V., McConnell, J. R., Miller, H., Mini, O., Miyamoto, A., Montagnat-Rentier, M., Mulvaney, R., Muscheler, R., Orsi, A. J., Paden, J., Panton, C., Pattyn, F., Petit, J. -R, Pol, K., Popp, T., Possnert, G., Prie, F., Prokopiou, M., Quiquet, A., Rasmussen, S. O., Raynaud, D., Ren, J., Reutenauer, C., Ritz, C., Rockmann, T., Rosen, J. L., Rubino, M., Rybak, O., Samyn, D., Sapart, C. J., Schilt, A., Schmidt, A. M. Z., Schwander, J., Schuepbach, S., Seierstad, I., Severinghaus, J. P., Sheldon, S., Simonsen, S. B., Sjolte, J., Solgaard, A. M., Sowers, T., Sperlich, P., Steen-Larsen, H. C., Steffen, K., Steffensen, J. P., Steinhage, D., Stocker, T. F., Stowasser, C., Sturevik, A. S., Sturges, W. T., Sveinbjornsdottir, A., Svensson, A., Tison, J. -L, Uetake, J., Vallelonga, P., van de Wal, R. S. W., van der Wel, G., Vaughn, B. H., Vinther, B., Waddington, E., Wegner, A., Weikusat, I., White, J. W. C., Wilhelms, F., Winstrup, M., Witrant, E., Wolff, E. W., Xiao, C., and Zheng, J.

Abstract

Efforts to extract a Greenland ice core with a complete record of the Eemian interglacial (130,000 to 115,000 years ago) have until now been unsuccessful. The response of the Greenland ice sheet to the warmer-than-present climate of the Eemian has thus remained unclear. Here we present the new North Greenland Eemian Ice Drilling ('NEEM') ice core and show only a modest ice-sheet response to the strong warming in the early Eemian. We reconstructed the Eemian record from folded ice using globally homogeneous parameters known from dated Greenland and Antarctic ice-core records. On the basis of water stable isotopes, NEEM surface temperatures after the onset of the Eemian (126,000 years ago) peaked at 8 +/- 4 degrees Celsius above the mean of the past millennium, followed by a gradual cooling that was probably driven by the decreasing summer insolation. Between 128,000 and 122,000 years ago, the thickness of the northwest Greenland ice sheet decreased by 400 +/- 250 metres, reaching surface elevations 122,000 years ago of 130 +/- 300 metres lower than the present. Extensive surface melt occurred at the NEEM site during the Eemian, a phenomenon witnessed when melt layers formed again at NEEM during the exceptional heat of July 2012. With additional warming, surface melt might become more common in the future., AuthorCount:133

Published
2013
Full Text
View/download PDF

32. Airborne-radar and ice-core observations of annual snow accumulation over Thwaites Glacier, West Antarctica confirm the spatiotemporal variability of global and regional atmospheric models

Author

Marine and Atmospheric Research, Sub Dynamics Meteorology, Medley, B., Joughin, I., Das, S.B., Steig, E. J., Conway, H., Gogineni, S., Criscitiello, A.S., McConnell, J.R., Smith, B.E., van den Broeke, M.R., Lenaerts, J.T.M., Bromwich, D.H., Nicolas, J.P., Marine and Atmospheric Research, Sub Dynamics Meteorology, Medley, B., Joughin, I., Das, S.B., Steig, E. J., Conway, H., Gogineni, S., Criscitiello, A.S., McConnell, J.R., Smith, B.E., van den Broeke, M.R., Lenaerts, J.T.M., Bromwich, D.H., and Nicolas, J.P.

Published
2013

33. Airborne-radar and ice-core observations of annual snow accumulation over Thwaites Glacier, West Antarctica confirm the spatiotemporal variability of global and regional atmospheric models

Author

Medley, Brooke, Joughin, Ian, Das, Sarah B., Steig, Eric J., Conway, Howard, Gogineni, S., Criscitiello, Alison S., McConnell, Joseph R., Smith, B. E., van den Broeke, Michiel R., Lenaerts, Jan T. M., Bromwich, D. H., Nicolas, J. P., Medley, Brooke, Joughin, Ian, Das, Sarah B., Steig, Eric J., Conway, Howard, Gogineni, S., Criscitiello, Alison S., McConnell, Joseph R., Smith, B. E., van den Broeke, Michiel R., Lenaerts, Jan T. M., Bromwich, D. H., and Nicolas, J. P.

Abstract

Author Posting. © American Geophysical Union, 2013. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 40 (2013): 3649–3654, doi:10.1002/grl.50706., We use an airborne-radar method, verified with ice-core accumulation records, to determine the spatiotemporal variations of snow accumulation over Thwaites Glacier, West Antarctica between 1980 and 2009. We also present a regional evaluation of modeled accumulation in Antarctica. Comparisons between radar-derived measurements and model outputs show that three global models capture the interannual variability well (r > 0.9), but a high-resolution regional model (RACMO2) has better absolute accuracy and captures the observed spatial variability (r = 0.86). Neither the measured nor modeled accumulation records over Thwaites Glacier show any trend since 1980. Although an increase in accumulation may potentially accompany the observed warming in the region, the projected trend is too small to detect over the 30 year record., This research was supported at UW by NSF OPP grants ANT-0631973 (B.M., I.J., E.J.S., and H.C.) and ANT-0424589 (B.M. and I.J.) and at WHOI by ANT-0632031 (S.B.D. and A.S.C.). D.H.B. and J.P.N. were supported by NASA grant NN12XAI29G. We acknowledge the work by the CReSIS team that went into developing the snow-radar system, which was partially supported with by NASA grant NNX10AT68G and by NSF OPP grant ANT-0424589 awarded to S.P., 2014-01-26

Published
2013

34. Airborne-radar and ice-core observations of annual snow accumulation over Thwaites Glacier, West Antarctica confirm the spatiotemporal variability of global and regional atmospheric models

Author

Medley, Brooke, Joughin, Ian, Das, Sarah B., Steig, Eric J., Conway, Howard, Gogineni, S., Criscitiello, Alison S., McConnell, Joseph R., Smith, B. E., van den Broeke, Michiel R., Lenaerts, Jan T. M., Bromwich, D. H., Nicolas, J. P., Medley, Brooke, Joughin, Ian, Das, Sarah B., Steig, Eric J., Conway, Howard, Gogineni, S., Criscitiello, Alison S., McConnell, Joseph R., Smith, B. E., van den Broeke, Michiel R., Lenaerts, Jan T. M., Bromwich, D. H., and Nicolas, J. P.

Abstract

We use an airborne-radar method, verified with ice-core accumulation records, to determine the spatiotemporal variations of snow accumulation over Thwaites Glacier, West Antarctica between 1980 and 2009. We also present a regional evaluation of modeled accumulation in Antarctica. Comparisons between radar-derived measurements and model outputs show that three global models capture the interannual variability well (r > 0.9), but a high-resolution regional model (RACMO2) has better absolute accuracy and captures the observed spatial variability (r = 0.86). Neither the measured nor modeled accumulation records over Thwaites Glacier show any trend since 1980. Although an increase in accumulation may potentially accompany the observed warming in the region, the projected trend is too small to detect over the 30 year record.

