Bulletin of the American Physical Society
APS March Meeting 2016
Volume 61, Number 2
Monday–Friday, March 14–18, 2016; Baltimore, Maryland
Session H51: Climate as a Nonequilibrium and Stochastic SystemFocus

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Sponsoring Units: GPC DFD GSNP Chair: Juan Restrepo, Oregon State University Room: Hilton Baltimore Holiday Ballroom 2 
Tuesday, March 15, 2016 2:30PM  3:06PM 
H51.00001: Fluctuations and Response in Geophysical Fluid Dynamics Invited Speaker: Valerio Lucarini The climate is a complex, chaotic, nonequilibrium system featuring a limited horizon of predictability, variability on a vast range of temporal and spatial scales, instabilities resulting into energy transformations, and mixing and dissipative processes resulting into entropy production. Despite great progresses, we still do not have a complete theory of climate dynamics able to account for instabilities, equilibration processes, response to changing parameters of the system, and multiscale effects. We will outline some possible applications of the response theory developed by Ruelle for nonequilibrium statistical mechanical systems, showing how it allows for setting on firm ground and on a coherent framework concepts like climate sensitivity, climate response, and climate tipping points, and to construct parametrizations for unresolved processes. We will show results for comprehensive global climate models. The results are promising in terms of suggesting new ways for approaching the problem of climate change prediction and for using more efficiently the enormous amounts of data produced by modeling groups around the world. Ref: V. Lucarini, R. Blender, C. Herbert, F. Ragone, S. Pascale, J. Wouters, Mathematical and Physical Ideas for Climate Science, Reviews of Geophysics 52, 809859 (2014) [Preview Abstract] 
Tuesday, March 15, 2016 3:06PM  3:18PM 
H51.00002: Balanced Dynamics in the MaddenJulian Oscillation Sharon Sessions, Stipo Sentic, Zeljka Fuchs, David Raymond Balanced dynamics describes the response of the tropical thermodynamic environment to changes in the atmospheric vorticity patterns. Observations and numerical simulations have demonstrated that positive midtropspheric vorticity anomalies produce a more stable thermodynamic environment with cool anomalies at low levels and warm anomalies aloft. The increase in atmospheric stability creates more bottomheavy convective profiles which are highly conducive for developing tropical cyclones. Balanced dynamics may also play a role in other varieties of tropical convection, including the most significant source of intraseasonal variability: the MaddenJulian Oscillation (MJO). Using data from DYNAMOa field program aimed to investigate the dynamics of the MJOwe investigate the role of balanced dynamics in the MaddenJulian Oscillation. [Preview Abstract] 
Tuesday, March 15, 2016 3:18PM  3:30PM 
H51.00003: Stochastic dynamics of melt ponds and sea icealbedo climate feedback Ivan Sudakov Evolution of melt ponds on the Arctic sea surface is a complicated stochastic process. We suggest a loworder model with icealbedo feedback which describes stochastic dynamics of melt ponds geometrical characteristics. The model is a stochastic dynamical system model of energy balance in the climate system. We describe the equilibria in this model. We conclude the transition in fractal dimension of melt ponds affects the shape of the sea ice albedo curve. [Preview Abstract] 
Tuesday, March 15, 2016 3:30PM  4:06PM 
H51.00004: A Novel Method to Unravelling Energy Pathways in the Ocean Invited Speaker: Hussein Aluie Largescale currents and eddies pervade the ocean and play a prime role in the general circulation and climate. The coupling between scales ranging from {\$}O(10\textasciicircum 4){\$} km down to {\$}O(1){\$} mm presents a major difficulty in understanding, modeling, and predicting oceanic circulation and mixing, where the energy budget is uncertain within a factor possibly as large as ten. Identifying the energy sources and sinks at various scales can reduce such uncertainty and yield insight into new parameterizations. To this end, we refine a novel coarsegraining framework, which accounts for the spherical geometry of the problem, to directly analyze the coupling between scales. We apply these tools to strongly eddying highresolution simulations using LANL's Parallel Ocean Program (POP). [Preview Abstract] 
