Variation in the Duration of Upper-Level Systems at 500 Hectopascals Constituting the Freezing Phenomenon in Iraq for the Period 1968-2021

Abstract

The research aims to study the variation in the duration of upper-level systems at 500 hectopascals constituting the freezing phenomenon, revealing a general trend towards a decrease in the rates of the duration of upper-level systems during the study months. The deep troughs recorded a downward trend, with the highest negative change rate (100%) at the Amarah station, while the lowest negative change rate was recorded at the Rabi'a station, amounting to (0.67%). Shallow troughs showed an upward trend in the duration rates across the study stations, with the lowest positive change rate recorded at the Erbil station (0.19%). Shallow ridges showed an upward trend in the duration rates of upper-level systems, while the surface waves recorded a downward trend during all study months. Finally, cut-off lows showed a downward trend across all study stations. From the above, it can be inferred that an increase in the duration of shallow troughs and shallow ridges corresponds to a decrease in the duration of deep troughs and surface waves. Cut-off lows indicate a weakening of surface system extensions and their filling with warm air, thus weakening freezing events.