CLASSIC: A proposed strategy to study CLouds And Smoke over the Southeast atlantIC

Description

Southern Africa is the world’s largest emitter of biomass burning aerosols. Their westward transport over the remote southeast Atlantic ocean colocates some of the largest atmospheric loadings of absorbing aerosol with the least examined of the Earth’s major subtropical stratocumulus decks. The processes modulating the cloud adjustments to aerosol-radiation interactions and to aerosol-cloud interactions remain poorly elucidated, and the associated irradiance changes remain uncertain. CLASSIC is a strategy to improve our understanding of these processes through a primary instrumentation of the remote St. Helena Island (5W, 15S), located directly west of the main stratocumulus deck, and a sparser instrumentation of Ascension Island (15W, 8S). Ascension Island lies within the trade-wind-cumulus-dominated regime located approximately downwind of St. Helena. St Helena Island lies within a stratocumulus-dominated regime (0.4-0.7 seasonally-varying low cloud fraction) with the cloud deck residing underneath a smoke layer of varying optical depth and vertical distribution from July through October. The driving science questions for CLASSIC are: 1) how do the low cloud properties at St. Helena vary as a function of the location, amount, and optical properties of the absorbing aerosol? 2) are carbonaceous aerosol present in the St. Helena boundary layer, and if so, are they capable of affecting the cloud microphysics, precipitation susceptibility, and cloud mesoscale organization? and, 3) is there a correlation between the smoke and cloud conditions at Ascension Island with those at St. Helena? We are proposing to apply AMF1 instrumentation to address these questions, and seek input from the DOE ASR community towards developing the best strategy. Additional information is also supplied by AERONET sites at one or both islands, as well as at least daily radiosondes launched by the UK Meteorological Office. This poster will provide an overview of our thoughts and planning to date.