Interactions between a Nocturnal MCS and the Stable Boundary Layer as Observed by an Airborne Compact Raman Lidar during PECAN

Abstract

Small-scale variations within the low-level outflow and inflow of an MCS can either support or deter the upscale growth and maintenance of the MCS. However, these small-scale variations, in particular in the thermodynamics (temperature and humidity), remain poorly understood, due to a lack of detailed measurements. The compact Raman lidar (CRL) deployed on the University of Wyoming King Air aircraft directly sampled temperature and water vapor profiles at unprecedented vertical and along-track resolutions along the southern margin of a series of mature nocturnal MCSs traveling along a frontal boundary on 1 July 2015 during the Plains Elevated Convection at Night (PECAN) campaign. Here, the capability of the airborne CRL to document interactions between the MCS inflow and outflow currents is illustrated. The CRL reveals the well-defined boundary of a cooler current. This is interpreted as the frontal boundary sharpened by convectively induced cold pools, in particular by the outflow boundary of the downstream MCS. In one CRL transect, the frontal/outflow boundary appeared as a distinct two-layer structure of moisture and aerosols formed by moist stable boundary layer air advected above the boundary. The second transect, one hour later, reveals a single sloping boundary. In both cases, the lofting of the moist stably stratified air over the boundary favors MCS maintenance, through enhanced elevated CAPE and reduced CIN. The CRL data are sufficiently resolved to reveal Kelvin–Helmholtz (KH) billows and the vertical structure of the outflow boundary, which in this case behaved as a density current rather than an undular bore.

Airborne Measurements of Scale‐Dependent Latent Heat Flux Impacted by Water Vapor and Vertical Velocity Over Heterogeneous Land Surfaces During the CHEESEHEAD19 Campaign

“…Net radiation ( Rnet ) data were also collected to provide information on theoretical maximum latent plus sensible heat fluxes. The UWKA also sampled 2D vertical profiles of water vapor, aerosols, and temperature below the flight level using a nadir‐pointing Compact Raman Lidar (CRL, Lin et al., 2019, 2023; Liu et al., 2014; Z. Wang, 2020; Wu et al., 2016) and aerosols with the zenith‐pointing Wyoming Cloud Lidar (Lin et al., 2021; Z. Wang et al., 2009) at 400 m height. Three IOPs with the UWKA were conducted during the experiment in each month from July to September (details in Table 1).…”

Airborne Measurements of Scale-Dependent Latent Heat Flux Impacted by Water Vapor and Vertical Velocity over Heterogeneous Land Surfaces During the CHEESEHEAD19 Campaign

“…Net radiation (Rnet) data were also collected to provide information on theoretical maximum latent plus sensible heat fluxes. The UWKA also sampled 2D vertical profiles of water vapor, aerosols, and temperature below the flight level using a nadir-pointing Compact Raman Lidar (CRL; Liu et al, 2014;Wu et al, 2016;Lin et al, 2019;Lin et al, 2023) and aerosols with the zenith-pointing Wyoming Cloud Lidar (Wang et al, 2009;Lin et al, 2021) at 400 m height. Three IOPs with the UWKA were conducted during the experiment in each month from July to September (details in Table 1).…”