Bulletin of the American Physical Society
APS March Meeting 2013
Volume 58, Number 1
Monday–Friday, March 18–22, 2013; Baltimore, Maryland
Session U15: Focus Session: The Physics of Climate |
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Sponsoring Units: GPC Chair: Robert Behringer, Duke University Room: 317 |
Thursday, March 21, 2013 11:15AM - 11:27AM |
U15.00001: The New APS Topical Group on the Physics of Climate: History, Objectives and Panel Discussion James Brasseur, Robert Behringer The GPC Chair will introduce the new APS Topical Group on the Physics of Climate (GPC), describe its history and objectives, and introduce the current GPC leadership before opening the floor to a panel discussion. The GPC resulted from two petitions that emerged from the controversy that followed the APS Statement on Climate Change (see APS website). The two proposals were merged and an organization committee formed by the APS leadership. After a long organizational period in 2011, the GPC bylaws were finalized with the following key objective: \textit{The objective of the GPC shall be to promote the advancement and diffusion of knowledge concerning the physics, measurement, and modeling of climate processes, within the domain of natural science and outside the domains of societal impact and policy, legislation and broader societal issues. The objective includes the integration of scientific knowledge and analysis methods across disciplines to address the dynamical complexities and uncertainties of climate physics.} The GPC Invited and Focus Sessions at this March meeting are the inaugural GPC events. The Program Committee Chair will moderate a panel between the attending GPC leadership and audience to solicit suggestions for potential future GPC events that advance the GPC objectives. [Preview Abstract] |
Thursday, March 21, 2013 11:27AM - 11:39AM |
U15.00002: Direct Statistical Simulation of Climate Brad Marston Non-equilibrium statistical mechanics opens up the possibility of modeling climate directly,\footnote{E. N. Lorenz, {\it The Nature and Theory of the General Circulation of the Atmosphere}, vol. 218. World Meteorological Organization (1967).} bypassing the traditional approach of accumulating statistics from lengthy numerical simulations. One way to implement such Direct Statistical Simulation (DSS) is by systematic expansion in equal-time cumulants.\footnote{J. B. Marston, E. Conover, and T. Schneider, J. Atmos. Sci. {\bf 65}, 1955 (2008).} Essential physics of the general circulation can be illustrated with idealized 1- and 2-layer models of the atmosphere.\footnote{J. B. Marston, Ann. Rev. Cond. Matt. Phys. {\bf 3}, 285 (2012).} A truncation at second order in the hierarchy of cumulants is equivalent to retaining the interaction between zonal mean flows and eddies. Eddy-eddy interactions appear at higher orders, but care must be taken to keep the higher-order expansions realizable with non-negative probability distribution functions. Live demonstrations of models, and their statistical mechanical solution, will be performed. Possible effects of polar amplification of warming, due to the melting of arctic sea ice, on the mid-latitude jet stream will be illustrated. [Preview Abstract] |
Thursday, March 21, 2013 11:39AM - 11:51AM |
U15.00003: Atmospheric Lifetimes and Radiative Forcing of CFC-11 and CFC-12 Kenneth Minschwaner, Lars Hoffmann, Alex Brown, Martin Riese, Rolf M\"uller, Peter Bernath Atmospheric lifetimes for chlorofluorocarbons (CFCs) are important for interpreting their temporal trends and for evaluating their impact on stratospheric chemistry and radiative forcing of climate. The lifetimes of CFC-11 and CFC-12 have been evaluated using global observations of their stratospheric distributions from satellite-based instruments between the period 1992 and 2010. The CFC data sets are from the Cryogen Limb Array Etalon Spectrometer (CLAES), the Cryogenic Infrared Spectrometers and Telescopes for the Atmosphere (CRISTA-1 and CRISTA-2), the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS), and the Atmospheric Chemistry Experiment (ACE). Stratospheric loss rates were calculated using an ultraviolet radiative transfer code with updated molecular cross section and solar irradiance data. Infrared radiative forcings (net flux changes at the tropopause) were determined using CFC distributions from the satellite observations. [Preview Abstract] |
Thursday, March 21, 2013 11:51AM - 12:03PM |
U15.00004: A cloud microphysical mechanism linking solar activity, atmospheric electricity, and climate Brian Tinsley The electrical current density from the ionosphere to the surface changes by tens of percent on the 11-year solar cycle and during transient solar events. This external forcing is accompanied by similar changes due to thunderstorm variability and atmospheric aerosols. The current density deposits space charge in gradients of conductivity associated with stratified clouds and aerosol layers. The space charge, which attaches to droplets and aerosol particles, can be carried deep into clouds by updrafts, and it affects collision rates between droplets and aerosol particles. The most important of these for cloud microphysics are collisions of cloud condensation nuclei (CCN) and ice forming nuclei (IFN) with droplets. These collision rate changes during in-cloud scavenging affect the concentrations of CCN and IFN and the rate of contact ice nucleation. Increases in CCN concentration in deep convective storms have recently been shown to decrease initial precipitation and invigorate the storm with extra release of latent heat of freezing from water not precipitated but carried above the freezing level. The changes in latent heat release account for several sets of correlations of storm vorticity changes with independent inputs that affect the current density. Such dynamical changes can result in regional climate change. A review of models of electrical effects on cloud microphysics, and of observed correlations which support the mechanism, will be presented. [Preview Abstract] |
