Mid-Latitude Anticyclones and Climate of Pakistan

Seasonal study of the impacts of mid-latitude blocking anticyclones occurring along -15 degrees to +15 degrees longitudes is carried out over Pakistan for 40 years (1968-2007). Composite anomalies of precipitation and temperature were analyzed along with 500 hPa geopotential height (GPH), sea level pressure (SLP) and moisture flux at 850 hPa. During four seasons; winter (December, January, February, March or DJFM), pre-monsoon (April, May, June or AMJ), monsoon (July, August, September or JAS) and post-monsoon (October, November or ON) the area average surface temperature anomaly difference from before to after blocking period is 0.5 degrees C, 2.1 degrees C, -1.9 degrees C and -23 degrees C respectively in the study region. Precipitation anomalies remain between 0:20 mm/day to -0.20 mm/day for during blocking period and become positive (negative) after blocking period, for DJFM and ON (AMJ and JAS). Mid-latitude blocking anticyclones attribute towards higher precipitation (temperature) variations during DJFM (AMJ, JAS and ON) in the study area.