Tuesday, March 15, 2016 4:06PM  4:18PM 
H51.00005: The impact of the diurnal insolation cycle on the tropical cyclone heat engine Morgan E. O'Neill, Diamilet PerezBetancourt, Allison A. Wing A hurricane, or tropical cyclone, is understood as a heat engine that moves heat from the warm sea surface to the cold tropopause. The efficiency of this engine depends in part on the strength and duration of solar heating. Over land, peak rainfall associated with individual thunderstorms occurs in the late afternoon. Over ocean, with its markedly higher surface heat capacity, deep convection responds more to radiational cooling than daytime surface heating. However, the role of daily varying solar forcing on the dynamics of tropical cyclones is poorly understood. Recently, Dunion et al. (2014) reported significant, repeating diurnal behavior propagating outward from tropical cyclone centers, using infrared imagery from nine years of North Atlantic tropical cyclones. We study the impact of the diurnal cycle on tropical cyclones using a high resolution 3D numerical model, the System for Atmospheric Modeling (Khairoutdinov and Randall 2003). Simulations are run with and without variable sunlight. We are able to reproduce the observational finding of Dunion et al. (2014), and further identify a diurnallyvarying residual circulation in the tropical cyclone at midlevels. The impact of the diurnal cycle on the equilibrium dynamics of tropical cyclones is also discussed. [Preview Abstract] 
Tuesday, March 15, 2016 4:18PM  4:30PM 
H51.00006: Towards a General Turbulence Model for Planetary Boundary Layers Based on Direct Statistical Simulation Brad Marston, Baylor FoxKemper, Joe Skitka Subgrid turbulence models for planetary boundary layers are typically constructed additively, starting with local flow properties and including nonlocal (KPP) or higher order (MellorYamada) parameters until a desired level of predictive capacity is achieved or a manageable threshold of complexity is surpassed. Such approaches are necessarily limited in general circumstances, like global circulation models, by their being optimized for particular flow phenomena. By using direct statistical simulation (DSS) that is based upon expansion in equaltime cumulants we offer the prospect of a turbulence model and an investigative tool that is equally applicable to all flow types and able to take advantage of the wealth of nonlocal information in any flow. We investigate the feasibility of a secondorder closure (CE2) by performing simulations of the ocean boundary layer in a quasilinear approximation for which CE2 is exact. As oceanographic examples, winddriven Langmuir turbulence and thermal convection are studied by comparison of the statistics of quasilinear and fully nonlinear simulations. We also characterize the computational advantages and physical uncertainties of CE2 defined on a reduced basis determined via proper orthogonal decomposition (POD) of the flow fields. [Preview Abstract] 
Tuesday, March 15, 2016 4:30PM  4:42PM 
H51.00007: Nonequilibrium Statistical Mechanics and the Sea Ice Thickness Distribution John Wettlaufer, Srikanth Toppaladoddi We use concepts from nonequilibrium statistical physics to transform the original evolution equation for the sea ice thickness distribution $g(h)$ due to Thorndike et al., (1975) into a FokkerPlanck like conservation law. The steady solution is $g(h) = {\cal N}(q) h^q \mathrm{e}^{~ h/H}$, where $q$ and $H$ are expressible in terms of moments over the transition probabilities between thickness categories. The solution exhibits the functional form used in observational fits and shows that for $h \ll 1$, $g(h)$ is controlled by both thermodynamics and mechanics, whereas for $h \gg 1$ only mechanics controls $g(h)$. Finally, we derive the underlying Langevin equation governing the dynamics of the ice thickness $h$, from which we predict the observed $g(h)$. This allows us to demonstrate that the ice thickness field is ergodic. The genericity of our approach provides a framework for studying the geophysical scale structure of the ice pack using methods of broad relevance in statistical mechanics. [Preview Abstract] 
Tuesday, March 15, 2016 4:42PM  4:54PM 
