Subsurface Ocean Characteristics and Their Impact on Indian Monsoon Advancement: An ORAS5-based Study (1992-2017)

Abstract

The monsoon system over the Indian Peninsula is significantly influenced by the complex interplay between the Indian Ocean and atmospheric conditions. This research investigates how potential temperature and salinity levels in the Indian Ocean vary during the monsoon's advancement phase. To analyse these patterns, we examine daily averages from the European Centre for Medium-Range Weather Forecasts' (ECMWF) Ocean Reanalysis System 5 (ORAS5), spanning 1992-2017. The study specifically explores how oceanic characteristics, including sea sub surface temperature and salinity, affect the timing, strength, and length of monsoon seasons. Prior to monsoon advancement, the Indian Ocean exhibits notable variations in potential temperature and salinity distribution. The Arabian Sea, in the western Indian Ocean, shows elevated salt concentrations in its upper subsurface waters. In contrast, the eastern Indian Ocean's Bay of Bengal demonstrates markedly lower salinity levels at similar depths. This east-west salinity contrast becomes less pronounced at greater depths, primarily due to the freshwater influx from rivers flowing into the Bay of Bengal. Highest potential temperature has been observed up to 20 meters depth and slightly later in fast advancement year than slow advancement year. Salinity between 60 to 80 meters depth in region R1 (AS) and R3, R4 shows different in nature. Contrast in temperature and salinity between AS and BoB has been observed higher in fast advancement year shows greater evaporation in 2005 than 2002 and wind play crucial role in transferring moisture all over India.