Changes in the large‐scale features associated with the Indian summer monsoon in the recent decades

Abstract

ABSTRACT:The inter-annual variability of the Indian summer monsoon rainfall (ISMR) has been examined in association with the variability of surface temperature, the mean sea level pressure (MSLP), the tropospheric geopotential height, and wind patterns over the globe to study the changes in the large-scale features associated with Indian summer monsoon (ISM) in the recent decades. The data for the study have been considered from 1949-2005 (for a period of 57 years). It has been found that, during the recent decades, the El Nino-Southern Oscillation (ENSO) relationship over ISMR has weakened while the northwest (NW) of North Atlantic sea surface temperature (SST) relationship has increased. A physical mechanism for the relationship of North Atlantic SST with ISMR is proposed, by which during the excess years of ISMR, the SST over NW of North Atlantic is above normal. The rise in SST is the consequence of intensification and a cell-type shaped Azores high with isobars parallel to the east coast of North America, which drives a subtropical oceanic gyre (Gulf stream) transporting equatorial warm water NW of North Atlantic. The Azores high act as a source of downstream Rossby wave train over Eurasian region having barotropic structure consisting of a successive pressure trough and ridge. The Rossby wave may be associated with intensifying the low surface pressure anomaly over the Iranian landmass, which intensify the monsoon current over the Indian region.

On the relationship between Iran surface temperature and northwest India summer monsoon rainfall

“…These wind anomalies are the source of moisture supply over NW India, as they are coming from warm desert land, they can hold more moisture after blowing over north Arabian Sea. Previous study by Yadav (2009a) has shown these relationships between ISMR and Iran surface temperature. The southerlies observed over north Pakistan hinders the intrusion of mid-latitude cold and dry air towards Indian subcontinent favouring excess monsoon over NW India.…”

Statistically related coupled modes of South Asian summer monsoon interannual variability in the tropics

“…Trenberth et al , ; Alexander et al , ; Deser et al , ). However, the effect of ENSO on SASM has become weaker in the recent decades (Krishna et al , ; Yadav et al , ). Some studies have suggested that the Indian Ocean Dipole (IOD), which has also an influence on SASM (e.g.…”

Midlatitude Rossby wave modulation of the Indian summer monsoon

“…This suggests that the dipole surface temperature and pressure anomalies are strongly associated. This dipole structure generates the anomalous northwesterlies over eastern Saudi Arabia, which further combines with the southwesterlies over the Arabian Sea and intensifies the lower‐level monsoon circulation, consistent with the previous studies of Yadav (, , ).…”

“…This study, for the first time, shows how the westward enhancement of the Tibetan High imposes a dipole pressure anomaly between Saudi Arabia and Iran, which intensifies the lower‐level monsoon circulation and moisture supply from the Arabian Sea. The anomalous cyclonic circulation with northerly winds over the Arabian landmass has gained its significance after the late 1970s climate shift (Yadav, , , ). This study is certainly going to improve the current understanding of ISM.…”

“…The teleconnections of ISM after the late 1970s have changed due to the major climate shift observed in the Indo-Pacific Ocean (Graham, 1994;Trenberth and Hurrell, 1994;Yadav, 2009a). The El Niño/Southern Oscillation (ENSO)-ISM relationship has changed from the role of east Pacific El Niño (weak teleconnection) to the central Pacific El Niño (strong teleconnection) on the monsoon in this period (Krishna Kumar et al, 2006).…”