فهرست مطالب vahid khojasteh gholami

Air temperature is very important among the climatic elements. Since Iran is located in the subtropical region, extreme temperature changes are one of its inherent characteristics, and for this reason, investigating temperature changes in Iran is essential. Fluctuations in temperature on a large and regional scale are more or less influenced by teleconnection patterns. This article aim is to investigate the simultaneous occurrence of the North Atlantic Oscillation (NAO) and the Arctic Oscillation (AO) with the Pacific-North American (PNA) and the Pacific Decadal Oscillation (PDO) and their effect on Iran's winter temperature. In this research, the monthly temperature data of 100 selected synoptic stations of Iran from the Islamic Republic of Iran Meteorological Organization (IRIMO) website and the PDO, PNA, NAO, and AO indices from the National Oceanic and Atmospheric Administration (NOAA) website for 1988-2019 were obtained as primary data. To determine Pearson's correlation coefficients, normalized monthly temperature data were entered into STATISTICA software as a dependent variable and teleconnection data as an independent variable. Then, the positive and negative phases of the mentioned teleconnections were identified. Numbers smaller than -0.5 were considered as the negative phase, between -0.5 and 0.5 as the neutral phase, and greater than 0.5 as the positive phase. Then, the monthly temperature anomaly was calculated for the mentioned months. The distribution of temperature anomaly changes in Iran was zoned in the GIS software using the inverse distance weighted (IDW) method. The results of examining the relationship between the studied variables and the winter temperature of Iran showed that there is significant inverse relationship between the AO index and the temperature of December, January, and February in most regions of Iran, especially in the western regions so, correlation coefficients can be seen in the northwestern regions of Iran up to -0.66. Also, in most investigated stations, there is a significant inverse relationship between the NAO index and the February temperature was observed, so the correlation coefficient was observed in the western parts of Iran up to -0.62. By increasing the numerical values of the studied teleconnections from negative to positive phases, the temperature of most regions of Iran decreases throughout the year, especially in February. In some studied stations, a direct and significant correlation was observed between the negative phases of PNA with January temperature and the negative phases of PDO with December temperature. By reducing the numerical values of PNA and PDO teleconnections from neutral to negative phases, the temperature of some regions of Iran decreases. The coincidence of the positive phases of NAO and AO with the negative and neutral phases of PDO and PNA has caused the occurrence of normal and lower-than-normal temperatures in most regions of Iran, especially the regions located in the northern and western half, so, the coldest months of the statistical period happened in this state. The simultaneous occurrence of negative phases of NAO and AO with negative and neutral phases of PDO and neutral and positive phases of PNA has caused normal and higher-than-normal temperatures in the northern and western parts of Iran; in such a way that the hottest months of the statistical period happened in this state. The simultaneous occurrence of neutral phases of NAO and AO with positive and negative phases of PDO and neutral and positive phases of PNA has caused the occurrence of normal and above-normal temperatures in most regions of Iran, especially in the western and northern parts. The coincidence of the neutral phases of NAO and AO teleconnections with the neutral phases of PDO and PNA has caused the absence of severe temperature anomalies (absence of much lower and higher-than-normal temperatures) in Iran. The results showed that the simultaneous occurrence of the positive phases of NAO and AO with the negative and neutral phases of PDO and PNA causes normal and lower-than-normal temperatures in most regions of Iran, especially in the western parts. The simultaneous occurrence of negative phases of NAO and AO with negative and neutral phases of PDO and neutral and positive phases of PNA has also caused higher-than-normal temperatures in the northern parts of Iran. Also, the coincidence of the neutral phases of NAO and AO with different phases of PDO and PNA has caused normal and higher-than-normal temperatures in most regions of Iran, especially in the northern and western parts.

Fluctuations in temperature are more or less influenced by teleconnections. The aim of this study is to investigate the simultaneous role of the North Atlantic Oscillation and the Arctic Oscillation with Quasi-Biennial Oscillation on the winter season temperature in Iran. For this purpose, the temperature data of 100 meteorological stations were used in the statistical period of 1988-2019. Correlation coefficients between QBO, NAO, and AO teleconnections data were calculated with monthly temperature. Then the possible states for the simultaneous occurrence of the teleconnection patterns were determined and the temperature anomaly for the determined states was analyzed by drawing a diagram and a map in the GIS environment. The results showed that there is an inverse and significant correlation between the positive QBO phases and February temperature in most of the northern and western regions, so the highest correlation coefficient was calculated at Ilam station as -0.81. An inverse and significant correlation was observed between NAO and especially AO cycles with northern and western half temperatures, especially in January and February. The simultaneous occurrence of the negative (positive) phases of NAO and AO with the negative (positive) phases of QBO causes the occurrence of higher than normal (normal and lower than normal) temperatures in the western (eastern) half so that the warmest winters of the statistical period happened during the simultaneous occurrence of negative NAO, AO, and QBO phases. On the other hand, the simultaneous occurrence of neutral QBO phases with positive NAO and AO phases causes normal and lower-than-normal temperatures in most regions except the southern and southeastern parts of Iran, contrary to this situation, the simultaneity of QBO neutral phases with NAO and AO negative phases has caused the absence of severe temperature anomalies and the possibility of higher than normal temperatures with high intensity is unlikely.