Published
2013

35. Multiple-pulse PIV: Numerical evaluation and experimental validation

Author

Ding, L. (author), Discetti, S. (author), Adrian, R.J. (author), Gogineni, S. (author), Ding, L. (author), Discetti, S. (author), Adrian, R.J. (author), and Gogineni, S. (author)

Abstract

Many conventional experimental methods in fluid mechanics, such as LDV and HWA, are not able to measure simultaneous acceleration fields directly. Double-pulse PIV is extended to the multiple-pulse PIV enabling people to directly extract acceleration fields as well as to achieve better accuracy in the velocity measurement [13]. We evaluate the performances of triple-pulse PIV and quadruple-pulse PIV based on PTV simulations. By investigating various flow conditions, optimizations are globally achieved to minimize the error in velocity and acceleration measurements for both triple-pulse and quadruple-pulse PIV. Compared to that with uneven time spacing, triple-pulse PIV with even time spacing yields better spatial resolution in velocity measurement. Moreover, quadruple-pulse PIV significantly reduces the error in both velocity and acceleration measurement relative to triple-pulse PIV. Experimental validation of the acceleration measurement from triple-pulse PIV is conducted by measuring the mean centerline acceleration profile of a round impinging air jet. A custom 8-pulse laser system in combination with an ultra high-speed 4-channel camera are utilized to well satisfy the requirements of multiple-pulse PIV. Conventional double-pulse PIV, together with the polynomial curve fitting, are used to obtain the ground truth for the mean centerline acceleration profile. The comparison between the ground truth and acceleration measurements by triple-pulse PIV shows a good agreement with the maximum error being 10% of the full scale acceleration. Several potential error sources are also discussed to provide the direction of making improvements in the following stage.

Published
2013

36. Eemian interglacial reconstructed from a Greenland folded ice core

Author

Dahl-Jensen, D., Albert, M.R., Aldahan, A., Azuma, N., Balslev-Clausen, D., Baumgartner, M., Berggren, A.-M., Bigler, M., Binder, T., Blunier, T., Bourgeois, J.C., Brook, E.J., Buchardt, S.L., Buizert, C., Capron, E., Chappellaz, J., Chung, J., Clausen, H.B., Cvijanovic, I., Davies, S. M., Ditlevsen, P., Eicher, O., Fischer, H., Fisher, D.A., Fleet, L.G., Gfeller, G., Gkinis, V., Gogineni, S., Goto-Azuma, K., Grinsted, A., Gudlaugsdottir, H., Guillevic, M., Hansen, S.B., Hansson, M., Hirabayashi, M., Hong, S., Hur, S.D., Huybrechts, P., Hvidberg, C.S., Iizuka, Y., Jenk, T., Johnsen, S.J., Jones, T.R., Jouzel, J., Karlsson, N.B., Kawamura, K., Keegan, K., Kettner, E., Kipfstuhl, S., Kjær, H.A., Koutnik, M., Kuramoto, T., Köhler, P., Laepple, T., Landais, A., Langen, P.L., Larsen, L.B., Leuenberger, D., Leuenberger, M., Leuschen, C., Li, J., Lipenkov, V., Martinerie, P., Maselli, O.J., Masson-Delmotte, V., McConnell, J.R., Miller, H., Mini, O., Miyamoto, A., Montagnat-Rentier, M., Mulvaney, R., Muscheler, R., Orsi, A.J., Paden, J., Panton, C., Pattyn, F., Petit, J.-R., Pol, K., Popp, T., Possnert, G., Prié, F., Prokopiou, M., Quiquet, A., Rasmussen, S.O., Raynaud, D., Ren, J., Reutenauer, C., Ritz, C., Röckmann, T., Rosen, J.L., Rubino, M., Rybak, O., Samyn, D., Sapart, C.J., Schilt, A., Schmidt, A.M.Z., Schwander, J., Schüpbach, S., Seierstad, I., Severinghaus, J.P., Sheldon, S., Simonsen, S.B., Sjolte, J., Solgaard, A.M., Sowers, T., Sperlich, P., Steen-Larsen, H.C., Steffen, K., Steffensen, J.P., Steinhage, D., Stocker, T.F., Stowasser, C., Sturevik, A.S., Sturges, W.T., Sveinbjörnsdottir, A., Svensson, A., Tison, J.-L., Uetake, J., Vallelonga, P., van de Wal, R.S.W., van der Wel, G., Vaughn, B.H., Vinther, B., Waddington, E., Wegner, A., Weikusat, I., White, J.W.C., Wilhelms, F., Winstrup, M., Witrant, E., Wolff, E.W., Xiao, C., Zheng, J., Dahl-Jensen, D., Albert, M.R., Aldahan, A., Azuma, N., Balslev-Clausen, D., Baumgartner, M., Berggren, A.-M., Bigler, M., Binder, T., Blunier, T., Bourgeois, J.C., Brook, E.J., Buchardt, S.L., Buizert, C., Capron, E., Chappellaz, J., Chung, J., Clausen, H.B., Cvijanovic, I., Davies, S. M., Ditlevsen, P., Eicher, O., Fischer, H., Fisher, D.A., Fleet, L.G., Gfeller, G., Gkinis, V., Gogineni, S., Goto-Azuma, K., Grinsted, A., Gudlaugsdottir, H., Guillevic, M., Hansen, S.B., Hansson, M., Hirabayashi, M., Hong, S., Hur, S.D., Huybrechts, P., Hvidberg, C.S., Iizuka, Y., Jenk, T., Johnsen, S.J., Jones, T.R., Jouzel, J., Karlsson, N.B., Kawamura, K., Keegan, K., Kettner, E., Kipfstuhl, S., Kjær, H.A., Koutnik, M., Kuramoto, T., Köhler, P., Laepple, T., Landais, A., Langen, P.L., Larsen, L.B., Leuenberger, D., Leuenberger, M., Leuschen, C., Li, J., Lipenkov, V., Martinerie, P., Maselli, O.J., Masson-Delmotte, V., McConnell, J.R., Miller, H., Mini, O., Miyamoto, A., Montagnat-Rentier, M., Mulvaney, R., Muscheler, R., Orsi, A.J., Paden, J., Panton, C., Pattyn, F., Petit, J.-R., Pol, K., Popp, T., Possnert, G., Prié, F., Prokopiou, M., Quiquet, A., Rasmussen, S.O., Raynaud, D., Ren, J., Reutenauer, C., Ritz, C., Röckmann, T., Rosen, J.L., Rubino, M., Rybak, O., Samyn, D., Sapart, C.J., Schilt, A., Schmidt, A.M.Z., Schwander, J., Schüpbach, S., Seierstad, I., Severinghaus, J.P., Sheldon, S., Simonsen, S.B., Sjolte, J., Solgaard, A.M., Sowers, T., Sperlich, P., Steen-Larsen, H.C., Steffen, K., Steffensen, J.P., Steinhage, D., Stocker, T.F., Stowasser, C., Sturevik, A.S., Sturges, W.T., Sveinbjörnsdottir, A., Svensson, A., Tison, J.-L., Uetake, J., Vallelonga, P., van de Wal, R.S.W., van der Wel, G., Vaughn, B.H., Vinther, B., Waddington, E., Wegner, A., Weikusat, I., White, J.W.C., Wilhelms, F., Winstrup, M., Witrant, E., Wolff, E.W., Xiao, C., and Zheng, J.

Abstract

Efforts to extract a Greenland ice core with a complete record of the Eemian interglacial (130,000 to 115,000 years ago) have until now been unsuccessful. The response of the Greenland ice sheet to the warmer-than-present climate of the Eemian has thus remained unclear. Here we present the new North Greenland Eemian Ice Drilling (‘NEEM’) ice core and show only a modest ice-sheet response to the strong warming in the early Eemian. We reconstructed the Eemian record from folded ice using globally homogeneous parameters known from dated Greenland and Antarctic ice-core records. On the basis of water stable isotopes, NEEM surface temperatures after the onset of the Eemian (126,000 years ago) peaked at 8 ± 4 degrees Celsius above the mean of the past millennium, followed by a gradual cooling that was probably driven by the decreasing summer insolation. Between 128,000 and 122,000 years ago, the thickness of the northwest Greenland ice sheet decreased by 400 ± 250 metres, reaching surface elevations 122,000 years ago of 130 ± 300 metres lower than the present. Extensive surface melt occurred at the NEEM site during the Eemian, a phenomenon witnessed when melt layers formed again at NEEM during the exceptional heat of July 2012. With additional warming, surface melt might become more common in the future.

