Controls of the sea ice extent in the Ross Sea and development of a wireless sensor network. (2011)
AuthorsWard, Robertshow all
Polar sea ice is an important climatic variable. In the Arctic, the steady decrease in sea ice since the 1970's is a direct result of global warming. Due to the different land and ocean distribution in the Southern Hemisphere as well as circulatory effects from the ozone hole, Antarctica is isolated from these changes. These along with other factors have meant that Antarctic sea ice has experienced a slight increase over the same time period. Sea ice extent (SIE) is controlled by physical processes such as wind and ocean currents and temperature gradients, and these contribute to the seasonal and long term patterns in the formation and melting of sea ice. To date, climate models have had only limited success in modelling SIE and its geographic variation. The most commonly used measure to compare observations and models is the total sea ice area. However, observations suggest that the spatial variability of sea ice in response to climate drivers is complicated and differs markedly around the Antarctic. Various studies have suggested schemes for analysing SIE in terms of regional effects, although these schemes are generally somewhat arbitrary and may not be optimal for analysis of certain atmospheric circulation patterns. This research examines a new method for Antarctic sea ice analysis. Using sets of satellite based observations of the SIE over the entire Antarctic continent, the edge of the sea ice can be described in terms of an ellipse. This provides an integrated measure of sea ice that also describes geographical variations while being mathematically simple to describe in terms of the five parameters that completely define an ellipse (centroid coordinates; major and minor axes lengths; rotation angle of major axis). This study demonstrates that the elliptical diagnostic analysis of sea ice captures seasonal and long term behaviour in sea ice well, and this behaviour was analysed in terms of atmospheric circulation patterns such as the El Ni~no Southern Oscillation (ENSO) and the Southern Annular Mode (SAM). Analysis of the ENSO and SAM on the Antarctic SIE show evidence that both are potentially important in controlling sea ice. Patterns in the ellipse parameters display results consistent with previous studies of the effect of ENSO and SAM on sea ice, but the significance of these forcings on sea ice remains an open question. Part of this research involved development of a method to measure the atmospheric parameters that affect sea ice in situ in Antarctica, known as SNOW-WEB. The aim of the SNOW-WEB project is to design and implement a network of weather stations that can communicate wirelessly to each other, allowing near real-time measurement of weather variables over very high spatial and temporal resolutions, in the order of kilometres and minutes. Measuring the wind velocity, temperature and pressure over such high resolutions allow small scale atmospheric phenomena to be analysed in terms of their effects on sea ice. The first deployment of the SNOW-WEB system was in January 2011 spanning the area between Scott Base and Windless Bight on Ross Island in Antarctica. One of the most important components of SNOW-WEB was its power supply system. A system was designed that would allow the SNOW-WEB nodes to operate continuously for over a week by a combination of lead acid batteries and a solar trickle charger. In addition, a research grade weather station was deployed as a reference and calibration point for the sensors on board each SNOW-WEB node. Due to the difficulties involved with Antarctic field work, the expectations for the performance of the SNOW-WEB were conservative, but the SNOWWEB exceeded these comfortably.