Principal Component Analysis of Summer Rainfall and Outgoing Long-Wave Radiation over Pakistan

The relationship between the inter-annual variability of precipitation and satellite derived Outgoing Long-wave Radiations (OLR) is studied over Pakistan during summer months for the period 1980-2007. Principal component analysis technique was applied in order to identify the major modes of oscillations present in the data series. The first four principal components explain 95% of the total variance for the OLR data while first eight principal components for precipitation data explain 80% of the total variance. The relationship between major principal mode for precipitation and OLR has remained around -0.78 for the summer season. The possible reason for this inverse relationship could be the overcast skies with clouds and frequent precipitation during the pre-monsoon, monsoon and post-monsoon season which might have contributed to lower OLR values.