Document Type : Research Paper

Authors

• vahideh abtahi ¹
• Saeed jahanbakhsh ²
• hashem rostamzadeh ³
• hasan lashkari ⁴

¹ PHD student in Tabriz university

² The University of Tabriz

³ Assistant Professor of Climatology, University of Tabriz, Iran

⁴ Professor, Department of Physical Geography, School of Earth Science, The University of Shahid Beheshti (SBU), Tehran, Iran

Abstract

Heavy rainfall is considered one of the climatic features of precipitation that can occur in any climate, but its occurrence in arid and semi-arid climates, due to the lack of adequate and appropriate infrastructure, is associated with greater damage. These rains occur under different synoptic conditions. In this study, the role of atmospheric rivers in the formation of heavy rainfall has been investigated. For this purpose, heavy rainfall data from stations in the west and northwest of the country were extracted for a 33-year period. Then, precipitation systems were separated in conjunction with atmospheric rivers. In the next step, using weather maps and the troposphere's underlying layer levels, synoptic patterns that lead to the formation of atmospheric rivers were identified. The results showed that atmospheric rivers were responsible for heavy rainfall in the study area, following three general patterns. The Sudanese low-pressure pattern and the combined pattern of Sudanese low-pressure and Mediterranean cyclone were responsible for the most significant role in the formation of atmospheric rivers leading to heavy rainfall, respectively. In the Sudanese low-pressure pattern, two to three days earlier, a broad tongue of Siberian high pressure spreads over the warm waters of the Oman, Arabian, and Aden seas, passing through Afghanistan, Pakistan, and the eastern part of Iran. This tongue, with the rotation of moisture, escapes from the Sudanese system. The Mediterranean trough deepens over western Asia and northeast Africa, and this moisture is strengthened along the southern currents and, by passing over the mountains,leads to the formation of atmospheric rivers. In the combined pattern, with the expansion of the Sudanese low-pressure tongue to the eastern Mediterranean and western Asia, the southern warm waters' moisture is released onto this region with the transport of moisture from the Mediterranean, it is strengthened, leading to the formation of atmospheric rivers.

Keywords

• Atmospheric river
• Sudan low
• heavy rain
• west and north-west of Iran
• Mediterranean cyclone

Main Subjects

• Climatology