149 results on '"Roscoe, H.K."'
Search Results
2. Three-dimensional model study of the Antarctic ozone hole in 2002 and comparison with 2000
- Author
-
Feng, W., Chipperfield, M.P., Roscoe, H.K., Remedios, J.J., Waterfall, A.M., Stiller, G.P., Glatthor, N., Hopfner, M., and Wang, D.-Y.
- Subjects
Weather -- Environmental aspects ,Ozone layer depletion -- Research ,Atmosphere -- Research ,Air pollution -- Research ,Earth -- Atmosphere ,Earth -- Research ,Earth sciences ,Science and technology - Abstract
An offline 3D chemical transport model (CTM) has been used to study the evolution of the Antarctic ozone hole during the sudden warming event of 2002 and to compare it with similar simulations for 2000. The CTM has a detailed stratospheric chemistry scheme and was forced by ECMWF and Met Office analyses. Both sets of meteorological analyses permit the CTM to produce a good simulation of the evolution of the 2002 vortex and its breakup, based on [O.sub.3] comparisons with Total Ozone Mapping Spectrometer (TOMS) column data, sonde data, and first results from the Environmental Satellite--Michelson Interferometer for Passive Atmospheric Sounding (ENVISAT--MIPAS) instrument. The ozone chemical loss rates in the polar lower stratosphere in September 2002 were generally less than in 2000, because of the smaller average active chlorine, although around the time of the warming, the largest vortex chemical loss rates were similar to those in 2000 (i.e., -2.6 DU [day.sup.-1] between 12 and 26 km). However, the disturbed vortex of 2002 caused a somewhat larger influence of polar processing on Southern Hemisphere (SH) midlatitudes in September. Overall, the calculations show that the average SH chemical [O.sub.3] loss (poleward of 30[degrees]S) by September was ~20 DU less in 2002 compared with 2000. A significant contribution to the much larger observed polar [O.sub.3] column in September 2002 was due to the enhanced descent at the vortex edge and increased horizontal transport, associated with the distorted vortex.
- Published
- 2005
3. Has the Antarctic vortex split before 2002?
- Author
-
Roscoe, H.K., Shanklin, J.D., and Colwell, S.R.
- Subjects
Antarctica -- Environmental aspects ,Vortex-motion ,Atmospheric circulation ,Earth sciences ,Science and technology - Abstract
In late September 2002, the Antarctic ozone hole was seen to split into two parts, resulting in large increases in ozone at some stations and the potential for significant modification of chlorofluorocarbon (CFC)-induced ozone loss. The phenomenon was dynamical (a split vortex), causing large increases in stratospheric temperature above stations normally within the vortex. Temperatures at Halley, Antarctica, at 30 hPa increased by over 60 K, and temperatures at South Pole at 100 hPa increased by over 25 K. It is important to know if this has happened before, since if it happens in the future, it would significantly alter the total hemispheric ozone loss due to chlorine from CFCs, particularly if it happens in August or September. Temperatures in winter and spring measured at Halley or the South Pole since 1957 and 1961, respectively, show no other comparable increases until the final warming in late spring, except for two dates in the 1980s at Halley when meteorological analyses show no vortex split. There are very few periods of measurements missing at both Halley and the South Pole, and analyses in those few periods show no vortex split. Measurements in August and September at sites normally near the edge of the vortex show very few suspicious dates, and analyses of those few suspicious dates again show no vortex split. It is concluded that the vortex has probably not split before the final warming since Antarctic records began in the late 1950s, and almost certainly not in August or September.
- Published
- 2005
4. A new software suite for NO 2 vertical profile retrieval from ground-based zenith-sky spectrometers
- Author
-
Denis, L., Roscoe, H.K., Chipperfield, M.P., Van Roozendael, M., and Goutail, F.
- Published
- 2005
- Full Text
- View/download PDF
5. Midwinter start to Antarctic ozone depletion: evidence from observations and models
- Author
-
Roscoe, H.K.
- Subjects
Antarctica -- Environmental aspects ,Ozone layer depletion -- Measurement -- Environmental aspects ,Science and technology - Abstract
Measurements of total ozone at Faraday, Antarctica (65 ° S), by a visible spectrometer show a winter maximum. This new observation is consistent with the descent of air within the polar vortex during early winter, together with ozone depletion starting in midwinter. Chemical depletion at these latitudes in midwinter is suggested by existing satellite observations of enhanced chlorine monoxide and reduced ozone above 100 hectapascals and by reduced ozone in sonde profiles. New three-dimensional model calculations for 1994 confirm that chemical ozone depletion started in June at the sunlit vortex edge and became substantial by late July. This would not have been observed by most previous techniques, which either could not operate in winter or were closer to the Pole., Dramatic ozone depletion was first reported at a high-latitude Antarctic site (76 ° S), where it was observed to start in late August(1). This is the time in the spring [...]
- Published
- 1997
6. Interpolation errors in UV-visible spectroscopy for stratospheric sensing: implications for sensitivity, spectral resolution, and spectral range
- Author
-
Roscoe, H.K., Fish, D.J., and Jones, R.L.
- Subjects
Optical spectrometers -- Research ,Remote sensing -- Equipment and supplies ,Astronomy ,Physics - Abstract
UV-visible measurements of stratospheric constituents require the ratio of a pair of spectra to be determined. If their wavelength calibrations differ and if an array detector is used, at least one spectrum must be interpolated. This introduces error if the spectrum is undersampled; the error is smaller if wavelength stability is good. Increasing the sampling ratio by making the spectral resolution poorer reduces the optical depths of absorption by constituents. Exact values of interpolation errors from real spectra are a difficult topic, but with a theoretical study with a simulated spectrum we show that the sampling ratio should exceed [approximately]4.5 pixels/FWHM but need not exceed 6.5 pixels/FWHM. To avoid significant reduction in the optical depth of N[O.sub.2], the resolution should be smaller than [approximately]1.0 nm FWHM. Hence a spectrometer system that measures both OClO and NOs by observing one order from one stationary grating should have more than [approximately]1500 pixels, more than many currently available array detectors.
- Published
- 1996
7. Possible descent across the “Tropopause” in Antarctic winter
- Author
-
Roscoe, H.K.
- Published
- 2004
- Full Text
- View/download PDF
8. Vertical resolution of oversampled limb-sounding measurements from satellites and aircraft
- Author
-
Roscoe, H.K. and Hill, J.G.T.
- Published
- 2002
- Full Text
- View/download PDF
9. Increased stratospheric greenhouse gases could delay recovery of the ozone hole and of ozone loss at Southern mid-latitudes
- Author
-
Roscoe, H.K. and Lee, A.M.
- Published
- 2001
- Full Text
- View/download PDF
10. Improvements to the accuracy of zenith-sky measurements of total ozone by visible spectrometers II: use of daily air-mass factors
- Author
-
Roscoe, H.K, Hill, J.G.T, Jones, A.E, and Sarkissian, A
- Published
- 2001
- Full Text
- View/download PDF
11. Improvements to the accuracy of measurements of NO 2 by zenith-sky visible spectrometers II: errors in zero using a more complete chemical model
- Author
-
Roscoe, H.K, Charlton, A.J, Fish, D.J, and Hill, J.G.T
- Published
- 2001
- Full Text
- View/download PDF
12. Combined characterisation of GOME and TOMS total ozone measurements from space using ground-based observations from the NDSC
- Author
-
Lambert, J.-C., Van Roozendael, M., Simon, P.C., Pommereau, J.-P., Goutail, F., Gleason, J.F., Andersen, S.B., Arlander, D.W., Bui Van, N.A., Claude, H., de La Noë, J., De Mazière, M., Dorokhov, V., Eriksen, P., Green, A., Karlsen Tørnkvist, K., Kåstad Høiskar, B.A., Kyrö, E., Leveau, J., Merienne, M.-F., Milinevsky, G., Roscoe, H.K., Sarkissian, A., Shanklin, J.D., Stähelin, J., Wahlstrøm Tellefsen, C., and Vaughan, G.
