Applications of Satellite Derived Ocean Surface Vector Winds in

Operational Marine Weather Forecasting

Joe Sienkiewicz, NOAA/NWS Ocean Prediction CenterZorana Jelenak, UCAR/NOAA NESDIS

How is Wind Measured Over the Ocean?

Direct Measurements

• Buoy, Ships– Pros

• Provide frequent updates at a single point, meeting or exceeding 1-hr refresh

• Provide reference points for real-time diagnostics in the generation of the forecast/warning package

• Complements synoptic scale satellite information by providing a frequently updated reference measurement

– Cons• Limited coverage – only provide limited point measurements

Indirect Measurements

OSCAT Descending Passes

ASCAT Descending Passes

Wind speed and direction information needs to be derived from satellite measurements

NSCAT

August 1996

Wind Vector Measurements Through History

Stick

Scatterometer

ERS 1 & 2

Aug 1991, April 1995

Stick

Scatterometer

SeaSAT 1978

110 days

SeaWinds+AMSR

Dec 2002

Pencil-beam

Scatterometer

QuikSCAT

June 1999-Nov 2009

Stick

ScatterometerASCAT-B

Sep 2012

C-band

Ku-band

Pencil-beam

Scatterometer

OceanSat-2

Sep 2009

ASCAT

Oct 2006

What are Scatterometers?• Microwave Radars on Polar orbiters

– C-band ~5GHz (~5cm), Ku-band ~14GHz (~2cm)

• C-band (less impacted by rain than Ku)

• Ku-band (rain impact)

– designed to measure ocean surface backscatter (0 )• Capillary waves• infer wind speed

– Multiple samples from different azimuth angles

• wind direction solutions

t

r0 P

PG

Pr

Pt

Surface roughness relates to 0 and depends on friction velocity

9

QuikSCAT Measurement Geometry

WVC – Wind Vector Cell

25km → 76 WVC across swath

Far Swath Far SwathMid Swath Mid SwathNadir

H-pol

V-pol

4 observations good azimuth diversity

4 observations poor azimuth diversity

2 observations

Measurement GeometryMeasurement Geometry

4-Look Solution

Most likely solution U=10m/s, χ=150°

16 December 2009

Rain EffectsRain Effects

• The radar signal is attenuated by the rain as it travels to and from the Earth’s surface σ0

•Retrieved wind speed

The radar signal is scattered by the raindrops. Some of this scattered energy returns to the instrument σ0

•Retrieved wind speed

•The roughness of the sea surface is increased because of the splashing due to raindrops σ0

•Retrieved wind speed•Directional information can be lost

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A S C A T

T R A C K

O S C A T

T R A C K

Rain Impact on OSCAT RetrievalsCase 1

Rain Impact on OSCAT RetrievalsCase 1

Examples

ASCAT 2100 UTC 02 NOV 2012

GDAS 2100 UTC 02 NOV 2012

NOAA Ocean Prediction Center – scatterometer impacts on operations

OSCAT and ASCAT Forecasters use every pass to: make warning and short-term forecast decisions and to estimate - cyclone location, intensity, extent of wind field - strength and extent of orographically enhanced jets - wind field near strong SST

gradientsResults in improved warning and forecast services over otherwise data sparse oceans

SUPER STORM Sandy – ASCAT 1419 UTC29 Oct 2012