Atmosphere Ocean Science Colloquium

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New Perspectives on El Nino Dynamics and East Asian Monsoon Variability

Speaker: Malte Stuecker, University of Washington

Location: Warren Weaver Hall 1302

Date: Wednesday, April 5, 2017, 3:30 p.m.

Synopsis:

It has been long known that the El Nino-Southern Oscillation (ENSO) exhibits pronounced climate impacts across the globe. However, it has been puzzling that many of El Nino's impacts, such as for instance East Asian Summer Monsoon (EASM) variability and associated Yangtze River Basin flooding events, do not exhibit any instantaneous correlation with commonly used ENSO indices (such as Nino3.4). We previously found that nonlinear interactions between ENSO and the Western Pacific warm pool annual cycle generate an atmospheric combination mode (C-mode) of atmospheric circulation variability. Using a framework of general circulation model experiments forced with an idealized sinusoidal ENSO temporal evolution allows us to demonstrate that ENSO's impacts are not limited to ENSO's intrinsic interannual periodicity. Instead, a deterministic frequency cascade mechanism transfers a considerable fraction of ENSO's power to near-annual and sub-annual timescales. We show that this deterministic high-frequency variability has large impacts for instance on the aforementioned East Asian Monsoon system and discuss the implications for seasonal climate predictability. Importantly, this framework can be applied in general to study seasonally modulated climate variability in the climate system.