IOP Conference Series: Earth and Environmental Science Study of wind variability over Moscow city by sodar To cite this article: V P Yushkov 2008 IOP Conf. Ser.: Earth Environ. Sci. 1 012046 View the article online for updates and enhancements. Related content - Wind profiles in Moscow city by the sodar data M A Lokoshchenko and E A Yavlyaeva - Use of sodar data for analysis of relationsbetween concentrations of minor atmospheric gases M A Lokoshchenko and N F Elansky - Mean wind field in the urban atmospheric boundary layer by sodar data V P Yushkov This content was downloaded from IP address 37.44.199.157 on 12/02/2018 at 03:46
Study of wind variability over the Moscow city by sodar V P Yushkov Faculty of Physics, Lomonosov Moscow State University, Lenin Hills, Moscow, 119992, Russia E-mail: yushkov@phys.msu.ru Abstract. We used sodar data to obtain spatial, diurnal and seasonal variability of wind speed variances. Comparison of measurements at two sites in Moscow megalopolis and at the rural site (45 km from Moscow) was carried out. A good agreement between sodar and insitu measurements by ultrasonic anemometer in rural and urban observations was obtained. Variances of radial velocities measured at sodar inclined antennae were compared with vertical wind variance as well as with wind components variances by sonic data. Experience in measuring of meso-scale wind variability by averaged on short time intervals data is demonstrated. Measurement of other statistical characteristics like vertical wind variances is discussed. 1. Introduction Remote sensing instruments for monitoring of atmospheric boundary layer (ABL) allow collecting detailed statistics of wind variability in ABL for different heights, time intervals, seasons and observing sites [1]. This paper presents such statistics from continuous sodar measurements in Moscow megalopolis (more then 10 millions inhabitants). To estimate an impact of urban environment on atmospheric pollutants transport, heat and momentum fluxes not only detailed measurements in short field experiments but statistics for long time are also required. The feature of this statistics is meso-scale variability, beyond inertial interval. Till now processes between synoptic scale (tens kilometres and tens minutes) and inertial interval of isotropic and homogeneous turbulence (centimetres and seconds) is researched insufficiently, statistics at this scale is fragmentary in spite of numerous field experiments and routine measurements. Experimental studies of atmospheric turbulence usually use high-frequency measurements in steady and homogeneous conditions. In field experiments, if it is possible, a flat terrain is used and data are divided by thermal stratification. So, in urban environment and if monitoring instruments have limited ability, adaptation of theoretical models to practice require the experimental estimation of measurement correctness. Measurements which are carried out on buildings, near buildings, above buildings are not allowed by meteorological requirements so urban environment impact has to be investigated in experiments. 2. Instrumentation and measurement sites Our measurements are carried out by PC-based mono-static three-component sodars Latan-3 developed at the Obukhov Institute of Atmospheric Physics (IAPh) for scientific purposes [2]. Detailed description of measuring procedure and accuracy can be found in [3, 2]. Two sodars c 2008 IOP Publishing Ltd 1
Figure 1. Mean seasonal profiles of vertical velocity variance (σ 2 w) in centre of Moscow for measurements in 2007. are synchronously operated at two sites: at the IAPh building in Moscow downtown and at Lomonosov Moscow State University (MSU) Physics Faculty building in the south-west district of Moscow. Continuous measurements are carried out since April 2005. Sodar in downtown is placed at the height of 13 m agl (about 195 m asl), in MSU sodar placed at 40 m agl. Distance between two sites is about 7 km. Mean height of Lenin Hills above Moscow River is about 70 m, however our measurements show that it has a matter because of layering of atmospheric flows. Common difference is same as difference in wind profiles and surface inversion thickness determined from echograms in our and earlier experiments [4]. Simultaneous measurements were carried out in rural area at Zvenigorod Scientific Station (ZSS of IAPh) in 45 km from Moscow in June 2005. Height range was chosen from 40 to 300 meters for data averaging and comparability in two urban and rural locations (at first level buildings influence is considerable). Vertical resolution of LATAN-3 is 20 meters. Carrying frequency is 1700 Hz, sounding frequency is 4x3 pulses per minute. Variances are calculated over 30 min intervals then means and distributions are computed for a long time (month, season, year). Daytime and night-time averaged data are also calculated. Night interval is from 0 to 6 hour of local standard time (LST) and day interval is from 10 to 16 hour. Data availability in series and at different height intervals is calculated as well as data control of rain and noise impact is carried out. It allows to control noisy environment and to make measuring in heavy traffic and rain conditions [3]. 2
