Rostislav Kouznetsov

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.

Structure parameters for temperature and humidity from simultaneous eddy-covariance and scintillometer measurements

Line-averaged values of the structure parameters of temperature and humidity, CT2 and Cq2, were estimated from simultaneous measurements with an optical and a microwave scintillometer over a path of 4.7 km length at the Meteorological Observatory Lindenberg during the LITFASS-2003 experiment. By cross-correlating the detected signals of the two scintillometers, the temperature-humidity structure parameter, CTq, and the temperature-humidity correlation, rTq, were also derived directly from the measurements. Comparison with corresponding values obtained from local measurements with an eddy-covariance system on a meteorological tower show a consistent behaviour in time (with some exceptions especially for Cq2 and rTq during nighttime). The deviations are of a magnitude between 20 % and 35 % of the typical daytime values of the structure parameters.

An Overview of the Urban Boundary Layer Atmosphere Network in Helsinki

The Helsinki Urban Boundary-Layer Atmosphere Network (UrBAN: http://urban.fmi.fi) is a dedicated research-grade observational network where the physical processes in the atmosphere above the city are studied. Helsinki UrBAN is the most poleward intensive urban research observation network in the world and thus will allow studying some unique features such as strong seasonality. The networks key purpose is for the understanding of the physical processes in the urban boundary layer and associated fluxes of heat, momentum, moisture, and other gases. A further purpose is to secure a research-grade database, which can be used internationally to validate and develop numerical models of air quality and weather prediction. Scintillometers, a scanning Doppler lidar, ceilometers, a sodar, eddy-covariance stations, and radiometers are used. This equipment is supplemented by auxiliary measurements, which were primarily set up for general weather and/or air-quality mandatory purposes, such as vertical soundings and t...

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.

On the Temperature Structure Parameter and Sensible Heat Flux over Helsinki from Sonic Anemometry and Scintillometry

Two commercial large-aperture scintillometers, Scintec BLS900, were tested on pathlengths of 1840 and 4200m at about 45–65m above ground in Helsinki, Finland. From July 2011 through June 2012, large variability in diurnal and annual cycles of both the temperature structure parameter C 2 and sensible heat flux H were observed. Scintillometer data were compared with data from two eddy-covariance stations. A robust method was developed for the calculation ofC 2 from raw sonic-anemometer data. In contrast to many earlier studies that solely present the values of H, the main focus here is on comparisons of C 2 T itself. This has advantages, because optical-wavelength scintillometers measure C 2 with few assumptions, while the determination of H implies the applicability of the Monin–Obukhov similarity theory, which has several inherent limitations.The histogramsofC2 comparewell between sonic andscintillometer. In-depthanalysis is focused on one of the scintillometer paths: both C2 T and H comparisons gave similar and surprisingly high correlation coefficients (0.85 for C2 and 0.84–0.95 for H in unstable conditions), given the differences between the two measurement techniques, substantial sensor separation, and different source areas.

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 multi-frequency sodar with high temporal resolution

The new sodar LATAN-3M with a frequency-coded sounding signal was developed, manufactured, and successfully tested at the Obukhov Institute for Atmospheric Physics. The sodar emits a sequence of sounding pulses at different frequencies and then averages the Doppler spectra for each range gate over the ensemble of frequencies. The field tests have proved the significant advantages of a multi-frequency technique in comparison with a single-frequency one. The use of eight different frequencies halves the minimal acceptable signal to noise ratio compared to single-frequency sounding. Moreover, the multi-frequency mode improves the accuracy of instantaneous values of measured parameters and significantly increases the reliability in recognizing noisy echo-signals.