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Impact of METOP ASCAT Ocean Surface Winds on Forecasts

Anomaly Correlation Scores for forecasts at day 5 without ASCAT (control) and with ASCAT (ASCAT) data for 500hPa and 1000 hPa heights for the Northern and Southern Hemispheres

Editor's Note: This article and the following one are the first of an occasional series of notes highlighting accomplishments by investigators supported under JCSDA's Federally Funded Opportunity or Directed (Partner Agency In-house) Research programs. Investigators are encouraged to submit contributions.

A two-season observing system experiment is being conducted to study the impacts of assimilating the EUMETSAT's MetOp Advanced SCATterometer (ASCAT) ocean surface winds. The assimilation system and forecast model are a recent version of the NCEP Global Data Assimilation/Global Forecast System (GDAS/GFS).

ASCAT impact is increased by thinning the data to 100 km, incorporating a sea surface temperature check to reject observations contaminated by sea ice, and applying a QC check based on the magnitude of innovation vector differences (observation minus background).

ASCAT winds have a 180 deg directional ambiguity. The NESDIS processing system selects a vector by comparing the ASCAT winds to a GFS model 6-hr forecast initialized without ASCAT winds. In our experiments, the selected ASCAT vectors were compared to a 6-hr forecast initialized with an analysis that includes the ASCAT winds. In less than 2% of the cases, we found that the difference between the selected vector and the 6-hr forecast was larger than that of its pair. Two schemes are being tested to correct for this problem. Scheme one removes observations where the vector difference of the selected vector is larger than its pair, while Scheme 2 replaces the originally selected vector with its pair.

ASCAT is the first operational scatterometer and follows the successful use of research instruments – NASA's QuikSCAT and ESA's ERS scatterometer – in NWP.

(Li Bi, Space Science and Engineering Center, University of Wisconsin-Madison)

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