Rapid forcing of the surface and near-surface atmosphere

In April 2005, we carried out a two-week experiment to study rapid forcing of the surface and the near-surface atmosphere by clouds, sun, and wind. To document the nature of the forcing and the surface's response, we deployed hemispherical, broadband longwave and shortwave radiometers looking both up and down; up-looking and down-looking infrared thermometers; an all-sky camera; and an infrared camera pointed at the surface. We sampled the radiometers and thermometers at 1 Hz. To document the coupled response of the near-surface atmosphere, near these instruments, we sampled a sonic anemometer/thermometer and fast-responding water vapor and carbon dioxide sensors at 10 Hz. Finally, to put our measurements in a larger context, we used a laser-based surface-layer scintillometer system to measure path-averaged values of the refractive index structure parameter and the inner scale of turbulence every minute along a 182-m propagation path that was centered on our point measurements. Although our analysis is just beginning, we plan to focus on one or two interesting case studies in this presentation. Our methods will include correlation and time series analyses on this suite of measurements to document how rapidly variables like surface temperature, air temperature, humidity, wind speed, and refractive index structure parameter respond to changes in the radiative forcing. Visual inspection of these rapidly sampled variables has already shown us that the surface and near-surface atmosphere are rarely stationary, despite analysis practices that assume the contrary. Our work thus has implications for observing and modeling micrometeorological processes.