Abstract
Hawaii regional climate model (HRCM), QuikSCAT, and ASCAT wind estimates are compared in the lee of Hawaii’s Big Island with the goal of understanding ultrahigh resolution (UHR) scatterometer wind retrieval capabilities in this area, which includes a reverse-flow toward the island in the lee of the predominate flow. A comparison of scatterometer measured σ 0 and model predicted σ 0 suggests that scatterometers can detect the reverse flow in the lee of the island; however, neither QuikSCAT- nor ASCAT-estimated winds consistently report this flow. Furthermore, the scatterometer UHR winds do not resolve the wind direction features predicted by the HRCM. Differences between scatterometer measured σ 0 and HRCM predicted σ 0 indicate possible error in the placement of key reverse flow features predicted by the HRCM. We find that coarse initialization fields and a large size median filter windows used in ambiguity selection can impede the accuracy of the UHR wind direction retrieval in this area, suggesting the need for further development of improved near-coastal ambiguity selection algorithms.
Highlights
Satellite radar instruments called wind scatterometers illuminate the Earth’s surface with microwaves and measure the normalized radar cross-section (σ0) of the surface [1]
Low differences in σ0 and low standard deviation values compared to Hawaii regional climate model (HRCM) predicted σ0 immediately west of the island suggest that the scatterometer σ0 can be detecting the reverse flow
Higher difference in σ0 and standard deviation values in the HRCM comparisons in the high wind speed areas suggest that HRCM is misplacing key wind features
Summary
Satellite radar instruments called wind scatterometers illuminate the Earth’s surface with microwaves and measure the normalized radar cross-section (σ0) of the surface [1]. The median filter selection preserves wind fronts and reduces noise, but as shown later, is limited by the size of the median filter window With their high topography, the Hawaiian Islands greatly affect nearby wind conditions. Complex fine resolution wind direction features and low wind speeds lead to systematic errors in L2B wind estimation in the lee of Hawaii’s Big Island for both QuikSCAT and ASCAT [15]. Wind directions in the lee of the Big Island can run counter to the prevailing trade winds, exhibiting a reverse flow toward the island.
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