LINKING BOUNDARY-LAYER CIRCULATIONS AND SURFACE PROCESSES DURING FIFE-89 .1. OBSERVATIONAL ANALYSIS

Surface, aircraft, and satellite observations are analyzed for the 21- day 1989 intensive field campaign of the First ISLSCP Field Experiment (FIFE) to determine the effect of precipitation, vegetation, and soil moisture distributions on the thermal properties of the surface inclu ding the heat and moisture fluxes, and the corresponding response in t he boundary-layer circulation. Mean and variance properties of the sur face variables are first documented at various time and space scales. These calculations are designed to set the stage for Part II, a modeli ng study that will focus on how time-space dependent rainfall distribu tion influences the intensity of the feedback between a vegetated surf ace and the atmospheric boundary layer. Further analysis shows strongl y demarked vegetation and soil moisture gradients extending across the FIFE experimental site that were developed and maintained by the ante cedent and ongoing spatial distribution of rainfall over the region. T hese gradients are shown to have a pronounced influence on the thermod ynamic properties of the surface. Furthermore, perturbation surface wi nd analysis suggests for both short-term steady-state conditions and l ong-term averaged conditions that the gradient pattern maintained a di urnally oscillating local direct circulation with perturbation vertica l velocities of the same order as developing cumulus clouds. Dynamical and scaling considerations suggest that the embedded perturbation cir culation is driven by surface heating/cooling gradients and terrain ef fects rather than the manifestation of an inertial oscillation. The im plication is that at even relatively small scales (<30 km), the differ ential evolution in vegetation density and soil moisture distribution over a relatively homogenous ecotone can give rise to preferential bou ndary-layer circulations capable of modifying local-scale horizontal a nd vertical motions.