1980 - National Institute of Oceanography

of temperature and salinity/conductivity mostly upto 2000 m depth were obtained at 41
stations. These data are being processed and some of the results are mentioned below:
(a) Surface boundary layer studies
Based on the surface meteorological and wave data collected from two
locations in the western Bay of Bengal in July 1979 during the 58th cruise, surface
layer conditions of the atmosphere of different surface circulations, associated sea
surface roughness and the height of surface roughness were studied. The thermal
stratification of the surface layer as inferred from the Bulk Richardson number
values revealed neutral and near-neutral conditions. The convective activity affected
the sea-air temperature difference and seemed to cause variations in the characteristic
height of the surface layer. Larger variations in the surface layer were encountered
during the rough condition of the sea. The wind hodographs of diurnal variations
showed anticyclonic and a precursor and cyclonic circulations.
(b) Sound velocity structure
Using the hydrographic data collected by R.V. Vityaz during the IIOE
(January-March 1961), sound velocity structure of the Bay of Bengal including the
Andaman Sea has been studied. In the upper 200 m, sound velocity varied significantly
with longitude (8-11 m/sec). It was relatively greater in the low latitude.
The depth of SOFAR channel (axis of primary sound channel) varied between 800 m
and 1750 m. Geographical variations of SOFAR axial velocities were found to be
related to the characteristics of general circulation in the area.
(c) Hydrographic features
Physical characteristics in the Andaman Sea during the winter were studied
using the data collected by R. V. Gaveshani during the period January-February in
1979 and 1980. Distributions of temperature, salinity and density along six transects
were studied and characteristics of watermasses were investigated. The Persian
Gulf water was identified in the depth range of 200-500 m with a characteristic
high salinity of about 35.l%o, temperature range 10 to 12°C and σ- t range 26.7 to 27.0.
Below this, in the depth range 500-900 m the water of the Red Sea seems to
be present. In the northern part of the study area, a mixed layer with thickness
upto 75 m was encountered. The presence of a warm deeper water in the Andaman
Sea area has also been confirmed.
(d) Wave characteristics
Using the wave data collected with a shipborn wave recorder during the 51st
and 52nd cruises (February 1979) and 67th cruise (January 1980) of R.V. Gaveshani
the wave characteristics of the seas around the Andaman and Nicobar islands were
studied. The distribution of zero crossing period, significant wave height and spectral
width parameter were also studied. The predominant zero crossing period and
significant wave heigh were found to be 6-12 secs and 0.6-1.4 metres respectively.
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