METR280 Satellite Meteorology/Climatology 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? Purposes – Augment information from rawinsonde data, typically for use in numerical models – Also used to determine concentrations of gases that are absorbers (such as ozone) Advantages – Complete temporal coverage (rawinsondes only 2X/day) – Much better spatial coverage... oceans Disadvantages – Much more difficult to interpret than radiosondes – Clouds (MW better than IR here) – Limited vertical resolution

What is a “sounder”? A sensor for collecting vertical profiles of temperature and moisture using sensors with multiple, narrow bands Narrow bands – Sensitive to a small electromagnetic region. Multiple bands? – Need 1 band for each level you wish to resolve

How do sounders work? Weak absorption channels effective emission level is near surface Strong absorption channels: upper atmosphere Moderate absorption channels: vary in altitude Absorption channel – Ranges of wavelengths (regions of the EM spectrum) that absorb (and therefore emit) radiation. This is due to “radiatively active” gasses such as CO2, H2O, O3. – Therefore, sensor operating in atmospheric channel can detect temperature of that gas or moisture content (if in a H2O abs.chan.) Effective emission level – Altitude from which radiation reaching the sensor is being emitted. – Weak absorption channel: surface energy absorbed close to surface, then relatively unaffected until it gets to satellite – Strong absorption channels: energy keeps getting emitted by each layer then absorbed by the next higher layer. Satellite sees “top” layer – Moderate absorption channel: These are the key to sounders

Sounding theory Assume free of scattering (no clouds) We must account for: Earth’s emission (“absorption spectra”) Transmission between layers Weighting function Weighting function – Tell us how important each channel is for determining the moisture (gas concentration) at a particular height – At each channel, the satellite “sees” to a different depth within the atmosphere... weaighting function tells us where each channel is looking – Where each channel “sees” overlaps (each channel may see an 8km thick layer), but they “see best” at a particular layer

Fundamentals of Soundings Absorption spectra Transmittances, weighting functions Examples of GOES sounder channels Longwave CO2 H2O Shortwave CO2 Visible

Absorption Spectra - IR Carbon dioxide (CO2) Longwave: 11 - 18 mm (Surface/ Atmospheric Temperature) Shortwave: 4 - 6 mm (Surface/Lower Atmospheric Temperature) Water Vapor (H2O) Midwave: 6 - 10 mm (Atmospheric Moisture) Ozone (O3) 9.6 mm: (Total Column Atmospheric Ozone)

Fundamentals of Soundings Absorption spectra Transmittances, weighting functions Examples of GOES sounder channels Longwave CO2 H2O Shortwave CO2 Visible

Transmittances and weighting functions Transmittance: Percent of radiation of particular wavelength transmitted through atmosphere Transmittance = 1 - Emissivity 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

Weighting Functions for GOES

Weighting Functions for GOES

Fundamentals of Soundings Absorption spectra Transmittances, weighting functions Examples of GOES sounder channels Longwave CO2 H2O Shortwave CO2 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 Statistical Hybrid Based on knowledge of radiative transfer Statistical Based on comparison to archive of radiosonde observations Hybrid Combination of physical and statistical Physical – Must start with some kind of “first guess” in order to find the right solution Climatology from radiosondes Recent, nearby radiosonde observations Statistical – Usually using regression analysis – A different set of regression coefficients for different latitudes (5 latitude bands for TOVS) and are frequenctly updated (weekly for TOVS)

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 8B 10 8A 8C

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

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

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

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

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

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

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

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

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

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

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

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

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

GOES-8 500mb Gradient Winds - Montserrat

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

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