Published
2013

37. A new bed elevation dataset for Greenland

Author

Bamber, J. L., Griggs, J. A., Hurkmans, R. T. W. L., Dowdeswell, J. A., Gogineni, S. P., Howat, I., Mouginot, J., Paden, J., Palmer, S., Rignot, E., Steinhage, D., Bamber, J. L., Griggs, J. A., Hurkmans, R. T. W. L., Dowdeswell, J. A., Gogineni, S. P., Howat, I., Mouginot, J., Paden, J., Palmer, S., Rignot, E., and Steinhage, D.

Abstract

We present a new bed elevation dataset for Greenland derived from a combination of multiple airborne ice thickness surveys undertaken between the 1970s and 2012. Around 420 000 line kilometres of airborne data were used, with roughly 70 % of this having been collected since the year 2000, when the last comprehensive compilation was un- dertaken. The airborne data were combined with satellite- derived elevations for non-glaciated terrain to produce a con- sistent bed digital elevation model (DEM) over the entire is- land including across the glaciated–ice free boundary. The DEM was extended to the continental margin with the aid of bathymetric data, primarily from a compilation for the Arc- tic. Ice thickness was determined where an ice shelf exists from a combination of surface elevation and radar soundings. The across-track spacing between flight lines warranted in- terpolation at 1 km postings for significant sectors of the ice sheet. Grids of ice surface elevation, error estimates for the DEM, ice thickness and data sampling density were also pro- duced alongside a mask of land/ocean/grounded ice/floating ice. Errors in bed elevation range from a minimum of ±10 m to about ±300 m, as a function of distance from an obser- vation and local topographic variability. A comparison with the compilation published in 2001 highlights the improve- ment in resolution afforded by the new datasets, particularly along the ice sheet margin, where ice velocity is highest and changes in ice dynamics most marked. We estimate that the volume of ice included in our land-ice mask would raise mean sea level by 7.36 m, excluding any solid earth effects that would take place during ice sheet decay.

Published
2013

38. Eemian interglacial reconstructed from a Greenland folded ice core

Author

Dahl-Jensen, D., Albert, M. R., Aldahan, A., Azuma, N., Balslev-Clausen, D., Baumgartner, M., Berggren, A.-M., Bigler, M., Binder, T., Blunier, T., Bourgeois, J. C., Brook, E. J., Buchardt, S. L., Buizert, C., Capron, E., Chappellaz, J., Chung, J., Clausen, H. B., Cvijanovic, I., Davies, S. M., Ditlevsen, P., Eicher, O., Fischer, H., Fisher, D. A., Fleet, L. G., Gfeller, G., Gkinis, V., Gogineni, S., Grinsted, A., Goto-Azuma, K., Gudlaugsdottir, H., Guillevic, M., Hansen, S. B., Hansson, M., Hirabayashi, M., Hong, S., Hur, S. D., Huybrechts, P., Hvidberg, C. S., Jenk, T., Iizuka, Y., Johnsen, S. J., Jones, T. R., Jouzel, J., Karlsson, N. B., Kawamura, K., Keegan, K., Kettner, E., Kipfstuhl, Sepp, Kjær, H. A., Koutnik, M., Kuramoto, T., Köhler, Peter, Laepple, Thomas, Landais, A., Langen, P. L., Larsen, L. B., Leuenberger, D., Leuenberger, M., Leuschen, C., Li, J., Lipenkov, V., Martinerie, P., Maselli, O. J., Masson-Delmotte, V., McConnell, J. R., Miller, Heinrich, Mini, O., Miyamoto, A., Montagnat-Rentier, M., Mulvaney, R., Muscheler, R., Paden, J., Orsi, A. J., Panton, C., Pattyn, F., Petit, J.-R., Pol, K., Popp, T., Possnert, G., Prié, F., Prokopiou, M., Quiquet, A., Rasmussen, S. O., Raynaud, D., Ren, J., Reutenauer, C., Ritz, C., Röckmann, T., Rosen, J. L., Rubino, M., Rybak, O., Samyn, D., Sapart, C. J., Schilt, A., Schmidt, A. M. Z., Schüpbach, S., Schwander, J., Seierstad, I., Severinghaus, J. P., Sheldon, S., Simonsen, S. B., Sjolte, J., Solgaard, A. M., Sowers, T., Sperlich, P., Steen-Larsen, H. C., Steffen, K., Steffensen, J. P., Steinhage, Daniel, Stocker, T. F., Stowasser, C., Sturevik, A. S., Sturges, W. T., Sveinbjörnsdottir, A., Svensson, A., Tison, J.-L., Uetake, J., Vallelonga, P., van de Wal, R. S. W., van der Wel, G., Vaughn, B. H., Vinther, B., Waddington, E., Wegner, Anna, Weikusat, Ilka, White, J. W. C., Wilhelms, Frank, Winstrup, M., Witrant, E., Wolff, E. W., Xiao, C., Zheng, J., Dahl-Jensen, D., Albert, M. R., Aldahan, A., Azuma, N., Balslev-Clausen, D., Baumgartner, M., Berggren, A.-M., Bigler, M., Binder, T., Blunier, T., Bourgeois, J. C., Brook, E. J., Buchardt, S. L., Buizert, C., Capron, E., Chappellaz, J., Chung, J., Clausen, H. B., Cvijanovic, I., Davies, S. M., Ditlevsen, P., Eicher, O., Fischer, H., Fisher, D. A., Fleet, L. G., Gfeller, G., Gkinis, V., Gogineni, S., Grinsted, A., Goto-Azuma, K., Gudlaugsdottir, H., Guillevic, M., Hansen, S. B., Hansson, M., Hirabayashi, M., Hong, S., Hur, S. D., Huybrechts, P., Hvidberg, C. S., Jenk, T., Iizuka, Y., Johnsen, S. J., Jones, T. R., Jouzel, J., Karlsson, N. B., Kawamura, K., Keegan, K., Kettner, E., Kipfstuhl, Sepp, Kjær, H. A., Koutnik, M., Kuramoto, T., Köhler, Peter, Laepple, Thomas, Landais, A., Langen, P. L., Larsen, L. B., Leuenberger, D., Leuenberger, M., Leuschen, C., Li, J., Lipenkov, V., Martinerie, P., Maselli, O. J., Masson-Delmotte, V., McConnell, J. R., Miller, Heinrich, Mini, O., Miyamoto, A., Montagnat-Rentier, M., Mulvaney, R., Muscheler, R., Paden, J., Orsi, A. J., Panton, C., Pattyn, F., Petit, J.-R., Pol, K., Popp, T., Possnert, G., Prié, F., Prokopiou, M., Quiquet, A., Rasmussen, S. O., Raynaud, D., Ren, J., Reutenauer, C., Ritz, C., Röckmann, T., Rosen, J. L., Rubino, M., Rybak, O., Samyn, D., Sapart, C. J., Schilt, A., Schmidt, A. M. Z., Schüpbach, S., Schwander, J., Seierstad, I., Severinghaus, J. P., Sheldon, S., Simonsen, S. B., Sjolte, J., Solgaard, A. M., Sowers, T., Sperlich, P., Steen-Larsen, H. C., Steffen, K., Steffensen, J. P., Steinhage, Daniel, Stocker, T. F., Stowasser, C., Sturevik, A. S., Sturges, W. T., Sveinbjörnsdottir, A., Svensson, A., Tison, J.-L., Uetake, J., Vallelonga, P., van de Wal, R. S. W., van der Wel, G., Vaughn, B. H., Vinther, B., Waddington, E., Wegner, Anna, Weikusat, Ilka, White, J. W. C., Wilhelms, Frank, Winstrup, M., Witrant, E., Wolff, E. W., Xiao, C., and Zheng, J.

