The land and atmosphere interact over a range of time scales. Here we focus on the rapid forcing of the land surface and the near-surface atmosphere by sun, clouds, and wind. During a two-week experiment over a vegetated field, we measured all the components in the surface radiation budget at 1 Hz sampling. We also measured the surface's infrared response to the shortwave and longwave forcing using narrow-beam and broadband infrared radiometers and an infrared camera.

Changes in surface forcing feed back almost immediately into changes in the properties and behavior of the near-surface atmosphere. To document this feedback, we also had at our site a full suite of turbulence instruments that measured the wind vector, air temperature, humidity, and carbon dioxide concentration with 10 Hz sampling. Working essentially with these high-frequency data, we concentrate in this presentation on a new technique for identifying nonstationarity in the atmospheric surface layer that results from the rapid forcing of surface temperature. Such procedures for isolating periods of nonstationarity are crucial for analyzing atmospheric surface layer data because the length of the window for any averaging must be chosen carefully when a time series is nonstationary.