Polynyas are areas of combined open water and thin ice surrounded by sea and/or land ice. They are important to the transfer of heat and moisture from the ocean to the atmosphere, as well as to the production of new ice, the formation of dense shelf water, the sustenance of primary and secondary productivity in polar regions, and to the spring disintegration of sea ice. This study examines some of the key physical controls affecting the rapid expansion of the Ross Sea Polynya during the onset of spring sea ice disintegration and the subsequent progression of this open water expansion throughout the summer, in support of the ROAVERRS study of the Ross Sea ecosystem.
Automatic weather station (AWS) data from Ferrell and Whitlock are composited around the onset of the rapid expansion phase of the Ross Sea Polynya. This period is generally characterized by a sudden shift from fairly steady total open water area to open water totals increasing by a few thousand square kilometers per day. Within 2-10 days of the onset, there is typically an explosive polynya expansion of 10-40 thousand square kilometers per day. Results reveal sharp increases in temperature and wind on the day of or before the onset of rapid expansion. Within two or three days, atmospheric pressure follows this upward trend, providing suggestive evidence that ridging frequently occurs at this time.
Satellite remote sensing data are used to produce cloud masking images and fractional cloud cover estimates in order to study the sea ice response to solar forcing for the same period. We will check for reduced cloud cover during the period of potential frequent ridging through a case study that uses available cloud masking imagery from two summer field seasons ('96/'97 and '97/'98), each characterized by drastically differing weather patterns and polynya configurations. Reduced cloud cover would result in more solar radiation reaching the open water and thus help explain the explosive polynya expansion that occurs almost immediately following the onset of the rapid expansion phase. After several days of explosive expansion, the rapid expansion continues throughout the summer at a rate of a few to several thousand square kilometers per day.