Flux Group Summary

C. Fairall

6/7/1999

The ETL flux group, in cooperation with F. Bradley of CSIRO, conducted air-sea flux and boundary-layer measurements from May 4 through June 1 and June 5-6. The ETL flux system was supplemented with atmospheric temperature and humidity measurements and IR measurements of the sea surface skin temperature. Additionally, a 915 MHz Doppler wind profiler and a 3 Ghz Doppler precipitation profiling radar were operated continuously. Approximately 30 days of time series (amounting to about 15 GB of data) were archived.

Several parts of the data were processed on board the ship and preliminary anlyses have been performed. Based on bulk calculations using the COARE flux algorithm, we find that the cruise- average heat budget components were significantly different that those found in the COARE experiment, which was done in the equatorial Pacific in 1992-3. For JASMINE, wind speed, stress, and latent heat fluxes were higher than COARE, but the additional heat loss was compensated by larger mean solar input. Thus, the cruise average total heat balance (about 25 W/m^2 into the ocean) was quite comparable to COARE. The heat balance in disturbed conditions was about -90 W/m^2 while the balance in suppressed conditions was about +90 W/m^2. Boundary-layer winds in disturbed conditions were 10-12 m/s. Total precipitation was also comparable to COARE, although this conclusion might be quite different if the ship had taken a different cruise track. There is some evidence that surface longwave cloud forcing, which is almost negligible in the west Pacific warm pool, is significant in the Bay of Bengal, even though the average downward longwave flux was 15 W/m^2 greater. In fact, even cirrus clouds caused a detectable increase in downward longwave on some occasions.

The wind profiler and S-band radar preformed well and provided interesting complements to the ship's scanning Doppler C-band radar and the ETL 8-mm cloud radar. The wind profiler revealed some very interesting structures on deep convective events in the Bay of Bengal. The typical event was a southwardly propagating squall line with northerly winds from the surface up to about 2 km, moving almost 90 degrees to the strong (15 m/s) westerlies in the lower troposphere. Convective events caused significant drops in surface air temperatures (as much as 5 C) but changes in specific humidity were quite small. In a few, a warm air mass was encountered just before the precipitation, wind, and cool sectors. Such behavior was not observed in the equatorial western Pacific.