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Investigations of profiles of vertical velocity skewness and sources of layers of strongly positive skewness as measured by Doppler lidar during COPS

Davis, Jenny and Davies, Fay and Pearson, Guy and Collier, Chris. and Burton, Ralph (2009) Investigations of profiles of vertical velocity skewness and sources of layers of strongly positive skewness as measured by Doppler lidar during COPS. In: The Royal Meteorological Society Conference, 29/6/09 - 02/07/09, The University of Reading.

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Abstract

The Convective and Orographically-Induced Precipitation Study, COPS, was conducted in the Black Forest region of Germany during the summer of 2007. Its aim was to advance the quality of forecasts of orographically induced convective precipitation by 4D observations and modelling. From the 13th June to the 16th August 2007, the Universities’ Facility for Atmospheric Measurement (UFAM) 1.5 micron scanning Doppler lidar, operated by the University of Salford, was deployed at Achern, Baden-Württemberg, Germany, in order to take part in the extensive COPS observation campaign. The University of Salford lidar system measures radial wind and aerosol backscatter from 105 m above the surface to the top of the boundary layer. Profiles of horizontal wind velocity are shown; these being derived from performing azimuth scans of 5 minute duration, approximately every 30 minutes. Between azimuth scans, the lidar pointed vertically. Profiles of vertical velocity, its variance and skewness are also shown. Knowledge of vertical velocity skewness is important as it can help understand the structure and origin of turbulent convection in the boundary layer. The skewness of vertical velocity can provide a measure of the asymmetry in the distribution of vertical velocity perturbations within the atmospheric boundary layer (ABL). In previous studies, under fair-weather conditions, when the ABL is heated from below, skewness profile tends to be positive throughout the ABL, while under cloudy conditions, the skewness profile can be affected by cloud processes and therefore predominantly negative. The behaviour of the boundary layer is investigated using data from the Salford University Doppler lidar, microwave radiometer and automatic weather station. In this paper, selected cases are compared and the similarities and differences are noted. Investigations of possible causes of layers of positive and negative skewness are presented, along with intercomparisons with radiosonde ascents from the Achern site.

Item Type:Conference or Workshop Item (Poster)
Uncontrolled Keywords:Doppler lidar Atmospheric Physics Turbulence
Subjects:Atmospheric Sciences
ID Code:341
Deposited By:Dr Jenny Davis
Deposited On:07 Sep 2009 10:21
Last Modified:07 Sep 2009 10:21

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