Observations on the growth of an internal boundary layer with a Lidar technique

The distribution of atmospheric water vapor across a step change in surface humidity (dry-wet) was observed by a Lidar measurement technique under neutral atmospheric stability condition. The technique uses multiple elevation scans from a scanning water Raman-Lidar to construct a time-averaged image of the variation in water vapor concentration with height and distance. The measurements were obtained from a bare soil field in California's central valley. The growth of the vapor blanket over the wet surface was identified by the spatial distribution of the specific humidity over the field. The height of the local humidity boundary layer under neutral atmospheric stability condition was observed to increase as δ_v ∝ X^0.87, where x is the downstream distance from surface humidity discontinuity line. Evaporation rates calculated from the humidity profiles agreed satisfactorily with the fluxes independently measured using a lysimeter.