Certain Seasonal Characteristic Features of Oceanic Heat Budget Components Over the Indian Seas in Relation to the Summer Monsoon Activity Over India

Abstract

The present study has been undertaken to examine the oceanic heat budget components and their variability over the Indian seas in relation to the extreme monsoon activity (flood/drought) over the Indian subcontinent. For this purpose, various components of oceanic heat budget have been analysed for pre-monsoon (March-May), monsoon (June-September), post-monsoon (October-December) and winter (January-February) seasons over India. The data base used in this study consists of mean monthly marine meteorological fields for 30 years (1950-1979), which is a part of the Comprehensive Ocean Atmosphere Data Set (COADS) analysed at I" latitude by 1" longitude resolution.The mean fields of incoming shortwave radiation flux over the Indian seas in different seasons vary in accordance to the sun's position and cloud cover variations. The latent heat flux undergoes considerable seasonal variations, particularly over the Arabian Sea. There is a dominance of latent heat flux (representing the oceanic heat loss) over shortwave solar flux (representing the oceanic heat gain) during the monsoon season, which results in a zone of net oceanic heat loss over the central Arabian Sea. This feature produces a positive feedback for the maintenance of deep cumulus convection over the Arabian Sea in this season.It is also found that oceanic heat budget components over the Indian seas exhibit significant variability in relation to the extreme monsoon activity leading to flooddrought over India. Based on the above analysis, mean monthly variations of the oceanic heat budget components over three smaller sectors of the Indian seas, namely west equatorial Indian Ocean, Arabian Sea and Bay of Bengal, are also examined. The variations are found to be considerably different between the two extreme categories of the monsoon. It becomes evident fiom this study that the oceanic sectors of west equatorial Indian Ocean and Bay of Bengal experience a large reduction of net heat flux from April to May prior to a flood monsoon season over India. This suggests that a spectacular increase of latent heat flux and decrease of shortwave flux occurs over these oceanic sectors, leading to a sharp reduction of net heat flux.

Prediction of winter precipitation over northwest India using ocean heat fluxes

“…html). Generally, the net download heat flux at the ocean surface (Q net ) is calculated as a sum of (see Mohanty et al 1996).…”

“…Further, ocean heat fluxes serve as lower boundary conditions for the atmosphere and upper boundary conditions for the ocean in driving large-scale ocean-atmosphere coupled processes (Manabe et al 1975). Earlier studies also highlighted the role of ocean heat fluxes on summer monsoon rainfall over the Indian sub-continent during different epochs (Pisharoty 1965;Das 1983;Mohanty et al 1983Mohanty et al , 1994Mohanty et al , 1996Mohanty and Mohan Kumar 1990;Mohanty and Ramesh 1993). The transfer of surface heat and moisture fluxes from the ocean surface to the atmosphere that determines the mass and wind fields exhibited significant variability over the Indian seas between the extreme categories of the monsoon (flood and drought) (Mohanty and Ramesh 1993).…”

“…The seasonal mean of winter VIMT (in kg/m-s) is computed by using specific humidity (q in kg/kg), zonal (u in m/s) and meridional (v in m/s) components of wind integrated from 1000 to 300 hPa for the study period 1980-2011 (Mohanty et al 1983(Mohanty et al , 1994(Mohanty et al , 1996Godfred-Spenning and Reason 2002;Konwar et al 2012). The VIMT closely resembles the large-scale wind circulation in the lower troposphere (~850 hPa) along with transport vector at 850 hPa pressure level, which is illustrated in Fig.…”

Positive correlation between d 18O in monsoon precipitation and atmospheric wind speed

“…Therefore, there is about 70% of amIual precipitation occurring in summer [7] in the monsoon-influenced region, where energy and moisture for maintaining the system [8] mainly originate from Arabian Sea and the Bay of Bengal of the tropical Indian Ocean. Table I lists the multi-year correlation coefficients between monthly 5 18 0 values, corresponding rainfall and air temperature at Bangkok, New Delhi, Kumning, Lhasa and Bombay from June to September, indicating that the amount effect in Bangkok but the temperature effect in New Delhi is most evident, with the respective correlation coefficients of -0.611 and 0.626, and that both the amount and temperature effects exist at four stations, except for that at Bombay.…”

Uncertainty Characterization of HOAPS-3.3 Latent Heat Flux Related Parameters

“…Monsoon-related characteristic features of Indian Ocean LH F variability, which also exhibit an impact on climatological uncertainties, are elucidated in e.g. Mohanty et al (1996). Minima in the order of 0.5 m s -1 are mostly confined to the eastern margins of all ocean basins (Fig.…”