Internal Generation of Low and Ultra-Low Frequency Variability in the Atmosphere

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This project will study the dynamical mechanisms by which the atmosphere can internally generate variability on timescales of months, seasons, and years. The focus will be on locating and understanding the feedbacks between the low frequencies and the shorter timescales at which the available energy of the atmosphere is released. These investigations will be carried out in the context of simple two-level primitive equation model and existing long runs of the NCAR Community Climate Model. The proposed work comprises the following specific studies: 1) Studies of the "index cycle in the two-level model to determine its dynamics and its effects on stationary eddies. 2) Studies of the interactions between internal variability and externally generated (by tropical heating) variability in the two-level model 3) Diagnostic analyses of extended simulations of the CCM to see if the dynamical mechanisms that generate low-frequency variability in the two-level model are relevant in a more realistic model. 4) Analysis of the low-frequency variability of the Rossby wave source in the CCM and its interaction with synoptic forcign of low-frequency features. 5) Studies of the dynamics of the inter-seasonal and longer timescale variability that is found at planetary spatial scales in the two-level model. This research is important because its seeks to improve understanding of the processes responsible for climate variations on time scales of great importance to human activities.