Surface meteorological observations taken onboard ORV Sagar Kanya were analyzed for the stationary ship location (17.5°N, 89°E) during Phases I and II of BOBMEX-1999. Contrasting features of Indian monsoon such as active and weak conditions were observed during these phases respectively.
The phase mean values of pressure and wind, heat flux and momentum flux showed lower MSL pressure, higher wind speed and larger latent heat flux and momentum flux during Phase I reflecting the active monsoon conditions. Phase II was marked with higher MSL pressure, weaker wind speed and lower latent heat flux and momentum flux.
A remarkable change in these parameters was, however, observed on 18 August (Phase II). This might be related to the north-south movement of the monsoon through across the ship location around this day.
The weather conditions observed over the ship indicated an event of continuous rainfall (from 14 to 16 August) which was followed by a substantial decrease in SST below 28°C. The effect of the rainfall event needs to be studied in detail.
21. On the cyclogenesis over the Southern Bay of Bengal during BOBMEX-Pilot-98
P. Seetaramayya, V.S.N. Murty, V. Ramesh Babu and L.V.G. Rao, Indian Institute of Tropical Meteorology, Pune.
The surface heat budget, upper ocean cyclone heat potential together with atmospheric specific humidity and virtual temperature were examined to understand the cyclogenesis over the southern Bay of Bengal (7° to 13°N; 85° to 87°E) during October-November, 1998 using BOBMEX-PILOT study data sets.
The study area north of 10°N was warm in the 0-50 m layer and was conducive for the formation of cyclones. Further, the cyclone heat potential was higher (about 6 x 108 J m-2) north of 10°N where two tropical cyclones formed during October-November, 1998.
The east-west shear line (equatorial trough) along 10°N characterized with wind speed minimum was found above the center of the sea surface cyclonic gyre, characterized by lower dynamic height.
The vertical profiles of specific humidity and virtual potential temperature showed north-south gradients above 750 hPa helping in organized convection in the study area.
22 Thermodynamic structure of the marine atmosphere over the Region 80°-87°E along 13°N during August (Phase II) BOBMEX-99
Savita B. Morwal and P. Seetaramayya, Indian Institute of Tropical Meteorology, Pune.
Thermodynamic structure of the marine boundary layer (MBL) along 13N over the Bay of Bengal region has been studied using 6-hourly radiosondes ascents made during the period 27-30 August 1999. The section is categorised into three