Figure 2. Averaged diurnal course of σ 2 w at 3 heights: 50, 100 and 200 m for each season. Moscow downtown, 2007. 3. Results 3.1. Vertical velocity variance Vertical velocity variance (σ 2 w) is most accurately measured by sodar characteristics of turbulent pulsations, however measurements of σ 2 w demand special equipment (not all commercial sodars Figure 3. Distribution of σ 2 w in summer and winter at 50, 150 and 250 m heights. Moscow downtown, 2007. 3
Figure 4. Mean summer profiles of σ 2 w at IAPh and MSU sites. Summer 2007 (June- August). can measure this value) and careful control of results [5]. Fig.1 shows seasonal means of σ 2 w profiles for each season in Moscow downtown. Data for 2007 year (December 2006-November 2007) averaged by 3 months are presented in this figure. Both all-data means and night-time daytime data are displayed. Main feature of variance profiles is considerable increasing of diurnal course in summer time. Minimum of diurnal course is observed in winter and autumn due to continuous cloudiness. Another feature of variance profiles is a weak variability with height above 150 m, i.e. main increase of σ 2 w is observed within sodar range and below. Similar results were demonstrated in Hanover measurements (Fig.5 in [6]). Averaged diurnal course for each season (about 90 values for seasonal means per one year) and its annual variability is presented in Fig.2. In summer time diurnal amplitude of σ 2 w in order of magnitude is larger then in winter. Distribution of wind velocity variance shows a synoptic variability of stratification. Fig. 3 demonstrates probability distributions (histograms) of σ 2 w at three heights (chosen by profiles varying): 50, 100 and 200 m. Histograms display occurrence of strong and weak stable conditions in night-time as well as strong and weak unstable stratification in daytime. Increase of wind variance with height and stabilization of its growing above 150 m are seen. Thus, statistical generalization presents common pattern of turbulence distribution in urban air. 3.2. Comparison of urban turbulence at two measurement sites Heterogeneity of turbulence within urban megalopolis is difficult to study, so a possibility of result extrapolation upon whole urban area demands careful investigation because of big city orography and heat island deform both mean flows and turbulence characteristics. Comparing of mean profiles of σ 2 w is shown in Fig. 4. Fig.5 demonstrates mean diurnal course of σ 2 w by measurements in Moscow downtown and at MSU site. Heights are shown from sodar placement level so height difference of IAPh and Physics Faculty buildings must be taken into account as well as MSU site elevation above Moscow River. An example of week course in Fig. 6 demonstrates this difference: at the left panel σ 2 w course at one height is displayed and at right panel - at different heights (with 100 m spread). Taking this difference into account accordance of diurnal course is good. 4
Figure 5. Averaged diurnal course of σ 2 w at 3 heights: 50, 150, and 250 at two urban sites. Summer 2007. 3.3. Comparison of urban and rural measurements Comparison of wind velocity variance at urban and rural area plays a major role in estimation of influence of urban heating and urban roughness on turbulence in ABL. Fig.7 shows comparison of monthly averaged σ 2 w profiles (July 2005). Fig. 8 demonstrates averaged diurnal course at the same heights: 50,100 and 200 m. Similarity of diurnal course in the centre of Moscow and above rural area is surprised as urban heat flux and urban roughness are larger considerably. Example of week course of σ 2 w at 100 m at two sites illustrates this phenomenon in Fig. 9. Probably, wind variances and momentum flux as well as heat flux are more independent then in analytical relations due to synoptic and meso-scale variability. 3.4. Comparison of in-situ and sodar measurements in urban area Measurements of wind velocity variance by sodar LATAN-3 with in-situ ones were compared at MSU site to estimate wind and turbulence perturbations due to buildings in urban area. Figure 6. Week example of σ 2 w at downtown and MSU site at one (left) and at different (right) heights. 5
