| Summary: | Some unique characteristics of the polar atmosphere affect the height assignment of cloud and water vapor features used in high-latitude wind estimation. In particular, low water vapor amounts, atmospheric temperature inversions, and low, thin clouds on height assignment can significantly impact the infrared window, CO2-slicing, and H2O intercept methods. Satellite-derived and modeled cloud and atmospheric properties show that 20-35 % of polar clouds are low (greater than 600 hPa) and thin (optical depths less than 5), with associated height assignment errors averaging 75 hPa. Total precipitable water (TPW) is less than 0.5 cm over most of the Arctic and Antarctic in winter and surface contamination in the 6.7 µm water vapor channel is apparent at TPW amounts less than approximately 0.3 cm. To mitigate the effects of low, thin clouds and the relatively dry polar atmosphere on height assignment, it is recommended that atmospheric motion vectors (AMV) based on clear sky water vapor features be flagged and adjusted for surface effects when TPW is less than approximately 0.3 cm, and that AMVs from low, thin water clouds be flagged and adjusted for cloud optical depth in a post-processing step.
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