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The wind rose over Moscow in the air layer from 40 to 500 m for the period from November 11, 2004 to December 31, 2014. The values of occurrence frequency in separate segments are presented in the form of color scale.
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Discussed are the data on wind direction in the air layer from 40 to 500 m over Moscow for the period of 2004–2014. The data was obtained with the MODOS sodar installed in Lomonosov Moscow State University. It is demonstrated that this wind direction has a stable southwestern mode in ten years on average. The western component of this mode strength...
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Context 1
... i.e., from 300 m to several kilometers. An advantage of these methods is that measurements can be carried out in the continuous automatic mode. Sodars have a relatively small altitude range (to 500–1000 m on average) as compared with other remote-sensing instruments but are notable for very high spatial resolution (10–20 m) [4, 8]. Besides, sodar data on the wind direction are more reliable as compared with data from the ground-based network because usually there are no vertical obstacles in the layer above the zone of silence of sodars (20–40 m, as a rule). 2. LONG-TERM DATA ON WIND DIRECTION OBTAINED AT MSU The acoustic sounding of the atmosphere in the Meteorological Observatory of the Department of Geography (The Faculty of Meteorology and Climatology) of Lomonosov Moscow State University (MSU) started in 1988. There it became round-the-clock and long-term for the first time in the former USSR. The METEK MODOS Doppler sodar (Germany) has been used since 2004. This is the first serial sodar in Russia. Its working frequency is 2 kHz, the altitude range is from 40 to 500 m, and the spatial resolution is 20 m. The data on wind profiles are available every 10 minutes on average. The long-term data on wind speed from this sodar were published in [7, 18, 19]. The objective of the present paper is to generalize separately the results of wind direction measurements in the air layer up to 500 m over Moscow which were collected during 10 years. On October 12–November 11, 2008 the MODOS sodar operated in Obninsk at the distance of 200 m from the Taifun Scientific Industrial Association meteorological tower [16]. The obtained data on wind speed at that period were analyzed by the author in [7]. In the present paper let us consider data on wind direction. Figure 1 presents the comparison of the results of measurements provided by the sodar for every 10 minutes on average within the limits of the pulse scattering volume from 290 to 310 m and by the M-47 anemometer installed at the tower at the height of 301 m. It is clear that the obtained readings form two dense areas concentrated close to the “one-to-one” fit line, and the gap between them is from 30 ° to 110 ° because the wind of eastern and northeastern directions was not observed during the experiment. The coefficient of the linear correlation of the data was equal to 0.98 and the coefficient in the equation of linear regression was equal to 1.00 with the accuracy to one hunderdth. The statistical relation is close to linear that is corroborated by the parabolic trend almost coinciding with the linear one (the parabolic correlation coefficient is also equal to 0.98). Thus, the experiment proved the high degree of reliability of the sodar data on wind direction. The MODOS sodar data on wind direction over Moscow for the period from November 2004 to March 2008 were presented for the first time in [18]. Later the data till August 2008 [19], February 2009 [8], and March 2009 [14] were presented. The wind direction under special conditions of abnormal heat was considered in [6]. The methodology of the analysis of these data is simpler than that of the analysis of the wind speed data because the errors typical of wind speed measurements (systematic bias in the estimates towards one or another direction) are absent in wind direction measurements [7]. It is obvious from physical considerations that at the high altitude the sodar registers the strong wind more often; at the same time, it registers any strong wind equally often regardless of its direction. The pointing of the MODOS sodar antenna system in the cardinal directions was carried out at the beginning of its operation in November 2014 using the usual compass. Therefore, all data on the wind direction are presented below not taking into account the magnetic declination, with the zero reading in the direction of the North Magnetic Pole. The position of the antenna system has been kept constant since then; therefore, the 10-year wind direction data series is homogeneous with the accuracy to ± 1 ° (the error in the installation of the antenna platform in the former position after the sodar was returned from Obninsk where the experiment was conducted, in 2008). Figure 2 presents the summary wind rose for the whole ten-year (2004–2014) period of measurements and for the whole sounding range from 40 to 500 m. Its computation using the MODOS software enables obtaining the uniform graphic data both on the wind direction and wind speed. The distribution of wind speed values for different wind directions is presented in the form of concentric circles