Near-real time CAPE East of the Rockies combining Hyperspectral IR Satellite Sounding and ASOS Surface Stations: Part I Validation at the ARM SGP Site

Near-real time satellite data can give forecasters the extra edge they need to issue timely and accurate watches and warnings. The Convective Available Potential Energy (CAPE) is a measure of atmospheric instability computed from vertical profiles of temperature and water vapor used the National Weather Service Storm Prediction Center (NWS SPC). CAPE can give forecasters valuable information as to the stability of the atmosphere and therefore the potential for severe weather. The value of using satellite vertical soundings from hyperspectral infrared sensors has been recognized at the NOAA Hazardous Weather Testbed workshops held at the NWS SPC (http://hwt.nssl.noaa.gov/).

Satellite overpass times from EUMETSAT METOP IASI at 10:30am/pm and NASA AQUA AIRS, Suomi-NPP CrIS, and JPSS J1 at about 1:30am/pm occur conveniently between the operational 0 and 12 UTC NWS radiosondes. Since the day’s first in-situ measurements are taken in the early morning there is a need for forecasters to see the SkewT vertical profiles of temperature and water vapor updated from the 6am (0 UTC) soundings. In addition to more temporal coverage, satellite date can provide spatial coverage between NWS radiosonde launch sites. Automated Surface Observing System (ASOS) stations currently operate routinely as U.S. airports and provide surface meteorological measurements at 1 minute intervals reported in METAR format.

In this study, a comparison of CAPE is made for the U.S. Southern Great Plains region using a combination of DOE ARM radiosondes, ERA model reanalysis fields, and hyperspectral infrared retrievals from NASA AIRS and EUMETSAT IASI sensors. The CAPE is computed using the SHARPpy python open source software (http://sharppy.github.io/SHARPpy/documentation.html) which has been validated against the same algorithms used by the NWS SPC. The CAPE is evaluated for a ten-year period from 2005 through 2014. This paper shows illustrates the use of the nearest ASOS surface observation station to the DOE ARM SGP site at Ponca City, Oklahoma airport (KPNC) as a substitute for the satellite IR estimate of the surface parcel. Using the KPNC surface temperature and dewpoint temperature instead of the AIRS (or IASI) and radiosonde surface estimates increases the correlation from about 0.35 to 0.95. This dramatic increase in correlation validates the use of the hyperspectral IR soundings for the computation of CAPE when the surface parcel estimates are obtained from surface observations instead of from the satellite soundings themselves. The application of this method to all ASOS stations east of the Rocky Mountains is presented in Part II of this two-part paper.