نشریه پژوهشهای تغییرات آب و هوایی
پیاپی 8 (زمستان 1400)

Researchers in various fields have given particular attention to the variability of temperature and precipitation components and the role of climate change as well as the effect of large-scale climate indicators in recent years. The North Caspian Sea (NCP) index is one of the most important regional-scale indicators that operates well in the East Atlantic with the NAO index. This study used three categories of data, including temperature and precipitation components, and reanalyzed geopotential altitude data of 500 hPa and geopotential altitude data of 500 hPa based on 14 climatic models. In the first stage, the NCP index was identified for future periods of development and generalization and then its positive and negative phases for the two scenarios RCP4.5 and RCP8.5. As well as maximum and minimum temperatures, precipitation rates, and number of precipitation days were displayed for future downscaling periods. Based on the forecasts for the positive and negative phases of this index, it was determined that for the next period 2060-2041, both the maximum and minimum temperatures will increase. Furthermore, the rate and number of rainy days in the future period will be more irregular than the temperature component compared to the base period. In the RCP4.5 scenario in both phases, it was found that the average number of rainy days will decline and, in both phases, rainfall rates will increase in stations that are near the Caspian Sea. In the RCP8.5 scenario, the average number of rainy days in the study area will decrease by about 5 days in the positive phase and increase by 4 days in the negative phase compared to the base period.

Industrial growth, deforestation and destruction of the environment increased the greenhouse gases in recent decades. Increase the concentration of greenhouse gases lead to rise in temperature of the earth's atmosphere globally which called global warming. These effects not only change the temperature of the atmosphere, but also have influence on other climatic parameters which called climate change. This study investigated the effects of climate change on the basin Gharasoo in periods of 30 years (2044-2015) and (20740245) has been done. 10 GCM models set of models AR4 to study climate change used in this study. 6 stations for temperature changes And 9 stations were chosen for the study precipitation changes. Based on the performance of GCM to forecast temperature and, precipitation. The weighting models based on their weight is defined the average pattern for all these models. And the emission scenarios A2 and B1, daily temperature and precipitation data were generated using LARS-WG model. Then, using the IDW method for regional meteorological data were converted. Results showed that among the ten GCM models weighted average model Model IPSL CM4.0 greatest accuracy in estimated temperature and GISS-ER models the most accurate estimated rainfall in the entire Gharasoo basin showed. Also the results related to changes in temperature and precipitation showed the summer and spring, respectively, the highest temperature rise in the near future two terms (2044-2015) and far future (2074-2045) for both A2 and B2, respectively. And winter had the highest decrease precipitation.

Positive and negative vorticity in the westerly winds wave cause changes in the type of precipitation. The purpose of this study is to investigate the relationship between vorticity fluctuations and precipitation in Sardasht region. First, daily precipitation data were obtained from Sardasht synoptic station and after statistical analysis of the data, synoptic maps of Sea level pressure (SLP), 500 millibar Geopotential height (HGT), omega and vorticity for representative days were extracted and analyzed using GAREDS software. The results indicate the creation of a front at surface in all SLP maps at Sardasht station. Also in the HGT map, the study area is located in the PVA section of the west wind troughs, which has created unstable conditions at the level of 500 millibar and has caused the rise of humidity. At sea level, the most important sources of moisture that strengthened the front and rainfall at the station were the Black Sea, the Mediterranean and the Caspian Sea. The direction of wind at sea level was northeast-southwest and in the upper level was west, southwest and northwest. Most of the day, we see the dominance of a cyclonic system in the region, which has occurred due to the creation of unstable conditions by the front. On omega map, all days are unstable and negative omega cores are formed in Sardasht station. The vorticity map shows the effect of positive vorticity in this station, which has caused precipitation, especially liquid precipitation in the area.

This research tries to investigate the nighttime land surface temperature (NLST) (22:30) in Tehran City and its suburbs by using MODIS satellite images from 2000 to 2021. In this regard, NLST characteristics in the urban and suburbs of Tehran were obtained through the MOD11A2 Version 6 product. These data provide an average 8-day per-pixel land surface temperature with a 1-kilometer spatial resolution in a 1200 by 1200 km grid. The NLST time series were obtained for the urban and suburbs, through which the nighttime surface urban heat island (NSUHI) time series were calculated. The results showed that the trend of NLST in the urban is completely different from suburbs. Although NLST shows a significant declining trend in the suburbs, it does not show any significant trend in the urban, Hence the further increase of NLST in the suburbs has caused the downward trend of NSUHI. The results of Mann-Kendall showed that the NSUHI time series had experienced a decreasing trend seasonally and annually, which is significant at the 99% confidence level. Although the earth has become warmer in recent years, the rate of warming in the urban and suburbs has not been the same, so NSUHI in Tehran has recorded a significant downward trend seasonally and annually.

Precipitation is the most important hydrological variable that connects the link between atmosphere and surface processes. Three-quarters of the atmosphere heat is the result of releasing the latent heat of evaporation. Therefore, climatic zoning of autumn precipitation is necessary for achieving comprehensive development in different spatial-temporal dimensions. For this purpose, the daily data of autumn season at 18 synoptic stations of the study area have been analyzed with a joint statistical period 32 (1989 - 2018). In this study, Kolmogorov-Smirnov test was used to find out the normality of the data and Mann-Kendall test was used for the process of their changes. Then by applying factor analysis based on principal component analysis and with orthogonal rotation of Varimax it was found that there are two effective precipitation factors in the climate of the region which in total account for more than 68.16% of the variance of the region's autumn precipitation climate. By performing hierarchical cluster analysis and by integrating the matrix of factor scores, two main and sub-regions were identified. These areas are: Areas of high precipitation and moderate precipitation. It can be said that in the high precipitation areas of the territory are located on the rainy of the Zagros, Sahand and Arasbaran mountain belts, stretching as a narrow strip from the north to the south parts of the region.

The main purpose of this study is to investigate changes in atmospheric thickness and its relationship with temperature changes during the cold period of the year. To achieve this goal, data on geopotential elevation and temperature of 1000 hPa for the years 1960 to 2020 have been extracted from the NCEP NCAR site. In the next step, using the programming capabilities of Gardes, numerical extraction of atmospheric thickness between the levels of 1000 to 5000 hPa per meter and temperature data of the level of 1000 hPa in degrees Celsius was performed. Four 15-year periods are divided. The spatial distribution of the 15-year average and the 60-year long-term average, as well as the positive anomalies showed that the thickness of the atmosphere increased significantly during the first to the fourth period, and this increase reached its maximum in the fourth period. The study of the trend in the first period has shown a decrease in the thickness of the atmosphere for the whole of Iran, but with the beginning of 1976 (beginning of the second period) we have witnessed a sharp increase in the thickness of the atmosphere, which continued until the fourth period. The results of Pearson correlation coefficient showed that there is a significant relationship between changes in atmospheric thickness and temperature changes in the cold period of Iran at the 95% confidence level. Spatially, this correlation reaches its highest level in the west, northwest and southwest of the country. As a result, it can be said that the thickness of Iran's atmosphere has increased significantly in recent years, and one of the reasons is the change in the nature of inflows to Iran and, of course, global warming.