Comparison of Convective Boundary Layer Characteristics from Aircraft and Wind Lidar Observations

Abstract

AbstractDuring the Convective Storm Initiation Project experiment, which was conducted in summer 2005 in southern England, vertical velocity in the convective boundary layer (CBL) was measured simultaneously with a research aircraft and a wind lidar. The aircraft performed horizontal flight legs approximately parallel to the prevailing wind direction and centered over the lidar. This measurement setup allows for the comparing of CBL characteristics (CBL depth zi, integral length scale lw, spectral peak wavelength ?m, and vertical velocity variance σw2) from temporal (lidar) and spatial (aircraft) measurements. For this, the lidar time series are transferred into space using the mean wind. While the statistics of the aircraft data are all based on the 34-km flight legs, the averaging interval for the lidar is either 1 h or a longer period that corresponds to the 34-km leg. Although the lw and ?m values from aircraft and lidar measurements are in the same range (100?200 and 500?2000 m) and agree well on the average, the correlation for individual legs is very low (R2 < 0.17). One possible explanation is the large uncertainty that arises from the transfer of the lidar time series to space. For σw2, the agreement between aircraft and lidar is better for individual legs (R2 ≥ 0.63), but the mean absolute difference in σw2 is about 2.5 times as large as the statistical error. We examine the nonstationarity and heterogeneity for the lidar and aircraft samples and can exclude these as the major sources for the large differences between lidar and aircraft data.