Indian summer monsoon features in the NCEP analysis and forecast system

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 fields 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 fields reasonably reproduced the variations in analyses and forecast fields 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 fields not only produces mean monsoonal flow, but also captures seasonal variability realistically. This is evident from the large-scale balances represented by the analyses and model forecasts. Highlights The NCEP global analyses and forecast System depicts less bias in low level circulation in day1 with respect to analysis field, albeit, this bias is increases with increase of forecast period. Overall, the mean monsoon circulation is captured by the NCEP analyzes and forecast system fairly well. The forecast fields illustrate the warm bias in the low levels with maximum over northwest India and monsoon through region, These warm bias in the forecast fields is due to the higher specific humidity over the monsoon trough region. In the forecast of day1, day3 and day5 show the warm bias in the low levels at 925 hPa with maximum over northwest India and monsoon trough region, whereas cold bias is observed over Gujarat and Western Ghat in day3 and day5 forecast. The significant seasonal variability perceived in two normal summer monsoon rainfall. This variability is captured by analysis and model forecasts realistically in terms of diagnostic fields of kinetic energy, heat and moisture.