Central Australian Cold Fronts

Abstract

This paper presents an observational study of the structure and behavior of cold fronts over central Australia during the late dry season, a time of year when the prefrontal convectively well-mixed layer is particularly deep. The study is based on the results of the Central Australian Fronts Experiments (CAFE) held in 1991. Three fronts were documented in unprecedented detail for the Australian region using a greatly enhanced surface-observing network and a boundary layer wind profiler, as well as serial upper-air soundings. Data on the surface energy balance were obtained also. A common feature of the fronts observed during CAFE was that they were dry. shallow (?1 km deep), and moved into a deep (?4 km) convectively well-mixed boundary layer. One of them initiated major dust storms across central Australia. A prominent feature of the fronts was the marked diurnal variation of their surface signature as they moved through the network. Noteworthy was the tendency during the night for the initiation in the accompanying trough of undular borelike structures or other nonlinear wave disturbances that moved ahead of the main airmass change. One well-documented case illustrates the generation of a southerly morning glory bore wave in the southern Gulf of Carpentaria region. During the daytime, fronts over central Australia are difficult to locate from surface data and appear to decelerate and to weaken greatly. Some dynamical aspects of the observations are discussed.