The Behavior of Dry Westerly Air Associated With Convection Observed during the TOGA-COARE R/V Natsushima Cruise

Abstract

Based on the R/V Natsushima stationary observations at (0°, 156°E) during the TOGA-COARE Intensive Observing Period, the atmospheric features for the period from February 5th to 14th were examined.
The radiosonde sounding results show the existence of dry westerly air at an altitude of 2-4km from February 6th to 9th. In particular, this dry air region subsided during this period and then became not well defined on February 10th. The convection was inactive from February 6th to 9th, while a deep convection developed on the 10th.
It is found that the inversion layer existed at 800hPa and the dry low potential temperature layer above the inversion suppressed the convective activity for the former period. This dry low potential temperature air mass was traced back to the northeast trade wind region. The subsidence of this air mass was associated with the existence of an inversion layer above and the compensating subsidence among the cloud clusters that existed to the north and/or to the south of this observational site where the inversion layer was formed.
The change of the wind direction at the lower level from northwesterly to westerly before and after February 10th may have accompanied the suppression and the development of the convective activity. It is suggested that the dry westerly air intrusion and the associated variation of the convective activity may be a part of the several-days scale atmospheric disturbances over the equatorial Pacific Ocean.