Seasonality and regional characteristics of sea-surface wind responses to mesoscale SST features

Ryusuke Masunaga, United States; University of Hawaii, Honolulu, HI, United States and Niklas Schneider, Univ Hawaii, Honolulu, HI, United States
Abstract:
It has been well established that mesoscale sea-surface temperature (SST) features near the midlatitude western boundary currents exert significant local impacts on mesoscale sea-surface wind distribution. Satellite observations capture high (low) sea-surface wind speed over warm (cool) SST anomalies.

It has been theoretically argued that the wind responses can depend on horizontal scales, background wind speeds and its direction relative to horizontal gradients in SST. In the present study, we investigate seasonality and regional characteristics in the sea-surface wind responses to mesoscale SST features based on satellite observations and an atmospheric reanalysis. We use the spectral transfer function approach (Schneider and Qiu 2015) to argue dependency of the wind responses on horizontal scales and background wind states.

Transfer functions reveal that annual-mean wind responses are qualitatively consistent between the Gulf Stream and the Agulhas Return Current regions. The wind responses over the Gulf Stream region exhibit distinct seasonality, which probably reflects distinct seasonality in background surface wind velocities. On the other hand, seasonality is less obvious over the Agulhas Return Current region, where background westerly winds dominate throughout a year.

Sea-surface wind fields in ERA5 atmospheric reanalysis exhibit much weaker responses. We will argue the causes of the discrepancies between satellite observations and reanalysis products.