Average empirical estimations of the surface air layer height in Moscow have been received by the data of long-term acoustic remote sensing of the atmosphere using MODOS Doppler sodar of METEK (Germany) production. Based on the assumption that the average conditions are close to neutral stratification, this height, as the top of the quasi-linear section of the average long-term wind velocity profile in semi-logarithmic coordinates, is 40–60 m. The wind rotation height, i. e. the height of intersection of day and night wind profiles is on average 95 meters per year. The roughness length in conditions of loose but high urban development in vicinity of Moscow State University in Moscow is 5 m. According to the criterion of the constant wind direction in the surface air layer, its height appears in the average monthly wind direction profiles over the “dead zone” of the sodar (40 m) in approximately one case out of three and usually amounts to 60 m, less often 80 or 100 m. In the rest cases, it is apparently masked by “dead zone”. The average height of the surface layer according to this approach is probably a little less than 50 m, which is close to the estimate obtained from the logarithmic distribution of wind velocity with height in this layer. The daily course of the surface air layer height is noted by the largest values in the afternoon (80–100 m in summer under conditions of prevailing unstable stratification and 60–80 m in winter) and the smallest ones (less than 40 m) in the late evening and at night in summer and from evening to noon in winter.

The influence of the COronaVIrus Disease 2019 (COVID-19) pandemic lockdown (the period of strict quarantine measures) in the spring of 2020 on the ‘Surface Urban Heat Island’ (SUHI) geographical phenomenon in Moscow has been studied. For this purpose, we used the measurements of the surface temperature TS made by Moderate Resolution Imaging Spectroradiometer (MODIS) radiometer installed on Terra and Aqua satellites. As a result, TS during the 2020 lockdown, both in the city and surrounding rural zone, was found lower than at the same calendar time in the previous 20 years due to the relatively cold spring. The SUHI intensity as the difference between TS inside Moscow and the surrounding rural zone around it during the lockdown was also lower than usual (on average in the previous 20 years), but this decrease is relatively small and nonsignificant. The Normalized Difference Vegetation Index (NDVI) in Moscow and Moscow region during the lockdown was close to its usual values, but the leaf area index (LAI) was significantly lower than its average values in the previous 20 years. Thus, the weakening of the SUHI during the lockdown in 2020 was caused mostly by lower heat loss due to transpiration in the rural zone. This was associated with the slowdown in vegetation development as a result of the cold spring. Besides, an additional possible reason was the reduction of human activity due to the collapse of many anthropogenic heat sources in the city. According to long-term MODIS data, the SUHI intensity in Moscow and the surface temperature in Moscow region, as well as the NDVI and LAI values, do not demonstrate statistically significant long-term trends in the spring season over the past 21 years, despite climate changes. In spring, during faster snow melting in cities, when it still persists in the rural zone, the SUHI intensity can be record high (up to 8 ºC).

The urban heat island (UHI) intensity in Moscow and the influence of various meteorological parameters are discussed using weather station data. The maximal and average in-space UHI intensities, i.e., a comparison of air temperature T either in the city centre or in the whole urban area together with rural zone have averaged 1.9 and 0.9 °C, respectively, in recent years. The UHI in Moscow has stabilized over the past decade and is not growing. Under conditions of a strong anticyclone, the maximal UHI intensity in space and time reaches 11–12 °C. Low cloudiness and amplitudes of diurnal air temperature, as well as surface temperature, demonstrate the closest relationship with the UHI intensity among other parameters with the correlation coefficient of up to −0.67 for low cloudiness and the maximal UHI intensity. The effect of wind speed, total cloudiness and relative humidity on the UHI is slightly weaker, but still significant. The relationships of all meteorological parameters with the maximal UHI intensity are closer than those with the average one. The multiple correlation coefficient between the maximal UHI intensity and both parameters (low cloudiness and average daily wind speed) is 0.76–0.82. The UHI intensity function of air temperature has a minimum in the range from −4 to 0 °C; its growth both at lower and higher T is due to the influence of anticyclonic weather. The UHI intensity function of wind speed decreases with wind strength. The threshold value at which this function asymptotically approaches its lower limit is 10 m/s in the 40–200 m air layer. The UHI intensity functions of both total and low cloudiness decrease with increasing cloudiness and the differences between them are significant if the cloud cover is more than 50%.

An Erratum to this paper has been published: https://doi.org/10.1134/S1028334X24010021

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).

