Atmospheric forcing of the Ross Sea Polynya during summer

A one-dimensional model is used to study the spatial and temporal behavior of a coastal polynya during the Antarctic summer months. Similar models have been applied to coastal polynyas during winter, when there is little or no shortwave radiation from the sun. However, very little work has been done to analyze the behavior of polynyas in the summer due to a lack of quality cloud cover data, which increases the uncertainty of the shortwave heat flux term. In order to offset uncertainty introduced by data, the model was run with three different data sets. The first data set consists of (3 hourly) measurements taken at Ferrell Automatic Weather Station (AWS), the nearest weather station to the Ross Sea Polynya and most representative of wind, temperature, and pressure conditions in the area. Cloud amount values for this data set were obtained from observations at McMurdo Station, the nearest manned site. The second data set contains model-derived data (12 hourly) from the ECMWF/WCRP level III-A Global Atmospheric Data Archive (TOGA). The third data set is derived from the Polar MM5 regional atmospheric model, run over Antarctica for 1993. The model was run from September 1993 through July 1998 for the first two data sets (only 1993 data was available for the third data set), as these years contain the highest percentage of reliable AWS data. The modeled polynya width is compared to satellite derived Special Sensor Microwave Imager (SSM/I) data for ice coverage (ice free pixels) during the same time period. Qualitative similarities between the modeled data and SSM/I data imply that the model is representative of the actual forcing conditions on seasonal and interannual scales. In this model, summertime polynya width is entirely a function of wind forcing (when the net heat flux is positive downward). This suggests that wind is the primary variable responsible for the rapid expansion of the Ross Sea (RS) Polynya in the summer months. This study is part of the Research on Ocean-Atmosphere Variability and Ecosystem Response in the Ross Sea (ROAVERRS) project.