- Published
- 2000
- Full Text
- View/download PDF
13. Atmospheric nitrogen oxides (NO and NO2) at Dome C, East Antarctica, during the OPALE campaign
- Author
-
Frey, M.M., Roscoe, H.K., Kukui, A., Savarino, J., France, J.L., King, M.D., Legrand, M., Preunkert, S., Frey, M.M., Roscoe, H.K., Kukui, A., Savarino, J., France, J.L., King, M.D., Legrand, M., and Preunkert, S.
- Abstract
Mixing ratios of the atmospheric nitrogen oxides NO and NO2 were measured as part of the OPALE (Oxidant Production in Antarctic Lands & Export) campaign at Dome C, East Antarctica (75.1° S, 123.3° E, 3233 m), during December 2011 to January 2012. Profiles of NOx mixing ratios of the lower 100 m of the atmosphere confirm that, in contrast to the South Pole, air chemistry at Dome C is strongly influenced by large diurnal cycles in solar irradiance and a sudden collapse of the atmospheric boundary layer in the early evening. Depth profiles of mixing ratios in firn air suggest that the upper snowpack at Dome C holds a significant reservoir of photolytically produced NO2 and is a sink of gas-phase ozone (O3). First-time observations of bromine oxide (BrO) at Dome C show that mixing ratios of BrO near the ground are low, certainly less than 5 pptv, with higher levels in the free troposphere. Assuming steady state, observed mixing ratios of BrO and RO2 radicals are too low to explain the large NO2 : NO ratios found in ambient air, possibly indicating the existence of an unknown process contributing to the atmospheric chemistry of reactive nitrogen above the Antarctic Plateau. During 2011–2012, NOx mixing ratios and flux were larger than in 2009–2010, consistent with also larger surface O3 mixing ratios resulting from increased net O3 production. Large NOx mixing ratios at Dome C arise from a combination of continuous sunlight, shallow mixing height and significant NOx emissions by surface snow (FNOx). During 23 December 2011–12 January 2012, median FNOx was twice that during the same period in 2009–2010 due to significantly larger atmospheric turbulence and a slightly stronger snowpack source. A tripling of FNOx in December 2011 was largely due to changes in snowpack source strength caused primarily by changes in NO3− concentrations in the snow skin layer, and only to a secondary order by decrease of total column O3 and associated increase in NO3− photolysis rates. A sourc
- Published
- 2015
14. Inclusion of mountain wave-induced cooling for the formation of PSCs over the Antarctic Peninsula in a chemistry-climate model
- Author
-
Orr, A., Hosking, J.S., Hoffmann, L., Keeble, J., Dean, S.M., Roscoe, H.K., Abraham, N.L., Vosper, S., Braesicke, P., Orr, A., Hosking, J.S., Hoffmann, L., Keeble, J., Dean, S.M., Roscoe, H.K., Abraham, N.L., Vosper, S., and Braesicke, P.
- Abstract
An important source of polar stratospheric clouds (PSCs), which play a crucial role in controlling polar stratospheric ozone depletion, is from the temperature fluctuations induced by mountain waves. However, this formation mechanism is usually missing in chemistry–climate models because these temperature fluctuations are neither resolved nor parameterised. Here, we investigate the representation of stratospheric mountain-wave-induced temperature fluctuations by the UK Met Office Unified Model (UM) at climate scale and mesoscale against Atmospheric Infrared Sounder satellite observations for three case studies over the Antarctic Peninsula. At a high horizontal resolution (4 km) the regional mesoscale configuration of the UM correctly simulates the magnitude, timing, and location of the measured temperature fluctuations. By comparison, at a low horizontal resolution (2.5° × 3.75°) the global climate configuration fails to resolve such disturbances. However, it is demonstrated that the temperature fluctuations computed by a mountain wave parameterisation scheme inserted into the climate configuration (which computes the temperature fluctuations due to unresolved mountain waves) are in relatively good agreement with the mesoscale configuration responses for two of the three case studies. The parameterisation was used to include the simulation of mountain-wave-induced PSCs in the global chemistry–climate configuration of the UM. A subsequent sensitivity study demonstrated that regional PSCs increased by up to 50% during July over the Antarctic Peninsula following the inclusion of the local mountain-wave-induced cooling phase.
- Published
- 2015
15. Particles and iodine compounds in coastal Antarctica
- Author
-
Roscoe, H.K., Jones, Anna E., Brough, N., Weller, R., Saiz-Lopez, A., Mahajan, Anoop S., Schoenhardt, A., Burrows, J.P., Fleming, Z.L., Roscoe, H.K., Jones, Anna E., Brough, N., Weller, R., Saiz-Lopez, A., Mahajan, Anoop S., Schoenhardt, A., Burrows, J.P., and Fleming, Z.L.
- Abstract
©2015. The Authors. Aerosol particle number concentrations have been measured at Halley and Neumayer on the Antarctic coast, since 2004 and 1984, respectively. Sulphur compounds known to be implicated in particle formation and growth were independently measured: sulphate ions and methane sulphonic acid in filtered aerosol samples and gas phase dimethyl sulphide for limited periods. Iodine oxide, IO, was determined by a satellite sensor from 2003 to 2009 and by different ground-based sensors at Halley in 2004 and 2007. Previous model results and midlatitude observations show that iodine compounds consistent with the large values of IO observed may be responsible for an increase in number concentrations of small particles. Coastal Antarctica is useful for investigating correlations between particles, sulphur, and iodine compounds, because of their large annual cycles and the source of iodine compounds in sea ice. After smoothing all the measured data by several days, the shapes of the annual cycles in particle concentration at Halley and Neumayer are approximated by linear combinations of the shapes of sulphur compounds and IO but not by sulphur compounds alone. However, there is no short-term correlation between IO and particle concentration. The apparent correlation by eye after smoothing but not in the short term suggests that iodine compounds and particles are sourced some distance offshore. This suggests that new particles formed from iodine compounds are viable, i.e., they can last long enough to grow to the larger particles that contribute to cloud condensation nuclei, rather than being simply collected by existing particles. If so, there is significant potential for climate feedback near the sea ice zone via the aerosol indirect effect.
- Published
- 2015
16. Resolution of an important discrepancy between remote and in-situ measurements of tropospheric Br0 during Antarctic enhancements
- Author
-
Roscoe, H.K., Brough, N., Jones, A.E., Wittrock, F., Richter, A., Van Roozendael, M., and Hendrick, F.
- Abstract
Tropospheric BrO was measured by a ground-based remote-sensing spectrometer at Halley in Antarctica, and BrO was measured by remote-sensing spectrometers in space using similar spectral regions and Differential Optical Absorption Spectroscopy 5 (DOAS) analyses. Near-surface BrO was simultaneously measured at Halley by Chemical Ionisation Mass Spectrometry (CIMS), and in an earlier year near-surface BrO was measured at Halley over a long path by a DOAS spectrometer. During enhancement episodes, total amounts of tropospheric BrO from the ground-based remotesensor were similar to those from space, but if we assume that the BrO was confined 10 to the boundary layer they were very much larger than values measured by either near-surface technique. This large apparent discrepancy can be resolved if substantial amounts of BrO were in the free troposphere during most enhancement episodes. Amounts observed by the ground-based remote sensor at different elevation angles, and their formal inversions to vertical profiles, also show that much of the BrO was of15 ten in the free troposphere. This is consistent with the � 5 day lifetime of Bry, from the enhanced BrO observed during some Antarctic blizzards, and from aircraft measurements of BrO well above the surface in the Arctic.
