Michael L. Van Woert

Thickness distribution of Antarctic sea ice

[1] Ship-based observations are used to describe regional and seasonal changes in the thickness distribution and characteristics of sea ice and snow cover thickness around Antarctica. The data set comprises 23,373 observations collected over more than 2 decades of activity and has been compiled as part of the Scientific Committee on Antarctic Research (SCAR) Antarctic Sea Ice Processes and Climate (ASPeCt) program. The results show the seasonal progression of the ice thickness distribution for six regions around the continent together with statistics on the mean thickness, surface ridging, snow cover, and local variability for each region and season. A simple ridge model is used to calculate the total ice thickness from the observations of level ice and surface topography, to provide a best estimate of the total ice mass, including the ridged component. The long-term mean and standard deviation of total sea ice thickness (including ridges) is reported as 0.87 ± 0.91 m, which is 40% greater than the mean level ice thickness of 0.62 m. Analysis of the structure function along north/south and east/west transects revealed lag distances over which sea ice thickness decorrelates to be of the order of 100–300 km, which we use as a basis for presenting near-continuous maps of sea ice and snow cover thickness plotted on a 2.5 � 5.0 grid.

Geosat and advanced very high resolution radiometer observations of oceanic planetary waves adjacent to the Hawaiian Islands

Geosat observations of the central North Pacific Ocean show westward propagating mesoscale features with length scales (>500 km), time scales (105–155 days), and observed zonal phase speeds commensurate with those of nearly nondispersive baroclinic Rossby waves. Advanced very high resolution radiometer-derived sea surface temperatures observed during April 1988 showed a cusp-shaped pattern north of the Hawaiian Islands congruent with concurrent Geosat-derived sea level height anomalies. It is believed that the cusp-shaped pattern is the surface manifestation of a baroclinic Rossby wave. The observed wavelength of the cusp-shaped pattern was 560 km. It had an observed meridional extent (horizontal amplitude) of 200–300 km and an inferred zonal propagation speed of 0.052 m s−1. The westward propagating sea level height structure was observed to amplify as it approached 150°W reaching amplitudes of 0.06–0.08 m in the vicinity of the cusp-shaped feature. These waves are believed to be locally forced by the topography, either as the result of eastward flow over the submerged island ridge or as a result of baroclinic instability during periods of westward flow.

Tidal currents of the Ross Sea and their time stability

Current measurements obtained from a sparse array of moorings on the Ross Continental Shelf during the 1980 and 90s are analysed for their tidal constituents. Diurnal (K1 and O1) tides are about five times stronger than semi-diurnal tides, and are strongest near the shelf break in agreement with recent model results. At some energetic locations the diurnal tides are significantly weaker at depth, presumably due to bottom friction. Complex demodulation analysis shows that at some locations the tidal response varies significantly in time. This time variability rises markedly above the noise floor expected from the spectral continuum between tidal bands, and does not scale with tidal bandwidth as would be expected of broadband noise. Further its magnitude is generally proportional to the associated tidal constituent, indicating that it is truly a varying tidal response. Space scales of this tidal instability were not resolved but are less than 150 km, while time scales appear mostly seasonal to interannual. The rms magnitude of the unstable response can be 1/3 of a given component’s mean magnitude, placing substantial limits on the ability of prognostic or even data assimilative models to accurately predict these tides for any specific time period.

On the possibility of a ridge current along the Hawaiian Islands

Four evenly spaced aircraft-deployed expendable bathythermograph and concurrent satellite advanced very high resolution radiometer (AVHRR) surveys were made over an extended area during a 1-year period to observe possible ridge currents along the Hawaiian Islands predicted or hypothesized by other investigators. None of the surveys found extended currents running along the ridge. Instead, fields of energetic eddies were found, and a curious cusp-shaped sea surface temperature pattern was observed in two of the AVHRR fields. Apparent cyclonic currents around the island of Hawaii were also observed. We conclude that either ridge currents do not exist or that they exist but are intermittent (episodic) in nature or exist in a form more complicated than could be observed by this study.

What are the Usage Dimensions of Open

What are the usage-related challenges currently faced by open efforts? For instance, open data is intriguing in principle, but in reality, making underlying data open can be problematic, conflicting with the need for research secrecy (whether driven by the desire to be first to publish, or the desire of funders to hold onto data to protect future discovery potential), the potential for misinterpretation by other researchers, and so on. Publishing clinical trial data in open formats is also intriguing but would run afoul of many current consent agreements, particularly older consents. Open access is similarly challenged in some instances by a conflict between which version of papers is allowed appear in open repositories. What is the value of archiving non-final versions? What are the range of issues here, what are the perspectives, and what might be some possible solutions?