An ERS 1 synthetic aperture radar image of atmospheric lee waves

Abstract

An ERS 1 synthetic aperture radar (SAR) image of the island Hopen shows a distinct 7.6-km wavelength wave phenomenon near the island. This wave phenomenon is interpreted as the surface imprint on open water of atmospheric lee waves. The pattern is visible in the SAR image, since the lee waves modulate the horizontal wind speed near the ocean surface which, in turn, modulates the surface roughness and the radar cross section. The physical setting for the observation is presented and discussed. The lower bound on horizontal wind speed modulation is estimated to range from 3±2 ms−1 (for the wind speed minima) to 12±2 ms−1 (for the wind speed maxima) based upon the observed radar cross-section modulation and the ERS 1 scatterometer wind retrieval model CMOD4. The wavelength and wind speed modulation are consistent with linear lee wave model predications. The model uses an atmosphere with an exponential profile of the Scorer parameter (ratio of buoyancy frequency to wind speed) to represent a shallow, ground-based inversion layer observed at Bear Island and a bell-shaped barrier to represent the forcing effects of Hopen.