- Published
- 2012
17. Intercomparison of slant column measurements of NO₂ and O₄ by MAX-DOAS and zenith-sky UV and visible spectrometers
- Author
-
Roscoe, H.K., Roozendael, Van, M., Fayt, C., Piesanie, du, A., Abuhassan, N., Adams, C., Akrami, M., Cede, A., Chong, J., Clémer, K., Friess, U., Gil Ojeda, M., Goutail, F., Graves, R., Griesfeller, A., Grossmann, K., Hemerijckx, G., Hendrick, F., Herman, J., Hermans, C., Irie, H., Johnston, P.V., Kanaya, Y., Kreher, K., Leigh, R., Merlaud, A., Mount, G.H., Navarro, M., Oetjen, H., Pazmino, A., Perez-Camacho, M., Peters, E., Pinardi, G., Puentedura, O., Richter, A., Schönhardt, A., Shaiganfar, R., Spinei, E., Strong, K., Takashima, H., Vlemmix, T., Vrekoussis, M., Wagner, T., Wittrock, F., Yela, M., Yilmaz, S.S., Boersma, K.F., Hains, J.C., Kroon, M., Piters, A.J.M., Kim, Y.J., and Fluids and Flows
- Abstract
In June 2009, 22 spectrometers from 14 institutes measured tropospheric and stratospheric NO2 from the ground for more than 11 days during the Cabauw Intercomparison campaign of Nitrogen Dioxide measuring Instruments (CINDI), at Cabauw, NL (51.97° N, 4.93° E). All visible instruments used a common wavelength range and set of cross sections for the spectral analysis. Most of the instruments were of the multi-axis design with analysis by differential spectroscopy software (MAX-DOAS), whose non-zenith slant columns were compared by examining slopes of their least-squares straight line fits to mean values of a selection of instruments, after taking 30-min averages. Zenith slant columns near twilight were compared by fits to interpolated values of a reference instrument, then normalised by the mean of the slopes of the best instruments. For visible MAX-DOAS instruments, the means of the fitted slopes for NO2 and O4 of all except one instrument were within 10% of unity at almost all non-zenith elevations, and most were within 5%. Values for UV MAX-DOAS instruments were almost as good, being 12% and 7%, respectively. For visible instruments at zenith near twilight, the means of the fitted slopes of all instruments were within 5% of unity. This level of agreement is as good as that of previous intercomparisons, despite the site not being ideal for zenith twilight measurements. It bodes well for the future of measurements of tropospheric NO2, as previous intercomparisons were only for zenith instruments focussing on stratospheric NO2, with their longer heritage.
- Published
- 2010
18. The impact of polar stratospheric ozone loss on southern hemisphere stratospheric circulation and climate
- Author
-
Keeble, J., Braesicke, P., Abraham, N.L., Roscoe, H.K., Pyle, J.A., Keeble, J., Braesicke, P., Abraham, N.L., Roscoe, H.K., and Pyle, J.A.
- Abstract
The impact of polar stratospheric ozone loss resulting from chlorine activation on polar stratospheric clouds is examined using a pair of model integrations run with the fully coupled chemistry climate model UM-UKCA. Suppressing chlorine activation through heterogeneous reactions is found to produce modelled ozone differences consistent with observed ozone differences between the present and pre-ozone hole period. Statistically significant high latitude Southern Hemisphere (SH) ozone loss begins in August and peaks in October-November, with >75% of ozone destroyed at 50 hPa. Associated with this ozone destruction is a >12 K decrease of the lower polar stratospheric temperatures and an increase of >6 K in the upper stratosphere. The heating components of this temperature change are diagnosed and it is found that the temperature dipole is the result of decreased shortwave heating in the lower stratosphere and increased dynamical heating in the upper stratosphere. The cooling of the polar lower stratosphere leads, through thermal wind balance, to an acceleration of the polar vortex and delays its breakdown by ~2 weeks. A link between lower stratospheric zonal wind speed, the vertical component of the EP flux, Fz, and the residual mean vertical circulation, w*, is identified. In December and January, increased westerly winds lead to increases in Fz, associated with an increase in tropopause height. The resulting increase in wavebreaking leads to enhanced downwelling/reduced upwelling over the polar cap. Many of the stratospheric signals modelled in this study propagate down to the troposphere, and lead to significant surface changes in December.
- Published
- 2014
19. Antarctic ozone loss in 1979-2010: first sign of ozone recovery
- Author
-
Kuttippurath, J., Lefèvre, F., Pommereau, J.-P., Roscoe, H.K., Goutail, F., Pazmiño, A., Shanklin, J.D., Kuttippurath, J., Lefèvre, F., Pommereau, J.-P., Roscoe, H.K., Goutail, F., Pazmiño, A., and Shanklin, J.D.
- Abstract
A long-term ozone loss time series is necessary to understand the evolution of ozone in Antarctica. Therefore, we construct the time series using ground-based, satellite and bias-corrected multi-sensor reanalysis (MSR) data sets for the period 1989–2010. The trends in ozone over 1979–2010 are also estimated to further elucidate its evolution in the wake of decreasing halogen levels in the stratosphere. Our analysis with ground-based observations shows that the average ozone loss in the Antarctic is about −33 to −50% (−90 to −155 DU (Dobson Unit)) in 1989–1992, and then stayed at around −48% (−160 DU). The ozone loss in the warmer winters (e.g. 2002 and 2004) is lower (−37 to −46%), and in the very cold winters (e.g. 2003 and 2006) it is higher (−52 to −55%). These loss estimates are in good agreement with those estimated from satellite observations, where the differences are less than ±3%. The ozone trends based on the equivalent effective Antarctic stratospheric chlorine (EEASC) and piecewise linear trend (PWLT) functions for the vortex averaged ground-based, Total Ozone Mapping Spectrometer/Ozone Monitoring Instrument (TOMS/OMI), and MSR data averaged over September–November exhibit about −4.6 DU yr−1 over 1979–1999, corroborating the role of halogens in the ozone decrease during the period. The ozone trends computed for the 2000–2010 period are about +1 DU yr−1 for EEASC and +2.6 DU yr−1 for the PWLT functions. The larger positive PWLT trends for the 2000–2010 period indicate the influence of dynamics and other basis functions on the increase of ozone. The trends in both periods are significant at 95% confidence intervals for all analyses. Therefore, our study suggests that Antarctic ozone shows a significant positive trend toward its recovery, and hence, leaves a clear signature of the successful implementation of the Montreal Protocol.
- Published
- 2013
20. Frost flowers in the laboratory: Growth, characteristics, aerosol, and the underlying sea ice
- Author
-
Roscoe, H.K., Brooks, B., Jackson, A.V., Smith, M.H., Walker, S.J., Obbard, R.W., Wolff, E.W., Roscoe, H.K., Brooks, B., Jackson, A.V., Smith, M.H., Walker, S.J., Obbard, R.W., and Wolff, E.W.
