Lead Scientist Abstract

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) field campaign in the Sierras de Córdoba mountain range of north-central Argentina is designed to improve understanding of cloud life cycle and organization in relation to environmental conditions so that cumulus, microphysics, and aerosol parameterizations in multiscale models can be improved. The Sierras de Córdoba 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 in a key agricultural region. Many environmental factors influence the convective life cycle 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, is common in the austral spring. 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 the Sierras de Córdoba an ideal location to improve understanding of cloud-environment interactions. The following primary science questions will be addressed through coordinated ARM Climate Research Facility and guest instrumentation observations:

• How are the properties and life cycles of orographically generated cumulus humilis, mediocris, and congestus clouds affected by environmental kinematics, thermodynamics, aerosols, and surface properties? How do these cloud types alter these environmental conditions?
• 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?

The ARM Aerial Facility Gulfstream-159 (G-1) aircraft will be deployed near the first ARM Mobile Facility (AMF1) location for approximately six weeks—November 1 to December 15, 2018—to support the CACTI science goals. The G-1 flight measurements will provide information on orographic cumulus clouds and deep convective systems. For orographic cumulus clouds, the G-1 measurements will characterize in-cloud dynamics, microphysics, and aerosols, as well as the environmental variability around the clouds focusing on conditions upstream and downstream of clouds at multiple altitudes in the vicinity of the AMF1 site. In situations of significant aerosol heterogeneity, emphasis will be placed on observations in and out of aerosol plumes in the vicinity of the clouds. For deep convective systems, the G-1 measurements will focus on characterizing the environmental conditions that lead to convective initiation and the vertical profiles of environmental properties around the growing deep convection and in adjacent regions that are not initiating deep convection so that the differences in environment can be compared. Convective inflow and free tropospheric properties from the G-1 aircraft will be important for putting AMF1 observations into context and for providing input to numerical simulations.