The Department of Energy Cloud, Aerosol, and Complex Terrain Interactions (CACTI) field campaign was selected for funding by the US Department of Energy Atmospheric Radiation Measurement program for 2018-19. This campaign will investigate the forcing, structure, and life cycle of orographic convection for a period of 8 months with the Atmospheric Radiation Measurement mobile facility 1 (AMF-1), CSAPR-2 dual polarization precipitation radar, a hydrometeorlogical network, and Mobile Aerosol Observing Facility (MAOS). A 1.5-month intensive observing period (IOP) during late 2018 will add the ARM Gulfstream-1 microphysics and aerosol sampling aircraft to study wet season convective development and upscale growth. The project description is below, also check out the DOE ARM CACTI web site. Our group will participate extensively in the planning and execution of this campaign.
General circulation models and downscaled regional models exhibit persistent biases in deep convective initiation location and timing, cloud top height, stratiform area and precipitation fraction, and anvil coverage. Despite important impacts on the distribution of atmospheric heating, moistening, and momentum, nearly all climate models fail to represent convective organization, while system evolution is not represented at all. Improving representation of convective systems in models requires characterization of their predictability as a function of environmental conditions, and this characterization depends on observing many cases of convective initiation, non-initiation, organization, and non-organization.
The Cloud, Aerosol, and Complex Terrain Interactions (CACTI) experiment in the Sierras de Córdoba mountain range of north-central Argentina is designed to improve understanding of cloud lifecycle and organization in relation to environmental conditions so that cumulus, microphysics, and aerosol parameterizations in multi-scale models can be improved. The Sierras de Córdoba range has a high frequency of orographic boundary layer clouds, many reaching congestus depths, many initiating into deep convection, and some organizing into mesoscale systems uniquely observable from a single fixed site. Some systems even grow upscale to become among the deepest, largest, and longest-lived in the world. These systems likely contribute to an observed regional trend of increasing extreme rainfall, and poor prediction of them likely contributes to a warm, dry bias in climate models downstream of the Sierras de Córdoba range in a key agricultural region.
Many environmental factors influence the convective lifecycle in this region including orographic, low level jet, and frontal circulations, surface fluxes, synoptic vertical motions influenced by the Andes, cloud detrainment, and aerosol properties. Local and long range transport of smoke resulting from biomass burning as well as blowing dust are common in the austral spring, while changes in land surface properties as the wet season progresses impact surface fluxes and boundary layer evolution on daily and seasonal time scales that feed back to cloud and rainfall generation. This range of environmental conditions and cloud properties coupled with a high frequency of events makes this an ideal location for improving our understanding of cloud-environment interactions.
The following primary science questions will be addressed through coordinated ARM and guest instrumentation observations:
1. How are the properties and lifecycles of orographically generated cumulus humulis, mediocris, and congestus clouds affected by environmental kinematics, thermodynamics, aerosols, and surface properties? How do these cloud types alter these environmental conditions?
2. How do environmental kinematics, thermodynamics, and aerosols impact deep convective initiation, upscale growth, and mesoscale organization? How are soil moisture, surface fluxes, and aerosol properties altered by deep convective precipitation events and seasonal accumulation of precipitation?