- Abstract
In the laboratory, we have investigated the growth and composition of frost flowers. Their ionic composition has shown little difference from those of field measurements. Young frost flowers grown on sea ice are saline, leading us to speculate that wicking occurs continually during their growth on sea ice. The surface area of frost flowers is only a little larger than the area of ice underneath, consistent with recent field measurements from the Arctic. Time-lapse photography has allowed us to observe the extreme mobility of freshly forming sea ice, at the stage at which the mush has become rather solid, and continuing while the flowers grow. This mobility results in new brine being expelled to the surface, which therefore remains wet. During various stages of frost flower growth, we observed their freshly formed dendritic parts rapidly diminishing in size after contacting the surface, consistent with repeated wicking. Frost flowers proved to be very stable in the presence of wind, such that no aerosol was observed when wind was blown across them in the laboratory chamber. This is consistent with recent field observations of frost flowers coexisting with wind-blown snow
- Published
- 2011
21. Estimation of Antarctic ozone loss from ground-based total column measurements
- Author
-
Kuttippurath, J., Goutail, F., Pommereau, J.-P., Lefevre, F., Roscoe, H.K., Pazmino, A., Feng, W., Chipperfield, M.P., Godin-Beekmann, S., Kuttippurath, J., Goutail, F., Pommereau, J.-P., Lefevre, F., Roscoe, H.K., Pazmino, A., Feng, W., Chipperfield, M.P., and Godin-Beekmann, S.
- Abstract
The passive tracer method is used to estimate ozone loss from ground-based measurements in the Antarctic. A sensitivity study shows that the ozone depletion can be estimated within an accuracy of ~4%. The method is then applied to the ground-based observations from Arrival Heights, Belgrano, Concordia, Dumont d'Urville, Faraday, Halley, Marambio, Neumayer, Rothera, South Pole, Syowa, and Zhongshan for the diagnosis of ozone loss in the Antarctic. On average, the ten-day boxcar average of the vortex mean ozone column loss deduced from the ground-based stations was about 55±5% in 2005–2009. The ozone loss computed from the ground-based measurements is in very good agreement with those derived from satellite measurements (OMI and SCIAMACHY) and model simulations (REPROBUS and SLIMCAT), where the differences are within ±3–5%. The historical ground-based total ozone observations in October show that the depletion started in the late 1970s, reached a maximum in the early 1990s and stabilised afterwards due to saturation. There is no indication of ozone recovery yet. At southern mid-latitudes, a reduction of 20–50% is observed for a few days in October–November at the newly installed Rio Gallegos station. Similar depletion of ozone is also observed episodically during the vortex overpasses at Kerguelen in October–November and at Macquarie Island in July–August of the recent winters. This illustrates the significance of measurements at the edges of Antarctica.
- Published
- 2010
22. Chemistry of the Antarctic boundary layer and the interface with snow: an overview of the CHABLIS campaign
- Author
-
Jones, A.E., Wolff, E.W., Salmon, R.A., Bauguitte, S.J., Roscoe, H.K., Anderson, P.S., Ames, D., Clemitshaw, K.C., Fleming, Z.L., Bloss, W.J., Heard, D.E., Lee, J.D., Read, K.A., Hamer, P., Shallcross, D.E., Jackson, A.V., Walker, S.L., Lewis, A.C., Mills, G.P., Plane, J.M.C., Saiz-lopez, A., Sturges, W.T., Worton, D.R., Jones, A.E., Wolff, E.W., Salmon, R.A., Bauguitte, S.J., Roscoe, H.K., Anderson, P.S., Ames, D., Clemitshaw, K.C., Fleming, Z.L., Bloss, W.J., Heard, D.E., Lee, J.D., Read, K.A., Hamer, P., Shallcross, D.E., Jackson, A.V., Walker, S.L., Lewis, A.C., Mills, G.P., Plane, J.M.C., Saiz-lopez, A., Sturges, W.T., and Worton, D.R.
- Abstract
CHABLIS (Chemistry of the Antarctic Boundary Layer and the Interface with Snow) was a collaborative UK research project aimed at probing the detailed chemistry of the Antarctic boundary layer and the exchange of trace gases at the snow surface. The centre-piece to CHABLIS was the measurement campaign, conducted at the British Antarctic Survey station, Halley, in coastal Antarctica, from January 2004 through to February 2005. The campaign measurements covered an extremely wide range of species allowing investigations to be carried out within the broad context of boundary layer chemistry. Here we present an overview of the CHABLIS campaign. We provide details of the measurement location and introduce the Clean Air Sector Laboratory (CASLab) where the majority of the instruments were housed. We describe the meteorological conditions experienced during the campaign and present supporting chemical data, both of which provide a context within which to view the campaign results. Finally we provide a brief summary of highlights from the measurement campaign. Unexpectedly high halogen concentrations profoundly affect the chemistry of many species at Halley throughout the sunlit months, with a secondary role played by emissions from the snowpack. This overarching role for halogens in coastal Antarctic boundary layer chemistry was completely unanticipated, and the results have led to a step-change in our thinking and understanding.
- Published
- 2008
23. On the vertical distribution of boundary layer halogens over coastal Antarctica: implications for O3, HOx, NOx and the Hg lifetime
- Author
-
Saiz-lopez, A., Plane, J.M.C., Mahajan, A.S., Anderson, P.S., Bauguitte, S.J., Jones, A.E., Roscoe, H.K., Salmon, R.A., Bloss, W.J., Lee, J.D., Heard, D.E., Saiz-lopez, A., Plane, J.M.C., Mahajan, A.S., Anderson, P.S., Bauguitte, S.J., Jones, A.E., Roscoe, H.K., Salmon, R.A., Bloss, W.J., Lee, J.D., and Heard, D.E.
- Abstract
A one-dimensional chemical transport model has been developed to investigate the vertical gradients of bromine and iodine compounds in the Antarctic coastal boundary layer (BL). The model has been applied to interpret recent year-round observations of iodine and bromine monoxides (IO and BrO) at Halley Station, Antarctica. The model requires an equivalent I atom flux of similar to 10(10) molecule cm(-2) s(-1) from the snowpack in order to account for the measured IO levels, which are up to 20 ppt during spring. Using the current knowledge of gas-phase iodine chemistry, the model predicts significant gradients in the vertical distribution of iodine species. However, recent ground-based and satellite observations of IO imply that the radical is well-mixed in the Antarctic boundary layer, indicating a longer than expected atmospheric lifetime for the radical. This can be modelled by including photolysis of the higher iodine oxides (I2O2, I2O3, I2O4 and I2O5), and rapid recycling of HOI and INO3 through sea-salt aerosol. The model also predicts significant concentrations (up to 25 ppt) of I2O5 in the lowest 10 m of the boundary layer. Heterogeneous chemistry involving sea-salt aerosol is also necessary to account for the vertical profile of BrO. Iodine chemistry causes a large increase (typically more than 3-fold) in the rate of O-3 depletion in the BL, compared with bromine chemistry alone. Rapid entrainment of O-3 from the free troposphere appears to be required to account for the observation that on occasion there is little O-3 depletion at the surface in the presence of high concentrations of IO and BrO. The halogens also cause significant changes to the vertical profiles of OH and HO2 and the NO2/NO ratio. The average Hg-0 lifetime against oxidation is also predicted to be about 10 h during springtime. An important result from the model is that very large fluxes of iodine precursors into the boundary layer are required to account for the observed levels of IO. The
- Published
- 2008
24. Halogens and their role in polar boundary-layer ozone depletion
- Author
-
Simpson, W.R., Von glasow, R., Riedel, K., Anderson, P.S., Ariya, P., Bottenheim, J.W., Burrows, J., Carpenter, L., Friess, U., Goodsite, M.E., Heard, D.E., Hutterli, M.A., Jacobi, H.-W., Kaleschke, L., Neff, W., Plane, J., Platt, U., Richter, A., Roscoe, H.K., Sander, R., Shepson, P.B., Sodeau, J., Steffen, A., Wagner, T., Wolff, E.W., Simpson, W.R., Von glasow, R., Riedel, K., Anderson, P.S., Ariya, P., Bottenheim, J.W., Burrows, J., Carpenter, L., Friess, U., Goodsite, M.E., Heard, D.E., Hutterli, M.A., Jacobi, H.-W., Kaleschke, L., Neff, W., Plane, J., Platt, U., Richter, A., Roscoe, H.K., Sander, R., Shepson, P.B., Sodeau, J., Steffen, A., Wagner, T., and Wolff, E.W.
