Summary

The Cloud and Aerosol Chemistry Experiment (CACHE) was designed to probe the remote marine atmosphere, and investigate its interaction with a montane, coastal forest on the Olympic Peninsula of Washington State.The prime objective of this experiment was to make in situ measurements of cloudwater fluxes to the forest canopy, and to identify the governing processes for cloud water deposition. Other goals included analysis of the relationship between cloud microphysics and precursor aerosol, and quantification of carbon dioxide exchange between forest and atmosphere.

Researchers believe cloud water deposition to be important both hydrologically and chemically for montane ecosystems where it occurs frequently, and it has been sited as a potential cause of forest injury in the Appalachian Mountains of the Eastern U.S. However, very few direct measurements of this process have been made; more often, researchers have resorted to the use of inferential measurements and models which have not been validated. In 1993 and 1994, Oregon State University (OSU) researchers conducted eddy correlation measurements (CACHE 1 and 2) of cloud water deposition at Cheeka Peak, Washington.They measured substantial liquid water fluxes of ~1mm per 24 hours of surface cloud, about twice the magnitude of those reported by researchers in the United Kingdom. The greatest uncertainty in the reported measurements is the degree to which the flux measured at a single point over the canopy is representative of fluxes over a broader area of complex terrain.