Estimating Wind Stress at the Ocean Surface From Scatterometer Observations

Abstract

Abstract-Wind stress is the most important ocean forcing for driving tropical surface currents. Stress can be estimated from scatterometer-reported wind measurements at 10 m that have been extrapolated to the surface, assuming a neutrally stable atmosphere and no surface current. Scatterometer calibration is designed to account for the assumption of neutral stability; however, the assumption of a particular sea state and negligible current often introduces an error in wind stress estimations. Since the fundamental scatterometer measurement is of the surface radar backscatter (sigma-0) which is related to surface roughness and, thus, stress, we develop a method to estimate wind stress directly from the scatterometer measurements of sigma-0 and their associated azimuth angle and incidence angle using a neural network approach. We compare the results with in situ estimations and observe that the wind stress estimations from this approach are more accurate compared with those obtained from the conventional estimations using 10-m-height wind measurements.

Importance of Ocean Heat Content for Cyclone Studies

“…They reported that out of 75 cyclones occurred in the tropical Indian Ocean during 1998-2011; more than 50% of the cyclones have no significant correlation between CI and SST. The number of cyclones with significant negative (positive) correlation are 31(3), 13(10) and 17 (14) with SST leading CI by one, two and three days respectively Figure 3 of Ali et al [15,16]. In these cases SST of previous days is correlated with CI.…”

“…Several other studies also reported that CIs are positively (negatively) correlated with positive (negative) SSHAs [3,13,14]. Ali et al [15,16] further analyzed TRMM Microwave Imager (TMI) daily SST and CI, defined as the maximum sustained winds from Joint Typhoon Warning Center (JTWC) best track data. They reported that out of 75 cyclones occurred in the tropical Indian Ocean during 1998-2011; more than 50% of the cyclones have no significant correlation between CI and SST.…”

A soft‐computing cyclone intensity prediction scheme for the Western North Pacific Ocean

“…Ali et al . (, ) suggested using ocean mean temperature, which can be computed from the ocean heat content (OHC) derivable from satellite altimetry, as an alternative to SST.…”

“…MLP approach has been used by Ali et al . (, , , , ) to estimate the tropical cyclone heat potential and the ocean windstress. We tried all the models and found that an MLP network provided the least error and best results.…”

“…Thus it is the deep surface layer, not simply the surface itself that is important to cyclone intensification. Ali et al . (2013aAli et al .…”