- Abstract
During springtime in the polar regions, unique photochemistry converts inert halide salt ions (e.g. Br-) into reactive halogen species (e.g. Br atoms and BrO) that deplete ozone in the boundary layer to near zero levels. Since their discovery in the late 1980s, research on ozone depletion events (ODEs) has made great advances; however many key processes remain poorly understood. In this article we review the history, chemistry, dependence on environmental conditions, and impacts of ODEs. This research has shown the central role of bromine photochemistry, but how salts are transported from the ocean and are oxidized to become reactive halogen species in the air is still not fully understood. Halogens other than bromine (chlorine and iodine) are also activated through incompletely understood mechanisms that are probably coupled to bromine chemistry. The main consequence of halogen activation is chemical destruction of ozone, which removes the primary precursor of atmospheric oxidation, and generation of reactive halogen atoms/oxides that become the primary oxidizing species. The different reactivity of halogens as compared to OH and ozone has broad impacts on atmospheric chemistry, including near complete removal and deposition of mercury, alteration of oxidation fates for organic gases, and export of bromine into the free troposphere. Recent changes in the climate of the Arctic and state of the Arctic sea ice cover are likely to have strong effects on halogen activation and ODEs; however, more research is needed to make meaningful predictions of these changes.
- Published
- 2007
25. The Brewer–Dobson circulation in the stratosphere and mesosphere – Is there a trend?
- Author
-
Roscoe, H.K. and Roscoe, H.K.
- Abstract
The Brewer–Dobson circulation brings tropospheric air, accompanied by CFCs and greenhouse gases, into the stratosphere. Many models predict an increased circulation associated with an increase in greenhouse gases, such as that since the 1960s. A recent observation supports this: the rate at which total ozone increases in Antarctica during early winter is consistent with the descent and convergence that are part of the Brewer–Dobson circulation; at 65°S the rate doubled between the 1960s and 1990s. Another recent observation may also support this: the decrease in temperature since 1960 in the Antarctic mid-winter lower stratosphere is much less than the decrease calculated from the greenhouse effect of increased H2O, suggesting less CH4 oxidation in the 1970s; this could be caused by an increase in Brewer–Dobson circulation during the 1970s. An important paradox may be resolved by an increase in Brewer–Dobson circulation: the decrease in tropical cold-point temperature since the 1960s conflicts with the increase in mid-latitude H2O in the lower stratosphere, if it represents an increase at tropical entry of H2O; the conflict could be resolved if dehydration during stratospheric entry is incomplete and the circulation has increased.
- Published
- 2006
26. Polar tropospheric ozone depletion events observed in the International Geophysical Year of 1958
- Author
-
Roscoe, H.K., Roscoe, J., Roscoe, H.K., and Roscoe, J.
- Abstract
The Royal Society expedition to Antarctica established a base at Halley Bay, in support of the International Geophysical Year of 1957–1958. Surface ozone was measured during 1958 only, using a prototype Brewer-Mast sonde. The envelope of maximum ozone was an annual cycle from 10 ppbv in January to 22 ppbv in August. These values are 35% less at the start of the year and 15% less at the end than modern values from Neumayer, also a coastal site. This may reflect a general increase in surface ozone since 1958 and differences in summer at the less windy site of Halley, or it may reflect ozone loss on the inlet together with long-term conditioning. There were short periods in September when ozone values decreased rapidly to near-zero, and some in August when ozone values were rapidly halved. Such ozone-loss episodes, catalysed by bromine compounds, became well-known in the Artic in the 1980s, and were observed more recently in the Antarctic. In 1958, very small ozone values were recorded for a week in midwinter during clear weather with light winds. The absence of similar midwinter reductions at Neumayer, or at Halley in the few measurements during 1987, means we must remain suspicious of these small values, but we can find no obvious reason to discount them. The dark reaction of ozone and seawater ice observed in the laboratory may be fast enough to explain them if the salinity and surface area of the ice is sufficiently amplified by frost flowers.
- Published
- 2006
27. Low potential for stratospheric dynamical change to be implicated in the large winter warming in the central Antarctic Peninsula
- Author
-
Roscoe, H.K., Marshall, G.J., King, J.C., Roscoe, H.K., Marshall, G.J., and King, J.C.
- Abstract
Stratospheric change associated with the Antarctic ozone hole is clearly implicated in changing surface climate near 65°S in late summer, in both measurements and models, via downward propagation of height anomalies following the final warming. But one of the largest changes in surface temperature in Antarctica has occurred in the Antarctic Peninsula at 60 to 65°S in winter, and most of the change at 65°S occurred before the ozone hole. Stratospheric change can cause tropospheric change in Antarctic winter by modifying the reflection and refraction of planetary waves, whereby a stronger stratospheric vortex moves the tropospheric jets polewards, which can modify the Southern Annular Mode (SAM) in surface pressure that forces the tropospheric circumpolar winds. We examine stratospheric influence on the SAM in winter by inter-annual correlation of the SAM with the solar-cycle and volcanic aerosols, which act to change forcing of the stratospheric vortex in winter. Correlations are a maximum in June (midwinter) and are significant then, but are poor averaged over winter months. Hence the potential of change in the stratosphere to change Antarctic tropospheric climate in winter by dynamical means is low. This negative result is important given the proven high potential for change in summer by dynamical means.
- Published
- 2006
28. Ozone profiles in the high-latitude stratosphere and lower mesosphere measured by the Improved Limb Atmospheric Spectrometer (ILAS)-II: comparison with other satellite sensors and ozonesondes
- Author
-
Sugita, T., Nakajima, H., Yokota, T., Kanazawa, H., Herber, A., von der Gathen, P., Konig-Langlo, G., Sato, K., Dorokhov, V., Yushkov, V.A., Murayama, Y., Yamamori, M., Godin-Beekman, S., Goutail, F., Roscoe, H.K., 23 others, ., Sugita, T., Nakajima, H., Yokota, T., Kanazawa, H., Herber, A., von der Gathen, P., Konig-Langlo, G., Sato, K., Dorokhov, V., Yushkov, V.A., Murayama, Y., Yamamori, M., Godin-Beekman, S., Goutail, F., Roscoe, H.K., and 23 others, .
