SOUTHERN-HEMISPHERE STORM TRACKS, BLOCKING, AND LOW-FREQUENCY ANOMALIES IN A PRIMITIVE EQUATION MODEL

The results of a study are presented that indicate three-dimensional i nstability theory is able to generate analogs of a wide variety of Sou thern Hemisphere observed fluctuations including those associated with cyclo-genesis, blocking, and low-frequency teleconnection patterns. T his study has been conducted with a two-level primitive equation eigen value model and the growing modes for both January and July averaged b asic states are examined. In both seasons, the fastest-growing cycloge nesis modes have largest amplitudes in the eastern part of the hemisph ere just downstream of the polar jet stream maxima. In July, there is a tendency to form elongated eddies in the region downstream of Austra lia where growth on both polar and subtropical jet streams occurs. The se results are in general agreement with the observational studies of Southern Hemisphere storm tracks. For both January and July, larger-sc ale slower-propagating dipole or multipole modes are found that are co nsistent with blocking in some or all of the observed locations in the Australian/New Zealand region, east of the Falklands, and to the sout heast of South Africa. The faster-growing low-frequency anomaly modes have their primary centers located to the south of 60-degrees-S and ha ve features in common with either or both of high-latitude and wavenum ber 3 observed Southern Hemisphere teleconnection patterns or, to a le sser extent, with the El Nino-Southern Oscillation anomaly patterns fo r 1982-1983. Perturbations similar to the Southern Hemisphere wavetrai n pattern mode extending from Australia to southern South America and to the global 30-60-day oscillation are also found.