عنوان مقاله [English]
Many precipitation and droughts oscillation had undesirable effects on national economic. One of the elements affecting precipitation oscillation of south and southwestern of Iran is El Nino and Enso. In this paper first is selected a period monthly mean precipitation data from 1969-1988. Then relationship between El Nino and La Nino years with Siberian high pressure and Sudan low pressure is analyzed. The researches on synoptic systems affecting the climate of case study region shows that systems arrangement in three-months studied(DEC- FEB) in La Nina years had more suitable for production of rain than El Nino year. In La Nina year Siberian high pressure and its southern flame has expanded effectively in Iran and with an increase of gradient in the case study region and its integration with Arabian high pressure cell and warm/wet air transmission has created suitable condition for precipitation. Also high pressure locating on Arabian Peninsula, conditions for North Africa ridge becoming deep and revival of Sudan low pressure and its transformation to a thermodynamic system in La Nina year and the entering of precipitationary systems have been provided. While in El Nino year in studied three-month, above-mentioned systems have not created suitable condition for unstability and occasionally prevented the revival of systems and their entrance to the case study region.