Sounders METR280 Satellite Meteorology/Climatology

Short Course on Satellite Meteorology Phoenix, Arizona Applications and Interpretation: Part 3 - Sounder Products and Applications Donald G. Gray NOAA/NESDIS Office of Research and Applications Washington, DC AMS 78th Annual Meeting Partially based on the following...

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

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

What is a “sounder”? n A sensor for collecting vertical profiles of temperature and moisture using sensors with multiple, narrow bands

How do sounders work? n Weak absorption channels effective emission level is near surface n Strong absorption channels: upper atmosphere n Moderate absorption channels: vary in altitude

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

n Absorption spectra n Transmittances, weighting functions n Examples of GOES sounder channels Longwave CO 2Longwave CO 2 H 2 OH 2 O Shortwave CO 2Shortwave CO 2 VisibleVisible Fundamentals of Soundings

Absorption Spectra - IR n Carbon dioxide (CO 2 ) Longwave:  m (Surface/ Atmospheric Temperature)Longwave:  m (Surface/ Atmospheric Temperature) Shortwave:  m (Surface/Lower Atmospheric Temperature)Shortwave:  m (Surface/Lower Atmospheric Temperature) n Water Vapor (H 2 O) Midwave:  m (Atmospheric Moisture)Midwave:  m (Atmospheric Moisture) n Ozone (O 3 ) 9.6  m: (Total Column Atmospheric Ozone)9.6  m: (Total Column Atmospheric Ozone)

n Absorption spectra n Transmittances, weighting functions n Examples of GOES sounder channels Longwave CO 2Longwave CO 2 H 2 OH 2 O Shortwave CO 2Shortwave CO 2 VisibleVisible Fundamentals of Soundings

Transmittances and weighting functions n Transmittance: Percent of radiation of particular wavelength transmitted through atmosphere Transmittance = 1 - Emissivity n Weighting Function: Derivative of transmittance with respect to height (lnP). Larger values correspond to atmospheric layers with the greatest contribution to radiance values.

Example: GOES-8 Transmittances

Weighting Functions for GOES

n Absorption spectra n Transmittances, weighting functions n Examples of GOES sounder channels Longwave CO 2Longwave CO 2 H 2 OH 2 O Shortwave CO 2Shortwave CO 2 VisibleVisible Fundamentals of Soundings

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” n What temperatures (gas concentrations) could have produced the observed set of radiances? n An infinite number of solutions exist n

Retrieval methods n Physical Based on knowledge of radiative transferBased on knowledge of radiative transfer n Statistical Based on comparison to archive of radiosonde observationsBased on comparison to archive of radiosonde observations n Hybrid Combination of physical and statisticalCombination of physical and statistical

Characteristics of GOES soundings n Spatial coverage and frequency n Production methodology Resolution, effect of cloudsResolution, effect of clouds Use of NWP model forecastsUse of NWP model forecasts n Quality assessment Radiosonde comparison statisticsRadiosonde comparison statistics ETA forecast model impact studyETA forecast model impact study

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

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

Characteristics of GOES soundings n Spatial coverage and frequency n Production methodology Resolution, effect of cloudsResolution, effect of clouds Use of NWP model forecastsUse of NWP model forecasts n Quality assessment Radiosonde comparison statisticsRadiosonde comparison statistics ETA forecast model impact studyETA forecast model impact study

Resolution and effect of clouds n GOES Sounder Field of View (FOV) - 10 km at nadir n Sounder Radiances Processed Using Arrays 5x5 FOV’s - Operational5x5 FOV’s - Operational 3x3 FOV’s - Experimental3x3 FOV’s - Experimental n Clouds Act as a Radiating Surface, Contaminate IR Measurements

Resolution and effect of clouds n Individual FOV’s Screened for Clouds n Cloud-Free Sounder FOV’s Used to Generate Sounding Clear FOV’s Required - Operational Clear FOV’s Required - Operational Clear FOV’s Required - Experimental1 - 9 Clear FOV’s Required - Experimental

Tan: mm Yellow: mm Green: mm GOES-9 TPW (mm) 8 JAN GMT

GOES-9 TPW (mm) – Phoenix, AZ

Characteristics of GOES soundings n Spatial coverage and frequency n Production methodology Resolution, effect of cloudsResolution, effect of clouds Use of NWP model forecastsUse of NWP model forecasts n Quality assessment Radiosonde comparison statisticsRadiosonde comparison statistics ETA forecast model impact studyETA forecast model impact study

ETA Forecast Used as Initial Conditions n Forecast Temperature and Moisture Profiles Interpolated to GOES Sounding Location and Time 00Z06Z12Z18Z00Z 12Z ETA 12,18hr Fcst 00Z ETA 06,12hr Fcst 00Z ETA 12,18hr Fcst 12Z ETA 06,12hr Fcst

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

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

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

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

Characteristics of GOES soundings n Spatial coverage and frequency n Production methodology Resolution, effect of cloudsResolution, effect of clouds Use of NWP model forecastsUse of NWP model forecasts n Quality assessment Radiosonde comparison statisticsRadiosonde comparison statistics ETA forecast model impact studyETA forecast model impact study

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

Characteristics of GOES soundings n Spatial coverage and frequency n Production methodology Resolution, effect of cloudsResolution, effect of clouds Use of NWP model forecastsUse of NWP model forecasts n Quality assessment Radiosonde comparison statisticsRadiosonde comparison statistics ETA forecast model impact studyETA forecast model impact study

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

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

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

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

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

ETA 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

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

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

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

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

GOES-8 500mb Gradient Winds - Montserrat

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

Derived Product Image - TPW 6 Jan GMT

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

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

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

Tim Schmit, Tony Schreiner, CIMSS, University of Wisconsin Bill Smith, Kit Hayden and Paul Menzel Jaime Daniels (NOAA), Gary Gray (Raytheon/Hughes) Web Addresses (NOAA/NESDIS/ORA) GOES Sounder Products Other GOES Quantitative Products POES/GOES Satellite Products Acknowledgements - Don Gray