Analysis of the effect of the simultaneous occurrence of some Teleconnection indices of the Northern Hemisphere on the winter temperature of Iran

Analysis of the effect of the simultaneous occurrence of some Teleconnection indices of the Northern Hemisphere on the winter temperature of Iran



Introduction

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.



Materials and methods

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.



Results and discussion

The results of examining the relationship between the studied variables and the winter temperature of Iran showed that there is an inverse and significant 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, an inverse and significant 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.



Conclusion

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 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.



Keywords: Iran, NAO, PDO, PNA, Winter Temperature.