Circannual Variations in Partial Oxygen Density Depending on Solar Activity Level and Climatic Zone

BACKGROUND: Some medical weather classifications identify reduced partial oxygen density in the air as a key parameter affecting human well-being. This parameter can be modulated not only by meteorological factors but also by the helio-geophysical environment. It should be noted that synoptic combinations with elevated oxygen content are not considered among the weather types, although several studies have shown that hyperoxia can have adverse effects on health. AIM: To assess the influence of circannual variations in solar activity on the changes of atmospheric partial oxygen density in subarctic and subtropical regions. METHODS: Calculations of partial oxygen density were based on daily average values of air temperature, atmospheric pressure, and relative humidity of the ambient air. Sunspot number data were obtained from publicly available sources provided by the Royal Observatory of Belgium. Data from 2007 (a year of low solar activity in the 23rd solar cycle) and 2001 (a year of high solar activity) were compared. Wavelet analysis was used for mathematical processing. RESULTS: The mesor, amplitude, coefficient of variation, and rhythm spectrum of sunspot numbers differed significantly between the years of low (2007) and high (2001) solar activity. In 2001, the dominant rhythm was close to a semiannual cycle. In 2007, the rhythm of sunspot numbers was 27.27 days. In Khanty-Mansiysk, the seasonal range of partial oxygen density was ~147 g/m3 in 2001 and ~70 g/m3 in 2007. The annual cycle was characterized by prevailing hyperoxia, with upper values reaching 395 g/m3 (normal: 285 g/m3). In Polokwane, the winter–summer variation in partial oxygen density in 2001 was approximately 24 g/m3 (virtually the same as in 2007, 30 g/m3), which falls into the category of unfavorable hypoxic weather. In the year of high solar activity (2001), a polyrhythmic pattern of both stable and transient rhythms of partial oxygen density was observed in both subarctic and subtropical regions. CONCLUSION: In the subarctic region, wintertime values of partial oxygen density were high in the year of low solar activity and very high in the year of high activity. Seasonal fluctuations between hyperoxia and hypoxia extended far beyond the range of favorable weather types. Fluctuations in partial oxygen density characteristic of the subtropical climate consistently remained within hypoxic ranges, regardless of solar activity levels. During the year of elevated solar activity, both examined regions exhibited polyrhythmic patterns of partial oxygen density, indicative of desynchronosis. It is recommended that medical weather classifications be expanded to include “hyperoxic day” and “hyperoxic weather type.”. © 2025 Elsevier B.V., All rights reserved.