Abstract

One of the largest uncertainties in climate change prediction is associated with cloud formation. A change in cloudiness small enough to be undetectable by satellites can have a large impact on global climate. It is therefore very important to accurately measure the meteorological parameters associated with cloud formation. These parameters include water vapor, cloud condensation nuclei (CCN), and vertical lofting of air to colder altitudes. For boundary layer clouds, the vertical velocities associated with lofting need only be a few centimeters per second. The vertical velocity can be induced by topographical features and/or surface heat flux. We will describe an experiment that used optical techniques to quantify surface heat flux changes related to boundary layer cloud formation and cloud shadowing effects and relate these changes to convergence associated with vertical velocities over a dry prairie grassland. The major result of this experiment showed that optical turbulence at different scales provides heat and momentum flux changes associated with cloud effects on a time scale fast enough to resolve cloud formation and movement. Standard tower measurements, because they are not spatially averaged, require tens of minutes for valid comparable estimates.

© 1993 Optical Society of America