Temporal and Spatial Variations of Monsoonal Upwelling along the South West and East Coasts of India

Abstract

The implicit/explicit impact of global warming or the anthropogenic climate change on the coastal upwelling processes affects the marine ecosystem significantly and continuous monitoring of the coastal upwelling along the coastal regions is essential. The Ekman transport due to alongshore winds and Ekman pumping due to wind stress curl play important roles on the coastal upwelling, especially along the southern part of Indian peninsula. Upwelling Indexes based on wind and SST are computed in the study to demarcate the upwelling features along the coasts. Since upwelling leaves its trail on surface features, long time series of satellite-derived wind, Sea Surface Temperature (SST), Sea level anomaly (SLA) and Surface Chlorophyll-a concentration (Chl-a) are analyzed to understand the upwelling along the coastal regions of south India. The present study reveals a decrease in the intensity of upwelling along the western coast (Chl-a ∼ 0.2 mg/m³ dec⁻¹, Upwelling Index based on wind (${\mathit{UI}}_{\mathit{wind}}$) and Vertical Velocity of Ekman Pumping (VVEP) is approximately 0.0012 m²/s dec⁻¹ and 0.120 cm/day dec⁻¹ respectively) and a slight increase all along the eastern coast of southern India during summer monsoon (Chl-a along 11.3°N and 13.9°N is 1 mg/m³ dec⁻¹, ${UI}_{\mathit{wind}}$ and VVEP along 10.5°N is 0.0023 m²/s dec⁻¹ and 0.2 cm/day dec⁻¹ respectively).

Keywords:

• Coastal upwelling
• Indian coasts
• long-term trend
• upwelling index
• vertical velocity of Ekman pumping

Acknowledgment

The authors would like to thank the Director of the Space Application Center (SAC), the Deputy Director, Earth, Ocean, Atmosphere, Planetary Sciences and Applications Area, Group Director, Atmospheric and Oceanic sciences group for the encouragement and for providing computational facility in SAC. The authors express their deep gratitude to Dr. Rashmi Sharma, Head, Oceanic Sciences Division for the continuous motivation and guidance. Author would like to thank Indus University for the motivation. Special appreciation to MOSDAC for the operationalization of upwelling index product. The work is supported by a research project ‘Ref.: SAC/EPSA/4.19/2017’ funded by SAC. Chlorophyll-a product downloaded from http://ftp://ftp.hermes.acri.fr. Sea Surface Temperature data downloaded from www.ncei.noaa.gov. Wind fields are obtained from http://ftp://ftp.remss.com/CCMP. Sea level anomaly is obtained from www.aviso.altimetry.fr.