CLASIC

Cumulus convection is an important component of the atmospheric radiation budget and hydrologic cycle of the Southern Great Plains (SGP), particularly during the summertime growing season. Continental cumulus convection is strongly modulated by land surface conditions, while at the same time influencing the land surface itself through rain-induced changes in soil moisture and through its impact on photosynthesis. Land surface conditions determine whether the partitioning of surface available energy is dominated by the sensible heat flux or by the latent heat flux, which is an important factor in the evolution of the convective boundary layer. Consequently, land surface characteristics influence the timing and evolution of cumulus convection, in particular the cloud base height, cloud depth, and convective available potential energy. The four ARM Working groups endorsed an Intensive Observation Period (IOP at the Southern Great Plains (SGP) Climate Research User Facility during the summer of 2007. The purpose of this IOP was to advance our understanding of cumulus convection and its controls, particularly those associated with land surface processes. The Cloud and Land Surface Interaction Campaign (CLASIC) IOP covered a period of 1-3 months straddled the winter wheat harvest when large changes in the land surface lead to large changes in the surface albedo, latent heat flux, and sensible heat flux. The working groups were particularly interested in the relationship between land surface processes and the observed cloud cover, and vice versa. The new science that was proposed addressed specific aspects of the problem, especially known model deficiencies and gaps in our physical understanding of cloud and land surface feedbacks. In addition to advancing climate science, the working groups believed that this IOP would help realize the potential of ARM’s new instrument capabilities, provide significant validation data for NASA’s new active satellite remote sensors, and enhance ACRF capabilities by expanding into cross-discipline research.

Science Questions:

1. What are the roles of cumulus convection and spatial variations in land cover in depleting low-level water vapor as it is advected into the SGP region?

2. What are the relationships between cumulus clouds and aerosols and the soil-plant-atmosphere exchange of energy, carbon, and water at the site?

3. How do soil moisture and land cover changes, such as agricultural harvesting, impact the surface energy, carbon, and water fluxes, and can they impact local and regional cumulus cloud formation at the SGP site?

4. How do land surface processes at the SGP affect atmospheric aerosol loading and chemistry and what are the resulting effects on the microphysical and macrophysical properties of cumulus cloud fields?

5. How well do the local measurements of the sensible, latent, and carbon fluxes made at the SGP represent the domain average fluxes?

For list of contributors to this field campaign, refer to the sponsors.

Campaign Data Sets

SGP Data Sources