Oceanic upwelling and downwelling processes in waters off the west coast of India

Abstract

A three-dimensional model based on the Princeton Ocean Model (POM) has been implemented to study the circulation of the west coast of India. The model uses a curvilinear orthogonal horizontal grid with higher resolution near the coast (3-9 km) and a terrain following sigma coordinate in the vertical. The model is able to simulate Lakshadweep High and Lakshadweep Low (LL) during the winter and summer monsoons, respectively. During winter, the downwelling processes noticed along the coast help in the formation of temperature inversions. The inversions can be seen even up to the depths of ∼50 m, which agrees with the available ARGO data in the region. Model simulations show that coastal upwelling off Kerala is at its peak in July. The intensity of upwelling reduces along the coast towards north. During the existence of LL, there is a cyclonic eddy in the sub-surface waters over the South-Eastern Arabian Sea, with vertical extent up to the depths of 100-150 m and it is strengthened due to the presence of northward counter current in the shelf region. The southerly coastal jet formed along the southern coast as a result of upwelling is noticed a westward shift along with LL. The location of the eddy off Kerala is tilted towards the open ocean with depth and our experiments suggest that this flow can be understood as a first baroclinic mode.

A Holistic Approach to Upwelling and Downwelling along the South-West Coast of India

“…During the summer monsoon, the WICC flows towards the equator along the west coast of India and reverses its direction towards the pole during the winter monsoon (Clarke 1983;Potemra, Luther, and O'Brien 1991;Yu, O'Brien, and Yang 1991;McCreary, Kundu, and Molinari 1993;McCreary et al 1996;Shetye and Gouveia 1998;Schott and McCreary 2001;Shankar, Vinayachandran, and Unnikrishnan 2002). The coast was characterized by upwelling during the summer monsoon and downwelling during the winter monsoon (Rao, Joshi, and Ravichandran 2008).…”

“…Compared to the south-west coast, north-west coast of India has a wider continental shelf (Carton, L'Hegaret, and Baraille 2012). A modeling study of Rao, Joshi, and Ravichandran (2008) concluded that upwelling along the southwest coast of India peaks during July and its intensity decreases towards North. Their study also revealed that temperature inversion along the coast is dependent mainly on downwelling during winter monsoon.…”

Observed low‐salinity plume off Gulf of Khambhat, India, during post‐monsoon period

“…The downwelled AS high‐saline sub‐surface waters are warm and lead to TI in the mixed layer. The dynamics of TI along the west coast of India is explained in detail by Rao et al [2008].…”

“…The Indus, Mahi, Narmada and Tapti are the main rivers which discharge freshwater into the eastern AS. The freshwater outflow from the Indus River inhibits the upwelling tendency of the isotherms in the surface layer [ Sanilkumar and Unny , 2005; Rao et al , 2005, 2008]. Shankar et al [2005] studied the water‐masses off the southeastern Arabian Sea during 2002 summer monsoon.…”

“…Though the model has been implemented for the entire eastern part of the AS, the simulations are focused particularly for the northeastern region near the Gulf of Khambhat. The details of the model setting and numerical experiments are given by Rao et al [2008] and hence not repeated here. However, it is worth mentioning that there are about 175 × 250 × 26 computational points in the model grid.…”