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Vasily Lyulyukin, Rostislav Kouznetsov, and Margarita Kallistratova

Abstract

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 speed and shear within them. The interconnection between echo intensity and wind shear variations within such patterns is shown. The typical distributions of velocity perturbation within various forms of billows are found.

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Rostislav Kouznetsov, Priit Tisler, Timo Palo, and Timo Vihma

Abstract

The three-axis “Latan-3” Doppler sodar was operated near the Finnish Antarctic station Aboa in Dronning Maud Land (73.04°S, 13.40°W) in the austral summer of 2010/11. The measuring site is located at a practically flat, slightly sloped (about 1%) surface of the glacier. The sodar was operated in multiple-frequency parallel mode with 20–800-m sounding range, 20-m vertical resolution, and 10-s temporal resolution. To reveal the wind and temperature profiles below the sounding range as well as turbulent fluxes at 2 and 10 m, the data from a 10-m meteorological mast were used. During the measurements, the atmospheric boundary layer was within the sounding range of the sodar most of the time. Despite a large variety of observed sodar echo patterns and wind speed profiles, several cases of clear steady katabatic flows were observed. Practically all of them were easterly, whereas the uphill direction is southern. The thickness of the katabatic flow varied from a few tens to several hundreds of meters; the wind speed maximum could be as low as 5 m. Thin katabatic flows had lower wind speed and much stronger temperature gradients (up to 1 K m−1) but had smaller surface heat flux than did the thicker ones.

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Margarita A. Kallistratova, Rostislav D. Kouznetsov, Valerii F. Kramar, and Dmitrii D. Kuznetsov

Abstract

Continuous 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 in horizontal variances was detected in zones of substantial wind shear, which agrees with earlier published lidar data.

Quasi-periodic structures in the sodar return signal, which appear in sodar echograms as braid-shaped patterns, were found to emerge preferably when a substantial increase of wind shear occurs at the top of the stable ABL. The braid patterns in the sodar echograms were not accompanied by any noticeable increase of observed σw, which disagrees with earlier data and indicates that such patterns may originate from various phenomena.

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Valery F. Kramar, Evgeniya Baykova, Margarita Kallistratova, Rostislav Kouznetsov, and Sergei Kulichkov

Abstract

Currently used methods to estimate surface pollutant emissions require a set of specific air-sampling surveys. Data from a network of ground-based sodars and a network of air-quality stations in Moscow, Russia, are used to estimate the emission rates of carbon monoxide (CO) and nitric oxide (NO). The sodar network, consisting of three “LATAN-3” Doppler sodars and three “MTP-5” microwave temperature profilers, is used to measure the vertical profiles of vertical and horizontal wind velocity, wind direction, and temperature, which are used to determine the average mixing-layer height. The network of ground-based air-quality stations, consisting of 17 automated stations distributed uniformly across Moscow, continuously measured the CO and NO concentrations. This study focuses on an anticyclonic episode of high surface pressure over Moscow during 30 July–1 August 2012. After sunrise, the solar-induced convection effectively moderated the pollutant levels in the lowest 100–200 m. After sunset, convective mixing stopped and the wind weakened, which allowed CO and NO to reach hazardous levels. With an assumption of an average mixing-layer height of 150 m, the resulting estimate of surface emission of CO is ~6 μg m−2 s−1, whereas that for NO is ~0.6 μg m−2 s−1.

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Stephan T. Kral, Joachim Reuder, Timo Vihma, Irene Suomi, Kristine F. Haualand, Gabin H. Urbancic, Brian R. Greene, Gert-Jan Steeneveld, Torge Lorenz, Björn Maronga, Marius O. Jonassen, Hada Ajosenpää, Line Båserud, Phillip B. Chilson, Albert A. M. Holtslag, Alastair D. Jenkins, Rostislav Kouznetsov, Stephanie Mayer, Elizabeth A. Pillar-Little, Alexander Rautenberg, Johannes Schwenkel, Andrew W. Seidl, and Burkhard Wrenger

Abstract

The Innovative Strategies for Observations in the Arctic Atmospheric Boundary Layer Program (ISOBAR) is a research project investigating stable atmospheric boundary layer (SBL) processes, whose representation still poses significant challenges in state-of-the-art numerical weather prediction (NWP) models. In ISOBAR ground-based flux and profile observations are combined with boundary layer remote sensing methods and the extensive usage of different unmanned aircraft systems (UAS). During February 2017 and 2018 we carried out two major field campaigns over the sea ice of the northern Baltic Sea, close to the Finnish island of Hailuoto at 65°N. In total 14 intensive observational periods (IOPs) resulted in extensive SBL datasets with unprecedented spatiotemporal resolution, which will form the basis for various numerical modeling experiments. First results from the campaigns indicate numerous very stable boundary layer (VSBL) cases, characterized by strong stratification, weak winds, and clear skies, and give detailed insight in the temporal evolution and vertical structure of the entire SBL. The SBL is subject to rapid changes in its vertical structure, responding to a variety of different processes. In particular, we study cases involving a shear instability associated with a low-level jet, a rapid strong cooling event observed a few meters above ground, and a strong wave-breaking event that triggers intensive near-surface turbulence. Furthermore, we use observations from one IOP to validate three different atmospheric models. The unique finescale observations resulting from the ISOBAR observational approach will aid future research activities, focusing on a better understanding of the SBL and its implementation in numerical models.

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