Monsoon Structure and Variability as Represented in Observations, Reanalysis, and Models

The spatial structure of precipitation in the Indian summer monsoon is examined in rainfall data from merged gauge-satellite observations (CMAP, GPCP), reanalysis, and numerical models. Comparison is made between four distinct areas from around the monsoon region: the Western Ghats (WG), the Ganges Basin (GB), the Bay of Bengal (BoB), and Bangladesh (BNG). We find that the strength of the correlation between these regions varies significantly with the choice of rainfall product, particularly for BoB and BNG. We find a particularly wide range in representation among the the Reanalysis products. More surprisingly, precipitation patterns analyzed from long integrations of the European Centre for Medium Range Weather Forecasting (ECMWF) Integrated Forecast System (IFS) model are found to be significantly closer to the merged satellite products than two of the three 'modern' reanlayses (ERA-Interim, MERRA, CFSR) considered.

In this study we also analyse 850mb circulation patterns associated with rainfall anomalies in each region. Bangladesh rainfall anomalies are closely associated with an anomalous circulation pattern that is easily distinguished from patterns associated with the other three regions, demonstrating that anomalous Bangladesh rainfall is associated with unique changes in the large-scale monsoon circulation.