Near-Real-Time CAPE Combining Hyperspectral IR Satellite Sounding and Surface Met Stations

Issuing severe weather statements is very important for the safety of people everywhere, but it can be hard to predict. 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 and is computed from vertical profiles of temperature and water vapor. Measuring CAPE is important in determining whether or not severe storms will occur. The value of using satellite vertical soundings from hyperspectral infrared sensors, using the NOAA Unique Combined Atmospheric processing System (NUCAPS) has been recognized at the NOAA Hazardous Weather Testbed workshops held at the NOAA/National Weather Service (NWS) Storm Prediction Center (SPC) in the past few years. In addition to more temporal coverage, NUCAPS data can provide spatial coverage between NWS radiosonde launch sites, which are only launched twice a day. These launch times are inconvenient in the continental United States for identifying severe weather because they are launched well before and after maximum daytime heating when convective weather often occurs. Satellite overpass times from EUMETSAT Metop with the IASI instrument at 10:30am and 10:30pm and NASA Aqua with the AIRS instrument, NASA Suomi-NPP with the CrIS instrument, and NASA/NOAA JPSS-1 at about 1:30am and 1:30pm occur conveniently between the operational 0 and 12 UTC NWS radiosondes. Being a modular design, NUCAPS has the capability to operationally process many platforms.

Satellite soundings struggle in the lower tropospheric region due to the increased opacity of the atmosphere. This is particularly true over land areas where surface dis-homogeneities and uncertainties in the surface emissivity penalize the accuracy of the lower tropospheric temperature and dewpoint temperature retrieval even further. Both parameters are key inputs to the computation of CAPE.

In this study, an investigation of the use of combined surface station data and NUCAPS profile data is conducted to create an accurate near-real time estimate of surface-based CAPE (SBCAPE). Hourly surface observations are matched up in space and time with NUCAPS vertical profiles to create a combined CAPE calculation using the SHARPpy tool. An automated process is used to calculate the SBCAPE on a 0.7x0.7 degree grid for each overpass of the Suomi-NPP satellite using the UW-Madison SSEC Direct Broadcast antennae. This innovative data fusion product will be compared to the operational NUCAPS-derived SBCAPE for validation. This comparison will serve as a baseline to evaluate future improvements in the NUCAPS retrieval system to better serve real time users applications over the CONUS region. A possible developmental solution for NUCAPS is the inclusion of these surface station data to better constrain the first guess regression solution of skin temperature. Future development plans include the validation of an experimental NUCAPS product, the 2-meter height temperature retrieval, for the computation of the mixed-layer CAPE (MLCAPE). Preliminary validation results will be presented at the conference using visualization tool, SSEC RealEarth^TM, in near-real time (https://realearth.ssec.wisc.edu/).