Matthew Lagor

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Matthew Lagor Remote Sensing Stability Indices
and Derived Product Imagery from the GOES
Sounder 5.8.02
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Introduction

• GOES Sounder Impact and DPI uses

• Atmospheric Stability Products

• Limitations of DPI

• Questions

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GOES Sounder Impact

• GOES Profile retrievals (in absence of clouds),
  typically have
• a separation of 50 km and are determined at 40
  pressure levels from
• 1000 to .1 hPa. Compared to horizontal
  resolution of the radiosonde
• stations that are roughly 400 km apart.

• The radiosonde network launches one balloon
  every 12 hours.
• The GOES Sounder retrieves temperature and
  moisture profiles
• over the entire US and ocean every hour. This
  corresponds to nearly
• 2000-3000 retrievals per hour.

• Sounder profiles are assimilated into the
  numerical prediction
• models.

• With the GOES Sounder capabilities, forecasters
  can accurately
• monitor and track atmospheric changes on both
  small and large
• scales. As well as improve both nowcasting and
  forecasting methods.

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GOES-8 Sounder Channels

• The GOES Sounder has 18 thermal infrared bands
  as well as a visible channel

Wavelength (um), Channel, Purpose
Longwave 14.71 1 Stratosphere temperature
14.37 2 Tropopause temperature 14.06 3
Upper-level temperature 13.96 4 Midlevel
temperature 13.37 5 Low-level temperature
Window 12.66 6 Total PW 12.02 7 Surface
temp., moisture 11.03 8 Surface temperature
Ozone 9.71 9 Total ozone Water vapor
7.43 10 Low-level moisture 7.02 11 Midlevel
moisture 6.51 12 Upper-level moisture
Shortwave 4.57 13 Low-level temperature
4.52 14 Midlevel temperature 4.45 15
Upper-level temperature
Nitrogen 4.13 16 Boundary-layer temperature
Window 3.98 17 Surface temperature 3.74 18
Surface temp., moisture Visible 0.94 Cloud
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Derived Product Imagery (DPI)

• Some of the products include Total Precipitable
  Water,
• Lifted Index, Cloud Amount, Cloud Top Pressure,
  
• Cloud Top Temperature, Ozone, and Land-Sea
  Surface
• Temperature.

• Pseudo Images such as CAPE and CIN can also be
  derived
• from the temperature and moisture profiles.

• Sounder derived products were experimentally
  used by
• forecasters dating back to 1996.

• Products such as LI, CAPE, and TPW have improved
• both real-time nowcasting and forecasting
  convective
• development and severe weather activity.

• GOES Sounder retrievals have also been used to
  forecast the
• potential for downbursts

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Total Precipitable Water

• Precipitable water is the total moisture content
  in a column of air
• condensed into millimeters of water.

• Values across the US range from 5 to 55 mm

• Calculated by integrating over the retrieved
  moisture profile

• Moisture profile is calculated through the
  radiance
• measurements found in the longwave split
  windows, the
• shortwave window, and the water vapor band.

• Used to delineate stable from unstable air
  masses, rainfall
• intensity, dry line location, and low
  temperatures.

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CAPE

• The available positive (buoyant) energy a parcel
  would
• obtain ascending from the LFC to the EL.

• CAPE is a pseudo DPI product values having been
• recreated after the fact in an image format from
  the
• CAPE values.

• A moderately unstable air mass would have a CAPE
• value close to 1500 J/kg. Typical values of
  severe
• weather CAPE values range from 3000-5000 J/kg.

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Lifted Index

• The Lifted Index is formed by lifting a boundary
  layer parcel
• to 500 mb and comparing the resultant
  temperature of the
• parcel with the ambient temperature.

• LI values are taken directly from the sounding.

• Negative values of LI indicate the parcel of air
  being warmer
• than the environment, therefore being indicative
  of an unstable
• environment.

• LI values from 4 to 8 degrees C correspond to
  significant
• potential instability.

• LI Images can be used to judge areas of
  potential convective
• development and current storm intensities.

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GOES Sounder Limitations

• Sounder data can only be retrieved in the absence
  
• of clouds.

• Timeliness and vertical resolution remain as a
  source
• for improvement

• Satellite and radiosonde measurements are not
• always concurrent in time or space

• Radiosonde data are point measurements, while
• satellite derived quantities are volumetric
• measurements.

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Questions?