THE DEVELOPMENT OF AN IMPROVED CONVECTIVE INITIATION SCHEME FOR MESOSCALE NUMERICAL WEATHER PREDICTION MODELS

A THREE-DIMENSIONAL, NONHYDROSTATIC CLOUD MODEL IS USED AS A TOOL TO INVESTIGATE THE PROBLEM OF THUNDERSTORM INITIATION. OPERATIONAL NUMERICAL MODELS DO A POOR JOB OF PREDICTING THE GEOGRAPHIC DISTRIBUTION OF CONVECTIVE ACTIVITY, ESPECIALLY DURING THE WARM SEASON, WHEN THE LARGE SCALE CIRCULATION IS RELATIVELY WEAK. THE CUMULUS PARAMETERIZATION SCHEMES USED IN CURRENT MESO-BETA-SCALE RESEARCH MODELS DISAGREE ON THE NECESSARY MESOSCALE CRITERIA FOR DEEP CONVECTION. CLOUD MODEL RESULTS WILL BE USED AS A SURROGATE ATMOSPHERE IN WHICH A BETTER UNDERSTANDING OF THE PHYSICAL FACTORS NECESSARY FOR THE INITIATION OF CONVECTION WILL LEAD TO AN IMPROVED SET OF CRITERIA SUITABLE FOR MESO-BETA-SCALE MODELS. IN THE PHASE I EFFORT, A CLOUD MODEL SIMULATION COVERING A LARGE DOMAIN WILL BE MADE WITH A COMPLEX PATTERN OF LOW-LEVEL SENSIBLE HEATING. THE HEATING OF THE LOWEST MODEL LAYER WILL LEAD TO THE INITIATION OF CONVECTION IN SEVERAL AREAS AT DIFFERENT TIMES. DYNAMIC AND THERMODYNAMIC VARIABLES WILL BE AVERAGED TO MESOSCALE GRID SIZES, THEN THE MESOSCALE DATASET WILL BE ANALYZED. A SUCCESSFUL RESULT WOULD BE THE IDENTIFICATION OF A RELATIONSHIP BETWEEN MESOSCALE VARIABLES WHICH IS ABLE TO ACCURATELY PREDICT THE INITIATION OF SUBGRID-SCALE DEEP CONVECTION.