بررسی اثر گرمایش جهانی بر روند گردش‌های وردسپهری در خاورمیانه در دوره آماری 2020-1961

ABSTRACT
Climate change refers to a change in the state of the climate that can be identified by changes in the mean and the variability of its properties and that persists for an extended period, typically decades or longer. In the present study, the temporal variability of the temperature, geopotential height, wind speed, specific humidity in pressure levels, and the mean sea level pressure in the Middle East in the cold season (December, January, February) are analyzed in two statistical periods of 1961-1990 and 1991-2020. These data are collected from the National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) archive. The Middle East region is considered as a study area. The temperature trend analysis of the cold season in standard pressure levels from 1991 to 2020 shows a positive trend in the southern Middle East.  This positive trend might cause an increase in thermal energy in the atmospheric layers, an increase in upward vertical motion, a thickness increase in the atmosphere, and more frequent convective phenomena. The positive trend of frequent intensified convective precipitation, extreme rainfalls, and devastating floods is obvious in the Middle East. With the revelation of the positive trend of the geopotential height in pressure levels and the negative trend of the wind speed in lower layers, the water vapor flux into the planetary layers has decreased.
Extended Abstract
Introduction
Adapting to climate change and mitigating its negative effects is the most important present challenges of the humankind. The Intergovernmental Panel on Climate Change confirms that human influence on the climate system is evident and increasing, and its adverse effects are visible on continents and oceans. Climate change refers to a change in the state of the climate that can be identified by changes in the mean and the variability of its properties and that persists for an extended period, typically decades or longer. Also, climate change can result from nature’s internal processes, the effect of external forces, persistent anthropogenic forces on atmospheric composition, or soil misuse. In addition, climate change occurs on a global scale, but its impacts are not the same from region to region. The change analyses over the meteorological variables represent a critical task in climatic change detection. Numerous studies have been done to detect the possible climate trends and changes across the world. However, most of these studies have focused on temperature, humidity, and precipitation changes. Numerous studies have examined the changes in meteorological variables in the Middle East and Iran. The results generally showed significant meteorological parameter changes in many observing stations. This paper aims to analyze the variability of temperature, geopotential height, wind speed, and humidity over the pressure levels in the Middle East during 1961-1990 and 1991-2020.
 
 
Methodology
In the present study, the temperature, geopotential height, wind speed, and specific humidity temporal variability over the pressure levels (1000, 925, 850, 700, 500, 300, 250, 200 hPa) and mean sea level pressure in the Middle East in the cold season (December, January, and February) are analyzed in the two statistical periods of 1961-1990 and 1991-2020. These data are collected from the National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) archive. The Middle East region is considered as a study area. This region is between 10° to 60° N latitude and 25° to 80° E longitude. The average quantity from December 1 to February 28 (29) is calculated and then fitted to the trend equation. The most commonly used non-parametric test to find the trends in meteorological variables is the Mann-Kendall one. The statistically significant trend was detected using a non-parametric model such as the Mann-Kendall test, and it was completed by Sens slope estimation to define the extent of the trend. Minitab statistical software was also used in this study.
 
Results and discussion
The cold season trend analysis of the temperature in pressure levels during 1991-2020 shows a positive trend in the southern Middle East. This positive trend can cause an increase in thermal energy in the atmospheric layers, an upward vertical motion intensification, an increase in the thickness and depth of the atmosphere, and more frequent convective phenomena. As a result, the intensification of convective precipitation can increase the number of flash floods in the Middle East. Comparing the second 30 years with the first one reveals that the frequency of micro-scale and medium-scale phenomena has increased compared to synoptic-scale low-pressure systems. The number of cold low-pressure systems also decreased regarding the occurrences in the first 30-year period. Regarding the positive trend of the geopotential height in different pressure levels and the negative trend of the wind speed in the planetary layers in this period, the water vapor flux into the low-pressure systems has decreased, and their precipitation contribution is weakened.
 
Conclusion
The variability of the temperature, geopotential height, wind speed, specific humidity, and mean sea level pressure of the Middle East in the cold season are analyzed in this paper for the 1961 to 2020 period. The results showed that in the southern Middle East and Iran, the meteorological variables have changed as follows:
1-The lower troposphere has shown a cooling of up to 1 K per decade (from 1961 to 1990) in the southwest of the Mediterranean Sea and north of Iran and a 0.5 K decadal warmup in the southern Indian Ocean.
2-The middle troposphere showed up to 0.5 K decadal (during 1991-2020) warming in the Indian Ocean, Red Sea, southeast of the Mediterranean Sea, and over the northern Black Sea.
3- The lower troposphere had 0.3 g/kg per decade drying in the western regions of Iran.
4- The wind speed during 1961-1990 in the upper northern troposphere had a 2 m/s per decadal increase in the northern Mediterranean Sea and east of the Caspian Sea. It decreased by 2 m/s per decade in the southern Mediterranean Sea and by 0.5 m/s per decade in the western regions of Iran.
 
Funding
There is no funding support.
 
Authors’ Contribution
All of the authors approved the content of the manuscript and agreed on all aspects of the work.
 
Conflict of Interest
Authors declared no conflict of interest.
 
Acknowledgments
We are grateful to all the scientific consultants of this paper.