Study of the daily cyclonicity indexes at two 1,000- and 500-hPa levels and their relationship with temperature and precipitation over south and east of Iran between 1961 and 2010

Abstract

Cyclonicity index indicates if an area is under the influence of cyclonic or anticyclonic circulations. Accordingly, five different types of atmospheric circulations, i.e., trough line (TL), trough edge (TE), ridge line (RL), ridge edge (RE), unclassified pattern (COL) can be identified. The daily cyclonicity index (DCI) at two 500 and 1,000 hPa level charts over Iran have been studied between 1961 and 2010. Then their relationships with temperature and precipitation over east and south of the country have been examined. The results have shown that the frequency of cyclonic systems is decreasing. Correlation coefficients between DCI (500 hPa) and temperature and precipitation in monthly scale have been, respectively, −0.89 and 0.55 for south and −0.80 and 0.51 for east of the country. Those values for 1,000 hPa were −0.52 and 0.36 for south and −0.54 and 0.33 for east. The results indicate that south has mainly been affected by the transient weather systems.