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Precipitation Retrievals Over Land Using SSMIS

Precipitation Retrievals Over Land Using SSMIS. Nai-Yu Wang 1 and Ralph R. Ferraro 2 1 University of Maryland/ESSIC/CICS 2 NOAA/NESDIS/STAR. Outline. Motivation Current status of GPROF land Profiling approach High frequency and temperature sounding channels from SSMIS

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Precipitation Retrievals Over Land Using SSMIS

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  1. Precipitation Retrievals Over Land Using SSMIS Nai-Yu Wang1 and Ralph R. Ferraro2 1 University of Maryland/ESSIC/CICS 2 NOAA/NESDIS/STAR

  2. Outline • Motivation • Current status of GPROF land • Profiling approach • High frequency and temperature sounding channels from SSMIS • Land precipitation retrievals in complex terrain • Conclusions and future work

  3. Motivation • Improve current precipitation retrievals over land (TMI GPROF 6.5 land) • Explore mid-latitude precipitation retrieval using passive microwave radiometer high frequency and sounding channels, in preparations for GPM • High frequency bands between 150 and 183 GHz • Less sensitive to surface emissivity variations • Respond to thick clouds, water vapor, and precipitation • Oxygen absorption bands between 50 and 60 GHz • Primarily probe atmospheric temperature and moisture profiles, might be critical in classifying different climate regimes (e.g., freezing height)

  4. Current status of GPROF Land • TMI GPROF 6.5 land • Ferraro’s scattering index (SI) and rainrate algorithm for SSMI and TMI, utilize 22 and 85 GHz • TRMM TMI SI and PR rainrate matchups, convective probability, separate convective and stratiform in the database; coastline improvements (McCollum and Ferraro) • Retrieve Surface rainrate

  5. Profiling Approach • Retrieve hydrometeor profiles using 150-183 GHz and 50-60 GHz brightness temperatures • Bayesian framework • Employ cloud resolving models (CRM), coupling CRM outputs with radiative transfer calculations to construct an a priori database of brightness temperatures and the hydrometeor profiles over land

  6. Profiling Approach • Use a probabilistic approach to calculate the most likely a posteriori distribution constrained by actual satellite measured brightness temperatures • Precipitation estimates are weighted averages of the mean precipitation values corresponding to the classes in the database R: retrieved hydrometeor profile

  7. Generate Database Observations Surface Screening Hydrometeor Microphysical schemes TOA multichannel Brightness Temperatures/ Hydrometeor Vertical profiles Observed Multichannel Brightness Temperatures Radiative Transfer Model Convective Stratiform ? Best matched Brightness Temperatures Hydrometeor profiles Surface rainrate

  8. Land Database • GPROF land profiles are selected exclusively from GPROF CRM simulations that are predominantly from tropical oceanic systems • Profiles tested: • GCE TRMM LBA: simulations of mesoscale convective system during Jan-Feb in Brazil • MM5 MIDACF: mid-Atlantic ocean cold front system • 5 classes of hydrometeor: cloud water, cloud ice, rain, ice and graupel • 1-1.5 km horizontal resolution, averaged to individual SSMIS resolutions (15 km for 150, 183 GHz) • Radiative transfer model: Eddington two-stream approximation (Kummerow)

  9. Land database issues • Bayesian approach • Strength : direct use of explicit microphysical mechanisms in CRM • Disadvantage: susceptible to errors in the a priori database in terms of the accuracy of microphysical details, and the fidelity with which the model outputs capture differences in climate regimes. An example.

  10. Conical scanned passive microwave radiometer, launched in Oct 2003 SSMI heritage channels 19-91 GHz Air temperature sounding channels near 60 GHz oxygen absorption band 150 GHz imaging channel and three 183 (+-1, +-3, +-6.6) GHz troposphere water vapor sounding channels Observations: SSMIS

  11. SSMIS IFOV FreqFootprint Sampling interval GHz (km) (km) 22 73X47 25 50 38X38 37.5 54 38X38 37.5 150 14X13 37.5 18314X13 37.5 Grid all channels to 0.15 deg in latitude/longitude grids Courtesy of Dr. Joe Turk

  12. NOAA HMT 2006 site • Complex terrain • Off coast of California • American river basin • Sierra mountain • Winter time flooding Instrumentations • Radar profilers • X-band polarimetric radar • GPS sounde • Disdrometer • Rain gauges IOP4 : DEC 30-31, 2005 Cold frontal system, moist oceanic air mass crossed the area, small scale rain band structure, high snow level on the ground

  13. High Frequency Precipitation signalsSSMIS Dec 31, 2005 1637Z

  14. Surface Screening • Surface ice and snow, and sand yield similar scattering signatures as precipitation • Screening surface scatters • “scattering index” SI to locate high scatters • combinations of low/high frequency channels to differentiate precipitation from surface scatters • TB(22 GHz) • TB(91 - 150 GHz) • TB(183+-7 - 150 GHz)

  15. Preliminary Rain RetrievalDecember 31, 2005 SSMIS retrieved rainrates from 50, 150, 183+-1/+-7 GHz at 1637Z Composite radar reflectivity at 1700Z

  16. Conclusions and Future Work • A framework of land precipitation profiling retrieval algorithm using passive microwave high frequency is established • Currently, retrieval does not have the ability to locate the freezing level and differentiate convective and stratiform systems from brightness temperatures • plan to gather large number of matchups between SSMIS, TRMM PR and CloudSat for different climate regimes to enhance the retrieval skill • Radar reflectivity/hydrometeor profiles will also used to build up hydrometeor database for land • Validate radiative transfer model with HMT ground radars and satellite radar matchups

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