Gholamreza Barati, Isaa Dehghan,
Volume 0, Issue 0 (3-1921)
Abstract
The Siberian High-pressure (HP) has various effects on Iran’s climate. Climate warming, especially in the last century, has raised the possibility of changes in the Outbreaks of the Siberian High-pressure extending toward Iran (OSH). In this study, to test the mentioned hypothesis, daily sea level pressure maps for 50 years (1972 to 2021) during the month in which the SH appeared more strongly in the monthly composite maps were downloaded from the NCEP/NCAR atmospheric data reanalysis database. The selection of this month was based on the highest central pressure intensity of the high (intensity index) and its greatest spatial extent (spatial index) compared to the other six months. The axes of the OSHs extending toward Iran were classified into four categories: “continuous and reaching,” “continuous and non-reaching,” “discontinuous and reaching,” and “discontinuous and non-reaching.” The design of their synoptic patterns showed a clear decrease in the frequency of “continuous and reaching” OSHs. Continuity refers to the directness of the OSH, and a reaching OSH is one that extends to the borders of Iran or penetrates into the country. Using two criteria— “the integrated advance of cold and dry air from the high-pressure center toward Iran” and “verification of the OSH entering or reaching Iran’s borders”—it was found that cold and dry air travels from Central Asia toward Iran through three main pathways: 1. The pathway of cold and dry air transfer from the western slopes of the Altai Mountains, then across the Turan Plain, and finally into central Iran. 2. The pathway of air transfer from the Dzungarian Plain in western China, then along the Tian Shan Mountains, through Afghanistan, and finally into the north of Sistan-va-Baloochestan Province. 3. The pathway of air transfer from the Kazakh steppes, through the Caucasus corridor (west of the Caspian Sea), reaching Azerbaijan, and extending along the Zagros Mountains. The frequency of OSHs has indicated a decline in five separated decades along all three pathways during the past half century. This decrease is more evident in the third pathway, namely the Caucasus corridor, which already had a lower frequency from the beginning.
Maryam Saghafi, Gholamreza Barati, Bohloul Alijani, Mohammad Moradi,
Volume 23, Issue 71 (12-2023)
Abstract
Precipitation is a phenomenon resulting from complex atmospheric interactions and among climatic events, due to its vital role, it has special importance. The importance of precipitation durability, especially in arid and semi-arid regions, which includes most of Iran, is greater than its volume. The purpose of this study is to identify Iran's precipitation areas in terms of precipitation durability and its characteristics in each area. In order to investigate the durability of Iran's precipitation and to define a precipitation day as " a day with equal precipitation or greater than 0.5 mm", used from daily precipitation data of 80 synoptic stations of the country during the 6 cold months of the year from October to March in a period of 30 years (2016 - 1987). Setting data in daily tables in the first step, made possible to program in MATLAB environment to separate precipitation in ten groups from "one day" to "ten days" and in the second step in SPSS environment based on frequency characteristics, amount and precipitations average in the mentioned groups was done by the method of Ward merging and clustering. The process of the clustering on Iran's durability precipitation showed that there are seven almost homogeneous precipitation zones in Iran; the geographical arrangement of Iran's precipitation areas, reveals the dependence of Iran's precipitations amount on roughness, the path of precipitation systems, its proximity to humidity sources, and the effect of the sea. In terms of area’s location, it can be said that; the settlement of the four zones in the western half of Iran, despite its small size in front of the eastern half, is a reason for its heterogeneity.
Mrs Maryam Sanaei, Dr Gholamreza Barati, Dr Alireza Shakiba,
Volume 24, Issue 72 (3-2024)
Abstract
Climate change, including spatial changes in rainfall following the increase in greenhouse gases, is a challenge that affects various aspects of life in human societies today. In this study, the long-term spatial changes of the rainy season from September to May were studied using the statistics of "local Moran" and "Hot spots of Getis Ord-J" during 5 5-year periods from 1991 to 2015. The application of local Moran statistics showed that areas with long rainfall periods are in good agreement with the countrychr('39')s rainfall pattern. This adaptation is accompanied by a negative spatial correlation in lands with short rainfall periods. The pattern obtained from the hot spot statistics also showed itself to be more consistent and corresponded to two very low rainfall regimes in the southeast and center, while according to local Moran statistics, this pattern was more scattered and parts of it had a low southern precipitation regime. . In addition, the results of Alexandersonchr('39')s statistics to identify mutations in the long-term series of the rainy season showed that the time series of 13 stations out of 108 stations studied experienced a sudden jump that these mutations are more in the southern stations in the country and in later years. It has occurred since 2000 AD.
