Boundary layer structure, including land-atmosphere interactions and turbulence
Description
Figure 1. Doppler lidar observations of the convective boundary layer and cloud layer development on 3 August 2017 at ARM SGP Central Facility. Vertical velocity is colored, with red (blue) indicating updrafts (downdrafts). Cloud base detections from the lidar are shown in green. The day was initially characterized by shallow convection, but the vigorous updraft near 21:30 UTC initiated a deep convective cloud
The evolution of the cumulus-topped convective boundary layer is examined using a network of Doppler lidars (DL) and a large sample of days with cumulus convection. The network comprises 5 DLs distributed within a 50 km radius of ARM-SGP, including one DL at the Central Facility. The time period for the study is the warm season (May-Sept) 2016-2017. The first part of this study focuses on shallow cumulus (ShCu) conditions (50+ days), whereas the second part examines processes affecting locally forced transitions from shallow to deep convective clouds (10+ days, c.f. Fig. 1). Vertical velocity, updraft frequency, cloud fraction, vertical velocity variance and vertical velocity skewness are compared amongst the sites. These results provide useful context for assessing the representativeness of single column observations for both boundary layer and cloud layer studies. They also elucidate some of the processes contributing to initiating and sustaining deep convection, including the vertical velocity structure of gust fronts (a.k.a. outflow boundaries, cold pools, gravity currents, etc.) and penetrative thermals.