with different radia. The occurrence frequency in the separate sectors can be judged by the color scale. The whole range of occurrence frequency (from the rarest to the most frequent values) corresponds to the gradual change of light purple into dark blue and black; the white color means the absence of data with the prescribed wind speed and wind direction. As clear from Fig. 2, the southwestern (225 ° to 235 ° ) moderate (with the speed from 5 to 10 m/s) wind is most frequently (black color) observed in the lower half-kilometer layer over Moscow. Taking into account the eastern (positive) magnetic declination for Moscow (+10 ° 1 6 ¢ ), the more accurate boundaries of this southwestern mode are from 235 ° to 245 ° . This is the principal mode in the wind direction distribution and it prevails absolutely within the whole wind speed range including the highest values from 20 to 25 m/s (the cases of record high wind speed equal to 30 m/s and more that are described in [7], are single and not manifested in the total sample with the prescribed lower limit of the scale). The rarest direction is northeastern for the light wind (<5 m/s) and northern for the moderate wind. The cases of strong wind for these directions were observed very rarely. The qualitatively similar annual wind rose with the strongly pronounced prevalence of southwestern direction was registered in all years of sounding. Thus, the principal southwestern mode is unconditionally stable in time. The differences in the conditions in separate years boil down to the additional features of distributions, namely, to the existence of a wider or narrower principal mode, secondary modes, and higher or lower occurrence frequency of values in different sectors. For example, in 2010, when the winter was very cold and the summer was abnormally hot, the average annual occurrence frequency of southeastern and eastern wind direction turned out to be much higher than in other years. The table presents the estimates of occurrence frequency of different wind directions including the intermediate ones for different seasons and for the year as a whole (~1220000 separate readings for every 10 minutes on average). The data only for the first four years (from November 11, 2004 to August 31, 2008) are generalized here; however, taking into account the temporal stability of occurrence frequency estimates, these data are also representative for the whole period of sounding. Such table with the values only for the principal directions and only for the year as a whole was published in [18] in its preliminary form and in [19] in its final form. Since the MSU area is the edge of Teplyi Stan Upland and is open and relatively flat, the presented estimates of occurrence frequency for separate wind directions are quite reliable. As clear from the table data, the distribution of occurrence frequency of wind directions corroborates the well-known climatologic features of large-scale circulation in the center of the European part of Russia. The southwestern wind direction is really most often observed here [12]. According to our data, the comparatively high average annual occurrence frequency (more than 6.25% that would correspond to the uniform distribution for all 16 wind directions in case of the symmetric wind rose) is typical of the wide sector from the southern to west-northwestern directions. The winds of west-southwestern and southwestern directions are observed most often: their average occurrence frequency exceeds even 12.5%, i.e., the doubled value for the case of the uniform distribution. It should be noted that the occurrence frequency of these wind directions within the annual course is maximum (about 15%) in autumn and winter that is associated with the fact that at that period Moscow is frequently (since late autumn) located on the southeastern periphery of the Icelandic low. The similarity of autumn and winter conditions should be noted, the estimates of occurrence frequency of different wind directions in these seasons almost coincide. On the contrary, the southern and southwestern wind is registered less frequently in summer and spring and the western direction becomes more frequent. As to eastern and northern winds, in spring and in summer their occurrence frequency is much higher than in winter and autumn. The eastern and southeastern wind directions are most often observed in spring whereas the northern direction, in summer. This is an effect of the meridional flows going along the periphery of stationary anticyclones which are formed rather often in the European part of Russia in summer under conditions of westerlies weakening. As known, at the middle latitudes in spring and summer the intensity of westerlies is lower as a whole than during the cold season due to decrease in the interlatitudinal temperature gradient. As applied to the spring months, this conclusion is also proved by increase in the occurrence frequency of the eastern wind. We can only admire B.P. Alisov for the accuracy of his formulation that absolutely agrees with our data: “...the Atlantic entries weaken in spring, ...the wind direction becomes unstable, and the eastern constituent arises” [1]. Nevertheless, as clear from the table, the eastern and northern winds over Moscow are the rarest during the year on average. The north-northeast direction has ...
