Interaction Between Scandinavian Low Pressure with Siberian- European and North West of Iran High Pressure Systems (Aggregate High Pressure System) Associated with Frost Wave Event in Iran: 11 to 16 December 2003

This study was made following the re-recognition of the cause of occurrences of severe, widespread and persistent frost event in 2003 in Iran. Based on previous studies, the cause of the creation and persistent of this sever frost is the dominancy of Siberian high pressure system. For this purpose, the gridded daily minimum temperature, northern hemisphere teleconnection indices and sea level pressure data have been used. Based on the indices of frost wave onset index (FWOI),ending and persistent of cold wave and by considering the spread, the location and time patterns, the frost wave of December 2004 was recognized. On this basis, its starting date was recognized 11 December 2011 and its ending as 16 December 2003, which was persisted for 6 days in Iran's area. Also the location pattern of cold wave has had an east ward arrangement and was dominant in more than 75% of Iran's area in its maximum intense.The highest continuation of cold wave was recorded in the Iranian plateau, while the northern shores of the Persian Gulf and Oman Sea on the southern slopes of the Zagros ruggedness have not received the cold wave. Increase and decrease pattern of spatial range of cold wave is a signal for accompany of some recognized systems of sea level pressure with Siberian high pressure system in its occurrence. For this purpose, long term time series (1950-2010) of tele-connection patterns of northern hemisphere were studied from October up to December. For example,co-phase coherence between the patterns of North Sea- Caspian sea, Arctic Oscillation and North Atlantic Oscillation and no phase coherence of the pattern of east of Atlas Ocean- West Russia and the North Pacific Ocean with the standardized index of intensity of Siberian high pressure are the reasons of other pressure systems at the sea level of high pressure system of Siberian in the event of the said frost wave. Assessment of spatial-temporal variability of sea level pressure systems in the before occurrence (08 to 10 December 2003) to occurrence (11 to 16 December 2003) showed that December frost wave has occurred in as a result of an interaction of High Pressure System (AHPS) include Europe, North West Iran and Siberian high pressure systems with Scandinavian low pressure system. Spatial-temporal array type of Scandinavian Low Pressure system has a great important role in the formation, persistent, intensity and rupture of aggregate high pressure system.