An Analysis on the Impacts of Zagros Heights on Life Cycle of Mesoscal Convective Systems in West of Iran

Document Type : مقاله پژوهشی

Authors

• Dariush Yarahmadi ¹
• Saeid Basati ¹
• Behrouz Nasiri ¹
• Somayeh Rafati ²

¹ University of Lorestan

² Seyed Jamaleddin Asadabadi

10.22067/geo.v5i2.53241

Abstract

1. Introduction
Mountains are the main sources of turbulence and change in the shape of atmospheric flows, and they can cause airflow upward as well as clouds formation and rain through productive mechanisms such as upslope condensation and convection. They also have an important effect on regional and world precipitation turbulence (Banta, 1990; Barros & Lettenmaier, 1994), and can cause severe incidents such as destructive floods (Pastor, Gomez, & Estrella, 2010).
Previous researchers have done numerous studies on mountainous region weather and climate, and cause of precipitation phenomenon using different methods such as numerical modeling of airflow and satellite images. Using RegCM model, Insel, Christopher, Poulsen and Ehlers (2009) have studied the effect of Andes Mountains on convection, precipitation and humidity transformation in South America. They showed that Andes Mountains have lots of effects on humidity transfer between Amazon basin and central Andes, deep convention processes and precipitation across South America through low–level jet (LLJ) and topographical blocking from Pacific Ocean.
Zagros mountain range located in west of Iran plateau is among vast mountain ranges that locates in path of zonory flows with its south-north expansion and can affect those flows.
Therefore, the present study aims to investigate different factors affecting mesoscal convective systems from Zagros heights, and analyze their life cycle dynamic conditions using brightness temperature threshold, area expansion and RegCM4 numerical modeling.
2. Material and Methods
This study was done in an area of about 220000 km2 in west of Iran including Kermanshah, Kurdistan, Hamadan, Khuzestan, Lorestan, Kohgiloyeh and Boyer Ahmad, Ilam, and cheharmahal and Bakhtiari provinces. Using satellite images obtained from infrared band of Meteosat geostationary satellite, GOES and GMS, the mesoscal convective systems and their life cycle were identified.
Regarding that Inoue, Vila, Rajendran, Hhamada, Wu and Machado (2009) proved if we use one colder or warmer threshold, both initiation and dissipation phases may not indicate the life cycle, in this study, brightness temperature threshold of 224 K (Volasco & Fritsch, 1987) and 243 K (Machado, 1998) were used for identifying and analyzing systems life cycle. The researchers have tried to choose some days for this study over which mesoscal convective systems have been made and spent their life cycle without merger or split.
By transfering these systems to GIS environment using area expansion index (∆E) whose validation and viability have been confirmed by Vila, Machado, Laurent, and Velasco (2008) its life cycle was verified (eq. 1).

∆E=(1 δA)/(A δt) (1)
A = the system area in a given time (Tir

Keywords

• Mesoscal Convective Systems
• Life Cycle
• West of Iran
• Brightness Temperature

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