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

Introduction GOES Sounder Impact and DPI uses Atmospheric Stability Products Limitations of DPI Questions

GOES Sounder Impact Sounder profiles are assimilated into the numerical prediction models. 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 retrievals per hour. 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.

GOES-8 Sounder Channels Wavelength (um), Channel, Purpose Longwave Stratosphere temperature Tropopause temperature Upper-level temperature Midlevel temperature Low-level temperature Window Total PW Surface temp., moisture Surface temperature Ozone Total ozone Water vapor Low-level moisture Midlevel moisture Upper-level moisture Shortwave Low-level temperature Midlevel temperature Upper-level temperature Window Surface temperature Surface temp., moisture Visible 0.94Cloud Nitrogen Boundary-layer temperature The GOES Sounder has 18 thermal infrared bands as well as a visible channel

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 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

Total Precipitable Water 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. 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

CAPE The available positive (buoyant) energy a parcel would obtain ascending from the LFC to the EL. A moderately unstable air mass would have a CAPE value close to 1500 J/kg. Typical values of severe weather CAPE values range from J/kg. CAPE is a pseudo DPI product values having been recreated after the fact in an image format from the CAPE values.

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. 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 values are taken directly from the sounding. LI Images can be used to judge areas of potential convective development and current storm intensities.

GOES Sounder Limitations Timeliness and vertical resolution remain as a source for improvement Sounder data can only be retrieved in the absence of clouds. Satellite and radiosonde measurements are not always concurrent in time or space Radiosonde data are point measurements, while satellite derived quantities are volumetric measurements.

Questions?