Overview of the HI-SCALE Field Campaign: A New Perspective on Shallow Convective Clouds

Abstract

Shallow convective clouds are common, occurring over many areas of the world, and are an important component in the atmospheric radiation budget. In addition to synoptic and mesoscale meteorological conditions, land–atmosphere interactions and aerosol–radiation–cloud interactions can influence the formation of shallow clouds and their properties. These processes exhibit large spatial and temporal variability and occur at the subgrid scale for all current climate, operational forecast, and cloud-system-resolving models; therefore, they must be represented by parameterizations. Uncertainties in shallow cloud parameterization predictions arise from many sources, including insufficient coincident data needed to adequately represent the coupling of cloud macrophysical and microphysical properties with inhomogeneity in the surface-layer, boundary layer, and aerosol properties. Predictions of the transition of shallow to deep convection and the onset of precipitation are also affected by errors in simulated shallow clouds. Coincident data are a key factor needed to achieve a more complete understanding of the life cycle of shallow convective clouds and to develop improved model parameterizations. To address these issues, the Holistic Interactions of Shallow Clouds, Aerosols and Land Ecosystems (HI-SCALE) campaign was conducted near the Atmospheric Radiation Measurement (ARM) Southern Great Plains site in north-central Oklahoma during the spring and summer of 2016. We describe the scientific objectives of HI-SCALE as well as the experimental approach, overall weather conditions during the campaign, and preliminary findings from the measurements. Finally, we discuss scientific gaps in our understanding of shallow clouds that can be addressed by analysis and modeling studies that use HI-SCALE data.

The Impact of Variable Land‐Atmosphere Coupling on Convective Cloud Populations Observed During the 2016 HI‐SCALE Field Campaign

“…One factor not considered in this study that affects the observed droplet number distribution is the variability in aerosol concentrations. Fast et al (2019) and Figure S8 show a large spatial gradient in aerosol number concentrations along the afternoon G-1 flight path on 30 August (Figure 1c). The highest concentrations greater than 8,000 cm 3 just east of the Central Facility are likely due to emissions from nearby refineries and a coal-fired power plant.…”

“…We note that the present simulations omit the effect of aerosols which could shift the simulated cloud droplet distribution to smaller sizes because of the Twomey effect (Twomey, 1977). As shown in Fast et al (2019) and Figure S8, there are strong gradients in particle concentrations along the G-1 flight legs on this day. Some clouds are embedded in high aerosol concentrations likely originating from refinery and power plant emissions near the SGP site, while other clouds are embedded in lower background aerosol concentrations.…”

The Added Value of Large-eddy and Storm-resolving Models for Simulating Clouds and Precipitation

“…Even approaches like the LES ARM Symbiotic Simulation and observation workflow (LASSO) which are centered around intensive field measurements still adopt semi-idealized approaches using small domains which necessitate periodic boundary conditions (Fast et al, 2019). Super-parameterization has begun to allow a broader look at how an explicit representation of clouds couples to large-scale circulations (e.g., Parishani et al 2018), but still using individual sub-domains that remain small and idealized.…”

Fine‐Scale Variability of Observed and Simulated Surface Albedo Over the Southern Great Plains

“…The HI‐SCALE field study was conducted during the 2016 growing season and included two aircraft intensive operations periods (IOPs) utilizing the Department of Energy's Gulfstream‐1 (G‐1) aircraft, one in the spring (24 April through 21 May) and one in the late summer/early fall (28 August to 24 September). Details of the HI‐SCALE field study and the aircraft payload are documented by Fast et al (2019). This study utilizes BB irradiance data collected using upward‐ and downward‐looking Delta‐T SPN1 pyranometers installed on the top and bottom of the fuselage.…”