Abstract

Efforts to extract a Greenland ice core with a complete record of the Eemian interglacial (130,000 to 115,000 years ago) have until now been unsuccessful. The response of the Greenland ice sheet to the warmer-than-present climate of the Eemian has thus remained unclear. Here we present the new North Greenland Eemian Ice Drilling (‘NEEM’) ice core and show only a modest ice-sheet response to the strong warming in the early Eemian. We reconstructed the Eemian record from folded ice using globally homogeneous parameters known from dated Greenland and Antarctic ice-core records. On the basis of water stable isotopes, NEEM surface temperatures after the onset of the Eemian (126,000 years ago) peaked at 8 ± 4 degrees Celsius above the mean of the past millennium, followed by a gradual cooling that was probably driven by the decreasing summer insolation. Between 128,000 and 122,000 years ago, the thickness of the northwest Greenland ice sheet decreased by 400 ± 250 metres, reaching surface elevations 122,000 years ago of 130 ± 300 metres lower than the present. Extensive surface melt occurred at the NEEM site during the Eemian, a phenomenon witnessed when melt layers formed again at NEEM during the exceptional heat of July 2012. With additional warming, surface melt might become more common in the future.

Published
2013

39. A new bed elevation dataset for Greenland

Author

Bamber, J. L, Bamber, J. L, Griggs, J. A, Hurkmans, R. T. W. L, Dowdeswell, J. A, Gogineni, S. P, Howat, I., Mouginot, J., Paden, J., Palmer, S., Rignot, E., Steinhage, D., Bamber, J. L, Bamber, J. L, Griggs, J. A, Hurkmans, R. T. W. L, Dowdeswell, J. A, Gogineni, S. P, Howat, I., Mouginot, J., Paden, J., Palmer, S., Rignot, E., and Steinhage, D.

Published
2013

40. Airborne-radar and ice-core observations of annual snow accumulation over Thwaites Glacier, West Antarctica confirm the spatiotemporal variability of global and regional atmospheric models

Author

Marine and Atmospheric Research, Sub Dynamics Meteorology, Medley, B., Joughin, I., Das, S.B., Steig, E. J., Conway, H., Gogineni, S., Criscitiello, A.S., McConnell, J.R., Smith, B.E., van den Broeke, M.R., Lenaerts, J.T.M., Bromwich, D.H., Nicolas, J.P., Marine and Atmospheric Research, Sub Dynamics Meteorology, Medley, B., Joughin, I., Das, S.B., Steig, E. J., Conway, H., Gogineni, S., Criscitiello, A.S., McConnell, J.R., Smith, B.E., van den Broeke, M.R., Lenaerts, J.T.M., Bromwich, D.H., and Nicolas, J.P.

Published
2013

41. A new bed elevation dataset for Greenland

Author

Bamber, J. L., Griggs, J. A., Hurkmans, R. T. W. L., Dowdeswell, J. A., Gogineni, S. P., Howat, I., Mouginot, J., Paden, J., Palmer, S., Rignot, E., Steinhage, D., Bamber, J. L., Griggs, J. A., Hurkmans, R. T. W. L., Dowdeswell, J. A., Gogineni, S. P., Howat, I., Mouginot, J., Paden, J., Palmer, S., Rignot, E., and Steinhage, D.

Abstract

We present a new bed elevation dataset for Greenland derived from a combination of multiple airborne ice thickness surveys undertaken between the 1970s and 2012. Around 420 000 line kilometres of airborne data were used, with roughly 70 % of this having been collected since the year 2000, when the last comprehensive compilation was un- dertaken. The airborne data were combined with satellite- derived elevations for non-glaciated terrain to produce a con- sistent bed digital elevation model (DEM) over the entire is- land including across the glaciated–ice free boundary. The DEM was extended to the continental margin with the aid of bathymetric data, primarily from a compilation for the Arc- tic. Ice thickness was determined where an ice shelf exists from a combination of surface elevation and radar soundings. The across-track spacing between flight lines warranted in- terpolation at 1 km postings for significant sectors of the ice sheet. Grids of ice surface elevation, error estimates for the DEM, ice thickness and data sampling density were also pro- duced alongside a mask of land/ocean/grounded ice/floating ice. Errors in bed elevation range from a minimum of ±10 m to about ±300 m, as a function of distance from an obser- vation and local topographic variability. A comparison with the compilation published in 2001 highlights the improve- ment in resolution afforded by the new datasets, particularly along the ice sheet margin, where ice velocity is highest and changes in ice dynamics most marked. We estimate that the volume of ice included in our land-ice mask would raise mean sea level by 7.36 m, excluding any solid earth effects that would take place during ice sheet decay.

