Abstract
AbstractKolmogorov second‐order structure functions are used to quantify and compare the small‐scale information contained in near‐surface ocean wind products derived from measurements by ASCAT on MetOp‐A and SeaWinds on QuikSCAT. Two ASCAT and three SeaWinds products are compared in nine regions (classified as rainy or dry) in the tropical Pacific between 10°S and 10°N and 140° and 260°E for the period November 2008 to October 2009. Monthly and regionally averaged longitudinal and transverse structure functions are calculated using along‐track samples. To ease the analysis, the following quantities were estimated for the scale range 50 to 300 km and used to intercompare the wind products: (i) structure function slopes, (ii) turbulent kinetic energies ( ), and (iii) vorticity‐to‐divergence ratios. All wind products are in good qualitative agreement, but also have important differences. Structure function slopes and differ per wind product, but also show a common variation over time and space. Independent of wind product, longitudinal slopes decrease when sea surface temperature exceeds the threshold for onset of deep convection (about 28°C). In rainy areas and in dry regions during rainy periods, ASCAT has larger divergent than SeaWinds, while SeaWinds has larger vortical than ASCAT. Differences between SeaWinds and ASCAT vortical and vorticity‐to‐divergence ratios for the convectively active months of each region are large.
Highlights
The ocean and atmosphere exchange heat, moisture, and momentum across the air/sea boundary through interactions with small-scale structures (i.e.,
We study Advanced Scatterometer (ASCAT) wind products and SeaWinds products at two different grid sizes (12.5 and 25 km); all products are level 2B swath winds produced from orbit data
The above error estimates are for directly calculated structure functions, whereas the results presented in this paper are calculated according to (10) and (11) and contain binning errors
Summary
The ocean and atmosphere exchange heat, moisture, and momentum across the air/sea boundary through interactions with small-scale structures (i.e.,
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