Empirical relations between T and surface concentrations of CO 2 and five minor air gases have been studied on a base of hourly data during 12 years. In wide range -6…+15 °C significant changes of minor gases are absent. Real tendencies are increase of O 3 and, vice versa, fall of NO and NO 2 with increasing T from +15.+17 to +38 °C. Both effects are a consequence of unstable stratification that enhances vertical mixing. In cool weather -7.-18 °C O 3 falls whereas nitrogen oxides grow with decreasing T due to frequent inversions and slowing down the NO oxidation rate. At an even lower temperature up to -30 °C NO and NO 2 , vice versa, decrease with decreasing T – probably, due to strong cold advection of clean Arctic air. Unlike minor gases, CO 2 decreases with increasing T up to 25 °C due to photosynthesis intensification from winter to summer. Seeming growth of CO at T>27 °C is fully explained by smoky haze during heat waves in 2010 and 2002. The CO 2 growth in hot weather is also created by heat stress of trees. Thus, except only oxidation rate, any influence of T is indirect as a result of stratification, photosynthesis, smoky haze, advection, etc.

Better understanding of current climate changes needs a full knowledge about regional specific of thermal conditions at the end of Little Ice Age. So, the earliest available meteorological data are important. First regular daily qualitative meteorological observations were taken in Moscow city from 1657 to 1675. Episodic short series of instrumental measurements were made there for the first time in 1731; regular daily measurements started in 1779 when one of Mannheim network stations was founded in Moscow.All known old data series of the air temperature T measurements in Moscow since 1779 were collected and analyzed. Mannheim station existed there from 1779 to 1797 but average values of T are available from issues of Ephemerides Societatis Meteorologicae Palatinae only for the period 1779–1792. High accuracy of measurements at Mannheim network is confirmed by high correlation co-efficient between monthly-averaged T values in Moscow and at closest stations (Warsaw and St. Petersburg): up to 0.82-0.84 on separate months.Different methodical questions (unknown location of the station, unknown conditions of thermometer installation, its height and shading, an accuracy of its calibration, etc.) were studied. As a result it was found that the most probable error due to thermometer installation close to the northern building wall is ±0.1÷0.2 ºС; the error of daily-averaged T due to unknown height of measurements is ±0.1 ºС; the calibration accuracy in Mannheim was about ±0.1 ºС. Thus, a total error of T on average of a day in the 18th century was not higher than ±0.3÷0.4 ºС. Probably it was even less because separate components of the error may be multidirectional. For the first time mean-annual T in Moscow was received for 1783, and the most probable values were estimated for 1784 and 1785 using the data of the closest Mannheim station (Saint-Petersburg) for separate months with data gaps. The end of Little Ice Age manifeted at extremely low minimal values of T: up to –31 ˚R (–38.8 ˚С) in December 17th, 1788. However, thermal conditions from June to September changed only a bit since the 18th century till nowadays (differences are not statistically significant with the 0.95 confidence probability).Later measurements in Moscow were renewed since 1808 and broken again in August of 1812 due to Napoleon’s invasion and terrible Moscow fire. For the first time unknown data series of everyday measurements which were made by Ivan Lange in 1816–1817 were found and studied. As is known the famous 1816 ‘Year Without a Summer’ was noted almost all over the World by extremely cold summer as probable result of Mount Tambora eruption in 1815. Nevertheless, it was found that summer of 1816 in Moscow was comparatively cool but not extremely cold: monthly-averaged T there was 15.7, 17.3 and 14.5 ˚С in June, July and August, respectively, and 15.8 ˚С on average of the summer. Thus, 1816 occupies only 27th place among the coldest summers in the city during 216 years.Author is thankful to the memory of his late PhD student Ekaterina L. Vasilenko.

Thermal stratification of the lower 800-m air layer over Moscow, including distribution functions of inversion heights and duration, has been studied in detail based on ECHO-1 sodar data. The distribution of the bottom height of elevated inversions, unlike the thickness of surface inversions, is bimodal, which reflects the diversity of their origin. The lifetime of morning elevated inversions (remains of night surface inversions) is, on average, ~ 3 h, and, in some cases, over 6 h; their bottom heights usually do not exceed 350 m. Superlong elevated subsidence inversions are more often observed in Moscow from November to February and may be detected on sodar records continuously up to 120 h. The influence of retentive inversion layers on the surface content of trace gases in the atmosphere over Moscow has been studied based on the 2002–2016 data. The final destruction of morning elevated inversions results in a rapid acceleration of increase in the content of O 3 and a start of decrease in the content of NO 2 in the atmospheric surface layer. Both effects reflect the intensification of a vertical turbulent exchange. Such a rapid increase in the rate of growth of ozone after the inversion destruction is not associated with its photochemical generation and is apparently the result of dynamic processes (increased downward ozone fluxes from upper air layers). In contrast, under the conditions of long-lived elevated subsidence inversions in fall and winter, no statistically significant variations in the surface contents of five trace gases (O 3 , NO, NO 2 , CO, and SO 2 ) have been found.