H51.00008: Largeeddy simulation of the transient and nearequilibrium behavior of precipitating shallow convection Thijs Heus, Axel Seifert, Robert Pincus, Bjorn Stevens Cloudaerosol remain one of the largest uncertainties in climate modeling. Many of the postulated cloudaerosol interactions involve precipitation to limit cloud size and life time, in particular for barely precipitating shallow cumulus clouds. If the precipitation exceeds a certain threshold, it will create feedback on the cloud field through cold pools and mesoscale organization. Such mesoscale responses have mostly been ignored so far in the discussion of aerosol indirect effects. We study the sensitivity of trade wind cumulus clouds to perturbations in cloud droplet number concentrations. Over time, the cloud system approaches a radiativeconvective equilibrium state. The transient behavior and the properties of the nearequilibrium cloud field depend on the microphysical state and therefore on the cloud droplet number density. The primary response of the cloud field to changes in the cloud droplet number density is deepening of the cloud layer, and results in a shorter cloud life time. If the atmospheric time scales are long enough compared to the microphysical time scales, the cloud field may reach a nearequilibrium regime. In this regime, the decrease in cloud cover compensates much of the brightening of the clouds, and the overall effect on the albedo is small. [Preview Abstract] 
Tuesday, March 15, 2016 4:54PM  5:06PM 
H51.00009: Statistical state dynamics of jet/wave coexistence in betaplane turbulence Navid Constantinou, Brian Farrell, Petros Ioannou Jets are commonly observed to coexist in the turbulence of planetary atmospheres with planetary scale waves and embedded vortices. These largescale coherent structures arise and are maintained in the turbulence on time scales long compared to dissipation or advective time scales. The emergence, equilibration at finite amplitude, maintenance and stability of these structures pose fundamental theoretical problems. The emergence of jets and vortices from turbulence is not associated with an instability of the mean flow and their equilibration and stability at finite amplitude does not arise solely from the linear or nonlinear dynamics of these structures in isolation from the turbulence surrounding them. Rather the dynamics of these largescale structures arises essentially from their cooperative interaction with the smallscale turbulence in which they are embedded. It follows that fundamental theoretical understanding of the dynamics of jets and vortices in turbulence requires adopting the perspective of the statistical state dynamics (SSD) of the entire turbulent state. In this work a theory for the jet/wave coexistence regime is developed using the SSD perspective. [Preview Abstract] 
Tuesday, March 15, 2016 5:06PM  5:18PM 
H51.00010: A stochastic shallow cumulus ensemble model as a scaleaware parameterization of convective fluctuations Mirjana Sakradzija, Axel Seifert, Thijs Heus, Anurag Dipankar Numerical models are approaching the highresolution limit where some aspects of deep convection and mesoscale convective systems can be explicitly modeled, while shallow cumuli are still a subgrid process that requires a parameterization. The classical assumption of a sufficiently large cloud sample within a model grid column breaks down in this regime, so it is crucial to develop scaleaware parameterizations. Therefore, we propose an approach to represent the variability of subgrid shallow cumuli about the ensemble average convective response. The shallow clouds are studied using Large Eddy Simulation (LES), where the original cloud field modeled on the grid of 25~m resolution is coarsegrained to mimic resolutions from 1 to 50~km. A canonical statistical ensemble is developed based on theoretical and LES findings and fluctuations of shallow convection are modeled by random subsampling of microstates from the convective ensemble distribution. The resulting distribution of subgrid convective states is scaleaware, and it represents stochastic fluctuations that increase with grid resolution and become substantial on the kilometrescale grids. We find that the local cloud memory plays an important role in defining the convective ensemble statistics in a steady cumulus regime. [Preview Abstract] 
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