Lagrangian Evolution of Cloud Systems in the North Pacific

Marine boundary layer clouds cover vast areas of the eastern subtropical oceans and have a significant impact on the Earth’s radiation budget. Marine stratocumulus (Sc) clouds form in regions with cold sea surface temperatures (SSTs) and strong boundary layer inversion that is maintained by a largescale subsidence. As these clouds are advected towards the trade-wind regions that have warmer SSTs and weak inversion, they get decouple from the surface and transition to broken cumulus (Cu) clouds. This transition from stratocumulus to cumulus cloud (Sc-to-Cu) regime is thought to occur due to a complex interplay of processes modulated by surface fluxes, boundary layer radiative cooling, inversion strength, aerosols, and precipitation. During the Cloud System Evolution in the Trades (CSET) field campaign, observations of the Sc-to-Cu transition in the North Pacific were made in Lagrangian setting using the instruments onboard the NCAR’s Gulfstream-V High-Performance Instrumented Airborne Platform for Environmental Research (HIAPER) aircraft. Detailed sampling of aerosol, cloud, precipitation, thermodynamic, and radiation fields within few air-masses were made on outbound flights from Sacramento, CA to Kona, HI. The same air-masses at their new advected locations were resampled on the inbound flights a day later, yielding a Lagrangian evolution over one day. Total of 18 air-masses encompassing variety atmospheric conditions were sampled twice during 7 transects made from Sacramento to Kona. In this study, we have used these observations to 1) characterize the changes in aerosol, cloud macro- and micro-physical, and boundary layer properties for the transition, and 2) study the evolution of boundary layer structure through the integrated energy and moisture budgets. We further intend to classify the sampled transitions (e.g. change in ratio of latent heat flux to radiative cooling, change in accumulation mode aerosol concentrations) to assess the impact of different mechanisms on the cloud transition.