Published
2013

42. Eemian interglacial reconstructed from a Greenland folded ice core

Author

Dahl-Jensen, D., Albert, M. R., Aldahan, A., Azuma, N., Balslev-Clausen, D., Baumgartner, M., Berggren, A.-M., Bigler, M., Binder, T., Blunier, T., Bourgeois, J. C., Brook, E. J., Buchardt, S. L., Buizert, C., Capron, E., Chappellaz, J., Chung, J., Clausen, H. B., Cvijanovic, I., Davies, S. M., Ditlevsen, P., Eicher, O., Fischer, H., Fisher, D. A., Fleet, L. G., Gfeller, G., Gkinis, V., Gogineni, S., Grinsted, A., Goto-Azuma, K., Gudlaugsdottir, H., Guillevic, M., Hansen, S. B., Hansson, M., Hirabayashi, M., Hong, S., Hur, S. D., Huybrechts, P., Hvidberg, C. S., Jenk, T., Iizuka, Y., Johnsen, S. J., Jones, T. R., Jouzel, J., Karlsson, N. B., Kawamura, K., Keegan, K., Kettner, E., Kipfstuhl, Sepp, Kjær, H. A., Koutnik, M., Kuramoto, T., Köhler, Peter, Laepple, Thomas, Landais, A., Langen, P. L., Larsen, L. B., Leuenberger, D., Leuenberger, M., Leuschen, C., Li, J., Lipenkov, V., Martinerie, P., Maselli, O. J., Masson-Delmotte, V., McConnell, J. R., Miller, Heinrich, Mini, O., Miyamoto, A., Montagnat-Rentier, M., Mulvaney, R., Muscheler, R., Paden, J., Orsi, A. J., Panton, C., Pattyn, F., Petit, J.-R., Pol, K., Popp, T., Possnert, G., Prié, F., Prokopiou, M., Quiquet, A., Rasmussen, S. O., Raynaud, D., Ren, J., Reutenauer, C., Ritz, C., Röckmann, T., Rosen, J. L., Rubino, M., Rybak, O., Samyn, D., Sapart, C. J., Schilt, A., Schmidt, A. M. Z., Schüpbach, S., Schwander, J., Seierstad, I., Severinghaus, J. P., Sheldon, S., Simonsen, S. B., Sjolte, J., Solgaard, A. M., Sowers, T., Sperlich, P., Steen-Larsen, H. C., Steffen, K., Steffensen, J. P., Steinhage, Daniel, Stocker, T. F., Stowasser, C., Sturevik, A. S., Sturges, W. T., Sveinbjörnsdottir, A., Svensson, A., Tison, J.-L., Uetake, J., Vallelonga, P., van de Wal, R. S. W., van der Wel, G., Vaughn, B. H., Vinther, B., Waddington, E., Wegner, Anna, Weikusat, Ilka, White, J. W. C., Wilhelms, Frank, Winstrup, M., Witrant, E., Wolff, E. W., Xiao, C., Zheng, J., Dahl-Jensen, D., Albert, M. R., Aldahan, A., Azuma, N., Balslev-Clausen, D., Baumgartner, M., Berggren, A.-M., Bigler, M., Binder, T., Blunier, T., Bourgeois, J. C., Brook, E. J., Buchardt, S. L., Buizert, C., Capron, E., Chappellaz, J., Chung, J., Clausen, H. B., Cvijanovic, I., Davies, S. M., Ditlevsen, P., Eicher, O., Fischer, H., Fisher, D. A., Fleet, L. G., Gfeller, G., Gkinis, V., Gogineni, S., Grinsted, A., Goto-Azuma, K., Gudlaugsdottir, H., Guillevic, M., Hansen, S. B., Hansson, M., Hirabayashi, M., Hong, S., Hur, S. D., Huybrechts, P., Hvidberg, C. S., Jenk, T., Iizuka, Y., Johnsen, S. J., Jones, T. R., Jouzel, J., Karlsson, N. B., Kawamura, K., Keegan, K., Kettner, E., Kipfstuhl, Sepp, Kjær, H. A., Koutnik, M., Kuramoto, T., Köhler, Peter, Laepple, Thomas, Landais, A., Langen, P. L., Larsen, L. B., Leuenberger, D., Leuenberger, M., Leuschen, C., Li, J., Lipenkov, V., Martinerie, P., Maselli, O. J., Masson-Delmotte, V., McConnell, J. R., Miller, Heinrich, Mini, O., Miyamoto, A., Montagnat-Rentier, M., Mulvaney, R., Muscheler, R., Paden, J., Orsi, A. J., Panton, C., Pattyn, F., Petit, J.-R., Pol, K., Popp, T., Possnert, G., Prié, F., Prokopiou, M., Quiquet, A., Rasmussen, S. O., Raynaud, D., Ren, J., Reutenauer, C., Ritz, C., Röckmann, T., Rosen, J. L., Rubino, M., Rybak, O., Samyn, D., Sapart, C. J., Schilt, A., Schmidt, A. M. Z., Schüpbach, S., Schwander, J., Seierstad, I., Severinghaus, J. P., Sheldon, S., Simonsen, S. B., Sjolte, J., Solgaard, A. M., Sowers, T., Sperlich, P., Steen-Larsen, H. C., Steffen, K., Steffensen, J. P., Steinhage, Daniel, Stocker, T. F., Stowasser, C., Sturevik, A. S., Sturges, W. T., Sveinbjörnsdottir, A., Svensson, A., Tison, J.-L., Uetake, J., Vallelonga, P., van de Wal, R. S. W., van der Wel, G., Vaughn, B. H., Vinther, B., Waddington, E., Wegner, Anna, Weikusat, Ilka, White, J. W. C., Wilhelms, Frank, Winstrup, M., Witrant, E., Wolff, E. W., Xiao, C., and Zheng, J.

Abstract

Efforts to extract a Greenland ice core with a complete record of the Eemian interglacial (130,000 to 115,000 years ago) have until now been unsuccessful. The response of the Greenland ice sheet to the warmer-than-present climate of the Eemian has thus remained unclear. Here we present the new North Greenland Eemian Ice Drilling (‘NEEM’) ice core and show only a modest ice-sheet response to the strong warming in the early Eemian. We reconstructed the Eemian record from folded ice using globally homogeneous parameters known from dated Greenland and Antarctic ice-core records. On the basis of water stable isotopes, NEEM surface temperatures after the onset of the Eemian (126,000 years ago) peaked at 8 ± 4 degrees Celsius above the mean of the past millennium, followed by a gradual cooling that was probably driven by the decreasing summer insolation. Between 128,000 and 122,000 years ago, the thickness of the northwest Greenland ice sheet decreased by 400 ± 250 metres, reaching surface elevations 122,000 years ago of 130 ± 300 metres lower than the present. Extensive surface melt occurred at the NEEM site during the Eemian, a phenomenon witnessed when melt layers formed again at NEEM during the exceptional heat of July 2012. With additional warming, surface melt might become more common in the future.

Published
2013

43. Airborne-radar and ice-core observations of annual snow accumulation over Thwaites Glacier, West Antarctica confirm the spatiotemporal variability of global and regional atmospheric models

Author

Marine and Atmospheric Research, Sub Dynamics Meteorology, Medley, B., Joughin, I., Das, S.B., Steig, E. J., Conway, H., Gogineni, S., Criscitiello, A.S., McConnell, J.R., Smith, B.E., van den Broeke, M.R., Lenaerts, J.T.M., Bromwich, D.H., Nicolas, J.P., Marine and Atmospheric Research, Sub Dynamics Meteorology, Medley, B., Joughin, I., Das, S.B., Steig, E. J., Conway, H., Gogineni, S., Criscitiello, A.S., McConnell, J.R., Smith, B.E., van den Broeke, M.R., Lenaerts, J.T.M., Bromwich, D.H., and Nicolas, J.P.

