9 Feb 2005, Miami 1 An Introduction to SeaWinds Near-Real Time Data Ross Hoffman Mark Leidner Atmospheric and Environmental Research, Inc. Lexington, MA 02421

9 Feb 2005, Miami 2 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.

9 Feb 2005, Miami 3 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

9 Feb 2005, Miami 4 QuikSCAT NRT passes November 1, 2000 Dark blue: descending, Light blue: ascending, Green: one pass

9 Feb 2005, Miami 5 History of SeaWinds 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.

9 Feb 2005, Miami 6 Representative data swath QuikSCAT data centered on 2207 UTC 28 September 2000 Rev 6659 Thinned to every 4 th 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

9 Feb 2005, Miami 7 Hurricane Isaac

9 Feb 2005, Miami 8 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

9 Feb 2005, Miami 9 Wind retrieval Maximum Likelihood Estimator (MLE) Minimizes difference between observations & simulated observations One measurement Single locus Speed roughly defined All directions equally likely Two measurements Superposition of two loci Four equally likely solutions Four measurements Superposition of four loci No common intersection Likelihoods vary

9 Feb 2005, Miami 10 Cross-swath variation in data quality

9 Feb 2005, Miami 11 Cross-swath variation in data quality

9 Feb 2005, Miami 12 Light winds Light winds (WVC 48)

9 Feb 2005, Miami 13 Rain effects on data quality

9 Feb 2005, Miami 14 Rain effects on data quality

9 Feb 2005, Miami 15 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

9 Feb 2005, Miami 16 end rhoffman at aer.com