Context 2
... wind direction) with high resolution (100 m) within the lower one-kilometer layer. The direct measurements of wind direction above 30 km are rarely feasible by means of the launch of weather rockets (with consequent observations of the horizontal displacement of the cloud of chaffs, falling spheres, or head of the rocket at the descending branch of its parachute flight) or using the data of observations of the movement of noctilucent clouds. Instruments for the remote sensing, namely, Doppler radiosondes, Doppler sodars (acoustic radars) or Doppler lidars hold a special place in the measurements. In the majority of cases the altitude range of their measurements holds an intermediate position between the data of high-altitude constructions and radiosondes, i.e., from 300 m to several kilometers. An advantage of these methods is that measurements can be carried out in the continuous automatic mode. Sodars have a relatively small altitude range (to 500–1000 m on average) as compared with other remote-sensing instruments but are notable for very high spatial resolution (10–20 m) [4, 8]. Besides, sodar data on the wind direction are more reliable as compared with data from the ground-based network because usually there are no vertical obstacles in the layer above the zone of silence of sodars (20–40 m, as a rule). 2. LONG-TERM DATA ON WIND DIRECTION OBTAINED AT MSU The acoustic sounding of the atmosphere in the Meteorological Observatory of the Department of Geography (The Faculty of Meteorology and Climatology) of Lomonosov Moscow State University (MSU) started in 1988. There it became round-the-clock and long-term for the first time in the former USSR. The METEK MODOS Doppler sodar (Germany) has been used since 2004. This is the first serial sodar in Russia. Its working frequency is 2 kHz, the altitude range is from 40 to 500 m, and the spatial resolution is 20 m. The data on wind profiles are available every 10 minutes on average. The long-term data on wind speed from this sodar were published in [7, 18, 19]. The objective of the present paper is to generalize separately the results of wind direction measurements in the air layer up to 500 m over Moscow which were collected during 10 years. On October 12–November 11, 2008 the MODOS sodar operated in Obninsk at the distance of 200 m from the Taifun Scientific Industrial Association meteorological tower [16]. The obtained data on wind speed at that period were analyzed by the author in [7]. In the present paper let us consider data on wind direction. Figure 1 presents the comparison of the results of measurements provided by the sodar for every 10 minutes on average within the limits of the pulse scattering volume from 290 to 310 m and by the M-47 anemometer installed at the tower at the height of 301 m. It is clear that the obtained readings form two dense areas concentrated close to the “one-to-one” fit line, and the gap between them is from 30 ° to 110 ° because the wind of eastern and northeastern directions was not observed during the experiment. The coefficient of the linear correlation of the data was equal to 0.98 and the coefficient in the equation of linear regression was equal to 1.00 with the accuracy to one hunderdth. The statistical relation is close to linear that is corroborated by the parabolic trend almost coinciding with the linear one (the parabolic correlation coefficient is also equal to 0.98). Thus, the experiment proved the high degree of reliability of the sodar data on wind direction. The MODOS sodar data on wind direction over Moscow for the period from November 2004 to March 2008 were presented for the first time in [18]. Later the data till August 2008 [19], February 2009 [8], and March 2009 [14] were presented. The wind direction under special conditions of abnormal heat was considered in [6]. The methodology of the analysis of these data is simpler than that of the analysis of the wind speed data because the errors typical of wind speed measurements (systematic bias in the estimates towards one or another direction) are absent in wind direction measurements [7]. It is obvious from physical considerations that at the high altitude the sodar registers the strong wind more often; at the same time, it registers any strong wind equally often regardless of its direction. The pointing of the MODOS sodar antenna system in the cardinal directions was carried out at the beginning of its operation in November 2014 using the usual compass. Therefore, all data on the wind direction are presented below not taking into account the magnetic declination, with the zero reading in the direction of the North Magnetic Pole. The position of the antenna system has been kept constant since then; therefore, the 10-year wind direction data series is homogeneous with the accuracy to ± 1 ° (the error in the installation of the antenna platform in the former position after the sodar was returned from Obninsk where the experiment was conducted, in 