Published
2013

44. Eemian interglacial reconstructed from a Greenland folded ice core

Author

Dahl-Jensen, D., Albert, M.R., Aldahan, A., Azuma, N., Balslev-Clausen, D., Baumgartner, M., Berggren, A.-M., Bigler, M., Binder, T., Blunier, T., Bourgeois, J.C., Brook, E.J., Buchardt, S.L., Buizert, C., Capron, E., Chappellaz, J., Chung, J., Clausen, H.B., Cvijanovic, I., Davies, S. M., Ditlevsen, P., Eicher, O., Fischer, H., Fisher, D.A., Fleet, L.G., Gfeller, G., Gkinis, V., Gogineni, S., Goto-Azuma, K., Grinsted, A., Gudlaugsdottir, H., Guillevic, M., Hansen, S.B., Hansson, M., Hirabayashi, M., Hong, S., Hur, S.D., Huybrechts, P., Hvidberg, C.S., Iizuka, Y., Jenk, T., Johnsen, S.J., Jones, T.R., Jouzel, J., Karlsson, N.B., Kawamura, K., Keegan, K., Kettner, E., Kipfstuhl, S., Kjær, H.A., Koutnik, M., Kuramoto, T., Köhler, P., Laepple, T., Landais, A., Langen, P.L., Larsen, L.B., Leuenberger, D., Leuenberger, M., Leuschen, C., Li, J., Lipenkov, V., Martinerie, P., Maselli, O.J., Masson-Delmotte, V., McConnell, J.R., Miller, H., Mini, O., Miyamoto, A., Montagnat-Rentier, M., Mulvaney, R., Muscheler, R., Orsi, A.J., Paden, J., Panton, C., Pattyn, F., Petit, J.-R., Pol, K., Popp, T., Possnert, G., Prié, F., Prokopiou, M., Quiquet, A., Rasmussen, S.O., Raynaud, D., Ren, J., Reutenauer, C., Ritz, C., Röckmann, T., Rosen, J.L., Rubino, M., Rybak, O., Samyn, D., Sapart, C.J., Schilt, A., Schmidt, A.M.Z., Schwander, J., Schüpbach, S., Seierstad, I., Severinghaus, J.P., Sheldon, S., Simonsen, S.B., Sjolte, J., Solgaard, A.M., Sowers, T., Sperlich, P., Steen-Larsen, H.C., Steffen, K., Steffensen, J.P., Steinhage, D., Stocker, T.F., Stowasser, C., Sturevik, A.S., Sturges, W.T., Sveinbjörnsdottir, A., Svensson, A., Tison, J.-L., Uetake, J., Vallelonga, P., van de Wal, R.S.W., van der Wel, G., Vaughn, B.H., Vinther, B., Waddington, E., Wegner, A., Weikusat, I., White, J.W.C., Wilhelms, F., Winstrup, M., Witrant, E., Wolff, E.W., Xiao, C., Zheng, J., Dahl-Jensen, D., Albert, M.R., Aldahan, A., Azuma, N., Balslev-Clausen, D., Baumgartner, M., Berggren, A.-M., Bigler, M., Binder, T., Blunier, T., Bourgeois, J.C., Brook, E.J., Buchardt, S.L., Buizert, C., Capron, E., Chappellaz, J., Chung, J., Clausen, H.B., Cvijanovic, I., Davies, S. M., Ditlevsen, P., Eicher, O., Fischer, H., Fisher, D.A., Fleet, L.G., Gfeller, G., Gkinis, V., Gogineni, S., Goto-Azuma, K., Grinsted, A., Gudlaugsdottir, H., Guillevic, M., Hansen, S.B., Hansson, M., Hirabayashi, M., Hong, S., Hur, S.D., Huybrechts, P., Hvidberg, C.S., Iizuka, Y., Jenk, T., Johnsen, S.J., Jones, T.R., Jouzel, J., Karlsson, N.B., Kawamura, K., Keegan, K., Kettner, E., Kipfstuhl, S., Kjær, H.A., Koutnik, M., Kuramoto, T., Köhler, P., Laepple, T., Landais, A., Langen, P.L., Larsen, L.B., Leuenberger, D., Leuenberger, M., Leuschen, C., Li, J., Lipenkov, V., Martinerie, P., Maselli, O.J., Masson-Delmotte, V., McConnell, J.R., Miller, H., Mini, O., Miyamoto, A., Montagnat-Rentier, M., Mulvaney, R., Muscheler, R., Orsi, A.J., Paden, J., Panton, C., Pattyn, F., Petit, J.-R., Pol, K., Popp, T., Possnert, G., Prié, F., Prokopiou, M., Quiquet, A., Rasmussen, S.O., Raynaud, D., Ren, J., Reutenauer, C., Ritz, C., Röckmann, T., Rosen, J.L., Rubino, M., Rybak, O., Samyn, D., Sapart, C.J., Schilt, A., Schmidt, A.M.Z., Schwander, J., Schüpbach, S., Seierstad, I., Severinghaus, J.P., Sheldon, S., Simonsen, S.B., Sjolte, J., Solgaard, A.M., Sowers, T., Sperlich, P., Steen-Larsen, H.C., Steffen, K., Steffensen, J.P., Steinhage, D., Stocker, T.F., Stowasser, C., Sturevik, A.S., Sturges, W.T., Sveinbjörnsdottir, A., Svensson, A., Tison, J.-L., Uetake, J., Vallelonga, P., van de Wal, R.S.W., van der Wel, G., Vaughn, B.H., Vinther, B., Waddington, E., Wegner, A., Weikusat, I., White, J.W.C., Wilhelms, F., Winstrup, M., Witrant, E., Wolff, E.W., Xiao, C., and Zheng, J.

Abstract

Efforts to extract a Greenland ice core with a complete record of the Eemian interglacial (130,000 to 115,000 years ago) have until now been unsuccessful. The response of the Greenland ice sheet to the warmer-than-present climate of the Eemian has thus remained unclear. Here we present the new North Greenland Eemian Ice Drilling (‘NEEM’) ice core and show only a modest ice-sheet response to the strong warming in the early Eemian. We reconstructed the Eemian record from folded ice using globally homogeneous parameters known from dated Greenland and Antarctic ice-core records. On the basis of water stable isotopes, NEEM surface temperatures after the onset of the Eemian (126,000 years ago) peaked at 8 ± 4 degrees Celsius above the mean of the past millennium, followed by a gradual cooling that was probably driven by the decreasing summer insolation. Between 128,000 and 122,000 years ago, the thickness of the northwest Greenland ice sheet decreased by 400 ± 250 metres, reaching surface elevations 122,000 years ago of 130 ± 300 metres lower than the present. Extensive surface melt occurred at the NEEM site during the Eemian, a phenomenon witnessed when melt layers formed again at NEEM during the exceptional heat of July 2012. With additional warming, surface melt might become more common in the future.

Published
2013

45. Multiple-pulse PIV: Numerical evaluation and experimental validation

Author

Ding, L. (author), Discetti, S. (author), Adrian, R.J. (author), Gogineni, S. (author), Ding, L. (author), Discetti, S. (author), Adrian, R.J. (author), and Gogineni, S. (author)

Abstract

Many conventional experimental methods in fluid mechanics, such as LDV and HWA, are not able to measure simultaneous acceleration fields directly. Double-pulse PIV is extended to the multiple-pulse PIV enabling people to directly extract acceleration fields as well as to achieve better accuracy in the velocity measurement [13]. We evaluate the performances of triple-pulse PIV and quadruple-pulse PIV based on PTV simulations. By investigating various flow conditions, optimizations are globally achieved to minimize the error in velocity and acceleration measurements for both triple-pulse and quadruple-pulse PIV. Compared to that with uneven time spacing, triple-pulse PIV with even time spacing yields better spatial resolution in velocity measurement. Moreover, quadruple-pulse PIV significantly reduces the error in both velocity and acceleration measurement relative to triple-pulse PIV. Experimental validation of the acceleration measurement from triple-pulse PIV is conducted by measuring the mean centerline acceleration profile of a round impinging air jet. A custom 8-pulse laser system in combination with an ultra high-speed 4-channel camera are utilized to well satisfy the requirements of multiple-pulse PIV. Conventional double-pulse PIV, together with the polynomial curve fitting, are used to obtain the ground truth for the mean centerline acceleration profile. The comparison between the ground truth and acceleration measurements by triple-pulse PIV shows a good agreement with the maximum error being 10% of the full scale acceleration. Several potential error sources are also discussed to provide the direction of making improvements in the following stage.

