Indian summer monsoon features in the NCEP analysis and forecast system
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Ó Indian Academy of Sciences (0123456789().,-vo lV)( 0123456789() .,-vol V)
Indian summer monsoon features in the NCEP analysis and forecast system P V S RAJU1,* , AKHILESH MISHRA1,2 and A B T SUNDARI1 1 Centre 2
for Ocean Atmospheric Science and Technology, Amity University Rajasthan, Jaipur, India. National Centre for Medium Range Weather Forecast, Noida, India. *Corresponding author. e-mail: [email protected] [email protected] MS received 4 February 2020; revised 23 June 2020; accepted 28 July 2020
The diagnosis of the summer monsoon features over India are investigated using global analysis and forecast system (GFS) of the National Center for Environmental Prediction (NCEP). In addition, the performance of the NCEP GFS model in capturing the observed rainfall variability of the summer monsoon features over India through diagnostic parameters. We delineate the variability between two normal monsoon seasons with basic meteorological Belds and significant parameters of kinetic energy, heat and moisture budgets. The 1200 UTC operational analyses and forecasts (day1 through day5) data for summer monsoon seasons of June, July, August and September (JJAS) of 2010 and 2011 are considered. Although both are normal monsoon seasons with seasonal rainfall (JJAS) departure of about 3.1% and 2.1% respectively, during 2010 and 2011, some differences are observed in the spatial distribution of rainfall. The diagnostic Belds reasonably reproduced the variations in analyses and forecast Belds of up to 5 days. The model forecasts of day1 delineated that the Indian summer monsoon features are well captured, whereas in day3 and day5, forecast depicts some differences. Overall the NCEP analysis and forecast Belds not only produces mean monsoonal Cow, but also captures seasonal variability realistically. This is evident from the large-scale balances represented by the analyses and model forecasts. Keywords. Summer monsoon; seasonal variability; NCEP analysis and forecast; kinetic energy; heat and moisture.
1. Introduction Each year Indian summer monsoon is beautifully illustrated as regional scale anomalies in general circulation of the atmosphere. Predicting monsoon rainfall is a challenging task due to the complex interaction between convective systems and largescale monsoonal Cow. Yield in agriculture sector is very much dependent on health of the monsoon; in a good monsoon year crop production increases while a bad monsoon season brings deBcit rainfall resulting in reduction in crop produce (Webster
and Yang 1992). It is therefore very important to have a seasonal outlook of the monsoon season with the comprehensive understanding. It is also important to understand the interannual variability of the seasonal monsoon rainfall. State of the monsoon climate can be characterized using climatological gradients of winds, temperature and moisture. Horizontal and vertical gradients of these parameters can cause thermodynamic and hydrodynamic instabilities. Energy is derived from the mean circulation for initiation of disturbance
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