Brigham Young University DGL Dec 03 Rain/Wind Backscatter Model Model for measured backscatter Radar signal scattered by falling droplets Surface.

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DGL Dec 03DGL Dec 03

Rain/Wind Backscatter Model Model for measured backscatterModel for measured backscatter

Radar signal scattered by falling Radar signal scattered by falling droplets droplets

Surface signal attenuated by Surface signal attenuated by atmospheric rainatmospheric rain

Surface wind-induced Surface wind-induced backscatter perturbed by rain backscatter perturbed by rain striking the waterstriking the water

Model derived from colocated Model derived from colocated TRMM PR and QuikSCAT dataTRMM PR and QuikSCAT data

Rain affects ~4% of SeaWinds dataRain affects ~4% of SeaWinds data oM

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DGL Dec 03DGL Dec 03

Simultaneous Wind/Rain Retrieval

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Wind Rain Regimes

Regime 1: rain dominates wind backscatter – poor quality wind estimates Regime 1: rain dominates wind backscatter – poor quality wind estimates (10% of rain (10% of rain cases*)cases*)

Regime 2: both wind and rain important – can retrieve wind and rain rate Regime 2: both wind and rain important – can retrieve wind and rain rate (34% of rain (34% of rain cases*)cases*)

Regime 3: rain effects insignificant – wind estimates unaffected by rainRegime 3: rain effects insignificant – wind estimates unaffected by rain (56% of rain (56% of rain cases*)cases*)

Note: globally, only about 4% of all QuikSCAT data effected by rain Note: globally, only about 4% of all QuikSCAT data effected by rain

* From collocated TRMM PR and QuikSCAT data in tropics* From collocated TRMM PR and QuikSCAT data in tropics

)()(,,,,, RRuMRu effo

)(Reff incorporates surface rain perturbation, atmospheric rain scattering, and attenuationincorporates surface rain perturbation, atmospheric rain scattering, and attenuation

- Empirical function of rain rate derived from collocated QuikSCAT and TRMM PR- Empirical function of rain rate derived from collocated QuikSCAT and TRMM PR

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DGL Dec 03DGL Dec 03

Wind/Rain Validation

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DGL Dec 03DGL Dec 03

Scatterometer Rain Retrieval Validation

Bias can be estimated and corrected for

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DGL Dec 03DGL Dec 03

Rain Estimate Validation

QuikSCAT-derived rain rates vs TMI-derived rain ratesQuikSCAT-derived rain rates vs TMI-derived rain rates

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DGL Dec 03DGL Dec 03

Storm Example

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Floyd (rev 1201, 11 Sept 1999)

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Typhoon (rev 1222, 12 Sept 1999)