Published
2013

46. Eemian interglacial reconstructed from a Greenland folded ice core

Author

Dahl-Jensen, Dorthe, Albert, M. R., Aldahan, A., Azuma, N., Balslev-Clausen, David Morten, Baumgartner, M., Berggren, A.-M., Bigler, M., Binder, Thomas, Blunier, Thomas, Bourgeois, J.C., Brook, E.J., Buchardt, Susanne Lilja, Buizert, Christo, Capron, E., Chappellaz, J., Chung, J., Clausen, Henrik Brink, Cvijanovic, Ivana, Davies, S.M., Ditlevsen, Peter, Eicher, O., Fischer, H., Fisher, D. A., Fleet, L.G., Gfeller, G., Gkinis, Vasileios, Gogineni, S., Goto-Azuma, K., Grinsted, Aslak, Gudlaugsdottir, H., Guillevic, Myriam, Hansen, S. B., Hansson, M., Hirabayashi, M., Hong, S., Hur, S.D., Huybrechts, P., Hvidberg, Christine Schøtt, Iizuka, Y., Jenk, Theo Manuel, Johnsen, Sigfus Johann, Jones, T.R., Jouzel, J., Karlsson, Nanna Bjørnholt, Kawamura, K., Keegan, K., Kettner, Ernesto, Kipfstuhl, S., Kjær, Helle Astrid, Koutnik, M., Kuramoto, T., Köhler, P., Laepple, T., Landais, A., Langen, Peter Lang, Larsen, Lars Berg, Leuenberger, D., Leuenberger, M., Leuschen, C., Li, J., Lipenkov, V., Martinerie, P., Maselli, O. J., Masson-Delmotte, V., McConnell, J. R., Miller, H., Mini, O., Miyamoto, A., Montagnat-Rentier, M., Mulvaney, R., Muscheler, R., Orsi, A.J., Paden, J., Panton, Christian, Pattyn, F., Petit, J.-R., Pol, K., Popp, Trevor James, Possnert, G., Prié, F., Prokopiou, M., Quiquet, A., Rasmussen, Sune Olander, Raynaud, D., Ren, J., Reutenauer, Corentin, Ritz, C., Röckmann, T., Rosen, J.L., Rubino, Mauro, Rybak, O., Samyn, D., Sapart, C.J., Schilt, A., Schmidt, Astrid Mariah Zelma, Schwander, J., Schüpbach, S., Seierstad, Inger Kathrine, Severinghaus, J. P., Sheldon, S., Simonsen, Sebastian Bjerregaard, Sjolte, Jesper, Solgaard, Anne Munck, Sowers, T., Sperlich, Peter, Steen-Larsen, Hans Christian, Steffen, K., Steffensen, Jørgen Peder, Steinhage, D., Stocker, T.F., Stowasser, Christopher, Sturevik, A.S., Sturges, W.T., Sveinbjörnsdottir, A., Svensson, Anders, Tison, J.-L., Uetake, J., Vallelonga, Paul Travis, Van De Wal, R.S.W., Van Der Wel, G., Vaughn, B.H., Vinther, Bo Møllesøe, Waddington, E., Wegner, A., Weikusat, I., White, J. W. C., Wilhelms, F., Winstrup, Mai, Witrant, E., Wolff, E.W., Xiao, C., Zheng, Jin, Dahl-Jensen, Dorthe, Albert, M. R., Aldahan, A., Azuma, N., Balslev-Clausen, David Morten, Baumgartner, M., Berggren, A.-M., Bigler, M., Binder, Thomas, Blunier, Thomas, Bourgeois, J.C., Brook, E.J., Buchardt, Susanne Lilja, Buizert, Christo, Capron, E., Chappellaz, J., Chung, J., Clausen, Henrik Brink, Cvijanovic, Ivana, Davies, S.M., Ditlevsen, Peter, Eicher, O., Fischer, H., Fisher, D. A., Fleet, L.G., Gfeller, G., Gkinis, Vasileios, Gogineni, S., Goto-Azuma, K., Grinsted, Aslak, Gudlaugsdottir, H., Guillevic, Myriam, Hansen, S. B., Hansson, M., Hirabayashi, M., Hong, S., Hur, S.D., Huybrechts, P., Hvidberg, Christine Schøtt, Iizuka, Y., Jenk, Theo Manuel, Johnsen, Sigfus Johann, Jones, T.R., Jouzel, J., Karlsson, Nanna Bjørnholt, Kawamura, K., Keegan, K., Kettner, Ernesto, Kipfstuhl, S., Kjær, Helle Astrid, Koutnik, M., Kuramoto, T., Köhler, P., Laepple, T., Landais, A., Langen, Peter Lang, Larsen, Lars Berg, Leuenberger, D., Leuenberger, M., Leuschen, C., Li, J., Lipenkov, V., Martinerie, P., Maselli, O. J., Masson-Delmotte, V., McConnell, J. R., Miller, H., Mini, O., Miyamoto, A., Montagnat-Rentier, M., Mulvaney, R., Muscheler, R., Orsi, A.J., Paden, J., Panton, Christian, Pattyn, F., Petit, J.-R., Pol, K., Popp, Trevor James, Possnert, G., Prié, F., Prokopiou, M., Quiquet, A., Rasmussen, Sune Olander, Raynaud, D., Ren, J., Reutenauer, Corentin, Ritz, C., Röckmann, T., Rosen, J.L., Rubino, Mauro, Rybak, O., Samyn, D., Sapart, C.J., Schilt, A., Schmidt, Astrid Mariah Zelma, Schwander, J., Schüpbach, S., Seierstad, Inger Kathrine, Severinghaus, J. P., Sheldon, S., Simonsen, Sebastian Bjerregaard, Sjolte, Jesper, Solgaard, Anne Munck, Sowers, T., Sperlich, Peter, Steen-Larsen, Hans Christian, Steffen, K., Steffensen, Jørgen Peder, Steinhage, D., Stocker, T.F., Stowasser, Christopher, Sturevik, A.S., Sturges, W.T., Sveinbjörnsdottir, A., Svensson, Anders, Tison, J.-L., Uetake, J., Vallelonga, Paul Travis, Van De Wal, R.S.W., Van Der Wel, G., Vaughn, B.H., Vinther, Bo Møllesøe, Waddington, E., Wegner, A., Weikusat, I., White, J. W. C., Wilhelms, F., Winstrup, Mai, Witrant, E., Wolff, E.W., Xiao, C., and Zheng, Jin

Abstract

Efforts to extract a Greenland ice core with a complete record of the Eemian interglacial (130,000 to 115,000 years ago) have until now been unsuccessful. The response of the Greenland ice sheet to the warmer-than-present climate of the Eemian has thus remained unclear. Here we present the new North Greenland Eemian Ice Drilling ('NEEM') ice core and show only a modest ice-sheet response to the strong warming in the early Eemian. We reconstructed the Eemian record from folded ice using globally homogeneous parameters known from dated Greenland and Antarctic ice-core records. On the basis of water stable isotopes, NEEM surface temperatures after the onset of the Eemian (126,000 years ago) peaked at 8 ± 4 degrees Celsius above the mean of the past millennium, followed by a gradual cooling that was probably driven by the decreasing summer insolation. Between 128,000 and 122,000 years ago, the thickness of the northwest Greenland ice sheet decreased by 400 ± 250 metres, reaching surface elevations 122,000 years ago of 130 ± 300 metres lower than the present. Extensive surface melt occurred at the NEEM site during the Eemian, a phenomenon witnessed when melt layers formed again at NEEM during the exceptional heat of July 2012. With additional warming, surface melt might become more common in the future.

