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B. Van Dam, D. Helmig, W. Neff, and L. Kramer

polar tropospheric chemistry. One important factor influencing surface trace gas levels is the atmospheric boundary layer. Studies at the South Pole (SP) have shown that a combination of conditions—including low snow accumulation rates allowing for efficient recycling of nitrogen, emissions of nitrogen oxides (NO x : NO + NO 2 ) from the snowpack, a long fetch allowing NO x accumulation in the surface layer, and sustained shallow stable boundary layers—promote elevated levels of nitric oxide (NO

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Qing Yang, Larry K. Berg, Mikhail Pekour, Jerome D. Fast, Rob K. Newsom, Mark Stoelinga, and Catherine Finley

of each simulation were spinup periods and were excluded from the analyses. The model output frequency is every 30 min. Lateral boundary conditions for the outer domain and initial conditions were obtained from the North American Regional Reanalysis dataset with 3-h temporal resolution and 32-km horizontal resolution. Simulations were conducted for May of 2011, which was the only period during which both RWP and sonic measurements on the 62-m-tall tower were available. In addition, May is one of

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Leslie M. Hartten and Paul E. Johnston

1. Introduction Extensive marine stratocumulus (Sc) clouds over the southeastern Pacific Ocean play a critical role in the dynamics of the ocean–atmosphere system as well as the global atmospheric circulation in the eastern Pacific ( Klein and Hartmann 1993 ). The tops of the Sc are coincident with the top of the marine boundary layer (MBL). Both the height z i of the inversion atop the MBL and the thickness of the Sc vary in space and time; these variations affect vertical mixing between the

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Jacob Berg, Jakob Mann, and Edward G. Patton

very close to zero throughout the ABL for all three stability classes. In the stable case, β turns negative at high altitudes. We attribute this to the 188-m boundary layer height in the simulations. Fig . 7. LES vertical profiles of the angles α (red), β (blue), and γ (green) from LES for (a) stable, (b) neutral, and (c) unstable conditions. 5. Discussion and conclusions The most striking finding in this paper is the misalignment between the stress vector and the vertical gradient of the

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Valery M. Melnikov, Richard J. Doviak, Dusan S. Zrnić, and David J. Stensrud

cover was reported at Oklahoma City and Tinker AFB, with cloud bases at 1.5 and 2.0 km, respectively, although cloudy conditions were observed at KOUN an hour earlier. The horizontal distance between KOUN and Oklahoma City is roughly 32 km, and the radar cross section in Fig. 3a extends from KOUN toward Oklahoma City. The 0000 UTC sounding from Norman indicates a cloud mixing layer from the top of the boundary layer to around 3 km AGL ( Fig. 2b ). A visible satellite image (not presented here

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

1. Introduction Short-range transport of pollutants depends on the wind field and the intensity of turbulent mixing in the atmospheric boundary layer (ABL; Monin and Yaglom 2007 ). As a result, to understand local pollutant transfer and dispersion over a city, researchers should know the wind field, the characteristics of the pollutant sources (including their positions, temperatures, and emission rates), the turbulent characteristics, and the pollutants’ deposition rates. In addition, to

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C. R. Wood, R. D. Kouznetsov, R. Gierens, A. Nordbo, L. Järvi, M. A. Kallistratova, and J. Kukkonen

problem also seen in EC flux data given detection limits and uncertainties on the order of 10 W m −2 . The climate conditions in Helsinki represent a challenge for scintillometry, given the urban surface and the high-latitude location giving rise to negative sensible heat fluxes even above an urban surface. The values of sensible heat flux are typically small, which poses a problem to MOST-based methods. Moreover, shallow boundary layers of a few tens of meters that often occur over Helsinki can

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S.-E. Gryning, E. Batchvarova, and R. Floors

variability of the synoptic conditions prevailing in the region. An assessment of the k profile from model output illustrates the ability of the model to simulate this balance. We found that nudging has a large impact on the shape parameter. When nudged, the simulation agrees very well with the measurements up to 100 m while it continues to underestimate the shape parameter above this height. The height of the internal boundary layer at Høvsøre is approximately 100 m and can influence the scale and

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

1. Introduction Katabatic winds are airflows that occur above a cold sloped surface. They are driven by gravity that causes colder and more dense air masses to move downhill. As velocity increases, the Coriolis force declines the flow from the downhill direction. As was done in Vihma et al. (2011) , we define the katabatic wind as a downslope wind initially generated by surface cooling. The katabatic winds occur near a surface in the stably stratified atmospheric boundary layer (ABL) and have

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Vasily Lyulyukin, Rostislav Kouznetsov, and Margarita Kallistratova

atmosphere. KHB are revealed by sodar, radar, and lidar under conditions of statical stability in the presence of strong vertical shear of wind velocity. Examples of KHB observations in the lower and middle atmosphere can be found in the monograph Gossard and Hooke (2003) , as well as in reviews in DeSilva et al. (1996) and Fukao et al. (2011) and references therein. Radar observations of KHB in the free atmosphere are numerous, but in the lowest atmosphere only a small number of KHB events (a

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