Cyclogenesis near the Adélie Coast and influence of the low-level wind regime

Previous studies have indicated that the Adélie Coast and George V Coast regions of Antarctica, near 150°E, feature a high frequency of cyclogenesis. However, little explanation has been given as to the physical mechanisms responsible for this frequency maximum. This study discusses the physical mechanisms responsible for cyclogenesis near 150°E from three years (2003-2005) of model output from the Antarctic Mesoscale Prediction System (AMPS). Composites and case study events are presented to analyze the physical mechanisms involved in cyclone development. Two primary cyclone development patterns are identified, termed Type I and Type II. The low-level wind regime is a prominent factor in cyclone development for both Type I and Type II cases. For Type I development, barrier winds and katabatic winds interact to form a low-level easterly jet along the Antarctic coast that leads to enhanced regions of low-level vorticity and baroclinicity that are favorable for cyclone development. In Type II development, low-level vorticity is enhanced on the cyclonic-shear side of the Adélie Land katabatic jet. The inference that cyclogenesis occurs in conjunction with an existing system is supported for both types of development, as upper-level support is present. However, at least for Type I systems, the initial cyclone development can be restricted to low levels, as favorable upper-level conditions are only required for further development and propagation of the system. The use of AMPS, a mesoscale model tailored for the polar environment, is necessary in order to study the physical development mechanisms associated with cyclogenesis in coastal Antarctica. Automated cyclone tracking studies utilizing global reanalyses can only infer possible reasons for cyclone development based on the time-averaged basic meteorological conditions.