Document Type : Full length article
Department of Physical Geography, Faculty of Social Sciences, University of Mohagegh Ardabili,
Department of Physical Geography, University of Mohaghegh Ardabili
I. R. of Iran Meteorological Organization, East Azerbaijan province central Bureau of meteorology
Analysis of Simultaneous occurrence of North Atlantic and North fluctuation phases with Enso phases and its effect on winter temperature in Iran
Among climatic elements, temperature measurement is very important. Due to Iran's location in the subtropical region, severe temperature changes are its inherent features, so it is necessary to predict and monitor air temperature. Temperature fluctuations on a global scale are somewhat affected by Tele-connections. Tele-connections patterns are intermittent anomalies that affect atmospheric patterns on a planetary scale and have a long return period. Southern Oscillation is one of the main indicators of global climate variability on an annual time scale and affects the Iranian climate by changing pressure patterns. The North Atlantic Oscillation (NAO) is the most obvious pattern of Tele-connections in the Northern Hemisphere, indicating the pressure difference between the northern latitudes (Iceland region) and the temperate latitudes (Azores region). Arctic Oscillation is the first active Tele-connection pattern in the subtropical region in mid-winter. The Earth's climate is not constant and environmental changes can be the result of changing climate systems. The behavior of a climatic pattern in each region is associated with Tele-connection patterns. The main purpose of this study was to determine the role of simultaneous occurrence between NAO and AO Tele-connections with SOI on winter temperature in Iran.
Methodology (Materials and methods or Data and methods)
In this study, the average monthly temperature data of 100 selected stations in Iran from the Islamic Republic of Iran Meteorological Organization (IRIMO) and Tele-connection indices including MEI, NAO and AO from the National-Oceanic and Atmospheric Administration (NOAA) for the thirty-year statistical period (2019-1988) were received and used as baseline data. First, all data were sorted by climatic seasons (December-January and February). Monthly normalized data were entered into STATISTICA software as dependent variable and Tele-connection data were entered as independent variable to determine Pearson correlation coefficients. Since the main purpose of this study was to investigate the simultaneous effect of North Atlantic Oscillation and Arctic Oscillation with Enso Tele-connection, the positive and negative phases of the mentioned Tele-connection were identified. Thus, numbers smaller than -0.5 negative phase, between -0.5 to 0.5 neutral phase and greater than 0.5 positive phase were considered. In the next step, the monthly temperature anomalies for the mentioned months were calculated and the distribution of its anomalous changes in GIS software was zoned by Inverse distance weighting (IDW) method. According to the results of correlation coefficients and the results observed in temperature anomaly maps, diagrams of the trend of changes in Tele-connection indices in comparison with the anomalies of changes in the average temperature of the studied stations were drawn. The results indicated that the simultaneous occurrence of the La-Nina phenomenon with the positive phases of the northern hemispheres provides the conditions for the intensification and development of cold in Iran, especially during January and February, and it is almost unlikely to expect a warm winter in this case. Comparing the trend of changes in Iran's average winter temperature with the trend of changes in North Atlantic Oscillation, Arctic Oscillation and Enso multivariate index in December, January and February showed that in recent years, the average temperature change in December remained constant but in January and February has been increasing for a variety of reasons, including climate change, climate change patterns, and teleportation. The gradual decrease of the North Atlantic oscillation indices, especially the Arctic oscillation, during January and February coincided with the increase of temperature, so that the average temperature of Iran was normal and more than normal during the simultaneous occurrence of the negative phases of the North Atlantic oscillation indices.
Results and Discussion
The results of this study showed that there is a significant inverse relationship between NAO and AO Tele-connections with temperature in the northern and western parts of Iran, especially in February and January. The highest correlation between temperature and AO index was observed in Tabriz station (up to -0.66) but no significant relationship was observed between MEI index and temperature in most regions of Iran (except the southern strip). The important result of this study is to reveal the role of separate phases of northern Tele-connections on winter temperature changes in Iran. The results showed that the positive phases of AO and NAO reduce the temperature of the northern and western parts of Iran and during the occurrence of severe positive phases of AO and NAO, the temperature anomalies of most parts of Iran change below normal. The results also showed that in the under study period, warm winters are associated with negative phases of northern indices. Also, the simultaneous occurrence of La-Nina and El-Nino phenomena with positive and negative phases of NAO and AO causes temperatures to occur below normal or above normal in most central and southern regions of Iran. Simultaneous occurrence of El-Nino and La-Nina phenomena with neutral phases of North Atlantic oscillation and Arctic oscillation moderates the temperature of Iran and reduces the possibility of widespread and severe positive and negative anomalies. Occurrence of El-Nino phenomenon with neutral phases of NAO and AO has caused the occurrence of normal and higher than normal temperatures in the eastern and southeastern half of Iran. The results also showed that the occurrence of La-Nina phenomenon with neutral phases of NAO and AO causes normal and higher than normal temperatures in the western half and especially in the northwestern regions.
The results showed that El-Nino and La-Nina phenomena do not have a direct and definite effect on winter temperatures in Iran. Simultaneous occurrence of La-Nina phenomenon with positive phases of North Atlantic oscillation and Arctic oscillation provides the conditions for a sharp decrease in winter temperature and causes normal and below-normal temperatures in most parts of Iran, while the occurrence of El-Nino phenomenon with negative phases of NAO and AO causes the occurrence of normal and higher than normal temperatures in the central and southern regions of Iran. Contrary to these conditions, the simultaneous occurrence of El-Nino and La-Nina phenomena with the neutral phases of NAO and AO causes a normal temperature in winter in Iran, and the possibility of a lower than normal temperature in this case is very unlikely.
Keywords: Enso, Iran, Tele-connection, North Atlantic oscillation, Winter Temperature.