Bulletin of the American Physical Society
APS March Meeting 2015
Volume 60, Number 1
Monday–Friday, March 2–6, 2015; San Antonio, Texas
Session G20: Invited Session: Stochastic Effects in Atmospheric and Oceanic Dynamics |
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Sponsoring Units: GPC Chair: John Wettlaufer, Yale University Room: Ballroom B |
Tuesday, March 3, 2015 11:15AM - 11:51AM |
G20.00001: Big science with little data: separating random waves from vortices in atmosphere and ocean fluid dynamics Invited Speaker: Oliver Buhler How to extract physical and conceptual meaning from limited data sets has been a perennial problem in atmosphere ocean science. This is especially pressing in the current era of large-scale numerical models that seek, for the first time, to simulate directly all the most energetic scales in these systems. This effort requires observational guidance at unprecedented small spatial scales. Progress in extracting physical meaning from data is therefore inseparable from progress in climate simulation and forecasting overall. For example, the successful planning of costly satellite missions depends crucially on the physical nature of the expected motions that are to be observed. In many cases, data are obtained along one-dimensional ship or flight tracks, in which case there are both kinematic and dynamic aliasing effects that obscure the physical meaning of the data. Here kinematic refers to well-known aliasing effects that arise when three-dimensional flow fields are observed only along a line. Dynamics aliasing refers to the more subtle situation when physically different processes project into the same data stream. Indeed, it is well known in atmosphere ocean science that random waves and vortices overlap and intermingle in a complex wave-turbulence jig-saw puzzle, which we need to solve! This talk describes recent progress on this problem, which led to a new method to decompose one-dimensional data into its wave and vortex constituents. The new method works by combining a new Helmholtz decomposition method for one-dimensional velocity spectra with a theoretical energy equipartition result that allows fingerprinting and identifying the random wave component in the track data. Applications of the new method to oceanic data sets and to the famous Gage--Nastrom spectrum in the atmosphere are presented, with surprising results. [Preview Abstract] |
Tuesday, March 3, 2015 11:51AM - 12:27PM |
G20.00002: Convection, Stability, and Turbulence Invited Speaker: Charles R. Doering Many natural flows are driven by buoyancy forces, perhaps the most familiar being those resulting from density variations due to temperature or compositional differences in the presence of a gravitational field. Buoyancy-driven flows of this sort play a major role in geophysical fluid mechanical processes and their transport properties and are central to climate dynamics. The simplest setting to study this phenomena is so-called Rayleigh-B\'enard convection, the buoyancy driven flow in a horizontal layer of fluid heated from below and cooled from above. This seminal problem has received tremendous attention over the last century but many riddles remain, especially regarding strongly nonlinear turbulent convection. In this presentation, following an introduction to the phenomena and its applications along with a review of the current state of theory and experiments on high Rayleigh number convection, I will describe some recent results that mathematical analysis has contributed to our understanding of turbulent heat transport. [Preview Abstract] |
Tuesday, March 3, 2015 12:27PM - 1:03PM |
G20.00003: A look at two disparate limits of the climate system: oceanic sub-mesoscales and global energy balance Invited Speaker: Balu Nadiga A common theme underlying this journey across scales is that of energy balance. The first topic considers scales from a few tens of meters to a few tens of kilometers and grapples with a fundamental question that concerns energetics of ocean circulation: how does ocean circulation equilibrate in the presence of continuous large-scale forcing and a tendency of geostrophic turbulence to confine energy to large and intermediate scales. In particular, interior instabilities are shown to provide an energy pathway between the largely-balanced, energetic oceanic mesoscales and smaller unbalanced scales (J. Fluid Mech. (2014), vol. 756, pp. 965-1006; doi:10.1017/jfm.2014.464). The second topic zooms out to the global scale and considers global warming from an energy balance perspective. With the global ocean sequestering in excess of 90\% of the recent warming due to energy imbalance at the top of the atmosphere, sensitivity of warming and depth of penetration of warming are characterized in a probabilistic fashion. [Preview Abstract] |
Tuesday, March 3, 2015 1:03PM - 1:39PM |
G20.00004: Stochastic models for tropical convection and extreme rainfall events Invited Speaker: Samuel Stechmann In the Tropics, storms and convection occur intermittently and have a major impact on weather and climate. In recent years, tropical rainfall statistics have been shown to conform to paradigms of critical phenomena and statistical physics. To gain further insight into these statistics and extreme events, this talk presents simple stochastic models for the statistics of precipitation events and water vapor dynamics (local in space, and evolving in time). Through exact solutions and simple numerics, a suite of observed rainfall statistics is reproduced by the model, including power-law distributions and long-range correlations. The key ingredients of the model are the dynamics of column water vapor, governed by a combination of Gaussian stochastic forcing and nonlinearity provided via a threshold and/or stochastic trigger. Finally, these statistics are being explored in climate model simulations with collaborators. [Preview Abstract] |
Tuesday, March 3, 2015 1:39PM - 2:15PM |
G20.00005: Climate Variability and Nonequilibrium Steady-States Invited Speaker: Jeffrey Weiss The climate system is forced by incoming solar radiation and damped by outgoing long-wave radiation. As a result, the climate system is not in thermodynamic equilibrium but is better conceptualized as residing in a nonequilibrium statistically steady-state. Nonequilibrium steady-states have internal fluctuations which appear as natural variability of the climate system. Additionally, the phase space has nonzero probability current loops which are manifested as preferred patterns of natural climate variability. Nonequilibrium steady-states are often modeled by stochastic Langevin dynamics, and many aspects of the physics of these models are well understood. Simple stochastic models have been applied to a variety of climate phenomena including El-Ni\~{n}o, the North Atlantic Gulf Stream, surface temperature patterns, ocean heat content, and atmospheric Storm Tracks. In their simplest form, these models describe a stable steady-state with linear nonconservative damping perturbed by additive Gaussian white noise and thus fall into the class of models capturing nonequilibrium steady-states where previous results from Langevin models apply while the climate context motivates additional new questions. [Preview Abstract] |
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