Abstract
This observational study during the 29-year period from 1979 to 2007 evaluates the potential role of Eurasian snow in modulating the North East-Indian Summer Monsoon Rainfall with a lead time of almost 6 months. This link is manifested by the changes in high-latitude atmospheric winter snow variability over Eurasia associated with Arctic Oscillation (AO). Excessive wintertime Eurasian snow leads to an anomalous cooling of the overlying atmosphere and is associated with the negative mode of AO, inducing a meridional wave-train descending over the tropical north Atlantic and is associated with cooling of this region. Once the cold anomalies are established over the tropical Atlantic, it persists up to the following summer leading to an anomalous zonal wave-train further inducing a descending branch over NE-India resulting in weak summer monsoon rainfall.
Highlights
The North East Indian Summer Monsoon Rainfall (NEISMR) over the eastern-most part of the country (Fig. 1a), which is joined via a narrow belt clasped betweenNepal and Bangladesh, is influenced by local and remote forces
Their study demonstrated that a high latitude mode explains more than 30% of the total variance in the Geopotential Height (GPH) and wind fields depending upon atmospheric pressure level and timescale considered
India Meteorological Department’s National Climate Centre (IMD-NCC) daily gridded rainfall data set at a spatial resolution of 0.25° × 0.25° (Pai et al 2014), which is constructed from a network of 6955 rain gauge stations spread across the country, is used in this study
Summary
The North East Indian Summer Monsoon Rainfall (NEISMR) over the eastern-most part of the country (Fig. 1a), which is joined via a narrow belt clasped between. The mechanism of snow cover and Indian summer monsoon teleconnection through an atmospheric bridge linking this remote low frequency variability has been investigated in several studies. The link between the three entities, namely, Atlantic SST, Eurasian snow and summer monsoon, is manifested through Rossby waves that modulate the Tibetan High thereby influencing rainfall over the northwest and central India (Hoskins and Ambrizzi 1993; Ambrizzi et al 1995). It is well known that mid-latitude Eurasian snow cover has a determining role in the interannual variability of Indian summer monsoon when we consider a large region over Indian subcontinent. The present study explores a robust physical mechanism linking north Atlantic SSTs with NEISMR by examining the role of high-latitude Eurasian snow in bonding the two.
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