2008). Figure 2 presents the summary wind rose for the whole ten-year (2004–2014) period of measurements and for the whole sounding range from 40 to 500 m. Its computation using the MODOS software enables obtaining the uniform graphic data both on the wind direction and wind speed. The distribution of wind speed values for different wind directions is presented in the form of concentric circles with different radia. The occurrence frequency in the separate sectors can be judged by the color scale. The whole range of occurrence frequency (from the rarest to the most frequent values) corresponds to the gradual change of light purple into dark blue and black; the white color means the absence of data with the prescribed wind speed and wind direction. As clear from Fig. 2, the southwestern (225 ° to 235 ° ) moderate (with the speed from 5 to 10 m/s) wind is most frequently (black color) observed in the lower half-kilometer layer over Moscow. Taking into account the eastern (positive) magnetic declination for Moscow (+10 ° 1 6 ¢ ), the more accurate boundaries of this southwestern mode are from 235 ° to 245 ° . This is the principal mode in the wind direction distribution and it prevails absolutely within the whole wind speed range including the highest values from 20 to 25 m/s (the cases of record high wind speed equal to 30 m/s and more that are described in [7], are single and not manifested in the total sample with the prescribed lower limit of the scale). The rarest direction is northeastern for the light wind (<5 m/s) and northern for the moderate wind. The cases of strong wind for these directions were observed very rarely. The qualitatively similar annual wind rose with the strongly pronounced prevalence of southwestern direction was registered in all years of sounding. Thus, the principal southwestern mode is unconditionally stable in time. The differences in the conditions in separate years boil down to the additional features of distributions, namely, to the existence of a wider or narrower principal mode, secondary modes, and higher or lower occurrence frequency of values in different sectors. For example, in 2010, when the winter was very cold and the summer was abnormally hot, the average annual occurrence frequency of southeastern and eastern wind direction turned out to be much higher than in other years. The table presents the estimates of occurrence frequency of different wind directions including the intermediate ones for different seasons and for the year as a whole (~1220000 separate readings for every 10 minutes on average). The data only for the first four years (from November 11, 2004 to August 31, 2008) are generalized here; however, taking into account the temporal stability of occurrence frequency estimates, these data are also representative for the whole period of sounding. Such table with the values only for the principal directions and only for the year as a whole was published in [18] in its preliminary form and in [19] in its final form. Since the MSU area is the edge of Teplyi Stan Upland and is open and relatively flat, the presented estimates of occurrence frequency for separate wind directions are quite reliable. As clear from the table data, the distribution of occurrence frequency of wind directions corroborates the well-known climatologic features of large-scale circulation in the center of the European part of Russia. The southwestern wind direction is really most often observed here [12]. According to our data, the comparatively high average annual occurrence frequency (more than 6.25% that would correspond to the uniform distribution for all 16 wind directions in case of the symmetric wind rose) is typical of the wide sector from the southern to west-northwestern directions. The winds of west-southwestern and southwestern directions are observed most often: their average occurrence frequency exceeds even 12.5%, i.e., the doubled value for the case of the uniform distribution. It should be noted that the occurrence frequency of these wind directions within the annual course is maximum (about 15%) in autumn and winter that is associated with the fact that at that period Moscow is frequently (since late autumn) located on the southeastern periphery of the Icelandic low. The similarity of autumn and winter conditions should be noted, the estimates of occurrence frequency of different wind directions in these seasons almost coincide. On the contrary, the southern and southwestern wind is registered less frequently in summer and spring and the western direction becomes more frequent. As to eastern and northern winds, in spring and in summer their occurrence frequency is much higher than in winter and autumn. The eastern and southeastern wind directions are most often observed in spring whereas the northern direction, in summer. This is an effect of the meridional flows going along the periphery of stationary anticyclones which are formed rather often in the European part of ...
