Ocean Upwelling Along the Yellow Sea Coast of China Revealed by Satellite Observations and Numerical Simulation

Satellite observations reveal that an ocean cooling event happened along the Yellow Sea coast of China intermittently in spring 2008, which lasted for days. During this period, the sea surface temperature (SST) dropped 3 °C-4 °C and the chlorophyll A (Chl-a) content increased by 0.5-1 mg/m
³
, as determined from satellite-derived products. The cold water also suppressed the sea surface capillary waves and made the ocean surface smooth, a distinct feature shown as dark patches observed in the synthetic aperture radar image acquired during this period of time. The surface wind direction varied between alongshore and offshore. We implemented an interactively coupled ocean (regional ocean modeling system) and atmosphere (Weather Research and Forecasting model) model to capture the dynamical processes of this seemingly wind-driven cooling event. When the wind changed direction such that the alongshore component blew with the land on its left side, stronger upwelling occurred; and when the wind blew offshore with no alongshore component, the upwelling still occurred in this area, but with less strength. Two simulations with idealized alongshore and offshore winds show that the upwelling can be set up within several hours. The alongshore wind is more effective than the offshore wind in transporting upper level water offshore and triggering upwelling and causing SST cooling areas that are relatively large in size, although the maximum SST cooling they cause is on the same order of magnitude.