Published
2013

48. Eemian interglacial reconstructed from a Greenland folded ice core

Author

Dahl-Jensen, Dorthe, Albert, M. R., Aldahan, A., Azuma, N., Balslev-Clausen, David Morten, Baumgartner, M., Berggren, A.-M., Bigler, M., Binder, Thomas, Blunier, Thomas, Bourgeois, J.C., Brook, E.J., Buchardt, Susanne Lilja, Buizert, Christo, Capron, E., Chappellaz, J., Chung, J., Clausen, Henrik Brink, Cvijanovic, Ivana, Davies, S.M., Ditlevsen, Peter, Eicher, O., Fischer, H., Fisher, D. A., Fleet, L.G., Gfeller, G., Gkinis, Vasileios, Gogineni, S., Goto-Azuma, K., Grinsted, Aslak, Gudlaugsdottir, H., Guillevic, Myriam, Hansen, S. B., Hansson, M., Hirabayashi, M., Hong, S., Hur, S.D., Huybrechts, P., Hvidberg, Christine Schøtt, Iizuka, Y., Jenk, Theo Manuel, Johnsen, Sigfus Johann, Jones, T.R., Jouzel, J., Karlsson, Nanna Bjørnholt, Kawamura, K., Keegan, K., Kettner, Ernesto, Kipfstuhl, S., Kjær, Helle Astrid, Koutnik, M., Kuramoto, T., Köhler, P., Laepple, T., Landais, A., Langen, Peter Lang, Larsen, Lars Berg, Leuenberger, D., Leuenberger, M., Leuschen, C., Li, J., Lipenkov, V., Martinerie, P., Maselli, O. J., Masson-Delmotte, V., McConnell, J. R., Miller, H., Mini, O., Miyamoto, A., Montagnat-Rentier, M., Mulvaney, R., Muscheler, R., Orsi, A.J., Paden, J., Panton, Christian, Pattyn, F., Petit, J.-R., Pol, K., Popp, Trevor James, Possnert, G., Prié, F., Prokopiou, M., Quiquet, A., Rasmussen, Sune Olander, Raynaud, D., Ren, J., Reutenauer, Corentin, Ritz, C., Röckmann, T., Rosen, J.L., Rubino, Mauro, Rybak, O., Samyn, D., Sapart, C.J., Schilt, A., Schmidt, Astrid Mariah Zelma, Schwander, J., Schüpbach, S., Seierstad, Inger Kathrine, Severinghaus, J. P., Sheldon, S., Simonsen, Sebastian Bjerregaard, Sjolte, Jesper, Solgaard, Anne Munck, Sowers, T., Sperlich, Peter, Steen-Larsen, Hans Christian, Steffen, K., Steffensen, Jørgen Peder, Steinhage, D., Stocker, T.F., Stowasser, Christopher, Sturevik, A.S., Sturges, W.T., Sveinbjörnsdottir, A., Svensson, Anders, Tison, J.-L., Uetake, J., Vallelonga, Paul Travis, Van De Wal, R.S.W., Van Der Wel, G., Vaughn, B.H., Vinther, Bo Møllesøe, Waddington, E., Wegner, A., Weikusat, I., White, J. W. C., Wilhelms, F., Winstrup, Mai, Witrant, E., Wolff, E.W., Xiao, C., Zheng, Jin, Dahl-Jensen, Dorthe, Albert, M. R., Aldahan, A., Azuma, N., Balslev-Clausen, David Morten, Baumgartner, M., Berggren, A.-M., Bigler, M., Binder, Thomas, Blunier, Thomas, Bourgeois, J.C., Brook, E.J., Buchardt, Susanne Lilja, Buizert, Christo, Capron, E., Chappellaz, J., Chung, J., Clausen, Henrik Brink, Cvijanovic, Ivana, Davies, S.M., Ditlevsen, Peter, Eicher, O., Fischer, H., Fisher, D. A., Fleet, L.G., Gfeller, G., Gkinis, Vasileios, Gogineni, S., Goto-Azuma, K., Grinsted, Aslak, Gudlaugsdottir, H., Guillevic, Myriam, Hansen, S. B., Hansson, M., Hirabayashi, M., Hong, S., Hur, S.D., Huybrechts, P., Hvidberg, Christine Schøtt, Iizuka, Y., Jenk, Theo Manuel, Johnsen, Sigfus Johann, Jones, T.R., Jouzel, J., Karlsson, Nanna Bjørnholt, Kawamura, K., Keegan, K., Kettner, Ernesto, Kipfstuhl, S., Kjær, Helle Astrid, Koutnik, M., Kuramoto, T., Köhler, P., Laepple, T., Landais, A., Langen, Peter Lang, Larsen, Lars Berg, Leuenberger, D., Leuenberger, M., Leuschen, C., Li, J., Lipenkov, V., Martinerie, P., Maselli, O. J., Masson-Delmotte, V., McConnell, J. R., Miller, H., Mini, O., Miyamoto, A., Montagnat-Rentier, M., Mulvaney, R., Muscheler, R., Orsi, A.J., Paden, J., Panton, Christian, Pattyn, F., Petit, J.-R., Pol, K., Popp, Trevor James, Possnert, G., Prié, F., Prokopiou, M., Quiquet, A., Rasmussen, Sune Olander, Raynaud, D., Ren, J., Reutenauer, Corentin, Ritz, C., Röckmann, T., Rosen, J.L., Rubino, Mauro, Rybak, O., Samyn, D., Sapart, C.J., Schilt, A., Schmidt, Astrid Mariah Zelma, Schwander, J., Schüpbach, S., Seierstad, Inger Kathrine, Severinghaus, J. P., Sheldon, S., Simonsen, Sebastian Bjerregaard, Sjolte, Jesper, Solgaard, Anne Munck, Sowers, T., Sperlich, Peter, Steen-Larsen, Hans Christian, Steffen, K., Steffensen, Jørgen Peder, Steinhage, D., Stocker, T.F., Stowasser, Christopher, Sturevik, A.S., Sturges, W.T., Sveinbjörnsdottir, A., Svensson, Anders, Tison, J.-L., Uetake, J., Vallelonga, Paul Travis, Van De Wal, R.S.W., Van Der Wel, G., Vaughn, B.H., Vinther, Bo Møllesøe, Waddington, E., Wegner, A., Weikusat, I., White, J. W. C., Wilhelms, F., Winstrup, Mai, Witrant, E., Wolff, E.W., Xiao, C., and Zheng, Jin

Abstract

Efforts to extract a Greenland ice core with a complete record of the Eemian interglacial (130,000 to 115,000 years ago) have until now been unsuccessful. The response of the Greenland ice sheet to the warmer-than-present climate of the Eemian has thus remained unclear. Here we present the new North Greenland Eemian Ice Drilling ('NEEM') ice core and show only a modest ice-sheet response to the strong warming in the early Eemian. We reconstructed the Eemian record from folded ice using globally homogeneous parameters known from dated Greenland and Antarctic ice-core records. On the basis of water stable isotopes, NEEM surface temperatures after the onset of the Eemian (126,000 years ago) peaked at 8 ± 4 degrees Celsius above the mean of the past millennium, followed by a gradual cooling that was probably driven by the decreasing summer insolation. Between 128,000 and 122,000 years ago, the thickness of the northwest Greenland ice sheet decreased by 400 ± 250 metres, reaching surface elevations 122,000 years ago of 130 ± 300 metres lower than the present. Extensive surface melt occurred at the NEEM site during the Eemian, a phenomenon witnessed when melt layers formed again at NEEM during the exceptional heat of July 2012. With additional warming, surface melt might become more common in the future.

Published
2013

50. CryoSat cal/val activities on Austfonna – Part II: Ground-based measurements using a Ku-band radar, for validation of the CryoSat-2 SIRAL data

Author

Langley, K., Patel, A., Hawley, R., Dunse, T., Hagen, J.O., Kohler, J., Skourup, H., Gogineni, S., Forsström, S., Eiken, T., Leuschen, C., Helm, Veit, Langley, K., Patel, A., Hawley, R., Dunse, T., Hagen, J.O., Kohler, J., Skourup, H., Gogineni, S., Forsström, S., Eiken, T., Leuschen, C., and Helm, Veit

Abstract

We show first results of a combined ground based and airborne validation campaign for CryoSat-2 synthetic aperture interferometric radar altimeter (SIRAL) measurements over Austfonna, Svalbard. A decade time series of glacier facies for this ice cap interpreted from 800 MHz ground-penetrating radar data clearly show there to be considerable variation within the firn pack, which needs to be captured by CryoSat-2 if we are to correctly interpret the satellite observed surface changes. The ground based radar data were obtained with a CRESIS Ku-band FMCW radar. The radar was operated to cover the frequency band of the CryoSat-2 SIRAL and the airborne version, Airborne Synthetic Aperture and Interferometric Radar Altimeter System (ASIRAS) carried by the Danish geophysics plane. Simultaneous profiles were obtained within half a day of each other with all three radars during the spring calibration/validation campaign on the Austfonna ice cap, Svalbard. The profiles, totaling approximately 200 km, span an elevation change of 400 m from the summit down to the ablation area, and cover a range of glacier facies and surface snow conditions. The ground based KU-band radar, which clearly images the near surface layering, was supported by manual snow depth sounding, 800 MHz radar, snow pits, firn cores, and borehole videos, all of which are used to validate interpretation of the CryoSat-2 data.

Published
2012

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