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Accueil du site → Doctorat → États-Unis → 1993 → Evaluation of the National Meteorological Center Mesoscale Model for Prediction of Severe Convection Over Central Arizona

UNIVERSITY OF UTAH (1993)

Evaluation of the National Meteorological Center Mesoscale Model for Prediction of Severe Convection Over Central Arizona

Dunn, Lawrence Bennet

Titre : Evaluation of the National Meteorological Center Mesoscale Model for Prediction of Severe Convection Over Central Arizona

Auteur : Dunn, Lawrence Bennet

Université de soutenance : UNIVERSITY OF UTAH

Grade : Doctor of Philosophy (PhD) 1993

Résumé
The utility of numerical model guidance produced by the National Meteorological Center has been evaluated for the forecast of convection over central Arizona during the summer monsoon season. Model output from the Nested Grid Model (NGM) and ETA model has been compared to observations taken during the 1990 field experiment referred to as the Southwest Area Monsoon Project (SWAMP). The NGM precipitation forecasts showed little skill for events in which heavy precipitation was observed over Phoenix, Arizona. Synoptic-scale rising motion associated with the heavy rain events was best identified in gridded model output in terms of differential advection of absolute vorticity between 300 and 500 mb, but the NGM correctly predicted these fields only 50% of the time. Selected events during the SWAMP period were simulated using the ETA model. Qualitative comparisons of the ETA model’s precipitation forecasts with lightning data and satellite imagery suggest that the model has skill in predicting precipitation 12-24 hours in advance in areas to the east of the Rockies and over Mexico. However, precipitation forecasts from the ETA model showed little skill over central Arizona as a result of inaccurate lower tropospheric moisture fields and the model’s inability to trigger convection. The moisture field over southern Arizona was inaccurately forecast since the model generated an unrealistically strong sea -breeze circulation in the vicinity of the Gulf of California. Insufficient moisture in the lower troposphere over Arizona inhibited the development in the model of the strong convective instability observed prior to the onset of convection. However, in some cases, the ETA model correctly predicted the vertical profile of temperature and moisture observed over central Arizona just prior to the outbreak of severe convection, but was still unable to predict any precipitation. The convective parameterization used in the ETA model was not able to generate precipitation in the arid environment over Arizona in which the relative humidity rarely exceeds 80% in the lower troposphere prior to the onset of convection. It is theorized that the lack of evaporative cooling processes in the model prohibits the development of colliding outflow boundaries that may initiate the severe convection in this region.

Présentation

Page publiée le 11 novembre 2013, mise à jour le 16 décembre 2019