Statistical-Synoptic Analysis of the Atmosphere Thickness Pattern of Iran’s Pervasive Frosts

Abstract

Abstract:The present study aimed at analyzing the synoptic pattern of atmospheric thickness of winter pervasive frosts in Iran. To this end, the data related to the daily minimum temperature of a 50-year period were gathered from 451 synoptic and climatology stations. Then, the instances in which the temperature was below 0 • C for at least two consecutive days and this phenomenon covered at least 50% of the entirety of Iran were selected. Subsequently, the atmosphere thickness pattern was extracted for these days, with the representative day being identified and analyzed through cluster analysis. The results showed that the Siberian high pressure plays a significant role in the occurrence of pervasive frosts in Iran. In some other cases, the northeast-southwest direction of this pattern leads to its combination with the East Europe high pressure, causing widespread frosts in Iran. Furthermore, the interaction between counter clockwise currents in this system and the clockwise currents in the Azores high pressure tongue directs cold weather from northern parts of Europe toward Iran. The formation of blocking systems leads to the stagnation of cold weather over Iran, a phenomenon that results in significant reduction of temperature and severe frosts in these areas. In addition, the omega pattern (the fifth pattern) and Deep Eastern European trough and polar low pressure pattern (the fourth pattern) were the most dominant and severe frost patterns in Iran respectively.

Investigation of the Spatio-Temporal Variations in Atmosphere Thickness Pattern of Iran and the Middle East with Special Focus on Precipitation in Iran

“…Occurrence of frosts was mainly influenced by five patterns, namely Siberian high-pressure and European high-pressure, deep trough pattern of Eastern Europe and Sudanese low pressure, dual-core pattern of Siberian high-pressure, deep Eastern European trough and polar low pressure pattern, and Omega pattern. The severest frosts occurred during the dominance of the Omega pattern [26]. Extreme and widespread precipitation in the northwest of Iran are caused by four patterns, which, in all of them, a trough is located in the west of Iran [50].…”

“…Therefore, with the fall of cold air, air mass becomes denser (thus, its density goes up), and, subsequently, the atmosphere becomes thicker. On the contrary, with the fall of hot air, air mass is expanded (hence, its density decreases) and molecules tend to diverge, which results in the increase of AT [26]. Thickness is one of the most important features of atmospheric dynamics and is under the influence of atmosphere temperature.…”

“…Iran's pervasive frosts occur alongside contours that have a thickness of 5300 to 5400 geopotential meters. In fact, pervasive frosts occur alongside these contours that are as thick as the atmosphere (especially the ones that are 5300 geopotential meters thick) [26]. In some other studies, AT patterns have been used to justify extreme precipitation.…”

“…It also dominates northern Pakistan to the west of the Mediterranean. Moreover, European high pressure, Kazakhstan high pressure, northern Caspian Sea high pressure, Mediterranean low pressure, and Siberian high pressure have profound influence on the climate of the Middle East in that order [26,27,51,52].…”

Decadal Spatial-Temporal Variations in the Spatial Pattern of Anomalies of Extreme Precipitation Thresholds (Case Study: Northwest Iran)

“…Changes in the frequency and intensity of climatic events are an indicator of climate change [2]. Considerable attention is being paid to the spatial-temporal pattern of precipitation.…”