Coastal katabatic winds imaged by SAR

Sea surface imprints of coastal katabatic winds are observed on a RADARSAT‐1 synthetic aperture radar (SAR) standard mode image off the U.S. west coast taken on January 21, 2003. The katabatic wind pattern is shown in the SAR image as a striking finger‐like bright‐dark region that mirrors the coastal mountain topography. We simulate the low‐level atmospheric circulation using the numerical weather model MM5 with a triply nested‐grid technique. The model simulation reproduces the finger‐like katabatic wind pattern at the SAR imaging time. Katabatic wind is strongest in the morning when the surface temperature gradient between ocean and land reaches a maximum. The sea surface wind simulated by the MM5 model and that derived from the calibrated SAR normalized radar cross section are in good agreement. The katabatic wind variation along the coastline is between 5–8 ms−1, and the longest wind finger stretches over 20 km offshore.