Thursday, March 21, 2013 12:03PM - 12:15PM |
U15.00005: Theory of Arctic Sea Ice Loss: Trends, Noise and Bifurcations John Wettlaufer, Woosok Moon, Sahil Agarwal Within the framework of lower order thermodynamic theories for the climatic evolution of Arctic sea ice we isolate the conditions required for the existence of stable seasonally- varying solutions, in which ice forms each winter and melts away each summer. This is done by constructing a two-season model from a continuously evolving theory and showing that seasonally-varying states are unstable under constant annual average short-wave radiative forcing. However, dividing the summer season into two intervals (ice covered and ice free) provides sufficient freedom to stabilize seasonal ice. Perturbation theory shows that the condition for stability is determined by the timing of when the ice vanishes in summer and hence the relative magnitudes of the summer heat flux over the ocean versus over the ice. This scenario is examined within the context of greenhouse gas warming, as a function of which stability conditions are discerned, and interpreted within the framework of a quantification of the noise extracted from satellite data using multifractal detrended fluctuation analysis. [Preview Abstract] |
Thursday, March 21, 2013 12:15PM - 12:27PM |
U15.00006: Coupling of ocean circulation and sea ice D.A. Kurtze, D. S. Comeau, K. Gimre, J.M. Restrepo We propose a simple model of the coupling between oceanic circulation and sea ice dynamics on long time scales. The model begins with a one-dimensional Budyko-Sellers energy balance model of ice-albedo feedback, with a linearized temperature dependence of outgoing longwave radiation. This sits atop a box model of ocean circulation, with conventional thermohaline forcing except that surface heat exchange occurs via the Budyko-Sellers model. The ocean and the ice sheet are coupled via advection and plastic flow of ice, and by the thermodynamics of the ice/seawater interface. We use this model to assess how (and by what mechanisms) ocean circulation and ice sheet dynamics affect one another, primarily to investigate the role played by changes in solar input and greenhouse gas forcing, e.g. in the Snowball Earth scenario. [Preview Abstract] |
Thursday, March 21, 2013 12:27PM - 1:03PM |
U15.00007: Ocean Circulation and its Role in Global Warming Invited Speaker: Geoffrey Vallis The surface of the planet is warming because of increased greenhouse gases in the atmosphere. To predict the rate of increase we need to understand how much heat and carbon dioxide are taken up by the ocean. This in turn requires an understanding of both turbulent processes in the upper ocean and the deep, quasi-laminar, overturning circulation. The timescale for the ocean to fully equilibrate to increased greenhouse gases is likely much longer than the timescale on which fossil fuels will still be readily available, and this has important ramifications for what we mean by climate sensitivity. I will discuss these issues with an emphasis on the physical processes of the ocean. [Preview Abstract] |
Thursday, March 21, 2013 1:03PM - 1:15PM |
U15.00008: Sea surface temperature and short term climate predictability Constantin Andronache Atmospheric processes have a relatively short memory of initial conditions of about two weeks for detailed daily weather prediction. Nevertheless, skilful seasonal forecast is possible in the presence of slow varying boundary conditions (BC) of the atmosphere, such as sea surface temperature anomalies (SSTA) over large oceanic regions. These conditions typically evolve on a much slower time scale than daily weather events and atmospheric predictability can be increased as long as the future evolution of such BC can be predicted. Given the importance of SSTA in the interaction between the ocean and atmosphere, it is of interest to investigate the nature of temporal persistence of large-scale SSTA in the global ocean. We use the global SSTA and investigate possible sources of predictability at seasonal time scale and its impact in various regions of the ocean. Data used are the NOAA Extended Reconstructed Sea Surface Temperature (SST). We show that: 1) SSTA has a persistence that depends largely on regional location in the global ocean; 2) A given SSTA distribution from a particular month, can have corresponding similar configurations in the past, largely due to the recurrence of ENSO events which affect SSTA distribution over vast regions of the global ocean. [Preview Abstract] |
Thursday, March 21, 2013 1:15PM - 1:27PM |
