Observational and Synoptical Study of Shamal wind in the North West Coast of Persian Gulf: Bushehr, Iran (2010)

Shamal winds recognized as a climate regime with a common occurrence in the Persian Gulf that makes the event of adverse weather conditions in this region periodically. Among the phenomenas that occurring under effect of Shamal wind, can be noted to dust storms, Low-level winds and inappropriate sea conditions. Shamal winds are categorized into two types, winter Shamal and summer Shamal. Sea-land breezes also are classified as a frequent mesoscale and heat driven flow associated with coastal areas. Temperature gradient between sea and land is the main reason for the formation of a sea breeze circulation that blows from sea to land in low level coastal atmospheric boundary layer. The suitable conditions for Sea-land breezes establishment when the synoptic winds are weak (low synoptic forcing) and temperature level is high in the coastal city of Bushehr. The purpose of this research is to investigate seasonal Shamal wind event and its associated synoptic conditions by observations analyzing and numerical expriments on Persian Gulf. The impact of these conditions on wind pattern in the northwestern Persian Gulf coastal area and in optional case in the coastal area of Bushehr are studied and it is intruded interaction between meteorological mesoscale (sea-land breeze) and large-scale (synoptic pattern Shamal wind) forcing effects in this area. North of middle east are areas that dominated by the seasonal Shamal wind regime, that begin from the central deserts of Iraq and the mountains of northern Iraq, Turkey and Syriat to Persian Gulf. In this study, the coastal city of Bushehr that located in the northwest of Persian Gulf and southwest Iran have been selected to investigate about interaction of Shamal wind pattern on local breeze on the coastal areas . Based on the location of the Bushehr and sea-land breeze definition, sea breeze will occurr in the sector of 180-270 degree.
In this study, in order to analyze the time series of coastal wind, it is used hourly wind speed and direction data from meteorological tower and meteorological station of Bushehr power plant and also wind data from Bushehr airport weather station. In the next step, the NCEP FNL data used to generat the initial and boundary conditions for regional simulations by WRF model. This data has 1° × 1° resolution and are available for every 6 hours. This data produce by Global Data Assimilation System (GDAS) that continuously receive monitoring global data for analyze from Global Telemetry System (GTS) and other resources.
The results of the observational time series analyzes from the meteorological tower of Bushehr power plant are shown for winter (January) and summer (May) selective periods. These results show the mean detail information of typical wind regimes such as summer and winter Shamal and sea-breeze regimes during January and May 2010. In this work is represented formation quality, duration, mean speed, mean direction of sea-breeze wind in the beginning and ending of sea-breeze regimes during these months. It also is represented frequency of daily occurrence of typical wind regimes with themselves mean speed in Bushehr coastal area. It was observed that the northern of Saudi Arabia is influenced by a high pressure system and Persian Gulf and west of Iran by a low pressure trough and a heat low pressure system is seen over east of Iran (region of Afghanistan, Pakistan and etc.) during summer Shamal. Turkey, Iraq and west of Zagross mountain rang regions are affected with interaction of these thermal and dynamical systems that lead to the creation of Shamal wind in north west of Persian gulf. This area is affected by winter Shamal wind regime with significant cold advection after passage of synoptical cold front of a dynamical mid-latitude cyclone.
In general, Shamal wind affects Turcy, Iraq, Iran, Arabian Peninsula and adjacent areas. The maximum activity during 2010 observe in the winter in late of January and in the summer in June by maximum number of Shamal days. This result is obtained by analyzing data from the meteorological tower at height of 100 meters in Bushehr weather station that the summer Shamal causing disruption of coastal wind pattern in 14 days of May, 14 days in June and about 10 days in July of 2010 and in other months, usually less than three to five days. Winter Shamal occurs at intervals of 3 to 9 days from December to March. During the period that the sea-breeze is removed by synoptical Shamal winds forcing, the average daily wind speed more than period of sea-breeze activity.