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2. Processes controlling upper‐ocean heat content in Drake Passage

Author

Stephenson, Gordon R, Gille, Sarah T, and Sprintall, Janet

Subjects
Life Below Water, Antarctic circumpolar current, Southern Ocean, heat, temperature, variability, eddies, Geophysics, Oceanography, Physical Geography and Environmental Geoscience
Abstract

A 16 year record of expendable bathythermograph transects across Drake Passage is used to examine variability in upper-ocean heat content that is not associated with the annual cycle. Links between upper-ocean heat content and anomalous heat fluxes, winds, two large-scale climate indices, and mesoscale eddies and meanders are examined. Results suggest that interannual variations in surface heat fluxes explain ∼5 to 10% of the variance in upper-ocean heat content. Anomalous surface heat fluxes are linked to meridional wind anomalies upstream of Drake Passage, which in turn are linked to forcing by El Niño/Southern Oscillation (ENSO) and the Southern Annular Mode (SAM). ENSO and SAM are correlated with upper-ocean heat content at near-zero lags, and statistically significant correlations occur at longer time lags as well. The impact of mesoscale eddies and meanders on upper-ocean heat content is explored with the use of a tracked eddy database. An empirical relationship is constructed relating upper-ocean heat content anomalies to eddy length scales and amplitudes. Eddies and meanders are estimated to account for more than one third of the nonannual cycle variance in Drake Passage upper-ocean heat content. © 2013. American Geophysical Union. All Rights Reserved.

Published
2013

8. Development of a global infrared land surface emissivity database for application to clear sky sounding retrievals from multispectral satellite radiance measurements

Author

Seeman, Suzanne W., Borbas, Eva E., Knuteson, Robert O., Stephenson, Gordon R., and Huang, Hung-Lung

Subjects
Artificial satellites in remote sensing -- Research, Emissivity -- Measurement, Radiation -- Measurement, Radiation -- Methods, Earth sciences
Abstract

A global database of infrared (IR) land surface emissivity is introduced to support more accurate retrievals of atmospheric properties such as temperature and moisture profiles from multispectral satellite radiance measurements. Emissivity is derived using input from the Moderate Resolution Imaging Spectroradiometer (MODIS) operational land surface emissivity product (MOD11). The baseline fit method, based on a conceptual model developed from laboratory measurements of surface emissivity, is applied to fill in the spectral gaps between the six emissivity wavelengths available in MOD11. The six available MOD11 wavelengths span only three spectral regions (3.8-4, 8.6, and 11-12 [micro]m), while the retrievals of atmospheric temperature and moisture from satellite IR sounder radiances require surface emissivity at higher spectral resolution. Emissivity in the database presented here is available globally at 10 wavelengths (3.6, 4.3, 5.0, 5.8, 7.6, 8.3, 9.3, 10.8, 12.1, and 14.3 [micro]m) with 0.05[degrees] spatial resolution. The wavelengths in the database were chosen as hinge points to capture as much of the shape of the higher-resolution emissivity spectra as possible between 3.6 and 14.3 [micro]m. The surface emissivity from this database is applied to the IR regression retrieval of atmospheric moisture profiles using radiances from MODIS, and improvement is shown over retrievals made with the typical assumption of constant emissivity.

Published
2008

10. Baroclinic energy flux at the continental shelf edge modified by wind-mixing

Author

Stephenson, Gordon R., Hopkins, Joanne E., Green, J.A. Mattias, Inall, Mark E., Palmer, Matthew R., Stephenson, Gordon R., Hopkins, Joanne E., Green, J.A. Mattias, Inall, Mark E., and Palmer, Matthew R.

Abstract

Temperature and current measurements from two moorings onshore of the Celtic Sea shelf break, a well-known hot spot for tidal energy conversion, show the impact of passing summer storms on the baroclinic wavefield. Wind-driven vertical mixing changed stratification to permit an increased on-shelf energy transport, and baroclinic energy in the semidiurnal band appeared at the moorings 1–4 days after the storm mixed the upper 50 m of the water column. The timing of the maximum in the baroclinic energy flux is consistent with the propagation of the semidiurnal internal tide from generation sites at the shelf break to the moorings 40 km away. Also, the ∼3 day duration of the peak in M2 baroclinic energy flux at the moorings corresponds to the restratification time scale following the first storm.

