by Conrad Ziegler

Mesoscale Convective Systems (MCSs) are large complexes of thunderstorms that account for over half of the annual warm-season precipitation in the United States east of the Rocky Mountains. MCSs generate frequent cloud-to-ground lightning and additionally may produce severe weather including hail, tornadoes, and strong straight-line winds. Hence, MCSs present a major public safety concern owing to effects on flooding, agriculture, transportation, communications, and property. NSSL is planning a field experiment called the "MCS Electrification and Polarimetric Radar Study" (MEaPRS), to investigate polarization radar signatures and electrification processes in MCSs. In July 1997, NSSL hosted a meeting with collaborating scientists from Colorado State University, the University of Mississippi, Texas A & M University, the University of Oklahoma, NASA/Marshall Space Flight Center (MSFC), National Center for Atmospheric Research (NCAR), the Los Alamos National Laboratory (LANL), and the Atlantic Oceanographic and Meteorological Laboratory (AOML) to refine the scientific focus for MEaPRS. An operations plan for MEaPRS is presently nearing completion.

MEaPRS will be conducted over the Oklahoma-Texas-Kansas region during the period from 15 May to 15 June 1998, seven days a week, using an array of fixed and mobile sensors to simultaneously sample a target MCS (Fig. 1). These special mesoscale observing facilities include a P-3 Orion "hurricane hunter" aircraft (Fig. 2), operated out of Oklahoma City by the NOAA/Aircraft Operations Center (AOC), the NSSL Cimarron radar (Fig. 3), and several mobile laboratories (Fig. 4a) from which atmospheric sounding profiles of the MCS will be obtained (Fig. 4b). A lightning mapping system will provide detection of all in-cloud and cloud-to-ground flashes produced by a target MCS.

A typical operations day in MEaPRS will begin with the preparation of a forecast for deep convection and MCSs for the current day and an outlook for MCSs for the following day over the target region. During the afternoon, nowcasters (short-range forecasters using observations) will monitor the initial convection, and the P-3 and mobile labs will be vectored toward the developing MCS. Both forecasting and field coordination will be conducted from the Science Support Area jointly maintained by the National Centers for Environmental Prediction (NCEP)/Storm Prediction Center (SPC) and NSSL. The nowcasters will remain on duty through the night, passing information on MCS location, movement, and evolution to the P-3 and mobile labs in the field. The P-3 will perform multiple horizontal passes and ascent or descent soundings, both ahead of the leading convective line and within the trailing, non-convective or stratiform precipitation region of the MCS. In close coordination with the P-3 legs, soundings with the balloon-borne electric field meters will also be obtained within the leading-line convection and the trailing stratiform region. As a target MCS moves into the central Oklahoma area, polarization measurements of the MCS will be collected by the Cimarron radar. A typical MCS mission may last around seven hours, ending somewhere between midnight and sunrise the following morning.

The MEaPRS data set will be used to advance NOAA's forecasting and warning capabilities by:

• determining the usefulness of polarization radar to identify precipitation types and intensity (this will set the stage for a possible upgrade of the WSR-88D network to include the polarization detection capability);
• refining conceptual models of how thunderstorms and MCSs develop charges and electric fields strong enough to produce lightning;
• developing new conceptual models to explain how MCSs form, move, and change their rainfall rates and airflow circulation intensities.

These advances in understanding and monitoring MCSs will assist the NWS by setting the stage for improved forecasts of dangerous flash flooding and hazardous cloud-to-ground lightning.

For more information contact: Conrad Ziegler at conrad.ziegler@nssl.noaa.gov