Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session C23: Climate Physics: Feedbacks in the Earth SystemFocus
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Sponsoring Units: GPC Chair: Peter Weichman, BAE Systems Room: BCEC 158 |
Monday, March 4, 2019 2:30PM - 3:06PM |
C23.00001: Arctic cloud and sea ice feedbacks from satellite observations and a global climate model Invited Speaker: Ariel Morrison Over the next century, the Arctic Ocean is projected to become seasonally sea ice-free. Assessing feedbacks between clouds and sea ice as the Arctic loses sea ice cover is important because of clouds’ radiative impacts on the Arctic surface. Here, present and future Arctic cloud-sea ice relationships are assessed using spaceborne lidar observations and a fully-coupled global climate model that incorporates a lidar simulator. Using a novel surface mask that restricts the analysis to where sea ice concentration varies, we isolate the influence of sea ice cover on Arctic Ocean clouds during summer and fall. Summer cloud structure and fraction are nearly identical over sea ice and over open water, but more clouds are observed over open water than over sea ice in the fall. With future sea ice loss, modeled summer cloud fraction, vertical structure, and optical depth barely change, while the boundary layer deepens and clouds become more opaque over open water during fall. There is little evidence for a summer cloud-sea ice feedback but strong evidence for a positive cloud-sea ice feedback that emerges during non-summer months as the Arctic warms and sea ice disappears. |
Monday, March 4, 2019 3:06PM - 3:18PM |
C23.00002: Spatiotemporal Dynamics of Lake Patterns in a Changing Arctic Tundra Landscape Thao N. Nguyen, Ivan A Sudakov The evolution of Arctic tundra lakes exhibits percolating properties. More specifically, there exists a threshold where initially disjoint lakes gradually transition into a network of complex, interconnected structures on a macroscopic level when the value of some parameter exceeds a critical value. Behaviors of these lakes, primarily characterized by the lake area fraction and fractal dimension of the system, are significant to statistical physics due to their analogous nature to phase transitions. On account of similarities in geographical characteristics of the Arctic tundra landscape and that of slow immiscible fluid invasion processes in porous media, we developed our model based on a standard invasion percolation model under the influence of changing temperature. This model helps to explain the critical percolation threshold in the lake system in order to understand long-term lake dynamics and its contribution to climate change. |
Monday, March 4, 2019 3:18PM - 3:30PM |
C23.00003: Homotopy Importance Sampler For Noisy Dynamics Juan Restrepo, Andrew Jensen, Robert Miller We propose a Bayesian estimation method for moments of a state vector |
Monday, March 4, 2019 3:30PM - 3:42PM |
C23.00004: Application of the Rayleigh-Debye-Gans (RDG)theory for determining optical properties of biomass burning aerosols. Emmanuel Sarpong, Damon Smith, Solomon Bililign Biomass burning emissions are a major source of fractal aggregates which are clusters of spherules forming aerosols of non-spherical shape. Both the developed and developing world are subject to biomass burning events through agricultural burning, wildfires, and domestic burning applications. Accurate quantification of their optical properties is important both for their measurement and for predicting their radiative effect on climate. RDG assumes that each monomer in the aggregate interacts independently with radiation, by neglecting multiple scattering and shadowing. Absorption is an incoherent process and as a result the absorption of the aggregate is equal to the number of monomers, N, times the absorption of a single monomer. TEM images are used to determine the size parameters of the fractal aggregates. We report use of the RDG theory to fit experimentally measured optical properties to extract the refractive indices of biomass burning aerosols. |
Monday, March 4, 2019 3:42PM - 3:54PM |
C23.00005: A theory for global precipitation change Nadir Jeevanjee, David Romps Global warming simulations robustly show that mean precipitation increases at 1-3% per Kelvin, but we do not know what sets these values. Mean precipitation is constrained by radiative cooling, however, and we demonstrate here that radiative cooling profiles exhibit a certain invariance under warming when plotted in temperature coordinates. This invariance can then be leveraged to derive simple analytical equations for precipitation change with warming. These equations are validated in cloud-resolving simulations of the tropics, and give intuition for why precipitation changes at a rate of 1-3% per Kelvin. |
Monday, March 4, 2019 3:54PM - 4:06PM |
C23.00006: Estimation of Hourly and Daily Clearness Indices and Diffuse Fraction, over Port Harcourt and Kano using National Centre for Environmental Prediction and National Centre for Atmospheric Research Satellite Data Opeyemi Omole, Babatunde Adeyemi Estimation of clearness index (KT) and diffuse fraction (KD) were calculated using satellite data obtained from National Centre for Environmental Prediction and National Centre for Atmospheric Research data base covering a period of 10 Years (2005 - 2014) for Port Harcourt and Kano stations which are Coaster and Sahel regions respectively. Direct solar data and diffuse solar data collected were added to give the Global solar radiation. The computed clearness index values were used to characterize the sky conditions into clear skies and overcast skies. Port-Harcourt with low clearness index indicated low global solar radiation while Kano with large clearness index indicated high global solar radiation. The implications of these results on the effective utilization of solar energy are discussed. The results also serve as very useful for solar energy collectors in designing and estimation of solar application systems |
Monday, March 4, 2019 4:06PM - 4:18PM |
C23.00007: Threshold dependence in the flip-flop model Douglas Kurtze The flip-flop salt oscillator model1 is a simplified dynamical model describing buoyancy-induced oscillations in the ocean. In this model, coupling to the atmosphere can increase the density of water at the surface to the point that it becomes denser than the water beneath, at which point vigorous vertical convection sets in and restores stable stratification. One parameter in this model quantifies the strength of the atmospheric forcing; the dependence of the amplitude and period of the oscillations in vertical mixing on this parameter has been well studied. However, in order for the model to produce oscillations at all, it must allow convective mixing to begin when the stratification is still slightly stable; a "threshold" parameter must be given to specify how close to unstable the stratification must be for convection to begin. The geophysical significance of this parameter is unclear, and typically it is set to some arbitrary small value. We show, however, that the amplitude and period of oscillations in the model depend strongly on this parameter, being proportional to its value and its square root, respectively. Thus numerical results from the flip-flop model need to be interpreted with care. |
Monday, March 4, 2019 4:18PM - 4:30PM |
C23.00008: Threshold phenomena in the marine carbon cycle Daniel Rothman The history of the marine carbon cycle is punctuated by transient |
Monday, March 4, 2019 4:30PM - 4:42PM |
C23.00009: Implications of Lorenz-Mie scattering by cloud droplets in an absorbing atmosphere for cloud feedbacks William Collins, Daniel R. Feldman, Chaincy Kuo There is still considerable uncertainty as to the magnitude of cloud feedbacks to anthropogenic climate change . The magnitude is determined by changes in the bulk cloud radiative effects (CREs) on both solar and terrestrial radiation in response to changes in the Earth's average surface temperature. The range of CRE responses of low-altitude liquid clouds is one of the dominant sources of uncertainty. To date, the CREs for these clouds have been computed using variants of classical far-field Mie theory applied to spherical particles (i.e., water droplets) embedded in a non-absorbing medium. At many wavelengths where water vapor is the predominant radiatively active gas, the assumption of a non-absorbing medium is manifestly violated, for example in the near-infrared near the primary and overtone absorption bands of H2O. For this reason, it is important to redo the calculation of CREs using new, generalized Lorenz-Mie scattering in an absorbing atmosphere (Mishchenko et al, 2017 and 2018). We quantify differences in reflection, transmission, and absorption of sunlight and terrestrial radiation by liquid clouds and the impacts of these differences on low-cloud feedbacks to increasing surface temperatures. |
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