U15.00009: Comparing the Standard Deviation from the Average Seasonal Surface Temperature Signal for Fourteen Years of Hourly Surface Temperature Data as Recorded at Twenty-Five Stations across the United States of America Joseph Trout In this project, Wavelet analysis was used to analyze and filter fourteen years of hourly temperature data recorded at twenty-five stations across the United States of America. The temperature records where filtered using a fast, discrete wavelet transform, keeping the parts of the signal with periods of approximately twelve months. From these filters signals an average seasonal temperature pattern was produced for each station. The standard deviation for each year at every station was then computed. The trends of the standard deviations were examined for each station for evidence of climate change. Wavelet analysis was used because of the ability of wavelet analysis to analyze both periodic and non-periodic behavior at different time or length scales. [Preview Abstract] |
Thursday, March 21, 2013 1:27PM - 1:39PM |
U15.00010: Dust shatters like glass: Implications for the climate forcing of mineral dust aerosols Jasper Kok Soil-derived mineral dust aerosols impact climate through interactions with clouds, ecosystems, and radiation, which contributes substantially to uncertainties in understanding past and future climate changes. One of the causes of this large uncertainty is that the size distribution of emitted dust aerosols is poorly understood. In fact, a compilation of measurements indicates that regional and global circulation models overestimate the emitted fraction of clay dust aerosols (\textless\ 2 $\mu $m diameter) by a factor of $\sim$ 2 -- 8. I resolve this discrepancy by deriving a simple theoretical expression for the emitted dust size distribution that is in excellent agreement with measurements. This expression is based on the analogy of dust emission with the scale-invariant fragmentation of brittle materials such as glass. Since regional and global circulation models are usually tuned to the shortwave radiative effect of dust, which is dominated by clay aerosols, these findings suggest that models have substantially underestimated the emission of larger silt (\textgreater\ 2 $\mu $m diameter) aerosols, which tend to produce a net warming effect. I show that this underestimation of silt aerosol emission has implications for the effect of dust on regional and global climate. [Preview Abstract] |
Thursday, March 21, 2013 1:39PM - 1:51PM |
U15.00011: Investigation of Solar Cyclic and Climatic Trends in Upper Atmospheric Hydrogen Distributions Susan Nossal, Edwin Mierkiewicz, Fred Roesler, L. Qian, S. Solomon, Alan Burns We will discuss work in progress to better understand solar cyclic and climatic influences on hydrogenous species budgets and distributions from both an observational and modeling perspective. Our Fabry-Perot observations of upper atmospheric hydrogen emissions during solar cycle 23 and during three solar minima (1985, 1997, 2006-2008) establish a reference data set of highly precise, consistently calibrated, thermospheric $+$ exospheric hydrogen column emission observations from Northern mid-latitudes that can be used to compare with future observations and with atmospheric models. We will also discuss use of the National Center for Atmospheric Research's global mean model for sensitivity studies to investigate the response of thermospheric hydrogen to a doubling of carbon dioxide and methane. The results from this study suggest a strong solar cycle dependence and that carbon dioxide cooling may have a greater impact upon the changes in the upper atmospheric hydrogen distribution at solar minimum than do methane increases. [Preview Abstract] |
Thursday, March 21, 2013 1:51PM - 2:03PM |
U15.00012: Using multiple equilibria in precipitation to understand self-aggregation of deep tropical convection in a warming climate Sharon Sessions, Stipo Sentic, David Raymond Understanding mechanisms of convective organization is currently an important problem in tropical meteorology. Recent numerical simulations show that the tendency for deep tropical convection to self-aggregate increases as sea surface temperatures (SSTs) increase. This has significant implications for hurricane genesis in a warming climate. Investigating the conditions over which convection self-aggregates requires large domains and is therefore computationally expensive. An alternative approach utilizes the analogy between multiple equilibria in limited domain simulations, and the dry and precipitating regions in a large domain with self-aggregated convection. Multiple equilibria refers to a steady state which either exhibits a completely dry troposphere or persistent precipitating deep convection under identical forcing conditions. The large scale circulation is parameterized based on the assumption that horizontal gradients in temperature are small in the tropics. Understanding the mechanisms which permit multiple equilibria on small domains is a computationally economic approach to understanding self-aggregation. We show how multiple equilibria depend on SSTs, and thus provide insight to self-aggregation in a warming climate. [Preview Abstract] |
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