Document Type : Research Article
Authors
1
Professor of Physical Geography, Faculty of Social Sciences, University of Mohaghegh Ardabili, Ardabil, Iran,
2
Phd Student of Physical Geography, Faculty of Social Sciences, University of Mohaghegh Ardabili, Ardebi, Iran
Abstract
Extended Abstract
Introduction
Earth's climate is not constant, and environmental changes are the result of changing climate systems. Temperature is one of the basic elements in climate and its change can cause changes in the climate structure of other regions. In atmospheric sciences, the relationship between circulation patterns in distant places and their relationship with the climate of different regions is called teleconnection. Teleconnection indices are known as factors affecting the climate on a large scale, and their effects on precipitation and temperature have been studied. The quasi-biennial oscillation is one of the main components on a global scale in the mantle layer with an average period of 26 months and is considered one of the main components in short-term climate fluctuations. The North Atlantic Oscillation indicates the westerly winds over the Atlantic Ocean, indicating the pressure difference between the northern latitudes (Iceland region) and the temperate latitudes (Azores region). The Arctic Oscillation is one of the most prominent patterns of sea level pressure changes in high latitudes (20° Northern Hemisphere). Considering the geographical location of Iran and consequently the influence of different weather masses from high latitudes, it is essential to know the factors affecting the climate of this region. The main aim of this study is to determine the role of the simultaneous occurrence of QBO with NAO and AO teleconnections on winter temperature in Iran.
Methodology
In this study, the average monthly temperature data of 100 selected stations in Iran obtained from the Iranian Meteorological Organization (IMO) and Tele-connection indices including QBO, NAO, and AO extracted from the National Oceanic and Atmospheric Organization (NOAA) for a statistical period of 30 years (1988-2019) were investigated. First, all data were sorted by weather seasons (December–January and February). To determine the Pearson correlation coefficient, monthly data as the dependent variable and Tele-connection indices as the independent variable were analyzed in STATISTICA software. The main purpose of this study was to investigate the simultaneous effect of North Atlantic Ocean Oscillations and Atlantic Oscillations with Quasi-Biennial Oscillation, their positive and negative phases were identified. In this way, for North Atlantic Ocean Oscillations and Atlantic Oscillation numbers less than -0.5 negative phase, numbers between 0.5 and -0.5 neutral phase, and more than 0.5 were considered positive phase. Considering that the range of changes in the cycle of quasi-biennial fluctuations is very large, in order to determine the phases of this cycle, after standardizing the existing values, its positive and negative phases were determined. In the next step, the monthly temperature anomalies for the mentioned months were calculated and their spatial distribution was zoned using the Inverse distance weighting (IDW) method.
Results and Discussion
The results of the research indicate that there is an inverse and significant relationship 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. There is a significant inverse relationship between NAO and AO teleconnection with temperature in northern and western parts, especially in February and January, so the highest correlation coefficient up to -0.66 with the Arctic Oscillation index was observed in Tabriz station. The warmest and coldest winters of the statistical period coincided with the simultaneous occurrence of negative and positive phases of NAO and AO (the very warm winter of 2010 and the very cold winter of 2008). The coincidence of the positive phases of NAO and AO with positive phases of QBO causes normal and subnormal temperatures in most regions of the country, especially in the eastern half. Contrary to this situation, the coincidence of the positive phases of NAO and AO with the negative phases of quasi-biennial fluctuations has no coherent and regular effect on temperature changes. The coincidence of the negative phases of NAO, and AO with the negative phases of QBO causes normal and higher-than-normal temperatures in most of the western half of Iran, especially in the northwest so, the warmest winters of the statistical period have happened in this case (December 2009, January and February 2010). The coincidence of the positive phases of North Atlantic Oscillations and Arctic Oscillations with the neutral phases of quasi-biennial oscillations provides the conditions for the occurrence of below-normal temperatures in most parts of Iran, especially in the western parts of Iran. If, contrary to this situation, the coincidence of the negative phases of the North Atlantic oscillations and the Arctic Oscillations with the neutral phases of the quasi-biennial oscillations does not have a tangible effect on the winter temperature anomaly, and only the possibility of a temperature much warmer than normal seems unlikely.
Conclusion
The results showed that the simultaneous occurrence of positive phases of NAO and AO with positive phases of QBO causes normal and lower-than-normal temperatures in half of eastern Iran. The coincidence of the negative phases of NAO and AO with the negative phases of QBO causes higher-than-normal temperatures in most of the western half of Iran. Also, the simultaneous occurrence of neutral phases of QBO with positive phases of NAO and AO causes normal and lower-than-normal temperatures in most regions of Iran except the southern and southeastern parts. If exactly opposite to this situation, the simultaneous occurrence of neutral phases of QBO with negative phases of NAO and AO does not have a noticeable effect on temperature changes, and only the possibility of much hotter than normal temperatures in these conditions seems unlikely.
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