نوع مقاله : مقاله پژوهشی

نویسنده

• سید حسین میرموسوی

دانشیار اقلیم شناسی، دانشگاه زنجان

چکیده

لایه مرزی سیاره‌ای پایین‌ترین بخش جوّ است که مستقیماً تحت‌تأثیر زمین بوده و مبادلات دما و تابش نقش کلیدی را در تغییرات ارتفاع این لایه دارد. تغییرات ارتفاع این لایه نیز می‌تواند نقش بسیار مهمی در کنترل پدیده‌های مختلف جوّی نظیر ابر، مه،آلاینده‌ها و... داشته باشد. ارتفاع لایه مرزی تحت‌تأثیر عوامل مختلفی نظیر تغییرات توپوگرافی، دما، رطوبت نسبی، شار تابشی و عرض جغرافیایی تغییر پیدا می‌کند. هر گونه تغییر در ارتفاع لایه مرزی می‌تواند پدیده‌های جوّی در زیر این لایه را تحت‌تأثیر قرار دهد. در این مطالعه تغییرات ماهانه ارتفاع لایه مرزی در ایران در طی دوره 62 ساله (2021-1959) با استفاده از داده‌های نسخه ERA5 سایت ECMWF مورد بررسی قرار گرفت و به منظور تحلیل الگوهای فضایی حاکم بر تغییرات ارتفاع لایه مرزی از مدل GETIS ORD استفاده شد. نتایج حاصل از مطالعه نشان داد که ارتفاع این لایه در طی ماه‌های مختلف سال از الگوهای خوشه‌ای تبعیت می‌کند. دو کانون مهم لکه‌های سرد (ارتفاع کم) در بخش شمال‌غرب و شمال‌شرق ایران از معنی‌داری بالایی برخوردار هستند و نیمه جنوبی ایران مخصوصاً استان خوزستان، استان کرمان و جنوب استان سیستان و بلوچستان مهم‌ترین لکه‌های داغ (مناطق با ارتفاع زیاد) هستند. نتایج حاصل از تحلیل رگرسیون چندمتغیره نشان داد که شش متغیر میانگین دما، میانگین رطوبت نسبی، ضریب رطوبت خاک، عرض جغرافیایی، ارتفاع و فشار هوا با میزان همبستگی کلی 70.73 به‌ترتیب مهم‌ترین عوامل مؤثر در تغییرات ارتفاع لایه مرزی در ایران هستند. 

کلیدواژه‌ها

• لایه مرزی سیاره ای
• ایران
• مدل GETIS ORD
• تحلیل فضایی

موضوعات

• استخراج، پردازش، تولید و نمایش داده های جغرافیایی

عنوان مقاله [English]

Spatial analysis of monthly changes in planetary boundary layer height in Iran

نویسنده [English]

• Seyed Hossein Mirmousavi

Associate professor of climatology, Zanjan University

چکیده [English]

Extended Abstract
Introduction
The planetary boundary layer (PBL) as the lowest part of the troposphere is the most dynamic part of the atmosphere that is directly affected by the interactions of the atmosphere and the surface of the Earth (Stell, 2012 and Gert, 1992). These atmospheric surface interactions occur in short periods of time and play an important role in the development of the boundary layer. The height of this layer is also influenced by atmospheric conditions, topography characteristics, and type of land cover, and is an important parameter for many meteorological phenomena that have various applications such as monitoring air quality, cloud formation and evolution, surface fluids, and atmospheric hydrological cycles (Garrett 1994). Since the height of the boundary layer indicates the depth of turbulent vertical mixing, it is very effective in increasing or decreasing the concentration of pollutants near the surface and is considered as an essential parameter in air quality monitoring (Su and Khan, 2018). In addition, the height of this layer is a key factor in numerical weather forecasts. Since the height of the base of clouds is usually close to the height of the boundary layer, this layer determines the extent of cloud development and causes the transition from shallow convection to deep in the clouds.           
Materials
The data used in this study included re-analysis data on the monthly time scale of the planetary boundary layer height for the entire Iranian region with a resolution of 0.25×0.25 which was obtained from the ERA5 version of ECMWF site during the period 1959-2021. In order to analyze the relationship between different climatic variables (mean temperature, mean relative humidity and air pressure), the meteorological data of 187 synoptic weather stations during the statistical period 2000-2022 has been used.
Methods
In this study, in order to prepare the data using programming capabilities in MATLAB software, maps with an average of 62 years old have been prepared and then using ARC GIS software to map the monthly average height of the boundary layer in Iran. In the next step, spatial statistics index of Getis-Ord Gi* was used to analyze the spatial changes in the height of the boundary layer in different months. In order to analyze the effective variables in elevation changes in the boundary layer temperature, relative humidity, soil moisture, etc. Multivariate standard regression method was used.
Conclusion and Discussion
The annual average elevation map of the boundary layer also shows that the maximum height of this layer in Iran is 1600 m which is located in the south of Iran in Kerman province and south of Sistan and Baluchestan province and in general, the southern half of Iran with the exception of a narrow strip of southern coasts is higher than the northern half. The lowest elevation between 520 and 1000 meters is mainly located in the northern half, the eastern part and a narrow strip of southern coast. The average height of the entire boundary layer of Iran during the year is 1131 meters. The height of the boundary layer in different months of the year has significant changes in Iran and in terms of spatial changes it follows severe cluster patterns. Analysis of hot and cold spots showed that the spatial distribution of the height of the boundary layer has completely homogeneous spatial patterns so that the northern half of the country, especially the northwest and northeastern regions of the country, have a high significance as cold spots in most months of the year.
Results
The results of this study showed that the elevation of the boundary layer in Iran during the year has a lot of spatial and temporal changes due to geographical diversity and climatic characteristics in different regions of the country. The existence of diverse topography, expansion in latitude, large differences in relative moisture content and soil moisture content are among the factors that have caused significant changes in the height of the boundary layer at different times and places. The results of multivariate regression analysis showed that the height of this layer is mainly affected by six parameters in particular, temperature and relative humidity.

کلیدواژه‌ها [English]

• Planetary boundary layer
• Iran
• GETIS ORD model
• Spatial analysis