M. A. Kallistratova

Wind and turbulence in the urban boundary layer - analysis from acoustic remote sensing data and fit to analytical relations

Mean seasonal profiles of wind speed, standard deviation of the vertical velocity and turbulence intensity from SODAR measurements in three cities of different size, Moscow, Hanover and Linz, are compared to analytical approximations for the Prandtl and Ekman layer. Typical urban features in the profiles and differences to measurements at rural sites are discussed. Typical urban features are a greater slope in the wind profiles, enhanced turbulence intensities, and a vertical increase in magnitude of the turbulence. The analytical approach proposed by ETLING (2002) for the description of the vertical wind profile in the whole boundary layer is amended in the Prandtl-layer part by a correction function for atmospheric stability. The amended profile description turns out to render the best results for the approximation of urban wind profiles within the lowest 500 m above ground.

Low-Level Jets in the Moscow Region in Summer and Winter Observed with a Sodar Network

We evaluate the statistical properties of low-level jets (LLJs) observed by means of a network of Doppler sodars in the Moscow region, Russia. Continuous long-term measurements of the echo-signal intensity and wind-velocity profiles were carried out in July 2005 and in 2008–2010 synchronously in the centre of Moscow and at a rural site. The summertime nocturnal LLJs have a very clear diurnal cycle and exhibit features predicted by the Blackadar mechanism. In contrast, the long-lasting wintertime jets do not have any clear diurnal variability. The urban environment strongly influences LLJs in both seasons: above the city LLJs are higher, weaker and observed more rarely than at the rural site. In very cold periods (air temperature below −8°C) no LLJs were observed over the city, instead convection emerged in the urban boundary layer. The results are based on observations made in July 2005, January and December 2009, and January 2011.

Determination of the turbulent fluxes of heat and momentum in the ABL by ground-based remote-sensing techniques (a Review)

During the past about 20 years, quite a number of methods for estimation of vertical profiles of the turbulent fluxes of heat and momentum, estimated or measured by means of ground-based remote-sensing techniques have emerged. This paper will focus attention on those, which refer to methods for windprofiler radar, radar/RASS, sodar, sodar/RASS, and to a lesser extent, also to lidar. The paper reviews the current state-of-the-art in flux profiling using these techniques and tries to summarize their capabilities and limitations. It is shown, that considerable progress has been reached over the last decades, although it has to be stated that flux determination by ground-based remote sensing still remains far from being an operational product. Nevertheless, with undergoing improvements in signal processing and hardware modifications, considerable improvements may still be possible in this field for the future. Already now, it can be summarized that ground-based remote-sensing techniques are of similar accuracy than expensive airborne campaigns.

Summertime low-level jet characteristics measured by sodars over rural and urban areas

This work is devoted to the study of nocturnal low-level jet streams (LLJ) at altitudes up to 400 m agl, with the help of Doppler sodars. The objective was twofold: firstly, to study the origin and behavior of LLJ in a mid-latitude region, and secondly, to compare the LLJ characteristics over urban and rural areas. To this end, simultaneous measurements of wind velocity profiles over the center of Moscow city and over a nearby countryside were carried out. The sodar data on wind speed and direction collected continuously during 27 days in July 2005 were analyzed together with in situ data from a meteorological mast. A good correlation between the height of the LLJ core and the inversion height was found. Empirical distributions of the maximum speed of the jet streams, the height of the jet core, and the wind turning across the stream were obtained. The relationships between the LLJs characteristics and some surface layer parameters were found. Over the urban area the jet streams appeared less frequently and at heigher altitudes than over the countryside.

The vertical structure of turbulent momentum flux in the lower part of the atmospheric boundary layer

The acoustic sounder (sodar) can be used to measure the parameters of turbulence in the lower part of the atmospheric boundary layer. We suggest a new method to estimate the vertical structure of the momentum flux up to the height of several hundred meters above the surface. The method uses sodar-measured profiles of mean wind and of the variance of vertical wind component σ 2 w . The field experiment have shown a good agreement of sodar-derived momentum flux values with those measured in situ. We obtained the typical profiles of momentum flux with the method.