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Citations
... Note that the wind direction averaged over individual months lies in the limits from southern to southwestern in the surface layer and from south-southwestern to west-southwestern direction at a height of 200 m. This corroborates the presence of the principal southwestern mode in the long-term wind rose according to data of the MODOS sodar in the whole sounding range (Lokoshchenko, 2015). The average value of the right wind rotation in the examples presented in Fig. 3 in the air layer of up to 200 m varies from 15° to 20°, which also corroborates the average long-term estimate of this quantity for conditions of Moscow: ~20° (Lokoshchenko, 2015). ...
... This corroborates the presence of the principal southwestern mode in the long-term wind rose according to data of the MODOS sodar in the whole sounding range (Lokoshchenko, 2015). The average value of the right wind rotation in the examples presented in Fig. 3 in the air layer of up to 200 m varies from 15° to 20°, which also corroborates the average long-term estimate of this quantity for conditions of Moscow: ~20° (Lokoshchenko, 2015). ...
... In Therefore, the average height of the surface air layer is apparently close to 40 m. It is particularly remarkable that preliminary estimates of H by data of 59 months up to 2010 turned out to be the same (Lokoshchenko and Nikitina, 2012;Lokoshchenko, 2015). Therefore, they are stable in time. ...
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 the MODOS Doppler sodar (METEK, Germany). 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 semilogarithmic coordinates , is 40-60 m. The wind rotation height, i.e., the height of intersection of day and night wind profiles, is 95 m per year on average. The roughness length in conditions of loosely packed but high urban development in the 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 manifests itself in the monthly average wind direction profiles over the "dead zone" of the sodar (40 m) in approximately one out of three cases and usually amounts to 60 m (less often 80 or 100 m). In all other cases, it is apparently masked by the dead zone. According to this approach, the average height of the surface layer 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 variation 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 dispersion of pollutants from cities can increase AOD for hundreds of kilometers downwind (Jacob et al., 2010;Wang et al., 2013). For the Moscow region, the predominant wind direction is west and northwest (Lokoshchenko, 2015). Therefore, the maximum values of the aerosol radiative effect due to 50% AOD quantile spatial distribution were slightly shifted towards the south and southeast of Moscow. ...
The rapid development of large megacities, coupled with emission regulations, can lead to long-term variations in aerosol optical depth over urban area which has an impact on radiation and temperature. This study aims to evaluate the radiation effects of aerosol pollution in Moscow and its surrounding areas using MAIAC data obtained from MODIS satellite data for three distinct periods: 2000–2006, 2007–2014, and 2015–2021. A methodology has been developed to incorporate MCD19A2/MODIS data with some additional information from the AERONET Moscow MSU site into the COSMO non-hydrostatic weather forecast model. The aerosol radiative and temperature effects were estimated for cloudless conditions. The highest aerosol optical depth with an average of 0.18 were observed during the 2007–2014 over the newly developed Moscow territory during the active building construction period. In the most recent period, from 2015 to 2021, the mean AOD decreased to 0.1. This reduction resulted in an increase of net shortwave radiation at the bottom of the atmosphere by 15–20 W/m2 and a slight rise in surface air temperature of 0.08 °C compared to 2007–2014. The parameterizations were proposed for net radiation and air temperature at 2 m as a function of aerosol optical depth and solar zenith angle at low surface albedo.
... The dispersion of pollutants from cities can increase AOD for hundreds of kilometers downwind (Jacob et al., 2010;Wang et al., 2013). For the Moscow region, the predominant wind direction is west and northwest (Lokoshchenko, 2015). Therefore, the maximum values of the aerosol radiative effect due to 50% AOD quantile spatial distribution were slightly shifted towards the south and southeast of Moscow. ...
Deàr Alexander, I am out of office now, but I will send the preprint as soon as I am back. Middle of the next week... nice to hear from you!
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... The differences between the administrative districts were insignificant; the values that exceed the maximum and the average pH were typical of the western, southern and eastern parts of Moscow, while minimum values were observed in its northern part (Table 2, Fig. 3a). The lowest average pH of 7.2 was recorded in the North-Western district due to the prevailing northerly winds which contribute to the translocation of alkaline technogenic dust to the south of Moscow (Lokoshchenko 2015) -the road dust pH in the Southern, South-Eastern and South-Western districts, as well as in the Eastern and Western districts, exceeded the value of 7.4. The coarse sand fraction (particles with diameter >500 μm) is suspended at wind speeds exceeding 10 m/s; the coarse silt (with diameter 10-50 μm) and smaller particles may suspend in fairly weaker winds. ...
