MONSOON DISTURBANCES, INTRASEASONAL OSCILLATIONS, TELECONNECTION PATTERNS, BLOCKING, AND STORM TRACKS OF THE GLOBAL ATMOSPHERE DURING JANUARY 1979 - LINEAR-THEORY

The results of a study are presented that indicate that a wide variety of atmospheric disturbances, including those associated with storm tr acks and blocking in both hemispheres, quasi-stationary global telecon nection patterns, and localized monsoon disturbances, as well as intra seasonal oscillations, may be generated through the instability of the three-dimensional global basic state for January 1979 including a wav e-CISK cumulus heating parameterization. The analysis has been conduct ed with a two-level primitive equation eigenvalue model, and the growi ng disturbances for various specifications of the strengths of the cum ulus heating have been analyzed. Within the parameter range studied, i nclusion of explicit moisture in the basic state has little effect on the structures of the storm track and onset-of-blocking modes in both hemispheres, but it increases growth rates as expected. It is also res ponsible for generating a significant amplitude of the tropical shear streamfunction of low-frequency and quasi-stationary teleconnection pa ttern modes, particularly in the Australian/South Pacific region where a coupling to the Australian monsoon appears to occur. Remarkable loc alized quasi-stationary monsoon disturbances of fairly small scale are found, which tend to produce either break or active periods of the Au stralian monsoon depending on their phase. The CISK heating focuses th ese modes in the Australian region and increases their growth rates. A group of intraseasonal oscillation modes with quite complex structure s and periods between about 20 and 60 days is also found. They have ea stward-propagating velocity potentials, peaking in the equatorial regi ons with a zonal wavenumber 1, and possibly 2, envelope wave within wh ich are embedded smaller-scale structures. They have equivalent barotr opic streamfunctions in extratropical regions with a baroclinic struct ure, typical of the first internal mode, in the tropical regions. At c ertain phases they can produce break or active periods of the Australi an monsoon. Both a three-dimensional large-scale basic-state flow and a cumulus heating parameterization appear to be necessary for generati ng, through instability, intraseasonal oscillation modes with realisti c structures.