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Sounders METR280 Satellite Meteorology/Climatology

Partially based on the following...

Short Course on Satellite Meteorology

AMS 78th Annual Meeting Phoenix, Arizona

Applications and Interpretation: Part 3 Sounder Products and Applications

Donald G. Gray NOAA/NESDIS Office of Research and Applications Washington, DC

Outline  Brief review of sounder fundamentals, including absorption spectra and weighting functions  Characteristics of GOES soundings (spatial coverage, production methodology, derived parameters) and validation  Applications of GOES sounding products to weather analysis and forecasting

Atmospheric Soundings  How can we retrieve vertical profiles of temperature and moisture information from satellite data?

What is a “sounder”?

 A sensor for collecting vertical profiles of temperature and moisture using sensors with multiple, narrow bands

How do sounders work?

 Weak absorption channels effective emission level is near surface  Strong absorption channels: upper atmosphere  Moderate absorption channels: vary in altitude

Sounding theory  Assume free of scattering (no clouds)  We must account for: • Earth’s emission (“absorption spectra”) • • Transmission between layers Weighting function

Fundamentals of Soundings  Absorption spectra  Transmittances, weighting functions  Examples of GOES sounder channels • • • • Longwave CO 2 H 2 O Shortwave CO 2 Visible

Absorption Spectra - IR  Carbon dioxide (CO 2 ) • Longwave: 11 - 18 m m (Surface/ Atmospheric Temperature) • Shortwave: 4 - 6 m m (Surface/Lower Atmospheric Temperature)   Water Vapor (H 2 O) • Midwave: 6 - 10 m m (Atmospheric Moisture) Ozone (O 3 ) • 9.6 m m: (Total Column Atmospheric Ozone)

Fundamentals of Soundings  Absorption spectra  Transmittances, weighting functions  Examples of GOES sounder channels • • • • Longwave CO 2 H 2 O Shortwave CO 2 Visible

Transmittances and weighting functions  Transmittance atmosphere : Percent of radiation of particular wavelength transmitted through  Transmittance = 1 - Emissivity Weighting Function radiance values.

: Derivative of transmittance with respect to height (lnP). Larger values correspond to atmospheric layers with the greatest contribution to

Example: GOES-8 Transmittances

Weighting Functions for GOES

Fundamentals of Soundings  Absorption spectra  Transmittances, weighting functions  Examples of GOES sounder channels • • • • Longwave CO 2 H 2 O Shortwave CO 2 Visible

GOES-8/9 Sounder - Channel 8

GOES-8/9 Sounder - Channel 7

GOES-8/9 Sounder - Channel 6

GOES-8/9 Sounder - Channel 5

GOES-8/9 Sounder - Channel 4

GOES-8/9 Sounder - Channel 3

GOES-8/9 Sounder - Channel 2

GOES-8/9 Sounder - Channel 1

GOES-8/9 Sounder - Channel 11 Water Vapor

GOES-8/9 Sounder - Channel 12 Water Vapor

The “retrieval problem”  What temperatures (gas concentrations) could have produced the observed set of radiances?  An infinite number of solutions exist  (#$%@!)

Retrieval methods  Physical • Based on knowledge of radiative transfer  Statistical • Based on comparison to archive of radiosonde observations  Hybrid • Combination of physical and statistical

Characteristics of GOES soundings  Spatial coverage and frequency  Production methodology • Resolution, effect of clouds • • Use of NWP model forecasts  Quality assessment • Radiosonde comparison statistics ETA forecast model impact study

Spatial coverage and frequency  Scan cycle is one hour  Two scans each, GOES 8 and 10  • • GOES-8 – 35 Minutes - Eastern CONUS – 20 Minutes - Selectable Atlantic Sector GOES-10 – 20 Minutes - Western CONUS – 35 Minutes - Pacific Sector No Southern Hemisphere coverage

GOES 8/10 hourly sounder coverage 10 10 8A 8 8C 8B

Resolution and effect of clouds  GOES Sounder Field of View (FOV) - 10 km at nadir  Sounder Radiances Processed Using Arrays • • 5x5 FOV’s - Operational 3x3 FOV’s - Experimental  Clouds Act as a Radiating Surface, Contaminate IR Measurements

Resolution and effect of clouds  Individual FOV’s Screened for Clouds  Cloud-Free Sounder FOV’s Used to Generate Sounding • • 9 - 25 Clear FOV’s Required - Operational 1 - 9 Clear FOV’s Required - Experimental

