About the Annual Course of Moscow Heat Island and the Impact on It of the Quarantine Measures to Prevent the COVID-19 Pandemic in 2020

Seasonal differences in the Moscow urban heat-island intensity (UHII) have been studied in detail based on data obtained in 2018–2020 by the meteorological network of stations located in Moscow and Moscow region. It is shown that the annual cycle of this phenomenon is slightly pronounced. In most cases, the UHI is manifested stronger in summer and weaker in winter; however, in some months, the situation may be reverse. The question of the statistical significance of seasonal differences remains open. The closest statistical relationship was revealed between the UHI and lower clouds during the night hours, so that its highest intensity is observed in the least cloudy seasons (usually in summer). The UHII distribution functions are close to the normal law in summer and spring, and, in winter and fall, they are characterized by a noticeable positive asymmetry, because their values decrease and the mode approaches the lower physical limit. The period of strict quarantine restrictions during the COVID-19 pandemic in the spring and early summer of 2020 led to a rapid and statistically significant decrease in the Moscow UHII, probably due to both natural factors (increased cloudiness) and human activities (rapidly decreased anthropogenic heat fluxes and a weakened urban industrial haze creating an additional counterradiation).