This research investigates linear and nonlinear features of westward traveling tropospheric planetary-scale waves, including those variable in both amplitude and phase. Studies will include wave forcing and decay, response in a single hemisphere (especially with respect to season), nonlinear interactions including chaos, and correlation with sudden stratospheric warmings at times of especially prominent wave activity. For example, the PI will diagnose wave forcing during 1976- 1986, with special emphasis on January 1979, when an extremely prominent wavenumber one was present in only the Northern Hemisphere and April 1980, when the same candidate wave was observed with equal amplitude in both hemispheres. Prior to now, researchers have explained the excitation of normal modes as being due to stochastic forcing without being more specific. This approach will enable the calculation of forcing from observations both directly and as a residual. With this knowledge, forcing can be mapped in space and analyzed in time. Another possibility which will be examined is whether the assumed stochastic behavior may in fact be "chaotic," i.e. deterministic but seemingly random through nonlinearity. This research is important because it attempts to understand the dynamical processes responsible for large-scale atmospheric variability on intra-and interseasonal time scales.
