Relationship between the Indian monsoon rainfall and the tropospheric temperature over the Eurasian continent

Abstract

Based on climatological data such as the all-India rainfall (AIR) for 1949–98, air temperatures in the troposphere and at the land surface for 1949–98 as well as precipitation and outgoing long-wave radiation (OLR) for 1979–98, the statistical relationship between the Indian monsoon rainfall and tropospheric temperature (TT) over the Eurasian continent is examined by using the correlation analysis and singular value decomposition (SVD) analysis methods. The main results are summarized as follows. (1) The June-September (JJAS) AIR has significant positive correlations with the 200–700 hPa TT averaged for Eurasia in JJAS. The area with the highest simultaneous correlation of upper TT with AIR for JJAS is located in western Eurasia. There is also a region with positive simultaneous correlations in the southern subtropics covering southern Africa. The JJAS AIR also shows significant positive correlations with TT over the Eurasian continent in March-May (MAM) and with the TT averaged over the Tibetan Plateau in September and October. Although some precursory springtime temperature signals for the anomalous summer monsoon are found in the upper TT over Eurasia, the variation in the upper TT appears mostly independent from that of the land surface temperature. (2) The anomalies of upper TT in JJAS are closely coupled with the variations in OLR related to the monsoon rainfall over tropical Asia and Africa. The spatial structure of the first SVD mode for OLR anomalies shows the coherent variations in convective activity from northern tropical Africa to India, while the pattern of the first SVD mode for 300 hPa temperature anomalies shows a distribution which is nearly symmetric with respect to the equator, with variations of the same sign over subtropical areas in both hemispheres and variations of the opposite sign around equatorial Africa. This pair of coupled patterns suggests that when the monsoon rains from tropical Africa to India become more intense, the upper troposphere from northern Africa to western Asia and over southern Africa becomes warmer. (3) The observed temperature variation in the upper troposphere over the Eurasian continent (especially western Eurasia) during the summer monsoon season is considered to be a result of the anomalous subsidence and thermal advection, dynamically induced by anomalous tropical heating associated with the enhanced monsoon rainfall. This study suggests that the tropical convective activity linked to the Indian monsoon rainfall has an impact on the atmospheric variability on a global scale.