Extended Abstract (48K)J1.3
Polynya meteorology: an evaluation of near-shore, downwind, and retrieved parameters
Erica L. Key, Univ. of Miami/RSMAS, Miami, FL; and P. J. Minnett
While multi-decadal meteorological time series analyzed by Rigor et al. (2000) and Polyakov et al. (2002) suggest that the Arctic is becoming warmer and moister – coincident with the shift to a positive AO/NAO phase and an increase in CO2 – measurements at polynyas and coastal weather station indicate surface air temperatures maintained close to 0° C from mid-summer into fall. These monthly-averaged polynya air temperatures, as compared to similar values from weather station data from Polyakov et al. (2002), indicate that the high heat capacity open water area moderates the range of air temperatures found within the polynya. During summer when land is exposed, air temperatures exceed those over ice-free waters by as much as 10°C; however, the most pronounced land-sea differences are observed during spring months (and to a lesser extent, fall), when land-based sites are covered with ice and snow.
Another moderating effect of these ice-free areas is the high relative humidity present with respect to neighboring land sites. This readily available moisture source also provides convective energy for the formation of cloud layers at many atmospheric levels downwind of the polynya or lead. Cloud analyses support this hypothesis through the shift in reporting from single cloud layers to multiple cloud at the end of the summer season, increasing in frequency with polynya fetch. However, much of the water content within these clouds is rapidly transformed to ice, accounting for the large effective cloud radii and the relatively low liquid water contents retrieved from lidar-radar in this region.
While air temperature and relative humidity can vary greatly over the land-sea boundary, sea level pressure changes little, even over distances of 300 km from the ship. Those small pressure changes generally favor lower pressure over the polynya than the surrounding coast, perhaps due to the convective heat rise over these open water areas. Some storm activity is also present within the sea level pressure time series, particularly in transition month data.
Storm passages were also present in the surface wind data, which catalogued a number of wind speeds greater than 10 m•s-1, again, most often during transition month cruises, such as in springtime studies of the St. Lawrence Island Polynya. At coastal sites, intense wind forcing included katabatic events, which flowed downslope from neighboring ice caps with occasional speeds of > 20 m•s-1. Average wind speeds, however, were below the global average of 7-10 m•s-1, due to weakened summertime pressure gradients over the Arctic. In winter, when the full effects of the positive phase Arctic Oscillation are exhibited, it is likely that wind speeds increase, perhaps opening latent heat polynyas not yet documented.
Joint Session 1, Polar Coastal Processes (Joint with Sixth Conference on Coastal Atmospheric and Oceanic Prediction and Processes and the 8th Conf on Polar Meteorology and Oceanography)
Monday, 10 January 2005, 8:55 AM-5:45 PM
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