CASES-99 Field Experiment: An Overview

The Cooperative Atmosphere - Surface Exchange Study (CASES) field experiment was conducted during October, 1999 near Leon, Kansas. The objectives were to: (1) to provide a time history of internal gravity waves, K-H shear instabilities, and turbulence in the nighttime stable layer and to evaluate the relative contributions to intermittent heat, moisture and momentum fluxes associated with these phenomena; (2) to measure heat and momentum fluxes and their divergences accompanying the events contributing to turbulence, transports, and mixing throughout the nocturnal boundary layer, especially the surface layer, to assess the departures from similarity theory under weakly stable and very stable conditions; (3) to define the relative importance of surface heterogeneity, particularly under very light stable wind conditions, on the initiation of shallow drainage currents, and the horizontal and vertical wind transports that accompany such boundary undulations; and (4) to acquire data during the transition form a convective to a stable boundary layer regime and vice-versa to compare with existing models of these transitions, and to assess the role of the transition periods in the inertial oscillations and the enhancement of low-level jets about 100 to 300 m above the surface.

This was truly a cooperative, multi-sponsor, multi-investigator, multinational field measurement program. Over twenty different measurement systems were deployed by twenty-four research teams to measure the structure and evolution of the nocturnal boundary layer. Eleven intensive operation periods were conducted using ground based systems, multiple towers, acoustic, laser, and radar profilers, an instrumented kite, scanning lidars, and two instrumented aircraft throughout most of the periods. Very preliminary results indicate that shear instabilities and significant wave activity were observed and measured with intermittent fluxes aloft and near the ground; development and decay of low-level jets were measured at various altitudes, and the evolving nocturnal boundary layer was observed at unprecedented time and space scales.

An overview of measurements, operations and some preliminary examples of observed data will be presented.