Pakistan Journal of Meteorology Vol. 10, Issue 19: July, 2013 Impact of South Asian High Variability on Monsoon Precipitation in Pakistan Zahid, M. 1, 2 , G. Rasul 2 Abstract The South Asian High (SAH) variability is known to have significant contribution in the success and failure of summer monsoon precipitation (JAS) of Pakistan situated within South Asia. This study aims to analyze the impact of South Asian High (SAH) variability on the summer monsoon precipitation in Pakistan. The principal component analysis shows strong positive temporal correlation coefficient between SAH (200 hPa) and monsoon (JAS) precipitation i.e. 0.7 for the period 1980-2010. The streamline and precipitation analysis shows that Pakistan receives heavy precipitation during strong SAH years (1988, 1992, 1994, 2010) due to westward (70°E-80°E) movement of SAH from its mean position and experience suppress precipitation during weak SAH year (1987, 1997, 2004, 2009) due to eastward (90°E-110°E) oscillation of SAH. The isotherms analysis shows negative anomalies in strong SAH years and positive anomalies in weak SAH years over most parts of Pakistan. The minimum values of divergence of moisture flux (DMF) at 850 hPa in strong SAH years and nil DMF in weak SAH years has been observed over western parts of Pakistan. The wind field (850 hPa) analysis has shown the evident stimulation of moisture from Arabian Sea incase of strong SAH years and quite minute stimulation of moisture in weak SAH years. Hence, it is evident from the study that the strength and oscillation of SAH and summer monsoon precipitation (JAS) in Pakistan are strongly inter-reliant upon each other. It is anticipated that climate change can lead the country towards extreme droughts and extreme flooding. This study will be helpful for the forecasters who can use the behavior of SAH (Tibetan High) as an indicator for prediction of intense and weak summer monsoon rainfall. Key Words: Monsoon, Pakistan, South Asian High, Precipitation, Divergence of Moisture flux Introduction The Asian monsoon is an imperative component of global climate system. The Asian monsoon is comprised of three sub-systems: the South Asian Summer Monsoon (SASM), the Western North Pacific Summer Monsoon and the East Asian Summer Monsoon. The Asian monsoon is referred to as seasonal reversal of winds. The South Asian High (SAH) remains centered at 30°N during South Asian summer monsoon (SASM) (Rasul and Chaudhry, 2010). The intense convection along with profuse amount of latent heat release from condensation is observed in SASM. Besides differential heating of land and sea the topographic effect of south Asia also has significant influence on the patterns of monsoon systems. The variability in monsoon precipitation affects human lives and agriculture sector both in South Asia and southwestern China (Liang-lei et al., 2006). The South Asian High which is also known as Tibetan High forms due to the intense heating of Plateau and the radiational balance. Tropical Easterly Jet (TEJ) subsists in its south and Westerly Sub-Tropical Jet (STJ) in north (Sarfraz, 2007). SAH is one of the principal circulations of the upper troposphere in summer over Asian regions. It plays significant role in the atmospheric circulation patterns of Asian continent. The weather and climate of South Asian region is highly dependent upon the variability of South Asian High. It may be attributed to the flooding or drought distribution in the Asian region (Zhang and Wu, 2001; Huang and Qian, 2004; Yonghua et al., 2006). Jiang et al., 2011 have also reported the interannual and Interdecadal variations of South Asian High and its association with summer climate over Asian regions. When SAH strengthen monsoon circulation becomes weaker over East Asia but stronger over South Asia. Zhao et al., 2011 has also supported this fact further that as the SAH intensifies in upper troposphere and low pressure intensifies in lower troposphere, southerly–southwesterly winds prevail 1 maidazahid.pmd@gmail.com 2 Pakistan Meteorological Department, Pitras Bukhari Road, Sector H-8/2, Islamabad. 1