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Comparison of Wind Trajectories, Cloud Frequency, and Weather During the FIRE/ACE Flights to Climatologies |
SSEC Univ. of Wisc.
Don.Wylie@ssec.wisc.edu
Cyclone and anticyclone activity in the spring and summer of 1998 appeared to be nearly normal in the number of systems and their movement when compared to the few other studies of the Arctic. An El-Nino/Southern Oscillation (ENSO) was occurring which probably contributed to the rapid melting of the Arctic Ocean ice in the Chukchi and Beaufort Seas. Qualitatively, the regression of the ice northward was among the largest seen in the region. Yet, the cyclone activity appeared to conform to expectations, as best as it is known by the study of Serreze et al. (1996). The tracks and movements of the cyclone and anticyclones revealed many erratic features which are common in the area. These synoptic systems came from all directions. They generally followed the eastward and northeastward directions of the Serreze et al. (1996) climatology. But they did not always obey the general eastward propagation of Rossby wave systems found at lower latitudes. Most of the northeastward propagating cyclones were originally part of the Aleutian Low in the Bering Sea. The other cyclones and anticyclones developed and decayed in an erratic, nature not conforming to any climatological pattern. The large anticyclone developed in the lower Beaufort Sea in July as predicted by climatology and dominated the area. But the daily analysis of it showed a wide variety of changes in intensity, location, and shape which affected the weather at the Ice Camp to its west. Arctic synoptic systems are more complicated than their relatives in lower latitudes.
Air temperatures rose from the winter-like conditions (-15° to -20° C) in early April to the freezing/thawing point at the end of May and remained close to this point through July. This too appears to conform to climatological norms.
Air trajectories were generally from the south and southeast. Some previous studies predicted that more air masses could be traced back to Europe and Russia. These cases were few in the April-July 1998 period. If air pollution sources are found in these data, they most likely will be in eastern Siberia, Alaska, or western Canada because most of the air entering the Arctic during the four months of FIRE/ACE came from these regions.
Clouds appeared to follow climatological norms. The SHEBA Ship Ice Camp was located where southerly flow is very common because of the anticyclone in the Beaufort Sea and the cyclonic activity to the west of it. The southerly flow brought moisture forming clouds at all levels. Boundary layer Arctic stratus usually occurred with other clouds above in June and July. The Wisconsin HIRS analysis indicates higher frequencies of clouds above 400 hPa (7 km) than normally found in the month of July 1998. In the other months, cloud statistics are reasonably close to the other climatologies.
Model analysis and forecast statistics indicate skill in the NCEP MRF model predictions out to three days. This success is surprising considering the lack of data for the model at high latitudes and the complicated and erratic movement of the synoptic systems.
