INITIAL RESULTS FROM LONG-TERM MEASUREMENTS OF ATMOSPHERIC HUMIDITY AND RELATED PARAMETERS IN THE MARINE BOUNDARY-LAYER AT 2 LOCATIONS IN THE GULF-OF-MEXICO

Measurements of boundary layer moisture have been acquired from Rotron ic MP-100 sensors deployed on two NDBC buoys in the northern Gulf of M exico from June through November 1993. For one sensor, which was retri eved approximately 8 months after deployment, the post- and precalibra tions agreed closely and fell well within WMO specifications for accur acy. The second sensor operated continuously from June 1993 to Februar y 1997 (similar to 3.5 years). Buoy observations of relative humidity and supporting data were used to calculate specific humidity and the s urface fluxes of latent and sensible heat. Specific humidities from th e buoys were compared with observations of moisture obtained from near by ship reports, and the correlations were generally high (0.7-0.9). S urface gravity wave spectra were also acquired. The time series of spe cific humidity and the other buoy parameters revealed three primary sc ales of variability, small (similar to h), synoptic (similar to days), and seasonal (similar to months). The synoptic variability was clearl y dominant and occurred primarily during September, October, and Novem ber. Most of the synoptic variability was due to frontal systems that dropped down into the Gulf of Mexico from the continental US followed by air masses which were cold and dry. Cross-correlation analyses of t he buoy data indicated that: (1) the moisture field was highly coheren t over distances of 800 km or more in the northern Gulf of Mexico; and (2) both specific humidity and air temperature served as tracers of t he motion associated with propagating atmospheric disturbances. These correlation analyses also revealed that the prevailing weather systems generally entered the buoy domain from the South prior to September, but primarily from the North thereafter. Spectra of the various buoy p arameters indicated strong diurnal and semidiurnal variability for bar ometric pressure and sea surface temperature (SST) and lesser variabil ity for air temperature, wind speed and significant wave height. The s urface fluxes of latent and sensible heat were dominated by the synopt ic events which took place from September through November with the tr ansfer of latent heat being primarily from the ocean to the atmosphere . Finally, an analysis of the surface wave observations from each buoy , which included calculations of wave age and estimates of surface rou ghness, indicate that major heat and moisture flux events coincide wit h periods of active wave growth, although the data were insufficient t o identify any causal relationships.