Long-Term Vertical Velocity Statistics Derived from Doppler Lidar in the Continental Convective Boundary Layer

Much of our knowledge of the behavior of vertical velocity in the convective boundary layer is based on a relatively small number of short-term observations made using either in situ or remote sensing techniques. Unfortunately, analysis of long-term statistics have been lacking due to the scarcity of appropriate measurements. The US Department of Energy's Atmospheric Radiation Measurement (ARM) Climate Research Facility is addressing this shortcoming through the deployment of a suite of scanning Doppler Lidars at a number of locations around the globe including one in the Southern Great Plains that is the basis of this work. In this study, we utilize data collected from a system that has been acquiring high-resolution (30 m and ~1 sec) vertical staring data nearly continuously since 2011 to examine the long-term behavior of vertical velocity variance and higher order statistics over the depth of the planetary boundary layer (PBL). The application of normalizations using typical PBL scales, such as the mixed-layer depth and Deardorff convective velocity scale, do a good job collapsing the data onto a single curve, albeit with considerable amounts of scatter. The observed behavior is robust, even when different wind directions, time of day, and atmospheric instabilities are considered. In contrast, systematic differences are noted for conditions with relatively small and large values of the friction velocity measured near the surface, with large values of friction velocity leading to larger values of vertical velocity variance regardless of the altitude. Overall, our results are consistent with previously published findings. There is, however, a tendency for the retrieved values of normalized variance to be smaller in magnitude than values seen in other studies, and possible causes for this inconsistency will be discussed.