An Evaluation of Tamdar Soundings In Severe Storm Forecasting

Abstract

Input from many sources is used in the short term prediction of severe thunderstorms. One of the more critical observations needed continues to be a vertical sounding of temperature, humidity and wind. National Weather Service (NWS) forecasters often call for special rawinsonde (hereafter, RAOB) launches at 1800 UTC on a potential severe storm day because they want to observe recent changes in the vertical structure of the atmosphere. Those changes include the depth of the surface-based moisture, cap strength, and the vertical wind shear. Automated soundings made by aircraft on ascent and descent via the Meteorological Data Collection and Reporting System (MDCRS), provide vertical information for temperature and wind. These soundings are generally limited to major airports, and moisture information, a critical parameter, is not included. In fact, the distribution of moisture in the vertical has been difficult to measure with sufficient accuracy and vertical detail except via the standard RAOB, launched twice per day at widely spaced upper-air rawinsonde sites. Over the past couple of years the NOAA/Earth Systems Research Lab (ESRL)/Global Systems Division (GSD), along with other groups, have been evaluating a new airborne sensor deployed on commercial aircraft, known as TAMDAR, for Tropospheric AMDAR (Aircraft Meteorological Data Relay). TAMDAR adds the critical measurement of moisture to wind and temperature observations in the vertical. In addition, the instrument, developed and deployed by AirDat, LLC, a private firm located in Raleigh, North Carolina, in part through funding from NASA, has been deployed experimentally on smaller regional aircraft. They fly lower than the larger commercial jets and service many more airports than the MDCRS fleet (Daniels et al., 2006). Furthermore, many of the flights are at levels well below the jet stream level of typical MDCRS aircraft, adding considerable amounts of data between approximately 14 to 20 kft AGL. These sensors have been deployed on 50 aircraft flying over the U. S. Midwest in an experiment called the Great Lakes Fleet Evaluation (GLFE). See the NOAA Web site at http://www.crh.noaa.gov/tamdar/. During this experiment more en route mid-tropospheric reports and sites for ascent/descent soundings were provided than had previously been available. This makes TAMDAR potentially valuable for forecasting the severe storm environment. In this paper we will show examples from the 2006 convective season of the potential value of TAMDAR soundings in GLFE area (see Fig. 1 for typical TAMDAR coverage). Comparisons will be made with standard and, when available, special RAOB launches.