The Heat Budget of the Near-Surface Atmosphere under Varying Cold-Fog Conditions

The Cold-Fog Amongst Complex Terrain (CFACT experiment), conducted in early 2022 in Heber Valley, Utah, offers a unique dataset to study the life cycle of ephemeral and persistent fog events. CFACT was designed to investigate the complex interactions between multi-scalar meteorological and microphysical processes that govern the formation of cold fog in a typical alpine basin.

Heber Valley was instrumented with two supersites and nine satellite sites with meteorological flux and surface energy balance towers. Microphysical and aerosol observations were made at the Deer Creek supersite. Doppler wind LiDARs, ceilometers, and a wind profiler probed the boundary layer. Intensive observational periods added a tethersonde and frequent radiosonde ascents.

This presentation aims at evaluating the differences in the heat budget in the lowest 30 m of the boundary layer under two different conditions conducive for the formation of cold fog: First, the formation of ephemeral (i.e. short-lived) fog that will be shown to be caused by intermittent mixing events, and secondly under conditions when more persistent fog covered the experimental area for up to several hours. By investigating the individual terms of the heat budget and their relative importance we can determine the different mechanisms modulating the fog life cycle. We will make extensive use of the NCAR/EOL provided flux tower datasets and microphysical observations with optical particle counters at the Deer Creek Supersite.