Comparison of atmospheric temperature structure at the wall and in the middle of a valley

Previously reported results indicate that measurements of temperatures near ground level on hillsides and valley walls serve as a reasonable approximation to the ambient nocturnal lapse rates. At Anderson Creek Valley in the Geysers area of California temperatures on the valley wall were compared with temperature profiles in the middle of the valley. An ensemble of temperature measurements including vertical soundings and surface based measurements from fixed stations and a mobile unit were analyzed. Although intercalibration was not rigorously conducted between the various systems, each system was calibrated independently and sufficient agreement exists when sensors were co-located to support confidence in the measurements. Surface measurements at various altitudes in Anderson Creek Valley were as much as 10/sup 0/C cooler than the temperature in mid-valley at the same altitude. The departures were smallest in the early evening and grew during the night. The cold air was quite shallow and if care were taken to make ground-based measurements on promontaries or towers, the gross stability could be characterized by surface temperature observations up the side of the valley. A more promising analysis of the data is to interpret the thermal gradients from the valley wall to the center in terms of the driving force they provide to the drainage flow. The circulations theorem of Bjerknes provides the link between the stable temperature gradients on sloping ground and the velocity field through pressure-density solenoids. By applying the theorem and accounting for frictional drag effects at the surface, a drainage domain about 100 m in depth with a speed of 4 m s/sup -1/ at TVR is estimated. Measured with profiles at that location show quite good agreement in a sublayer although larger scale driving forces account for a complex structure of wind speed and direction above the 100 to 200 m layer. (JGB