This study investigates the subtropical anticyclones and summer monsoons of the north hemisphere in the 500 hPa level, effective on Iran in a 38-year period (1975-2012). For this purpose, the data of geopotential heights of 500 hPa at 12 UTC with a spatial resolution of 2 by 2 degrees of the (NCEP/NCAR) were used. Results show that three independent patterns (Azores anticyclone, Saudi anticyclone and North West Africa anticyclone) and four combinatory patterns derived from the independent patterns have controlled the atmosphere of 500 hPa level of Iran. In most cases, the maximum in geopotential heights in above-mentioned anticyclone centers reach to more than 5920 geopotential meters, but often the tongue of these anticyclones control the atmosphere of 500 hPa levels of Iran with the geopotential height of 5880 to 5900 meters. In contrast, at this pressure level, the large-scale monsoon system is very weak and the maximum geopotential height of this system is about 5840 meters. The extent and intensity of the monsoon system has been reduced so that its tongues do not affect the 500 hPa level of Iran at any time. Given that the main factor in the development of large-scale monsoon system is the surface heating (bottom-up formation) and the main factor in the development of subtropical anticyclone is descending of atmospheric dynamics, the main reason for the development of summertime subtropical dynamic anticyclone should be a very strong and unit agent, something other than the summer monsoons.

This study investigates the spatial dynamics of the subtropical anticyclone over Iran during boreal summer, using daily ERA5 reanalysis data (1980–2020) and the Getis-Ord Gi* statistic to identify statistically significant hotspots (p < 0.01) in 500-hPa geopotential height (Z500) anomalies for June–August. Results reveal that the peak statistical hotspot occurs in July: a prominent warm cluster with Z-scores up to +4.1 (99% confidence level) forms over southwestern Iran (27°–32°N, 48°–60°E), reflecting the strongest positive departure from the long-term Z500 climatology. Conversely, a cold cluster with Z-scores reaching −10.2 emerges over the northwest (West Azerbaijan and Kurdistan provinces)—the lowest value recorded over the entire period—indicating pronounced geopotential depression driven by the orographic influence of the Alborz–Zagros ranges and incursions of mid-latitude systems. Histogram analysis of Z-scores confirms a distinctly bimodal distribution in July, with high frequencies in the [+2.5, +4.1] and [−10.2, −2.5] ranges and a pronounced trough near Z ≈ 0, underscoring strong spatial segregation between warm and cold clusters. Notably, the eastern half of Iran (central and eastern regions) consistently lacks significant hotspots across all three months, suggesting the presence of a dynamic transition zone shaped by the competition between subtropical and mid-latitude circulations. In August, although absolute Z500 exceeds 5890 m, the Z-score diminishes (+4.0), indicating that cumulative surface heating elevates the mean geopotential height—but its anomalous intensity relative to climatology weakens compared to July. Collectively, these findings suggest that the dynamical peak of the Iranian subtropical high lags the peak of surface heating by approximately one month.