- Abstract
A solar occultation sensor, the Improved Limb Atmospheric Spectrometer (ILAS)-II, measured 5890 vertical profiles of ozone concentrations in the stratosphere and lower mesosphere and of other species from January to October 2003. The measurement latitude coverage was 54–71°N and 64–88°S, which is similar to the coverage of ILAS (November 1996 to June 1997). One purpose of the ILAS-II measurements was to continue such high-latitude measurements of ozone and its related chemical species in order to help accurately determine their trends. The present paper assesses the quality of ozone data in the version 1.4 retrieval algorithm, through comparisons with results obtained from comprehensive ozonesonde measurements and four satellite-borne solar occultation sensors. In the Northern Hemisphere (NH), the ILAS-II ozone data agree with the other data within ±10% (in terms of the absolute difference divided by its mean value) at altitudes between 11 and 40 km, with the median coincident ILAS-II profiles being systematically up to 10% higher below 20 km and up to 10% lower between 21 and 40 km after screening possible suspicious retrievals. Above 41 km, the negative bias between the NH ILAS-II ozone data and the other data increases with increasing altitude and reaches 30% at 61–65 km. In the Southern Hemisphere, the ILAS-II ozone data agree with the other data within ±10% in the altitude range of 11–60 km, with the median coincident profiles being on average up to 10% higher below 20 km and up to 10% lower above 20 km. Considering the accuracy of the other data used for this comparative study, the version 1.4 ozone data are suitably used for quantitative analyses in the high-latitude stratosphere in both the Northern and Southern Hemisphere and in the lower mesosphere in the Southern Hemisphere.
- Published
- 2006
29. SAOZ measurements of stratospheric NO2 at Aberystwyth
- Author
-
Vaughan, G., Quinn, P.T., Green, A.C., Bean, J., Roscoe, H.K., Roozendael, M. Van, Goutail, F., Vaughan, G., Quinn, P.T., Green, A.C., Bean, J., Roscoe, H.K., Roozendael, M. Van, and Goutail, F.
- Abstract
We present in this paper fifteen years measurements, from March 1991 to September 2005, of stratospheric NO2 vertical columns measured by a SAOZ zenith-sky visible spectrometer. The instrument spent most of its time at Aberystwyth, Wales, with occasional excursions to other locations. The data have been analysed with the WinDOAS analysis program with low-temperature high-resolution NO2 cross-sections and fitting a slit function to each spectrum. Because of a change in detector in May 1998 there is some uncertainty about the relative changes before and after this date, which are partially constrained by the results of an intercomparison exercise. However, the effect of the Mt Pinatubo aerosol cloud is very evident in the data from 1991–94, with a decrease of 10% in NO2 in the summer of 1992 (the SAOZ was located in Lerwick, Scotland during the winter of 1991–92 and observed very low NO2 values but these cannot be directly compared to the Aberystwyth data). To focus more on interannual and long-term variations in NO2, a seasonal variation comprising an annual and semi-annual component was fitted to the morning and evening twilight separately from 1995 to the present. This fit yielded average NO2 columns of 4.08 × 1015 cm–2 and 2.68 × 1015 cm–2 for the evening and morning twilight, respectively, with a corresponding annual amplitude of ±2.08 × 1015 cm–2 and ±1.50 × 1015 cm–2. Departures from the fitted curve show a trend of 6% per decade, consistent with that reported elsewhere, for the period 1998–2003, but in the past two years a distinct interannual variation of amplitude of 8% has emerged.
- Published
- 2006
30. The 2002 split ozone hole - the wave of the century?
- Author
-
Roscoe, H.K., Carver, G.D., Haynes, P.H., Roscoe, H.K., Carver, G.D., and Haynes, P.H.
- Abstract
No abstract available for this article.
- Published
- 2005
31. A new software suite for NO2 vertical profile retrieval from ground-based zenith-sky spectrometers
- Author
-
Denis, L., Roscoe, H.K., Chipperfield, M.P., Van Roozendael, M., Goutail, F., Denis, L., Roscoe, H.K., Chipperfield, M.P., Van Roozendael, M., and Goutail, F.
- Abstract
Here we present an operational method to improve accuracy and information content of ground-based measurements of stratospheric NO2. The motive is to improve the investigation of trends in NO2, and is important because the current trend in NO2 appears to contradict the trend in its source, suggesting that the stratospheric circulation has changed. To do so, a new software package for retrieving NO2 vertical profiles from slant columns measured by zenith-sky spectrometers has been created. It uses a Rodgers optimal linear inverse method coupled with a radiative transfer model for calculations of transfer functions between profiles and columns, and a chemical box model for taking into account the NO2 variations during twilight and during the day. Each model has parameters that vary according to season and location. Forerunners of each model have been previously validated. The scheme maps random errors in the measurements and systematic errors in the models and their parameters on to the retrieved profiles. Initialisation for models is derived from well-established climatologies. The software has been tested by comparing retrieved profiles to simultaneous balloon-borne profiles at mid-latitudes in spring.
- Published
- 2005
32. Measurements from ground and balloons during APE-GAIA – A polar ozone library
- Author
-
Roscoe, H.K., Colwell, S.R., Shanklin, J.D., Karhu, J.A., Taalas, P., Gil, M., Yela, M., Rodriguez, S., Rafanelli, C., Cazeneuve, H., Villanueva, C.A., Ginsburg, M., Diaz, S.B., de Zafra, R.L., Muscari, G., Redaelli, G., Dragani, R., Roscoe, H.K., Colwell, S.R., Shanklin, J.D., Karhu, J.A., Taalas, P., Gil, M., Yela, M., Rodriguez, S., Rafanelli, C., Cazeneuve, H., Villanueva, C.A., Ginsburg, M., Diaz, S.B., de Zafra, R.L., Muscari, G., Redaelli, G., and Dragani, R.
- Abstract
Many long-term monitoring sites in Antarctic regions, which deploy ground-based stratospheric remote sensors and fly radiosondes or ozonesondes on balloons, supported the Airborne Polar Experiment in September and October 1999. Support consisted of supplying data to the campaign in real time, and in some cases by increasing the frequency of measurements during the campaign. The results will strengthen scientific conclusions from the airborne measurements. But results from these sites are allowing important scientific studies of new aspects of the ozone hole in their own right, because like the aircraft and its campaign, many sites traverse the vortex edge and are close to the largest source of lee waves, or measure infrequently observed trace gases such as HNO3. Examples of such studies are the behaviour and value of NO2 in midwinter, ozone filamentation with no apparent horizontal advection, the frequency and amplitude of gravity waves over the Antarctic Peninsula, mixing in the lowest stratosphere in Antarctic spring, the mechanism and frequency of HNO3 enhancement above the ozone peak in midwinter, and trends in UV dose in southern South America.
- Published
- 2005
33. The influence of volcanic activity on large-scale atmospheric processes: continuing the discussion
- Author
-
Roscoe, H.K. and Roscoe, H.K.
- Abstract
Jodie Dunn is to be commended for her entertaining and well-researched article in Weather (Dunn 2004). However, some of the arguments deserve to be amplified, and they demonstrate interesting and equally entertaining synergies with other aspects of atmospheric science – with the aerosol indirect effect on climate, with the Rayleigh scattering which makes the sky blue, with changes to Antarctic climate, with changes to the Brewer–Dobson circulation (from tropics to poles in the stratosphere), and with the physics of volcanic plumes.
- Published
- 2004
34. Possible long-term changes in stratospheric circulation: evidence from total ozone measurements at the edge of the Antarctic vortex in early winter
- Author
-
Roscoe, H.K., Fowler, C.L., Shanklin, J.D., Hill, J.G.T., Roscoe, H.K., Fowler, C.L., Shanklin, J.D., and Hill, J.G.T.
- Abstract
Measurements of total ozone in Antarctica during early winter show an increase, consistent with the observed descent of stratospheric air and the convergence that accompanies descent. Measurements in the vortex edge region at Faraday (65°S) show that the rate of increase has on average doubled between the 1960s and the 1990s. We speculate that this increase in rate of ozone change is caused by an increase in convergence. If so, it suggests that the strength of the Brewer–Dobson residual stratospheric circulation, which brings tropospheric air into the stratosphere with its accompanying chlorofluorocarbons and greenhouse gases, increased significantly. There is no obvious explanation for an increase in the circulation. Models predict that an ozone hole increases vortex strength, but only later in the spring. Models also predict that increased greenhouse gases increase the circulation, but the convergence did not increase gradually whereas greenhouse gases did. Some of the measurements in the 1990s are able to distinguish the different rates of increase of ozone in individual years, which show considerable variability, as expected following the eruption of Pinatubo.
