Iranian surface air temperature periodicities and correlations with the North Atlantic and Indian Ocean sea surface temperature variations

Abstract

Monthly mean surface air temperature data of synoptic meteorological stations in Iran have been analysed in order to detect probable periodicities and corresponding amplitudes. Statistically meaningful annual periodicity and its harmonics, quasi-biennial (2–3 year), interannual (3–5 year) and quasi-decadal (8–12 year) periodicities have been detected. The ensemble average of the spectra shows statistically meaningful harmonic components in 2.2, 2.5, 3.6, 4.0, 4.9, 8.0 and 9.9 years. The amplitude maps of these harmonic components show variations, with higher amplitudes in north and northwest Iran compared to the south and southeast (north of the Persian Gulf and Oman Sea). The cumulative amplitude map of detected periodicities indicates that the Iranian surface air temperatures have an average periodic oscillation of 0.8 °C in a decade, from a minimum of 0.2 °C in the southeast to a maximum of 1.4 °C in the northwest of Iran. The influence of the Indian Ocean Dipole (IOD) and the Atlantic Multidecadal Oscillation (AMO), which are two major sea surface temperature variations in the Indian and Atlantic Oceans, has been analysed by partial correlation analysis. This showed that the Iranian surface air temperature is mostly affected by the Atlantic Ocean sea surface temperature variations rather than those of the Indian Ocean. The mean absolute values of the partial correlation for the IOD and the AMO are 30.8% and 49.6% respectively. In corresponding partial correlation maps, a regular and partitionable behaviour was not observed. However, a maximum influence of the AMO and a minimum influence of the IOD occur in the northwest of Iran.