Figure 7. Monthly mean profiles of σ 2 w in Moscow downtown and at ZSS rural site for July 2005. Figure 8. Averaged diurnal course of σ 2 w at 3 heights in centre of Moscow and at rural site. Figure 9. Example of week course of σ 2 w at 100 m height in Moscow downtown and at ZSS site. 9-16 July 2005. 6
Ultrasonic anemometer (USA-1, Metek) was mounted at the mast, 10 m above roof level. Data analysis shows increase of mean vertical velocity for east wind direction due to influence of Physics Faculty building shape and also weak alteration of wind direction for north wind due to influence of Main MSU building. Comparison of σ 2 w measured by sodar at the lowest level (50 m) and in-situ one shows a key role of height above roof (10 m) and above ground level (+40 m) in data analysys. 3.5. Wind variances in inclined antennae. In-situ measurements in labs and field experiments show stability-dependent relations between longitudinal, transversal and vertical variances of velocity [7]. Measuring of vertical velocity variance by sodar is widely used and using of radial velocity variances by inclined antennae demand realization. Preliminary experiments were carried out to calculate a ratio of variance components by in-situ measurement in urban environment (at MSU site) and ratio of radial velocity variances by sodar measurement. Qualitative accordance between components of variances by in-situ and sodar measurements was detected. Fig. 10 illustrates these relations in a week series in summer-time. Upper panel shows sodar radial velocity variances calculated over 30 min intervals. Antennae 1 and 2 inclined to vertical at 30 and so (neglecting momentum flux) σ1 2 = 0.75σ2 w + 0.25σu1 2 and σ2 2 = 0.75σ2 w + 0.25σu2 2. Second panel shows variance of wind components (not components of variance). Stability-dependent relation between components is seen. Bottom panel shows wind velocity averaged over 5 minute at the lowest level to compare variances in inertial interval (sonic, 1 sec), at its border (sodar, 15 sec) and at meso-scale (300 sec). 3.6. Meso-scale variability of horizontal wind Meso-scale variations of all wind components may be estimated by sodar measurements using averaging on short time intervals (3-5 minute). Open architecture of LATAN-3 allows varying of sounding parameters and of collected data processing. Three components of wind velocity vector averaged over 5 minutes (up to 20 measurements) were calculated. Then each variance components (longitudinal, transversal and vertical) for long time interval (60-90 minutes) may be studied as well as their vertical profiles, diurnal course and distributions. Fig. 11 demonstrates ability of such calculation and qualitative behaviour of horizontal wind variances. Two summer days of measurements by short series are shown in Fig. 11. Mesoscale and synoptic variability is seen. At high levels also data gap and poor data availability are present. Thus difficulties of direct measurement of meso-scale variations are remained but efforts in this direction continue. 4. Conclusion and outlook Ability to measure of vertical wind variances (σ 2 w) by sodar with high accuracy permits to study a diurnal variability of turbulence and its annual course and to collect a climatological statistics. Statistics of wind variance for a long time in continuous measurements earlier was not analysed. Joint efforts in long-term sodar measurements [6] will be continued. Main increasing with height of vertical wind velocity variance and total kinetic energy of turbulence (if TKE connected with σ 2 w by stability- dependent function) take place within the lowest 150-250 m and so sodars will play a major role in ABL turbulence investigating. Main feature of turbulent exchange in ABL is diurnal course and its annual variations. Vertical velocity variance (and TKE) increases in summer days in 3-4 times to night ones. Diurnal amplitude (difference between day and night values) increases in order of magnitude towards winter value. 7
Figure 10. Comparison of sodar radial velocity variances (top panel), in-situ measured variances of wind components (middle) and variability of horizontal wind speed averaged over 5 minutes (bottom). MSU site, 1-8 July 2007. 8
