Extended Abstract (940K)4.4
Short time fluctuations of the convective boundary layer height and entrainment observed with Doppler lidar
Katja Träumner, Forschungszentrum Karlsruhe, Eggenstein-Leopoldshafen, Germany; and A. Wieser, C. Kottmeier, and U. Corsmeier
Boundary layer height is a fundamental parameter in research of the lower troposphere. The principal daily evolution of the convective boundary layer is well known, but the short time fluctuations of the boundary layer height are usually averaged and not taken into account, although they may be responsible for the downward entrainment of warmer and dryer air and the coupling of the boundary layer with the free troposphere.
We use a commercial 2023 nm Doppler lidar to determine boundary layer height and entrainment zone thickness at high vertical and temporal resolution (10 seconds). Different automated algorithms from literature are applied to detect boundary layer height and entrainment zone thickness from the aerosol backscatter signal and a new algorithm using the variance of the vertical wind speed is tested. For our studies, data from two campaigns called “Convective Storms Initiation Project”, CSIP (summer 2005, southern UK) and “Convective and Orographically Induced Precipitation Study”, COPS (summer 2007, south-western Germany) are used. The two campaigns differ highly concerning the terrain: during CSIP the lidar measured over flat terrain, during COPS it was located on the top of the highest mountain (1160 m asl) of the northern Black Forest.
Our results show that convective boundary layer heights determined from aerosol backscatter are not always consistent with turbulent motions typical for convective boundary layers, especially not in complex terrain. The additionally use of the variance of the vertical wind velocity as a measure for the turbulence, helps to distinguish within the daytime boundary layer between layers of high aerosol content and layers with enhanced turbulence. The entrainment zone is seen in literature either as a transition zone or as the metrics of the variability of the boundary layer height. We show up to which extend these two quantities differ from each other. Concerning entrainment processes the use of the vertical wind data, additionally to the boundary layer height information, allows us to get a picture of the link between updrafts and downdrafts and changes in the boundary layer height.
Session 4, Lidar Application Studies in The Boundary Layer and Lower Troposphere - I
Tuesday, 13 January 2009, 1:30 PM-3:00 PM, Room 122A
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