GOES-9 TPW (mm) 8 JAN 1998 1500 GMT Tan: 0 - 9 mm Yellow: 10 - 19 mm Green: 20 - 29 mm

GOES-9 TPW (mm) – Phoenix, AZ

ETA Forecast Used as Initial Conditions  Forecast Temperature and Moisture Profiles Interpolated to GOES Sounding Location and Time 00Z 06Z 12Z 12Z ETA 12,18hr Fcst 00Z ETA 06,12hr Fcst 00Z ETA 12,18hr Fcst 18Z 12Z ETA 06,12hr Fcst 00Z

NAM Forecast Used as Initial Conditions  Sounder Radiances Computed from NAM Forecast  Observed Radiances Corrected for Bias Relative to Forecast  Differences Between Computed and Observed Radiances Used to Modify Initial NAM Profile  Adjustments Made Primarily to Moisture Profile

Little Change to ETA T/Td Forecast GOES-9 Sounding - Phoenix, AZ 6 JAN 98 15 GMT

Big Change to ETA T/Td Forecast GOES-9 Sounding - Gainesville, FL 6 JAN 98 15 GMT

GOES Observed BT’s - ETA Computed BT’s  Larger differences are observed in Gainesville sounding, particularly in channels sensitive to atmospheric moisture

Colocation Statistics - TPW (mm) Radiosondes vs. ETA Forecast and GOES Soundings Root Mean Square Error

ETA Model Impact Study (NCEP) August 1997 Equitable Threat Score - Precipitation

Applications/Examples  Nowcasting/Forecasting of severe weather  Individual soundings and associated parameters (e.g. stability indices)  Horizontal fields of derived products  Gradient winds  Derived product images  Sounder water vapor winds  Cloud amount and cloud top pressure

Eastern Kansas, July 13-14, 1997  GOES visible  Severe weather reports  ETA precipitation forecast  Precipitable water and lifted index fields • • ETA forecast GOES soundings  Time tendency analyses

GOES-8 Visible Imagery 1915Z 7/13/97 - 0115Z 7/14/97

Severe Weather Reports: 23Z 7/13/97 - 05Z 7/14/97

ETA 00-12 Hour Precip Forecast (mm) Valid 00Z 7/14/97 GOES-8 Visible Image 00Z 7/14/97

ETA Forecast TPW 18Z-00Z 7/13/97 (2 Hour Intervals)

GOES TPW 18Z-00Z 7/13/97 (2 Hour Intervals)

ETA Forecast LI 18Z - 00Z 7/13/97 (2 Hour Intervals)

GOES LI 18Z - 00Z, 7/13/97 (2 Hour Intervals)

ETA/GOES 4 Hour Time Tendency (LI) 18Z-22Z

ETA/GOES 4 Hour Time Tendency (TPW) 18Z - 22Z

Phoenix, Arizona 6 Jan 98 20 GMT - 7 Jan 98 19GMT

GOES-8 500mb Gradient Winds - Montserrat

Derived Product Image - TPW 6 Jan 98 21 GMT

Summary     GOES Soundings Provide 24 Hour High Resolution Coverage for CONUS and Adjacent Ocean Areas Horizontal Resolution of ~50KM (~30KM Currently in Experimental Mode) Provide Information on Mesoscale Features of Moisture and Stability in Pre-Convective Environments Case Studies Indicate Strong Correlation Between GOES Soundings’ Fields and Convective Development

Summary   Positive impact demonstrated using GOES TPW in ETA Forecast Model Other Applications: Depiction of Moisture: Eastern Pacific, Gulf of Mexico Return Flow, Southwest Monsoons, East Coast Winter Storms

Summary  Limitations • Coarse vertical resolution (~3 - 4 km) • • • Soundings Precluded in Cloudy Areas Geographic Coverage Limited by Slow Scan Rate Retrieval of Boundary Layer T/Td Not Possible

Acknowledgements - Don Gray Bill Smith, Kit Hayden and Paul Menzel Tim Schmit, Tony Schreiner, CIMSS, University of Wisconsin Jaime Daniels (NOAA), Gary Gray (Raytheon/Hughes) Web Addresses (NOAA/NESDIS/ORA) http://orbit7i.nesdis.noaa.gov:8080/temp.html

GOES Sounder Products http://orbit7i.nesdis.noaa.gov:8080/goes.html

Other GOES Quantitative Products http://orbit7i.nesdis.noaa.gov:8080/index.html

POES/GOES Satellite Products

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