On the Correlation between Convective Plume Updrafts and Downdrafts,Lidar Reflectivity and Depolarization Ratio |
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| Authors: | Fabien Gibert Juan Cuesta Jun-Ichi Yano Nicolas Arnault Pierre H Flamant |
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| Institution: | (1) Institut Pierre Simon Laplace, Laboratoire de Météorologie Dynamique, Ecole Polytechnique, Palaiseau Cedex, 91128, France;(2) Centre National de Recherche en Météorologie, Toulouse, France |
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| Abstract: | We question the correlation between vertical velocity (w) on the one hand and the occurrence of convective plumes in lidar reflectivity (i.e. range corrected backscatter signal Pz
2) and depolarization ratio (Δ) on the other hand in the convective boundary layer (CBL). Thermal vertical motion is directly
investigated using vertical velocities measured by a ground-based Doppler lidar operating at 2 μm. This lidar provides also
simultaneous measurements of lidar reflectivity. In addition, a second lidar 200 m away provides reflectivities at 0.53 and
1 μm and depolarization ratio at 0.53 μm. The time series from the two lidars are analyzed in terms of linear correlation
coefficient (ρ). The main result is that the plume-like structures provided by lidar reflectivity within the CBL as well as the CBL height
are not a clear signature of updrafts. It is shown that the lidar reflectivity within the CBL is frequently anti-correlated
(ρ (w, Pz
2 )) with the vertical velocity. On the contrary, the correlation coefficient between the depolarization ratio and the vertical
velocity ρ (w, Δ ) is always positive, showing that the depolarization ratio is a fair tracer of updrafts. The importance of relative humidity
on the correlation coefficient is discussed.
An erratum to this article can be found at |
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| Keywords: | Depolarization ratio Doppler lidar Lidar reflectivity Thermals Vertical velocities |
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