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Water vapour variability within a convective boundary layer assessed by Large Eddy Simulations and IHOP_2002 observations

Couvreux, F. and Guichard, F. and Redelsperger, J.-L. and Kiemle, Ch. and Masson, V. and Lafore, J.-P. and Flamant, C. (2005) Water vapour variability within a convective boundary layer assessed by Large Eddy Simulations and IHOP_2002 observations. Quarterly Journal of the Royal Meteorological Society, 131, pp. 2665-2693. DOI: 10.1256/qj.04.167.

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Official URL: http://www3.interscience.wiley.com/cgi-bin/abstract/113522716/ABSTRACT?CRETRY=1&SRETRY=0

Abstract

This study presents a comprehensive analysis of the variability of water vapour in a growing convective boundary-layer (CBL) over land, highlighting the complex links between advection, convective activity and moisture heterogeneity in the boundary layer. A Large-eddy Simulation (LES) is designed, based on observations, and validated, using an independent data-set collected during the International H2O Project (IHOP_2002) field-experiment. Ample information about the moisture distribution in space and time, as well as other important CBL parameters are acquired by mesonet stations, balloon soundings, instruments on-board two aircraft and the DLR airborne water-vapour differential-absorption lidar. Because it can deliver two-dimensional cross-sections at high spatial resolution (140 m horizontal, 200 m vertical), the airborne lidar offers valuable insights of small-scale moisture-variability throughout the CBL. The LES is able to reproduce the development of the CBL in the morning and early afternoon, as assessed by comparisons of simulated mean profiles of key meteorological variables with sounding data. Simulated profiles of the variance of water-vapour mixing-ratio were found to be in good agreement with the lidar-derived counterparts. Finally, probability-density functions of potential temperature, vertical velocity and water-vapour mixing-ratio calculated from the LES show great consistency with those derived from aircraft in situ measurements in the middle of the CBL. Downdraughts entrained from above the CBL are governing the scale of moisture variability. Characteristic length-scales are found to be larger for water-vapour mixing-ratio than for temperature The observed water-vapour variability exhibits contributions from different scales. The influence of the mesoscale (larger than LES domain size, i.e. 10 km) on the smaller-scale variability is assessed using LES and observations. The small-scale variability of water vapour is found to be important and to be driven by the dynamics of the CBL. Both lidar observations and LES evidence that dry downdraughts entrained from above the CBL are governing the scale of moisture variability. Characteristic length-scales are found to be larger for water-vapour mixing-ratio than for temperature and vertical velocity. In particular, intrusions of drier free-troposphere air from above the growing CBL impose a marked negative skewness on the water-vapour distribution within it, both as observed and in the simulation. Copyright © 2005 Royal Meteorological Society.

Document Type:Article
Title:Water vapour variability within a convective boundary layer assessed by Large Eddy Simulations and IHOP_2002 observations
Authors:
AuthorsInstitution or Email of Authors
Couvreux, F.CNRM/GAME, F
Guichard, F.CNRM/GAME, F
Redelsperger, J.-L.CNRM/GAME, F
Kiemle, Ch.UNSPECIFIED
Masson, V.CNRM/GAME, F
Lafore, J.-P.CNRM/GAME, F
Flamant, C.IPSL/SA, F
Date:2005
Journal or Publication Title:Quarterly Journal of the Royal Meteorological Society
Refereed publication:Yes
In Open Access:No
In SCOPUS:Yes
In ISI Web of Science:Yes
Volume:131
DOI:10.1256/qj.04.167
Page Range:pp. 2665-2693
Status:Published
Keywords:water vapour lidar, convective boundary layer, IHOP_2002 campaign, Heterogeneities, High-resolution simulations, Humidity Lidar data
HGF - Research field:Aeronautics, Space and Transport
HGF - Program:Aeronautics
HGF - Program Themes:L VU - Air Traffic and Environment (old)
DLR - Research area:Aeronautics
DLR - Program:L VU - Air Traffic and Environment
DLR - Research theme (Project):L - Air Traffic and Weather (old)
Location: Oberpfaffenhofen
Institutes and Institutions:Institute of Atmospheric Physics > Lidar
Deposited By: Christiane Münster
Deposited On:31 Jul 2007
Last Modified:11 Nov 2014 21:56

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