Published
2015

15. Storms modify baroclinic energy fluxes in a seasonally stratified shelf sea: inertial-tidal interaction

Author

Hopkins, Joanne E., Stephenson, Gordon R., Green, J. Mattias, Inall, Mark E., Hopkins, Joanne E., Stephenson, Gordon R., Green, J. Mattias, and Inall, Mark E.

Abstract

Observations made near the Celtic Sea shelf edge are used to investigate the interaction between wind-generated near-inertial oscillations and the semidiurnal internal tide. Linear, baroclinic energy fluxes within the near-inertial (f) and semidiurnal (M2) wave bands are calculated from measurements of velocity and density structure at two moorings located 40 km from the internal tidal generation zone. Over the 2 week deployment period, the semidiurnal tide drove 28–48 W m−1 of energy directly on-shelf. Little spring-neap variability could be detected. Horizontal near-inertial energy fluxes were an order of magnitude weaker, but nonlinear interaction between the vertical shear of inertial oscillations and the vertical velocity associated with the semidiurnal internal tide led to a 25–43% increase in positive on-shelf energy flux. The phase relationship between f and M2 determines whether this nonlinear interaction enhances or dampens the linear tidal component of the flux, and introduces a 2 day counter-clockwise beating to the energy transport. Two very clear contrasting regimes of (a) tidally and (b) inertially driven shear and energy flux are captured in the observations.

Published
2014

21. LACTOSE NEGATIVE ESCHERICHIA COLI FROM RANGELAND STREAMS: SOURCE, ANTIBIOTIC RESISTANCE, AND COLICINOGENICITY.

Author

Rychert, Robert C. and Stephenson, Gordon R.

Abstract

BSTRACT: Lactose-negative Escherichia coil from cattle feces appeared as yellow, atypical colonies on m-FC medium plates with water samples from rangeland streams. The lactose-negative E. coil may impact stream water quality analyses if infrequent samples are collected; are less antibiotic resistant than the lactose-positive E. coili isolated from rangeland streams; and are colicinogenic toward all the laboratory strains of E. coil examined and toward 61 percent of the lactose-positive E. coil rangeland-stream isolates that were tested. This latter result could explain the potentially low degree of antibiotic resistance transfer from lactose-positive to lactose-negative E. coil. In addition, the colicinogenicity of the lactose-negative E. coil may interfere with microbiological water quality analyses that depend upon lactose fernientations with mixed populations of coliforms. [ABSTRACT FROM AUTHOR]

Published
1986
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22. A Computerized Method of Describing Phase-Related Interactive Events Infant Feeding as an Example

Author

Stephenson, Gordon R., Pridham, Karen F., and Mlynarczyk, Susan

Abstract

A generalizable, computerized method has been designed to describe in detail interactive events that occur within phases of a process involving two or more interactants. The objectives of the method are (A) visual discernment of patterns of events within and across phases through graphically displayed data and (B) summarization of events within phases for comparison of events across phases. Stages of the implementation of these objectives are illustrated with data obtained from observations of mother-infant feeding interaction. The method provides a means for an investigator to structure the exploration of patterns of behaviors in the context of the social activity in which the behaviors occur and to develop hypotheses about the data.

Published
1996

23. The Clinically Focused Descriptive Study

Author

Hansen, Marc F., Pridham, Karen F., Stephenson, Gordon R., and Tsui, Paul

Abstract

The problem of making sense of data collected in broadly descriptive studies of a process of clinical interest (e.g., mother-infant interaction) is complicated by the relatively large number of types of events that must be recorded and the large amount of data generated. Furthermore, a process is likely to be organized in terms of phases and to vary in structure over time. The nature or meaning of an event is likely to vary with its context. The use of observational data for the purpose of hypothesis generation must, therefore, take into account the phase and structure of the process as well as the context in which events occur. However, phase, structure, and context are obscured by summary statistics, and the pattern of events in relation to each other cannot be extracted in a linear printout of the data stream. This article describes a method of presenting and summarizing complex observational data graphically, using a study of mother-infant interactions during feeding to illustrate its application for examination of events in context and across phases of the process over time.

Published
1987

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