- Published
- 2004
35. A review of stratospheric H2O and NO2
- Author
-
Roscoe, H.K. and Roscoe, H.K.
- Abstract
Twenty years ago there were large disagreements between instruments measuring stratospheric H2O and NO2, and there were no reliable long-term records. Now, there is greatly improved agreement between techniques, there are 20-year records of profiles of stratospheric H2O and of total NO2 at single sites, there is a qualified H2O record extending back 40 years and 12-year records of total NO2 from many sites, and there are reliable global measurements from satellites to form the basis of climatologies. This excellent progress is marred by a discrepancy between the observed trend in lower stratospheric H2O and temperatures at the tropical cold point, and by a possible discrepancy between the observed trend in total NO2 and the trend in the source of NO2. The second discrepancy would be resolved by a trend in the residual circulation in the stratosphere, in the same way as variability in the residual circulation was responsible for variability in the trend in H2O in the upper stratosphere in the 1990s.
- Published
- 2004
36. Frost flowers on sea ice as a source of sea salt and their influence on tropospheric halogen chemistry
- Author
-
Kaleschke, L., Richter, A., Burrows, J., Afe, O., Heygster, G., Notholt, J., Rankin, A.M., Roscoe, H.K., Hollwedel, J., Wagner, T., Jacobi, H.-W., Kaleschke, L., Richter, A., Burrows, J., Afe, O., Heygster, G., Notholt, J., Rankin, A.M., Roscoe, H.K., Hollwedel, J., Wagner, T., and Jacobi, H.-W.
- Abstract
Frost flowers grow on newly-formed sea ice from a saturated water vapour layer. They provide a large effective surface area and a reservoir of sea salt ions in the liquid phase with triple the ion concentration of sea water. Recently, frost flowers have been recognised as the dominant source of sea salt aerosol in the Antarctic, and it has been speculated that they could be involved in processes causing severe tropospheric ozone depletion events during the polar sunrise. These events can be explained by heterogeneous autocatalytic reactions taking place on salt-laden ice surfaces which exponentially increase the reactive gas phase bromine ("bromine explosion"). We analyzed tropospheric bromine monoxide (BrO) and the sea ice coverage both measured from satellite sensors. Our model based interpretation shows that young ice regions potentially covered with frost flowers seem to be the source of bromine found in bromine explosion events.
- Published
- 2004
37. Observation of the 8-micrometer N2O5 thermal emission feature in the stratosphere: comment
- Author
-
Roscoe, H.K.
- Subjects
Stratosphere -- Research ,Infrared spectra -- Analysis ,Nitrogen dioxide -- Research ,Emission spectroscopy -- Case studies ,Astronomy ,Physics - Abstract
The measurement of [N.sub.2 O.sub.5] by Evans [Appl. Opt. 25, 1866-1868 (1986)] contains several serious errors. A reanalysis of the published infrared spectra gives the more realistic error bar of [+ or -] 45%.
- Published
- 1992
38. Stratospheric temperatures in Antarctic winter: does the 40-year record confirm mid-latitude trends in stratospheric water vapour?
- Author
-
Roscoe, H.K., Colwell, S.R., Shanklin, J.D., Roscoe, H.K., Colwell, S.R., and Shanklin, J.D.
- Abstract
Water vapour is a potent greenhouse gas, and the observed increases in water vapour in the stratosphere act to cool it. Possible changes in stratospheric temperatures are important for future ozone loss because colder temperatures in the edge region of the Antarctic ozone hole act to increase polar stratospheric clouds there, and so delay recovery of the ozone hole. Trends in lower-stratospheric temperature within the core of the Antarctic vortex in winter should be a unique indicator of trends in stratospheric water vapour, because neither changes in CO2 nor in ozone have a large effect on temperature in the lower stratosphere in the dark. Here, measured stratospheric temperatures southward of 70 S in winter are presented and their quality and corrections discussed. The character and magnitude of the long-term changes at Halley (76 S) are similar from 100 to 70 hPa and at 50 hPa, whether corrected for sonde changes or not, and are also similar to those at other Antarctic sites. We found no significant trend in temperatures at Halley between 1960 and 2000, which is inconsistent with the change calculated from the trend in lower-stratospheric water vapour in northern hemisphere midlatitudes between 1960 and 2000. Over the shorter interval between 1980 and 2000 at Halley, the change in temperature was -1.8 +/- 0.6 K, in agreement with the change calculated from the trend in stratospheric water vapour in northern hemisphere midlatitudes between 1980 and 2000. The differences between these periods are discussed in terms of: possible fortuitous agreement between 1980 and 2000; the poorer representation and quality of the measurements of stratospheric water vapour between 1960 and 1980; and a possible large variation in the rate of oxidation of CH4 to H2O in the upper stratosphere between 1960 and 1980. Such a variation in oxidation rate was observed by satellite between 1992 and 1999.
- Published
- 2003
39. Measuring air from polar vortices
- Author
-
Roscoe, H.K.
- Subjects
Atmospheric circulation -- Measurement ,Ozone layer depletion -- Research ,Polar vortex -- Research ,Environmental issues ,Science and technology ,Zoology and wildlife conservation - Published
- 1991
40. Improvements to the accuracy of measurements of NO2 by zenith-sky visible spectrometers. II: Errors in zero using a more complete chemical model
- Author
-
Roscoe, H.K., Charlton, A.J., Fish, D.J., Hill, J.G.T., Roscoe, H.K., Charlton, A.J., Fish, D.J., and Hill, J.G.T.
- Abstract
Using a flexible chemical box model with full heterogeneous chemistry, intercepts of chemically modified Langley plots have been computed for the 5 years of zenith-sky NO2 data from Faraday in Antarctica (65°S). By using these intercepts as the effective amount in the reference spectrum, drifts in zero of total vertical NO2 were much reduced. The error in zero of total NO2 is plus/minus 0.03 x 10 15 from one year to another. This error is small enough to determine trends in midsummer and any variability in denoxification between midwinters. The technique also suggests a more sensitive method for determining N2O5 from zenith-sky NO2 data.
- Published
- 2001
41. Improvements to the accuracy of zenith-sky measurements of total ozone by visible spectrometers II: use of daily air-mass factors
- Author
-
Roscoe, H.K., Hill, J.G.T, Jones, A.E., Sarkissian, A, Roscoe, H.K., Hill, J.G.T, Jones, A.E., and Sarkissian, A
- Abstract
Ozone at Faraday in Antarctica is measured by a ground-based visible spectrometer. Total ozone is deduced from the slant column measurements by means of calculated air-mass factors (AMFs), which have now been calculated for each month of the observations with a mixture of climatological and measured parameters as input. The intercepts of Langley plots using these AMFs had less seasonal variability than hitherto, but the ratio of total ozone to that measured by the Dobson at Faraday still showed a significant dependence on season and on presence of the ozone hole. This latter dependence was reduced by blending ozone-hole AMFs on appropriate days, resulting in ratios which vary by less than ±9% over the three years of observations. When using these daily AMFs, we estimate the potential for errors in seasonal trends in total ozone at less than 6%/month in the worst-case outside ozone-hole break-up, with a more usual value between 2 and 3%/month. There remain clear artifacts due to the ozone hole and to summer–winter differences, which cannot be resolved without new ozone-sonde flights.
