Abstract
This study investigates the spatial-temporal variability of winter-spring (February-March-April) precipitation (WSP) in Pakistan over the period of 1961-2006 by making use of Empirical Orthogonal Function (EOF). The EOF analysis is based on ground observed data, reanalysis NCEP/NCAR of various geopotential heights and NOAA extended reconstructed sea surface temperatures (ERSST.v3). The significant modes are obviously variable at interannual time scale. The leading mode shows the node of maximum spatial variability anchored over the Peshawar Valley and Azad Kashmir (PVAK) axis. The pattern is associated with strong (weak) westerly jet over the Middle East. The pattern is also found closely associated with post monsoon and early winter El Nino. The Nino4 index can be an appropriate predictor for the first consistent single node pattern. The second significant mode represents a tripole pattern with areas of prominent variability over northwestern Pakistan, Quetta-Kalat region and northeastern Punjab. The pattern is found to be pro-NAO and in relation to this pattern, warm and stable SST anomalies appearing in the southern mid-latitudes of Indian and Atlantic basins.
Highlights
In the wake of 1997-1998 El Niño/Southern Oscillation (ENSO), world wide climatic repercussions were felt, South West Asia were subjected to sever drought [1] [2]
Pakistan is located on the eastern border of western disturbances (WDs) system which is embedded in the westerlies flow and the precipitation anomalies in Pakistan during the winter spring (WS) period can not be isolated from the influence of North Atlantic Oscillation (NAO) and ENSO
The winter-spring (February-March-April) precipitation (WSP) has close link with post monsoon and early positive ENSO phase Niño4 index can be used as model predictor
Summary
In the wake of 1997-1998 ENSO, world wide climatic repercussions were felt, South West Asia were subjected to sever drought [1] [2]. The Krishna Kumar et al [17] argue that El Niño is the major driver behind droughts in subcontinent and they [18] highlighted that central Pacific Ocean based El Niño have strong negative impact on Indian summer monsoon (ISM) while eastern Pacific based El Niño have less impact on ISM comparatively In this context, the time period of El Niño (La Niña) evolution matters a lot. Pakistan is located on the eastern border of WDs system which is embedded in the westerlies flow and the precipitation anomalies in Pakistan during the winter spring (WS) period can not be isolated from the influence of NAO and ENSO. We have tried to seek out the relation of WSP index with atmospheric circulations and global sea surface temperature anomalies (SSTA) by making use of EOF as diagnostic tool, and locate potential predictors
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