Abstract
Subseasonal tropical-extratropical teleconnections are recognized as untapped po- tential sources of subseasonal predictability, but a comprehensive theoretical frame- work of the teleconnections is missing. The Madden-Julian Oscillation (MJO) is the dominant mode of subseasonal variability. Upper-level divergence associated with the MJO tropical convection drives quasi-stationary Rossby wave responses to the mid- latitudes. Composite analyses show that the MJO impacts North American rainfall through perturbations in both the upper-tropospheric flow and regional low-level moisture availability. Similar composite analyses with low-level winds and sea level pressure were applied to U.S. tide gauge coastal water levels.
The results presented in this thesis show compelling evidence for subseasonal variability within the interannual ENSO teleconnections in the North Pacific and North America due to the MJO. As the MJO propagates through the tropical Indian and Pacific Oceans, it can strengthen or weaken the persistent ENSO signal for days to weeks. This MJO interference with the ENSO signals has consequential impacts and large implications in predictability, as constructive interference is shown to potentially lead to extreme events. Thus, MJO teleconnections must be considered in the context of the ongoing ENSO event.
Implications for predictability and future work, including additional hierarchical modeling studies, teleconnections in a warming world, and applications to machine learning, are discussed. This work has deepened our knowledge of the dynamics and mechanisms of remote responses from tropical subseasonal variability and how ENSO modulates the MJO teleconnections. Ultimately, these discoveries can increase skill and confidence in subseasonal forecasts, particularly for specific regions of North America.