Figure 11. Horizontal wind velocity averaged over 5 minutes at 2 levels: 100 and 300 m. 17-18 July 2007, Moscow downtown. X-axe shows LST. Probably, Moscow city isn t a fine example of turbulence variability in winter period. More significant diurnal amplitude may be obtained in South Europe cities or under breeze circulations, i.e. regional climatology of turbulence remains important area of research. Turbulence statistics demonstrates wide synoptic variability and confirms stabilization of turbulence above 150 meters. From 50 to 150 m distribution of variances show clear tendency, that can be analytically described. Wind velocity variance above 150 m in urban area is strongly varied, perhaps, due to influence of urban noise. Our experiments show that mean values of σ 2 w averaged for long interval as well as distributions are sensitive to noise filtration procedure. So, comparison of different methods of remote measuring of wind variances must be performed at heights where data availability decreases (above 200 meters). Important part of turbulence increasing takes place below the lowest measuring level by sodar, so for more detailed study of canopy and wake layers in urban area combination of remote and in-situ (at mast) measurement is actual (or using additionally of minisodar). Comparison of measurements in two urban points confirms major role of lower part of ABL in turbulence increase. Measurements at Physics Faculty building show that turbulence changing takes place below sodar bottom range. In-situ measurements at mast on the roof of building confirm this. Diurnal course of variance in MSU demonstrates main influence of unstable stratification on increase of σ 2 w with height. Comparison of diurnal course in IAPh and in MSU shows that increase of wind variance depends on stratification: in night-time variance in MSU increases faster. Comparison of urban and rural measurements demonstrates that diurnal variability in centre 9
of Moscow and at rural site in summer-time is very similar at least at 100 m height. Probably, roughness and heating differences manifest itself in canopy and wake layers below 100 m. Comparison of radial velocities variances on inclined antennae qualitatively confirms the ratio between longitudinal, transversal and vertical components, obtained in laboratories and field experiments over flat terrain. Method suggested in[8] allows calculating of both σ 2 w and TKE from inclined antennae measuring. Sodar Latan-3 permit to measure three components of wind velocity over short time intervals (3-5 minutes). Variability at this scale allows calculating of three components of meso-scale variance and their ratio; however, calculation must consider a rapid change of average velocity in synoptic processes, and decrease of data availability with height. Vertical velocity component is also convenient to measurement of autocorrelation time and spectrum, because of vertical velocity doesn t have a meso-scale (at tens minutes) variability. Wind velocity correlations between nearby pulses show variability at scale of tens seconds and spatial correlation between adjacent heights gives estimation of variability at scale of tens meters. Obtained data permit to calculate these characteristics. Acknowledgments Measurements in IAPh and at ZSS cite were carried out by Rostislav Kouznetsov, we thank him also for helpful discussion. We are grateful to M.A. Kallistratova for study initialization and numerous remarks. This work is supported by Russian Foundation for Basic Research, projects nos. 05-05-64786, 07-05-13610 and 08-05-00984. References [1] Kallistratova M A and Coulter R L 2004 Application of sodars in the study nad monitoring of the environment Meteorol. Atmos. Physics 85 21 37 [2] Kouznetsov R D 2006 The new PC-based sodar LATAN-3. Extended Abstr. 13th Int. Symp. On Advancement of Boundary Layer Remote Sensing(ISARS-2006), 18-20 July 2006, Garmisch-Partenkirchen, Germany 97 98 [3] Yushkov V P, Kallistratova M A, Kuznetsov R D, Kurbatov G A and Kramar V F 2007 Experience in measuring the wind-velocity profile in an urban environment with a Doppler sodar Izvestiya Atmospheric and Oceanic Physics 43 No. 2 168 80 [4] Pekour M S and Kallistratova M A 1993 Study of the boundary layer over Moscow for air-pollution application Appl. Phys. B 57 49-55 [5] Coulter R L and Kallistratova M A 2004 Two-decade progress in sodar techniques: a review of 11 ISARS proceedings Meteorol. Atmos. Physics 85 3 19 [6] Emeis S, Baumann-Stanzer K, Piringer M, Kallistratova M, Kouznetsov R and Yushkov V 2007 Wind and turbulence in the urban boundary layer - analysis from acoustic remote sensing data and fit to analytical relations Meteorologische Zeitschrift 16 No 4 393 06 [7] Kouznetsov R D, Kramar V F, Beyrich F and Engelbart D 2004 SODAR-Based Estimation of TKE and Momentum Flux Profiles in the Atmospheric Boundary Layer: Test of a Parameterization Model Meteorol.Atmos. Phys 85 93 99 [8] Kouznetsov R D 2003 Estimates of Vertical Turbulence Structure by Sodar in the Urban Air Proceedings of 5th International Conference on Urban Climate, Lodz, Poland 2 345 48 10