The urban heat island (UHI) in Moscow was for the first time studied not only at the ground air level, but also at different heights, depths and on the surface using stationary, radiosonde and satellite data. Long-term dynamics of the UHI intensity in the ground air layer has been estimated since the end of the 19th century both as traditional 'maximal intensity' (the difference between the city centre and rural zone), and as 'average intensity' (the difference between all urban and all rural stations). In recent years they have been 2.0 and 1.0 degrees C, respectively. The quasi-stabilization of both parameters in the second half of the 20th century was probably the result of extensive city growth at that time; the new increase in the UHI intensity seems to be connected with the densification of urban development and heat sources in the last 20 years. The mean daily vertical extension of the UHI in the atmosphere is approximately 300 m. In the upper soil layer (up to 160 cm deep) the maximal UHI intensity was about 1.6-1.7 degrees C half a century ago. The average UHI intensity at the field of the surface temperature in recent years is 2.7 degrees C.

The dependence of energy consumption on air temperature for every day of the period from 1990 to 2015 is for the first time studied for mid-latitudes using the long-term observational data of the Moscow State University Meteorological Observatory. It is demonstrated that this dependence is generally descending in the Moscow region: energy consumption decreases as air temperature rises. At the same time, the energy consumption increase slows down due to energy saving in case of severe frosts, whereas the opposite trend is manifested in case of abnormally hot weather, that is, the energy consumption increase along with the air temperature rise due to additional consumption for air conditioning. The optimum temperature for energy saving is 18°C. The relationship between energy consumption and air humidity characteristics is analyzed. There is almost no link with relative humidity, while in the link with the partial pressure of water vapor, the dependence of the latter on air temperature is reflected indirectly.

Modern climatic changes for 1991–2013 in the lower 4-km layer of the atmosphere in the Moscow region are discussed based on long-term measurements using radiosondes in Dolgoprudny near Moscow and sensors installed on a high mast in Obninsk and on a television tower in Ostankino in Moscow. It is shown that at the end of the 20th century and the beginning of the 21st century the mean-annual air temperature at all heights from 2 to 4000 m increased by an average of 0.1°C per year. In recent years, the warming has slowed. Over the last two decades, long-term changes were multidirectional, depending on the season: warming in May–December, cooling in January–February, and no statistically significant changes in March and April. The probable reason for the temperature decrease in the middle of the cold period is changes in the large-scale atmospheric circulation during recent years (the negative phase of the North Atlantic Oscillation in early 2010s). In recent years, the Moscow region climate continentality has increased because of warming in summer and cooling in winter, despite the secular decreasing trend, which was noted before. Mean daily and annual warming rates in Dolgoprudny were higher than in Obninsk. The probable reason is the northward construction expansion and the strengthening of the Moscow heat island. The highest annual temperature amplitude is recorded at heights of 200–300 m.

The long-term dynamics of both urban heat island (UHI) and urban dry island (UDI) intensities over the city of Moscow, Russia, has been analyzed for the period from the end of the nineteenth century until recent years using data of the ground meteorological network. Besides traditional maximum heat/dry island intensity, an additional parameter-station-averaged intensity as a mean difference between the data of all urban and rural stations-has been used. The traditional maximum (mean annual) UHI intensity in Moscow was nearly 1.0 degrees C at the end of the nineteenth century, 1.2 degrees C one century ago, 1.5 degrees-1.6 degrees C both in the middle and at the end of the twentieth century, and 2.0 degrees C in recent years. The station-averaged UHI intensity was equal to 0.7 degrees-0.8 degrees C in the second half of the twentieth century and increased up to 1.0 degrees C in recent years. It is probable that stabilization of both parameters from the 1950s to the 1990s was connected with the extensive city growth at that time (mass resettlement of inhabitants from the overpopulated city center to the new urban periphery since the 1960s). The new increase of UHI intensities is the result of the new intensive city growth. The relative humidity in Moscow significantly decreased during the last 146 years (mostly because of warming), unlike water vapor pressure. The UDI is closely connected with the UHI; the absolute value (modulus) of its intensity is increasing in time from -4% at the end of the nineteenth century to -9% now. During the last two decades, the UDI as well as the UHI became much stronger than before.

The dynamics of the air temperature in the lower 4-km layer have been studied during the heat wave in the summer of 2010 by the radio sounding data from Dolgoprudny and ground-based meteorological measurements at Moscow State University. The results have been compared with the aeroclimatic data for the previous 19 years. According to these data, the long-term average estimates of vertical thermal gradients and thickness and intensity of nocturnal surface inversions (200–300 m and 2.0°С, respectively) are presented for summer months in the Moscow region. A record high air temperature for the period from at least 1991 has been shown in the air layer up to 2 km above Moscow in the summer of 2010. Among others, the 30°С value has been detected for the first time in the air layer from 400 to 800 m. During the heat wave in 2010, as a result of clearly pronounced anticyclone conditions, the thickness and intensity of nocturnal surface inversions were higher than usual (up to 700 m and 12°С, respectively). The mean temperature profiles have been studied for different types of air masses. It is shown that the tropical air mass predominated over the Moscow region in the summer of 2010 during more than half of the period.

