Nocturnal boundary-layer flow over a long low ridge in central Australia

The results of a field investigation of the nocturnal boundary-layer flow across a low (~250 m) east-west ridge in central Australia during September to December 1988 are presented. At this location, the most common geostrophic wind directions are easterly and south-southeasterly. We found that easterly geostrophic flow tends to be associated with northerly downslope winds peaking about sunrise, while the south-southeasterly geostrophic flow tends to be associated with southerly down- slope winds peaking about midnight. Hydraulic jumps associated with these downslope winds are evident from sudden changes in wind and temperature at the leeward sites. Other interesting features found during the field investigation were quasi-stationary lee rotors and nocturnal leeward wind surges associated with cold frontal passages.