The impact of two types of E1 nino on northern hemisphere upper tropospheric circulations in summer season
Karori, M.A. (Pakistan Meteorological Dept., Islamabad (Pakistan))
The northern hemisphere (NH) stationary Circumglobal teleconnection (CGT) pattern in boreal summer season was identified and discussed in previous studies. The evidences were also found that the tropical thermal forcing can modulated this pattern. It is conceivable that warming in the eastern and central Pacific Ocean may influence the CGT pattern. The impacts of two types of El Nino on NH at 200 hPa height (H 200) have been investigated in this sturdy. The observed data analysis revealed that the H200 anomalies are opposite in polarity during two types of El Nino Southern Oscillations (ENSO) i.e. Warm pool (WP) El Nino and Cold Tongue (CT) El Nino. During IG'P (El Nino), a tonal wave train is observed with phase opposite to that of well known CGT pattern in boreal summer season. During CT (El Nino) the Eurasian part is similar to the CGT pattern and opposite to that observed in WP El Nino. These contrasting impacts may be attributed to the different patterns of tropospheric warming and upper air divergence related to different convection centers in the Pacific Ocean during two types of El Nino. Moreover, negative anomaly of the central Asian High was observed during WP (El Nino), which may result in weaker summer monsoon over the south Asian region, especially over Pakistan and northwest India. A coupled general circulation model also simulated upper air wave patterns related to the two types of El Nino, which confirms our findings based on observed data analysis.
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