A Numerical Simulation Study of the Indian Summer Monsoon of 1994 using NCAR MM5

摘要

In this study, the National Center for Atmospheric Research Mesoscale Model, NCAR MM5 adopted for the Indian region has been integrated for a four month period from 1 May 1994, to study the Indian summer monsoon during the months of June, July and August. This version of the MM5 mesoscale model has a horizontal resolution of 30 km, and 23 vertical levels. The initial and boundary conditions are taken from NCEP/NCAR reanalysis data available at 2.5° grid interval, and interpolated to the model domain.The results indicate that the NCAR MM5 model simulates many observed features of the Indian summer monsoon on a regional scale, which otherwise cannot be simulated using a global general circulation model. The simulated features of sea level pressure, 925 hPa temperature, low level wind flow are compared with NCEP and precipitation fields with GPCP. Significant features of the monsoon circulation, such as the monsoon trough, heat low over northwest India, and mesoscale precipitation patterns are well simulated. The model precipitation is also well simulated with the strengths and locations of the maxima and minima agreeing with the observations. The advancement of the monsoon current during the onset phase, as simulated by the model, is evaluated by comparing the pentad rainfall during June, 1994, with the advancement of monsoon reported by the India Meteorological Department. Model simulated area averaged time series of precipitation, and 850 hPa geopotential for five different zones covering the Indian subcontinent are evaluated through correlation, root mean square error, bias and threat score.