An Introduction toSeaWinds Near-Real Time Data Ross Hoffman Mark Leidner Atmospheric and Environmental Research, Inc. Lexington, MA 02421
Acknowledgements Thanks to NASA scatterometer projects and OVWST for support. Information in this presentation is taken from the article: Hoffman, R. N., and S. M. Leidner, 2005: An introduction to the near real-time SeaWinds data. W. Fore. In Press.
Overview • The SeaWinds scatterometer • Measurement principles • Data processing • Instrument history • A representative data sample • Features of interest within the data • Data assimilation impact • Quality control • Summary
QuikSCAT NRT passes • November 1, 2000 • Dark blue: descending, Light blue: ascending, Green: one pass
History ofSeaWinds on QuikSCAT • Launch: 19 June 1999 • Valid measurements: 19 July 1999 to present. • Outages are infrequent and brief • Planned: Leonids meteor showers • Unplanned: Attitude control anomalies, system resets • Retrieved winds have been very accurate • Wind speed: 1 m/s RMS • Wind direction: 15 deg RMS Less than 1.2% of data between beginning of mission and June 2004 are missing.
Representative data swath QuikSCAT data centered on 2207 UTC 28 September 2000 Rev 6659 Thinned to every 4th along & across track ~12 minutes of data Green: rain contaminated Red: negative sigma0 GOES image valid 2215 UTC 28 September 2000 NCEP GFS MSLP analysis valid 00 UTC 29 September 2000
Hurricane Isaac Green: rain contaminated Red square: best track location at time of satellite image Central pressure: 948 hPa Estimated maximum winds: 59 m/s (115 kt) Ambiguity removal error Rain flag too aggressive Maximum scatterometer winds, 36.4 m/s (71 kt), only 60% of estimated maximum winds
Wind retrieval Maximum Likelihood Estimator (MLE)Minimizes difference between observations & simulated observationsOne measurementSingle locusSpeed roughly definedAll directions equally likelyTwo measurementsSuperposition of two lociFour equally likely solutionsFour measurementsSuperposition of four lociNo common intersectionLikelihoods vary
Light winds Light winds (WVC 48)
Summary • QuikSCAT provides comprehensive and accurate view of the surface wind field over the global ocean • QuikSCAT has been a reliable mission • Quality control is key for proper use of the data • Rain contamination • Ambiguity removal errors • Low and high wind speeds
end • rhoffman at aer.com • 781.761.2288