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... The mean wind speed in these conditions is 3.6 m/s with standard deviation σ = 2.9. Therefore, it is possible to define three sectors for Moscow city, with the following average wind speed: 4.0 m/s, 3.6 m/s and 4.5 m/s [41], [42]. ...
In this paper, we focus on reducing the on-grid energy consumption in Heterogeneous Radio Access Networks (HetNets) supplied with hybrid power sources (grid and renewables). The energy efficiency problem is analyzed over both short-and long-timescales by means of reactive and proactive management strategies. For short-timescale case, a renewable-energy aware User Equipment (UE)-Base Station (BS) association is proposed and analyzed for the cases when no storage infrastructure is available. For long-timescale case, a traffic flow method is proposed for load balancing in renewable energy BSs, which is combined with a model predictive controller (MPC) to include forecast capabilities of the renewable energy source behavior in order to better exploit a Green HetNet with storage support. The mechanisms are evaluated with data of solar measurements from the region of Valle de Aburrá, Medellín, Colombia and wind estimations from the Moscow region, Russian Federation. Results show how the green association proposal can reduce on-grid energy consumption in a HetNet by up to 34%, while is able to exceed the savings obtained by other methods, including the best-signal level policy by up to 15%, additionally providing high network efficiency and low computational complexity. For the long-timescale case, MPC attainable savings can be up to 22% with respect to the on-grid only Macro-BS approach. Finally, an analysis of our proposals in a common scenario is included, which highlights the relevance of storage management, although emphasizing the importance of combining reactive and proactive methods in a common framework to exploit the best of each approach.
... -The acoustic calibration of sodars has been implemented [40], which made it possible to carry out absolute measurements of the vertical profiles of the 1 Currently, in Russia the small-scale production of scanning MTP-5 radiometers is arranged in CAO Rosgidromet [20]. There is also one unit of the Doppler sodar (METEK, Germany) at the faculty of geography of Moscow State University [21] and one unit of the Doppler coherent lidar (HaloPhotonic, United Kingdom) at the Institute of Atmospheric Optics, Russian Academy of Sciences [22]. structural parameters of the refraction index in a number of mountain astronomical observatories and reject the concept of the efficiency of building tall astronomical towers to enhance the quality of images [41]. ...
Acoustic sounders (sodars) are the simplest and economically most effective devices for the ground-based remote sensing of the lower troposphere. Using sodars, a vast amount of knowledge about the structure and dynamics of the atmospheric boundary layer (ABL) has been obtained. The principal physics of sodar sounding was given by A.M. Obukhov in two short theoretical articles published in the Reports of the USSR Academy of Sciences in 1941: “On the Scattering of Sound in a Turbulent Flow” and “On the Distribution of Energy in the Spectrum of a Turbulent Flow.” In the late 1950s, Obukhov initiated the development of theoretical and experimental studies of sound scattering by turbulence, as well as a practical sodar sounding of the ABL at the Institute of Atmospheric Physics (IAPh). The present work is a short review of sodar applications in studies of the ABL based on results obtained at IAPh in the 1980s–2000s. The results of recent studies of low-level jets and Kelvin–Helmholtz billows in the stable stratified ABL are described in more detail.
... The vertical wind shear to the right was equal to 20° (from 42° at the height of 40 and 60 m to 62° at the height of 440 m and higher). As demonstrated in [5,7], this is a quite usual value of the average vertical wind shear for the center of the European part of Russia. The lo ca tion of ob ser va tion site on the pe riph ery of the large-scale pres sure for ma tion far from its cen ter im plies the sig nif i cant wind speed. ...
... As dem on strated from sodar data in [5], the av er age vari a tion in wind di rec tion with height in the lower 500-meter air layer over Mos cow is char ac ter ized by the clock wise shear of about 20°. How ever, in some cases ex tremely dra matic wind shears with height are observed. ...
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.
