Interactions between a nocturnal mcs and the stable boundary layer as observed by an airborne compact raman lidar during PECAN

Small-scale variations within the low-level outflow and inflow of an MCS can either support or deter theupscale growth and maintenance of the MCS. However, these small-scale variations, in particular in thethermodynamics (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 aircraftdirectly sampled temperature and water vapor profiles at unprecedented vertical and along-track resolutionsalong the southern margin of a series of mature nocturnal MCSs traveling along a frontal boundary on 1 July2015 during the Plains Elevated Convection at Night (PECAN) campaign. Here, the capability of the airborneCRL to document interactions between the MCS inflow and outflow currents is illustrated. The CRL revealsthe well-defined boundary of a cooler current. This is interpreted as the frontal boundary sharpened byconvectively induced cold pools, in particular by the outflow boundary of the downstream MCS. In one CRLtransect, the frontal/outflow boundary appeared as a distinct two-layer structure of moisture and aerosolsformed 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 boundaryfavors MCS maintenance, through enhanced elevated CAPE and reduced CIN. The CRL data are sufficientlyresolved to reveal Kelvin-Helmholtz (KH) billows and the vertical structure of the outflow boundary, whichin this case behaved as a density current rather than an undular bore.