Precipitation is the result of complex atmospheric and oceanic phenomena and it has a special importance due to its vital role among other climatic events and is more complex than other climatic phenomena. Iran is located in the world's arid and semi-arid belt and receives more than half of its annual rainfall in the winter. teleconnection is the alternating and continuous anomalies of atmospheric patterns and particularly pressure on the planetary scales with relative prolonged return period. So it can be considered one of the key elements on climatic forecasts. Quasi-Biennial Oscillation (QBO), recognized in 1961,is one of the main oscillations on the planetary scale in the stratosphere layer with a mean return period of 26 months and is also one of the main components of short-term fluctuations in the climate. QBO can vary the surface weather with effect on polar atmospheric patterns. It can also affect the amount of ozone depletion on high geographical latitudes, in addition to the effect on solar cycle and connection with other teleconnections such as ENSO resulting in the climate change of the earth.

The total monthly precipitation from 100 synoptic stations from Iranian Meteorological Organization and QBO index data of National Oceanic and Atmospheric Administration(NOAA) during 1988-2017were used as the basic input data of the study. First, rainfalls from December to February were considered as winter precipitation and the corresponding QBO index was used. Then, precipitation data were standardized in order to make comparable data with QBO. The normalized data of winter rainfall as dependent variable and QBO index as independent variable were entered into the STATSTICA software. Pearson correlation coefficients were performed between them in each station. No simultaneous effect may be observed due to long distance between QBO generation areas and Iran, therefore, a three months lack also was tested, and hence, the correlation coefficients between autumn QBO and winter precipitation of the stations were calculated. In order to validate of correlation coefficients, precipitation difference of the stations in the positive phases of QBO compared with negative phases. In the next step, the correlation coefficients outputs entered into the GIS environment and mentioned maps were drawn using IDW approach. Finally, the trend chart of the winter precipitation anomaly was prepared to study the impacts of autumn and winter QBO on it.

The results showed that there is a significant inverse relationship between the positive phases of autumn QBO with winter rainfall in most stations, especially in the central and southern parts of Iran. The increase in the intensity of the positive phases in autumn QBO causes subnormal winter rainfall in the central and southern parts of the country. On the other hand, the occurrence of negative autumn QBO causes a minor increase in the rainfall rates of most parts of Iran. However, the occurrence of rainy winter in the case of autumn negative phases is not conclusive. But, the winter time extreme negative phases of QBO index lead to a significant decrease in the precipitation rates of most areas of the country especially southern and western parts, while the positive phases lead to minor decrease (increase) in the precipitation rates of the southern (northern)parts of Iran. The separate study of positive and negative phases of QBO in autumn and winter seasons revealed a contradictory effect on winter rainfalls in different parts of Iran, and in short, the effect of QBO on winter precipitation is lower in northern parts. The final results showed that the occurrence of rainy winter has been linked to the mild phases of QBO index in the autumn and winter. It can be concluded that the QBO teleconnection is one of the main factors controlling winter precipitation in different parts of the country, especially in the southern, central and western sectors. The main and tangible role of QBO is reducing the amount of precipitation. Meanwhile, there is no significant relationship between QBO index and winter precipitation of the northern parts of Iran, especially the northwest and Caspian Sea coasts.

In general, the correlation between the autumn and winter QBO index and winter precipitation is negative in the western half and positive in the eastern and southern parts of the country. So, by moving from the extreme negative values of QBO to the positive ones, a relative partial reduction is observed in the precipitation rate of northwest regions, western sides of Alborz Mountains and the western parts respectively, and there is an increase in other parts especially in the Caspian Sea coasts and the southern Iran. The autumn phases of QBO index are slightly more related to winter precipitation. Unlike the previous condition, there is a negative correlation between the positive phases of QBO and winter precipitation rates and this is more significant in most regions especially in central and southern parts of Iran. The highest correlation coefficient (-0.65 to -0.82) was observed on the shores of the Persian Gulf and the positive phases of this index happened to decrease the precipitation rates in the central and southern regions of Iran. There is no significant relationship between the negative phases of autumn QBO and winter precipitation rates. On the other hand, positive phases of winter QBO reduced precipitation rate in south and southwest regions and partially increased rainfalls in the northwest of Iran. However, the amount of rainfall decrement is more significant in the southern regions. Also, the occurrence of negative phases in the winter reduced the precipitation rate in most parts especially in the western parts, the coast of Persian Gulf and some parts of the eastern Iran. The occurrence of rainy winter has always been linked to the gentle phases of QBO index and it has not been associated with strong positive and negative phases. It seems that the extreme positive phases in autumn and the extreme negative phases in winter time have more significant effects on the reduction of rainfall in most parts of Iran especially in southern regions.