Convective Parameterization in a Model for the Prediction of Heavy Rain in Southern Thailand
Sugunyanee YAVINCHAN
Weather Forecast Bureau, Thai Meteorological Department (TMD), Bangkok, Thailand
The Joint Graduate School of Energy and Environment, Center for Energy Technology and Environment,King Mongkut’s University of Technology Thonburi, Bangkok, Thailand
Robert H. B. EXELL
The Joint Graduate School of Energy and Environment, Center for Energy Technology and Environment, King Mongkut’s University of Technology Thonburi, Bangkok, Thailand
and
Dusadee SUKAWAT
Department of Mathematics, King Mongkut’s University of Technology Thonburi, Bangkok, Thailand
(Manuscript received 10 May 2010, in final form 19 October 2010)
Abstract
Numerical weather predictions of three heavy rainfall events in the northeast monsoon causing floods and damage in southern Thailand are reported in this paper. The Pennsylvania State University/National Center for Atmospheric Research (PSU/NCAR) mesoscale model (MM5) was used with the Betts-Miller (BM), Grell (GR), and new Kain-Fritsch (KF2) convective parameterization (CP) schemes at 5 km resolution, and also with an unparameterized or explicit (EX) scheme, to look for a promising method for precipitation forecasting. The accumulated precipitation amounts predicted by the model were evaluated qualitatively by comparison with the Tropical Rainfall Measuring Mission (TRMM) maps, and quantitatively by calculating statistical score indices for di¤erent rainfall thresholds. The simulations were evaluated by comparing the synoptic near surface fields with the NCEP FNL objective analysis fields and also with the vertical profiles of wind speed, temperature and mixing ratio at Songkhla station. The simulations gave generally satisfactory predictions of the synoptic fields, except for an overprediction of the relative humidity. The heavy rainfall was associated in each case with a small vortex where the northeasterly wind interacted with a warm humid southerly wind. The model underestimated the heavy rainfall amounts, and widely di¤erent rainfall patterns were produced by the di¤erent schemes used. The KF2 and EX schemes generally gave better results than the BM and GR schemes.
Journal of the Meteorological Society of Japan, Vol. 89A, pp. 201--224, 2011.
DOI:10.2151/jmsj.2011-A13
Corresponding author: Sugunyanee Yavinchan,
Weather Forecast Bureau, Thai Meteorological Department
(TMD), Bangkok 10140, Thailand.
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6 2011, Meteorological Society of Japan
