Tropical‐extratropical cloudbands in the Australian region

Abstract

AbstractThe climatology of the tropical‐extratropical cloudbands (TECBs) in the Australian region is examined, using a subdivision of the cloudband phenomena, according to their convective sources of origin. In addition to previously described parameters (e.g. amplitude of mid‐latitude troughs, cross‐equatorial flow, jet stream), the 1979–1983 TECB activity is analysed with respect to other indices, such as global pressure and sea‐surface temperature, the Southern Oscillation Index (SOI), 40–50‐day oscillation, Hadley cell circulation or cloudiness anomalies. It is shown that during a period marked by a significant decrease in the TECB activity, 5–6 months prior to the lowest value of the SOI, the TECB tends to develop in 40–50‐day intervals, whereas otherwise, its development can be associated with higher frequency (18–21 day) oscillations. Similar fluctuations have also been observed in tropical cloudiness in the TECB area of origin. On a large‐scale, the TECB activity seems to be closely linked to large‐scale pressure fluctuations in the Indian and northern Pacific Oceans.