- Published
- 2001
42. Ozone loss episodes in the free Antarctic troposphere, suggesting a possible climate feedback
- Author
-
Roscoe, H.K., Kreher, K., Friess, U., Roscoe, H.K., Kreher, K., and Friess, U.
- Abstract
Sudden loss of tropospheric ozone well above the boundary layer was observed on three occasions at two coastal sites in Antarctica in spring 1995. Back trajectories show that the air sampled the boundary layer near the northern edge of the sea ice (1000 km from the coast) between 3 and 5 days previously. Enhanced BrO observed over sea ice in spring suggests that such ozone loss is common offshore, hence it may cause a small climate effect whose sign would create positive feedback, if sea ice reduced during warming.
- Published
- 2001
43. Improved air-mass factors for ground-based total NO2 measurements: a sensitivity study
- Author
-
Harris, N.R.P., Guirlet, M., Amanatidis, G.T., Sarkissian, A., Richter, A., Van Roozendael, M., Lambert, J.-C., Granville, J., Vendenberghe, J.-M., Buchwitz, M., Hoiskar, B.A.K., Floisland, I., Tornkvist, K., Roscoe, H.K., Goutail, F., Pommereau, J.-P., Harris, N.R.P., Guirlet, M., Amanatidis, G.T., Sarkissian, A., Richter, A., Van Roozendael, M., Lambert, J.-C., Granville, J., Vendenberghe, J.-M., Buchwitz, M., Hoiskar, B.A.K., Floisland, I., Tornkvist, K., Roscoe, H.K., Goutail, F., and Pommereau, J.-P.
- Abstract
We present an overview of exisiting problems in air-mass factor calculations for NO2 vertical column measurements by UV-visible ground-based spectrometry, Sensitivity studies made using different radiative transfer models allow us to identify and to quantify sources of uncertainties in clculations, and domiment effects are multiple scattering (4%) and profile variations due to diurnal (10%) and seasonal changes (16%)
- Published
- 2000
44. A surface acoustic wave frost-point hygrometer for measurements of stratospheric water vapour
- Author
-
Harris, N.R.P., Guirlet, M., Amanatidis, G.T., Turnbull, K.F.V., Ostanin, V.P., Hadaway, D.E., Hill, J.G.T., McIntyre, J.D., Roscoe, H.K., Jones, R.L., Harris, N.R.P., Guirlet, M., Amanatidis, G.T., Turnbull, K.F.V., Ostanin, V.P., Hadaway, D.E., Hill, J.G.T., McIntyre, J.D., Roscoe, H.K., and Jones, R.L.
- Abstract
Conventional frost-point hygrometers observe frost on their cold point by optical means [1,2,3], thereby requiring several micrometres of ice to form. We have developed a new hygrometer which uses surface acoustic wave (SAW) devices to determine when condensation has occurred. At the oscillation frequencies used (hundreds of MHz), the SAW device is capable of responding to a few monolayers of condensate, increasing sensitivity and reducing response time. The principle of the method has been demonstrated in the laboratory by calibration against a chilled mirror frost-point hygrometer, and the sensor has had a number of technical balloon flights. Here we describe the principle of the technique and present some preliminary results.
- Published
- 2000
45. Long duration balloon flights in the Arctic: the THESEO-Lagrangian Experiment
- Author
-
Harris, N.R.P., Guirlet, M., Amanatidis, G.T., Pommereau, J.P., Garnier, A., Goutail, F., Nunes-Pinharanda, M., Denis, F., Vial, F., Nouel, F., Dubourg, V., Letrenne, G., Jones, R.L., Hansford, G., Freshwater, R.A., Turnbull, K., Roscoe, H.K., Williams, D.E., Woods, P., Gardiner, T., Adriani, A., Cairo, F., Pulvirenu, L., Di Donfrancesco, G., Yushkov, V., Merkoulov, S., Knudsen, B., Harris, N.R.P., Guirlet, M., Amanatidis, G.T., Pommereau, J.P., Garnier, A., Goutail, F., Nunes-Pinharanda, M., Denis, F., Vial, F., Nouel, F., Dubourg, V., Letrenne, G., Jones, R.L., Hansford, G., Freshwater, R.A., Turnbull, K., Roscoe, H.K., Williams, D.E., Woods, P., Gardiner, T., Adriani, A., Cairo, F., Pulvirenu, L., Di Donfrancesco, G., Yushkov, V., Merkoulov, S., and Knudsen, B.
- Published
- 2000
46. Model and measurements show Antarctic ozone loss follows edge of polar night
- Author
-
Lee, A.M., Roscoe, H.K., Oltmans, S., Lee, A.M., Roscoe, H.K., and Oltmans, S.
- Abstract
A three‐dimensional chemical‐transport model of the stratosphere has been used to study the 1996 austral winter and spring. Both the model and ozonesonde measurements show that ozone depletion associated with the Antarctic ozone hole follows the edge of polar night: very little ozone‐depleted air mixes ahead of the terminator as it sweeps poleward, until the terminator reaches 80°S. Other details of the model ozone field show very good agreement with measurements.
- Published
- 2000
47. Solid state ozone sensors for the future: light weight, low power and continuous operation
- Author
-
Harris, N.R.P., Guirlet, M., Amanatidis, G.T., Hansford, G.M., Sanderson, M.G., Freshwater, R.A., Utembe, S., Bosch, R., Cox, R.A., Jones, R.L., Pratt, K.E., Williams, D.E., Smit, H., Helten, M., O'Connor, F., Vaughan, G., Roscoe, H.K., Harris, N.R.P., Guirlet, M., Amanatidis, G.T., Hansford, G.M., Sanderson, M.G., Freshwater, R.A., Utembe, S., Bosch, R., Cox, R.A., Jones, R.L., Pratt, K.E., Williams, D.E., Smit, H., Helten, M., O'Connor, F., Vaughan, G., and Roscoe, H.K.
- Published
- 2000
48. Possible causes of stratospheric NO2 trends observed at Lauder, New Zealand
- Author
-
Fish, D.J., Roscoe, H.K., Johnston, P.V., Fish, D.J., Roscoe, H.K., and Johnston, P.V.
- Abstract
A recently published analysis of slant columns of NO2 observed at twilight at 45°S has identified trends of about 5%/decade between 1980 and 1998. This is twice the trend in tropospheric N2O, which is the source of stratospheric NO2. By means of a column photochemical model, we explore the sensitivity of NO2 to the observed trends in stratospheric temperature, O3 and H2O. The resulting calculated trends in NO2 are smaller than observed, and we cannot force agreement by varying the ozone or temperature trends. The calculated sensitivity of NO2 to stratospheric aerosol is large, and a 20% per decade decrease in aerosol surface area creates agreement. We conclude that a small residual in the statistical fit of aerosol to the NO2 measurements may remain, and is a likely cause of the trends found in the NO2 measurements.
- Published
- 2000
49. The Brewer–Dobson circulation in the stratosphere and mesosphere – Is there a trend?
- Author
-
Roscoe, H.K., primary
- Published
- 2006
- Full Text
- View/download PDF
50. A new software suite for NO2 vertical profile retrieval from ground-based zenith-sky spectrometers
- Author
-
Denis, L., primary, Roscoe, H.K., additional, Chipperfield, M.P., additional, Van Roozendael, M., additional, and Goutail, F., additional
- Published
- 2005
- Full Text
- View/download PDF
Catalog
Discovery Service for Jio Institute Digital Library
For full access to our library's resources, please sign in.