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  • 16th International Symposium for the Advancement of Boundary-Layer Remote Sensing (ISARS 2012) x
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Margarita A. Kallistratova, Rostislav D. Kouznetsov, Valerii F. Kramar, and Dmitrii D. Kuznetsov

turbulence ( Baas et al. 2010 ). The low-level jet (LLJ) is a flow, specific to stable ABLs, that has a distinct maximum of wind speed within a few hundreds of meters above ground. LLJs form in stably stratified atmospheres resulting from the small vertical exchange between atmospheric layers that favor the formation of wind shears. LLJs can originate from local circulations because of orography and/or thermal inhomogeneity of the ground surface, from inertial oscillations resulting from the nocturnal

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

. 8 ) are used to further understand ramp events. For up-ramps under stable conditions (UP-STAB; Fig. 8a ), the observed composite profiles show a low-level jet with a maximum located at ~200 m AGL. Note that in this study low-level jet is loosely defined as low-level wind maxima at an altitude of 200–300 m with strong shears below the maxima (wind speed below the nose of the maximum wind speed is smaller by, at least, 2 m s −1 ). The S YSU agrees the best with the mean observed profile below

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

. The echo intensity is given in decibels. Below we consider three of about a dozen clear cases of steady katabatic flows observed during the campaign ( Fig. 4 ). All three cases were observed under clear sky and very weak wind in the free troposphere (<2 m s −1 ) but showed different heights of a jet core and different thicknesses of a mixed layer above the core. Fig . 4. The time series of the data from the meteorological mast and the sodar for the selected katabatic flows. The data of the CSAT3

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Vasily Lyulyukin, Rostislav Kouznetsov, and Margarita Kallistratova

significantly exceed those obtained by time averaging, and the profile of the low-level jet (LLJ) is also less smooth ( Fig. 4 ). Fig . 4. Wind speed profile for the sample observed on 29 Jan 2010. (a) Composite profile and (b) profile obtained by averaging over 30 min. Fig . 5. The variability of the shape and structure of KHB with the influence of the average wind profile. (top) LLJ maximum is located above the KHB layer (29 Jan 2010); (bottom) LLJ maximum is within the KHB layer (3 Dec 2008). (left

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A. B. White, M. L. Anderson, M. D. Dettinger, F. M. Ralph, A. Hinojosa, D. R. Cayan, R. K. Hartman, D. W. Reynolds, L. E. Johnson, T. L. Schneider, R. Cifelli, Z. Toth, S. I. Gutman, C. W. King, F. Gehrke, P. E. Johnston, C. Walls, D. Mann, D. J. Gottas, and T. Coleman

not available over land, given the poorly known microwave emissivity of land surfaces ( Prigent et al. 2000 ). In addition, satellites do not measure the winds in the low-level jet ( Neiman et al. 2002 ) that focus the transport of moisture onshore and determine which watershed(s) will be impacted most by the AR ( Ralph et al. 2003 ). Fig . 1. Global composite satellite image of IWV (cm) measured with the Special Sensor Microwave Imager (SSM/I) aboard the Defense Meteorology Satellite Program

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