IJSRP, Volume 6, Issue 5, May 2016 Edition [ISSN 2250-3153]
Dhuha S. Zaiter, Kais J. Al-Jumaily
Two fundamental wind systems in dynamical meteorology are the gradient wind that extends the geostrophic wind to curved trajectories and the thermal wind that describes the vertical change in the geostrophic wind in a baroclinic atmosphere. The aim of this work is to investigate the characteristics of thermal wind over Iraq and surrounding regions. NCEP long term monthly data of potential temperature at 850 hPa pressure level and meridinal wind component at 925 hPa and 700 hPa pressure levels for the northern hemisphere were used for calculating the LHS and RHS of the thermal wind equation. Quantities were averaged between the longitude limits of 30 to 50 oE within which Iraq is located. Analysis of the thermal wind equation suggests that thermal wind balance exists during all the time of the year for regions north of 45 oN latitude. In the mid-latitude region (between 20 and 45 oN) the balance holds only during winter time. A case study of heavy rain storm over southern Iraq was used to investigate the situation of thermal wind association with rainstorm. The results indicated a thermal wind situation could lead to a rapid convection that can help in forming a deep convective cloud. In such case, a heavy rain is likely to be expected at the ground surface. The results also showed that a strong south easterly wind existed on the southern part of Iraq, where the rain storm occurred. This wind pattern was caused by the occurrence of a deep low pressure system over northern part of the Kingdom of Saudi Arabia, just west of the core of rain region. As a result, more moist air was transported to the region which helped in producing the heavy rain event.