Journal of Geographical Studies of Mountainous Areas

Journal of Geographical Studies of Mountainous Areas

The multiscale relationship between monthly temperature variations in Iraq and the north Atlantic oscillation using MODWT

Document Type : Original Article

Authors
Khadir Mizhar Sajit
Hamid Mirhashemi
Dariush Yarahmadi
Department of Geographical, Faculty of Literature and Humanities, Lorestan University, Khorramabad, Iran.
10.22034/gsma.2025.2068828.1113
Abstract
1. Introduction
The North Atlantic Oscillation (NAO) is one of the most influential large-scale modes of atmospheric variability, exerting significant impacts on the climate systems of various regions including Europe, the Middle East, and parts of Asia (Hurrell, 1995; Trigo, Osborn, & Corte-Real, 2002; Wallace & Gutzler, 1981). This teleconnection pattern is defined by the fluctuations in the difference in sea-level pressure between the Icelandic Low and the Azores High. Depending on whether this pressure gradient is stronger or weaker than normal, the NAO oscillates between two distinct phases—positive and negative-each associated with pronounced and spatially extensive changes in temperature, precipitation, and wind circulation patterns. In its positive phase, the enhanced pressure gradient strengthens the westerlies, directing milder maritime air masses toward northern Europe while diverting storm tracks away from southern regions. Conversely, during its negative phase, a weakened pressure gradient allows cold Arctic air to penetrate further south, while warmer subtropical air may be advected northward. Such large-scale shifts in atmospheric circulation exert substantial control over seasonal to interannual climate variability. Several studies have documented NAO-related temperature and precipitation anomalies in various parts of the world (Cullen, Kaplan, Arkin, & Demenocal, 2002), but relatively few have addressed its influence on the Middle East, particularly over Iraq. This study seeks to fill that gap by examining the temporal relationship between NAO and surface air temperature in Iraq over a 30-year period, applying advanced wavelet-based analysis techniques to capture both time and frequency domain characteristics.
2. Methodology
Three primary datasets were employed: 1. NAO index – monthly values sourced from established climate data repositories. 2. Surface temperature data – monthly maximum temperatures from 16 synoptic meteorological stations distributed across Iraq, covering January 1990 to December 2020. 3. Upper-air data – monthly geopotential height fields and zonal wind speeds at standard pressure levels, used for circulation analysis. To explore the temporal link between NAO and air temperature over Iraq, the Maximum Overlap Discrete Wavelet Transform (MODWT) with the sym3 wavelet filter was applied to both datasets. The decomposition was performed at six resolution levels. Wavelet variance and wavelet coherence were computed to identify shared periodicities, and multiresolution analysis was used to detect dominant temperature patterns across time scales. Additionally, composite maps of the 500 hPa and 250 hPa levels were generated for different NAO phases to examine large-scale circulation features.
3. Results
The correlation between NAO and maximum temperature across the 16 Iraqi stations was consistently negative, ranging from –0.29 in Mosul to –0.35 in Kirkuk. The most pronounced correlations occurred at the 8–16-month time scale (level 3 of the wavelet decomposition), corresponding to annual and sub-annual variability. This scale accounted for over 70% of the total variance in temperature, indicating its climatic dominance. The reconstructed MRA components at this scale exhibited strong, regular oscillations that closely mirrored the NAO signal.
Positive NAO phases were generally associated with lower-than-average maximum temperatures in Iraq, a result of strengthened westerly flow patterns bringing cooler maritime air and reducing the frequency of warm air intrusions from the southwest. In contrast, negative NAO phases were linked to higher temperatures, attributable to a weakened westerly circulation and a greater incidence of warm southwesterly advection. Composite analysis further supported these findings. During negative NAO phases, the 250 hPa jet stream was displaced southward and eastward over Iraq, altering wind intensity and facilitating the interaction of cold westerlies with warm subtropical flows. This configuration enhanced horizontal temperature gradients and contributed to regional warming. At the 500 hPa level, anomalies were consistent with those at 250 hPa, indicating that changes in upper-level circulation propagate downward, influencing near-surface temperature conditions.
4. Discussion
The observed inverse relationship between NAO and temperature in Iraq aligns with prior studies conducted in the broader Middle East region (Hassan & Al-Asadi, 2023; Khidher & Pilesjö, 2015). The dominance of the annual to sub-annual band in explaining temperature variance suggests that NAO’s primary influence operates at multi-seasonal to yearly scales. This has important implications for seasonal forecasting, as NAO phase predictions could be used as indicators for temperature anomalies in Iraq. The results also highlight the role of jet stream dynamics in mediating NAO’s influence. Shifts in jet stream latitude, intensity, and curvature during different NAO phases alter large-scale thermal advection patterns, storm track positions, and vertical motion fields. These mechanisms are consistent with the findings of Parker et al. (2019) and Hall et al. (2014), which emphasize the importance of upper-level circulation anomalies in explaining surface climate variability
5. Conclusion
This study confirms that NAO is a key driver of temperature variability in Iraq, with its strongest impact observed at the annual to sub-annual scale. The inverse relationship between NAO and maximum temperature, combined with the high proportion of variance explained at this frequency band, underscores the potential for incorporating NAO indices into regional climate prediction frameworks. The linkage between NAO phase and jet stream dynamics provides a physical basis for understanding these temperature anomalies.
Acknowledgments
The present research is the result of the scientific activity of the authors.
Keywords
Iraq
temperature
composite maps
jet stream
NAO phases
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Journal of Geographical Studies of Mountainous Areas
Volume 6, Issue 3 - Serial Number 23
Autumn
Summer 2025
Pages 93-110