Regional forest-ABL coupling: influence on CO{sub 2} and climate. Progress to date

Abstract

A National Center for Atmospheric Research (NCAR) Integrated Sounding System (ISS) was deployed about 5 km east of the WLEF-TV tower in Chequamegon National Forest, Wisconsin. The tower is instrumented for high-precision, high-accuracy CO{sub 2} mixing ratio measurements at six levels up to 396 m above ground and continuous eddy-covariance flux measurements at three levels up to 396 km. The ISS, including boundary layer radar profile, radio acoustic sounding system, and rawinsonde system was operated from March through October of 1998 and 1999. The NCAR ISS was also deployed at the Walker Branch flux tower in Oak Ridge, Tennessee from March through November of 1999. Continuous observations of atmospheric structure including radar reflectivity and horizontal wind profiles were collected at each site, and rawinsondes were launched at midday once per week. Boundary layer depths were derived from the radar reflectivity data. A combination of tall tower and radar boundary layer depths was us ed to describe the seasonal evolution of the diurnal mixing depth and its relationship to local turbulent forcing and synoptic conditions. These depths were compared with model predictions from a General Circulation Model (GCM). The proposed method of computing the jump in CO{sub 2} mixing ratio across the convective boundary layer top was tested on data from September, 1995; a journal publication is in preparation. A paper describing the comparison between GCM boundary layer depths and the observations, as well as the covariance between mixing depth and surface fluxes (the forcing for the rectifier effect) has been drafted.