Experience in measuring the wind-velocity profile in an urban environment with a Doppler sodar

The experience of long-term acoustic remote measurements of vertical wind-velocity profiles at two sites in Moscow is reported. Equipment performances and measurement conditions are described. Acoustic measurement features characteristic of a large city with high traffic noise and spurious reflections from buildings are discussed. Criteria and techniques of rejecting noisy and false signals are described as well as the methods of statistical data processing suitable in the case of a signal-to-noise ratio rapidly varying in time and a significant number of rejected signals. Preliminary results of measurements are given.

The Composite Shape and Structure of Braid Patterns in Kelvin–Helmholtz Billows Observed with a Sodar

The structure and dynamic characteristics of the Kelvin‐Helmholtz billows (KHB), observed with a sodar in the stable atmospheric boundary layer, are studied by means of composite analysis, which consists in the averaging of samples selected according to certain criteria. Using a specific kind of this method allowed the authors to obtain the fine structure of the perturbation velocity fields from the sodar data. The events of most pronounced KHB were visually selected from echograms of continuous sodar measurements in the Moscow region over 2008‐10. The composite patterns of KHB have been constructed for a few cases of clear inclined‐ stripes echogram patterns to derive a typical finescale structure of billows and a spatial distribution of wind speedandshear withinthem.Theinterconnectionbetweenechointensityandwind shearvariations within such patterns is shown. The typical distributions of velocity perturbation within various forms of billows are found.

Profiles of Wind Speed Variances within Nocturnal Low-Level Jets Observed with a Sodar

AbstractContinuous sodar measurements of wind profiles have been carried out at the Zvenigorod Scientific Station of the Obukhov Institute of Atmospheric Physics since 2008. The station is located in a slightly inhomogeneous rural area about 45 km west of Moscow, Russia. The data were used to determine the parameters of wind and turbulence within low-level jets in the stable atmospheric boundary layer (ABL). Along with the mean velocity profiles, the profiles of variances of wind speed components from the sodar and the profiles of temperature from a microwave radiometer have been used to quantify turbulence and thermal stratification. Data from two sonic anemometers were used to get the near-surface parameters.The typical standard deviation of the vertical wind component σw within the low-level jet is about 5% of the maximum wind speed in the jet. No noticeable vertical variation of σw across the jets was detected in several earlier sodar campaigns, and it was not found in the present study. An increase i...

Internal gravity-shear waves in the atmospheric boundary layer from acoustic remote sensing data

The year-round continuous remote sounding of the atmospheric boundary layer (ABL) by means of the Doppler acoustic radar (sodar) LATAN-3 has been performed at the Zvenigorod Scientific Station of the Obukhov Institute of Atmospheric Physics, Russian Academy of Sciences, since 2008. A visual analysis of sodar echograms for four years revealed a large number of wavelike patterns in the intensity field of a scattered sound signal. Similar patterns were occasionally identified before in sodar, radar, and lidar sounding data. These patterns in the form of quasi-periodic inclined stripes, or cat’s eyes, arise under stable stratification and significant vertical wind shears and result from the loss of the dynamic stability of the flow. In the foreign literature, these patterns, which we call internal gravity-shear waves, are often associated with Kelvin-Helmholtz waves. In the present paper, sodar echograms are classified according to the presence or absence of wavelike patterns, and a statistical analysis of the frequency of their occurrence by the year and season was performed. A relationship between the occurrence of the patterns and wind shear and between the wave length and amplitude was investigated. The criteria for the identification of gravity-shear waves, meteorological conditions of their excitation, and issues related to their observations were discussed.

Mean wind speed profiles in the air basin of Moscow

Results of measurements of mean wind speed profiles and direction during two years in the center of the city of Moscow are presented. These measurements were performed with a Doppler acoustic profiler (sodar), which was used for continuous monitoring of the wind speed within the height range from 40 to 250–500 m. The averaged seasonal mean profiles are presented along with other observational data, including diurnal cycle parameters, wind speed and direction frequencies at chosen levels, and frequencies and duration of strong winds and calm weather.