Impact of Parameterized Cumulus Convection on Meso-Alpha Scale Cyclone Prediction

Abstract

 On 28-30 March 1984, a complicated case of cyclone development occurred in the southeastern region of the United States. A synoptic-scale cyclone moved from east Texas to North Carolina and several meso-alpha scale cyclone centers developed within the larger scale cyclone. One of the mesoscale centers rapidly grew into a 966 mb low along the east coast of the U. S. A. at 18 GMT 29 March 1984.
 An updated version of the Navy Operational Regional Atmospheric Prediction System (NORAPS) is used to study the impact of cumulus convection, parameterized by a Kuotype scheme, on numerical prediction of this meso-alpha scale cyclone development. Two 36 h predictions are made starting from 00 GMT 28 March 1984. The Control prediction is a simulated operational run with full model physics. The Experimental prediction is similar to the Control except the Kuo-type cumulus parameterization is removed, so that the non-convective precipitation is the only process for latent heat release. The impacts of parameterized cumulus convection on meso-alpha scale cyclone prediction are examined by comparing the predicted cyclone development and the heating and moisture distributions around the cyclone center in the Control and Experimental predictions. At 00 GMT 29 March, a newly generated smaller scale (meso-alpha) low appears to be imbedded in the larger scale cyclone in both predictions. The smaller scale cyclone did not grow in the Control run. However, the cyclone deepened 13 mb within 12 hours in the Experimental run. Delayed and more intense latent heat release is clearly observed in the Experimental prediction, which reflects the result of removing the cumulus parametepization and may be responsible for the development of meso-alpha scale cyclone in the later periods.