| Abstrakt: |
The main purpose of the current research is to investigate the nighttime LST climatology in Iran. The study of the seasonal regime and annual temperature differences along with the identification of the role of different temperature thresholds and the spatial analysis of Iran's cold spots are among the climatic features studied in the current research. For this purpose, the MYD11A1 product (version 6.1) of the MODIS which is a key instrument onboard the Aqua Satellite with a horizontal resolution of 1000 meters has been used for a period of 19 years (2003-2021). This product is related to the nighttime passage of the satellite at 1:30 local time. Satellite data were validated using daily soil temperature data from 174 meteorological stations. The accuracy of satellite data showed that the area average values of root mean square error (RMSE) and mean bias error (MBE) compared with station data are 1.7℃ and 1.39℃ respectively. Also, the PBias statistics results show that the underestimation prevails in the night LST data compared to the soil temperature. In total, the MODIS sensor estimates LST in most regions of the country with an error of less than 10%, which indicates the high efficiency of the MYD11A1 product in assessing Iran's nighttime LST. The findings showed that the combination of altitude and higher latitude has significant importance in the seasonal changes of nighttime minimum LST in Iran. So, the combination of these two factors plays an important role in the occurrence of the lowest night temperatures in the country in the middle parts of central Alborz and the highlands of Azerbaijan. Thus, the longest period of dominance of low temperatures in Iran is related to 38°N and 36°N latitudes, respectively. The results also indicate that the prevailing temperature zones in Iran fluctuate from the minimum temperature in January to the maximum temperature in July. In the transitional seasons, only April and October have distinct and independent temperature identities, and the rest of the months of the transitional seasons are either connected to winter or connected to summer according to the pattern. Examining the course of intra-annual temperature changes shows that the highest intra-annual temperature concentration and the highest homogeneity are observed in the summer season. On the other hand, the highest level of heterogeneity and the lowest level of temperature concentration are related to the autumn season. Examining the average nighttime temperature difference in Iran also shows that the highest values of the earth surface temperature difference occur in the winter season and the lowest values in the summer season. In a general view, the temperature difference curve fluctuates between a maximum of 56.6℃ in January and a minimum of 46.5℃ in July. Spatial analysis of nighttime temperature difference showed that the Lut desert experiences the highest average values of nighttime temperature difference throughout the year. In general, lack of moisture, very low percentage of cloud cover, lack of vegetation cover, and very low soil moisture seem to have led to high nighttime temperature fluctuations in the Lut desert. On the other hand, a narrow strip along the southern coastline of the Caspian Sea experiences the lowest nighttime temperature difference in the country. Clearly, the high humidity of the southern coastline of the Caspian Sea plays the main role in reducing the temperature fluctuations of this region. The geographical analysis of cold spots indicates that the coldest spots of Iran are observed in the high peaks, located in high latitudes. Also, the highest geographical concentration of cold spots in Iran is related to the summer season. Meanwhile, the largest spatial distribution of Iran's cold spots can be seen in the winter season, especially in December. The findings also indicate the existence of a regular annual cycle in the spatial arrangement of cold spots in Iran. In this way, in the warm period of the year, the cold spots of Iran are concentrated only in the middle part of the central Alborz. With the beginning of the cold period of the year, we are witnessing a northwest shift of cold spots toward the highlands of Azerbaijan. So that a bimodal pattern replaces the summer concentrated pattern. The bimodal pattern continues at the height of winter with the dispersion of cold spots in Alborz and Azerbaijan, but with the arrival of the warm period of the year, a southeastward shift of cold spots towards the Alborz Mountains begins, with the cold spots completely concentrated on the Damavand peak, this annual cycle ends in the summer season. [ABSTRACT FROM AUTHOR] |
