Routine AAF Clouds with Low Optical Water Depths (CLOWD) Optical Radiative Observations (RACORO)
As in other mid-latitude regions, low-level boundary-layer clouds occur frequently at the ACRF Southern Great Plains site.
Clouds with low-optical water depths (CLOWD) refer to "thin" clouds that contain a limited amount of water, which are often below 100 g/m2. This cloud type is very common—occurring in the earth's boundary-layer (from the earths' surface up to about 2.5 km) throughout the globe. However, because these clouds are thin and often broken, even the best ground-based instruments have trouble accurately measuring their cloud properties. Attempts to retrieve these properties by different methods produces varying results, and such discrepancies prevent resolving uncertainties within climate models. To resolve this dilemma, a better understanding of this cloud type is needed that can only be achieved by acquiring the critical in-situ data needed to evaluate and refine existing retrieval algorithms from ground-based instruments.
This figure shows a potential flight configuration during RACORO. The Twin Otter aircraft will take measurements at five different altitudes, up to 12,000 ft (about 3600 m), then spiral down in close proximity to the SGP site. Flights will occur at different times throughout the day to sample variations in cloud properties.
Between January and June 2009, the RACORO field campaign will conduct routine flights below, within, and above these boundary layer liquid-water clouds in the vicinity of the ACRF Southern Great Plains site. Coordinated by the ARM Aerial Facility*, a Twin Otter aircraft equipped with a full payload of research instrumentation will obtain representative statistics of cloud microphysical, aerosol, and radiative properties of the atmosphere. The data will be used to validate retrieval algorithms and support process studies and model simulations of boundary layer clouds and, in particular, CLOWD-type clouds.
For additional details, see the RACORO Science Questions web page or the RACORO Data Guide. The data guide includes a summary of contacts, aircraft instrumentation, instrument status per flight, and flight patterns used.
*The ARM Aerial Facility was previously known as the ARM Aerial Vehicles Program.