Eddy-Jet Interaction and Climate

University Of Chicago, Chicago IL

Investigators

Abstract

In the context of climate change, detecting long-term modulations in the general circulation and in the global transport of tracers is important, but it is made difficult by the low signal-to-noise ratio. Dr. Nakamura will alleviate this problem by introducing a new partition between the eddies and the background flow and their interaction. Preliminary results using this novel method have been obtained, and a global, multi-year amplification of the eddies and jets, over the period 2001-5 is revealed. This amplification is not detected using traditional methods. This method will be applied to meteorological analyses and to long-term climate-model simulations under global warming scenarios, to measure the frequency and intensity of modulations of the general circulation. Idealized models (shallow water and two-level models) will be employed to explore the dynamics that underlies such modulations. The effects of jets and their modulations on global mixing properties will be studied using a passive tracer subject to advection by the observed large-scale flow together with small-scale diffusivity. The decay rate of the variance of the tracer is a metric of global mixing, and contributions from the jet regions to the decay rate will be quantified with a new diagnostic. The proposed activity will provide a new diagnostic platform for the tropospheric general circulation and transport, suitable for the detection of long-term shifts in the climatic regime. The Lagrangian-mean approach bypasses the complication of eddy-mean flow interaction in the traditional sense, and it allows simpler interpretations in terms of nonconservative processes. The broader impacts of this activity are that the diagnostic framework can be applied to a wide class of flows, including the stratosphere, troposphere, possibly the oceans, and numerical simulations. Two graduate students will be supported.