The vertical extension of the urban "heat island" (UHI) has been studied on the basis of long-term data of contact air temperature measurements at three places for the example of Moscow. The existence of steady thermal anomaly related to the city in the form of a UHI in the surface layer at any time of the day and also the existence of a cold layer over it at heights higher than 100 m at night were confirmed. The mean daily altitudinal extension of this anomaly is approximately 300 m.

Nonperiodic vertical and temporal variations in wind direction in the lower 500-meter air layer related to synoptic conditions are studied using the long-term data of acoustic remote sensing by the MODOS sodar at Moscow State University. Average values of wind shear to the right (clockwise) with time as a result of the passage of atmospheric fronts are 55° for cold fronts, 40° for warm fronts, and 45° for occlusion fronts. In some cases the clockwise wind shear may reach 180° per 30 minutes and 720° per several hours. The wind shear to the left with time is usually observed if the northern periphery of anticyclones or the ridge axis pass by. It takes more time than the clockwise wind shear does. Dramatic variations in wind direction with height including synchronous opposite air flows at different heights are observed in the zones of fronts, axes of ridges and troughs (if they are inclined), and cols. The vertical wind shear may reach 250° in the lower 300-meter air layer. Thunderstorms in Moscow are usually accompanied by the average wind speed increase by 1 m/s during 30-40 minutes after their beginning.

The results of the 2002–2012 continuous once-a-minute measurements of the composition of the surface air over Moscow, which were taken at the joint ecological station of the Obukhov Institute of Atmospheric Physics, Russian Academy of Sciences, and the Geographic Faculty of Moscow State University, are discussed. It is shown that the annual increase (on the order of 1%) in the content of surface ozone is stable and the decrease in the content of nitric oxide is statistically significant, while the content of nitric dioxide remains almost unchanged. Reliable regularities in both diurnal and annual variations in the contents of the five trace gases O3, NO, NO2, CO, and SO2 have been studied in detail. Statistical relations of the content of sulfur dioxide with the amount of reserve fuel (black oil) used in city heating (this relation is the strongest one), wind velocity in an atmospheric layer up to a height of 200 m, and air temperature have been analyzed. The influence that wind velocity has on the surface contents of trace gases and carbon dioxide has been studied for the first time on the basis of long-term ‘MODOS’ sodar data. It is shown that, with an increase in wind velocity, the contents of nitric and carbon oxides generally decrease, the content of ozone increases, and the content of sulfur dioxide decreases starting from an intermediate value of 1–2 m/s due to the prevalence of high sources of this gas. An additional maximum found in the content of carbon dioxide at high wind velocities may be associated with the long-range transport of CO2.

Long-term measurements of the soil temperature on different depths in Moscow and its suburbs have been collected since the end of the XIX century. At Moscow University this parameter has been measured simultaneously at two locations since 1954: one below the usual natural cover and one below a special naked area. Following the air warming, in the last 116 years the soil temperature increased in Moscow by 1.8-1.9 degrees C (at 160 cm depth). During the last half a century the temperature increased much faster at the University below the naked area (+ 0.04 degrees C/year) than below the natural cover (meaning the snow cover in winter and grass and sod cover during other seasons): + 0.02 degrees C/year.The spatial distribution of the soil temperature in Moscow region has been discussed using the simultaneous data of ground meteorological network. Mean annual values of the surface temperature (0 cm) and soil temperature at eight depths from 20 to 320 cm have been analyzed. Mean annual soil temperature in the city center is higher by up to 1.0-1.2 degrees C than at the city periphery and by up to 1.6-1.7 degrees C than in Moscow region rural zone (at the depths of 120 and 160 cm). At smaller depths these differences are a bit less but still statistically significant. Thus, an underground urban heat island exists at any depth. The evident cause of this phenomenon is human activity which has resulted in a lot of factors. A special index has been suggested for estimation of the average intensity of the underground urban heat island. According this index, the mean difference of the soil temperatures can amount to + 0.6...+ 0.8 degrees C if we compare the city with the rural zone and from + 0.4 to + 0.6 degrees C if we compare only urban periphery (without city center) with the rural zone. Another discovery was that the underground heat island evidently extends below the depth of 320 cm. The annual dynamic of the difference between urban and rural soil temperatures reaches its maximum in winter (+ 0.9...+ 1.2 degrees C depending on the depth) due to strong urban heating and drops to its minimum in summer (-0.5...+ 0.4 degrees C at different depths). (C) 2015 Elsevier B. V. All rights reserved.