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Benjamin M. Sanderson

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One tool for studying uncertainties in simulations of future climate is to consider ensembles of general circulation models where parameterizations have been sampled within their physical range of plausibility. This study is about simulations from two such ensembles: a subset of the climateprediction.net ensemble using the Met Office Hadley Centre Atmosphere Model, version 3.0 and the new “CAMcube” ensemble using the Community Atmosphere Model, version 3.5. The study determines that the distribution of climate sensitivity in the two ensembles is very different: the climateprediction.net ensemble subset range is 1.7–9.9 K, while the CAMcube ensemble range is 2.2–3.2 K. On a regional level, however, both ensembles show a similarly diverse range in their mean climatology. Model radiative flux changes suggest that the major difference between the ranges of climate sensitivity in the two ensembles lies in their clear-sky longwave responses. Large clear-sky feedbacks present only in the climateprediction.net ensemble are found to be proportional to significant biases in upper-tropospheric water vapor concentrations, which are not observed in the CAMcube ensemble. Both ensembles have a similar range of shortwave cloud feedback, making it unlikely that they are causing the larger climate sensitivities in climateprediction.net. In both cases, increased negative shortwave cloud feedbacks at high latitudes are generally compensated by increased positive feedbacks at lower latitudes.

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Benjamin M. Miller

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Knowing the benefits of creating or expanding programs is important for determining optimal levels of investment. Yet estimates of the benefits of weather warning systems are sparse, perhaps because there is often no clear counterfactual of how individuals would have fared without a particular warning system. This paper enriches the literature and informs policy decisions by using conditional variation in the initial broadcast dates of the National Oceanic and Atmospheric Administration’s Weather Radio All Hazards (NWR) transmitters to produce both cross-sectional and fixed effects estimates of the causal impact of expanding the NWR transmitter network. Results suggest that from 1970 to 2014, expanding NWR coverage to a previously untreated county was associated with an almost 40% reduction in injuries and as much as a 50% reduction in fatalities. The benefits associated with further expansion of this system have likely declined over time.

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Benjamin M. Herman

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Benjamin M. Sanderson and Karen M. Shell

Abstract

Radiative kernels have become a common tool for evaluating and comparing radiative feedbacks to climate change in different general circulation models. However, kernel feedback calculations are inaccurate for simulations where the atmosphere is significantly perturbed from its base state, such as for very large forcing or perturbed physics simulations. In addition, past analyses have not produced kernels relating to prognostic cloud variables because of strong nonlinearities in their relationship to radiative forcing. A new methodology is presented that allows for fast statistical optimizing of existing kernels such that accuracy is increased for significantly altered climatologies. International Satellite Cloud Climatology Project (ISCCP) simulator output is used to relate changes in cloud-type histograms to radiative fluxes. With minimal additional computation, an individual set of kernels is created for each climate experiment such that climate feedbacks can be reliably estimated even in significantly perturbed climates.

This methodology is applied to successive generations of the Community Atmosphere Model (CAM). Increased climate sensitivity in CAM5 is shown to be due to reduced negative stratus and stratocumulus feedbacks in the tropics and midlatitudes, strong positive stratus feedbacks in the southern oceans, and a strengthened positive longwave cirrus feedback. Results also suggest that CAM5 exhibits a stronger surface albedo feedback than its predecessors, a feature not apparent when using a single kernel. Optimized kernels for CAM5 suggest weaker global-mean shortwave cloud feedback than one would infer from using the original kernels and an adjusted cloud radiative forcing methodology.

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Benjamin A. Stephens, Charles S. Jackson, and Benjamin M. Wagman

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We find that part of the uncertainty in the amplitude and pattern of the modeled precipitation response to CO2 forcing traces to tropical condensation not directly involved with parameterized convection. The fraction of tropical rainfall associated with large-scale condensation can vary from a few percent to well over half depending on model details and parameter settings. In turn, because of the coupling between condensation and tropical circulation, the different ways model assumptions affect the large-scale rainfall fraction also affect the patterns of the response within individual models. In two single-model ensembles based on the National Center for Atmospheric Research (NCAR) Community Atmosphere Model (CAM), versions 3.1 and 5.3, we find strong correlations between the fraction of tropical large-scale rain and both climatological rainfall and circulation and the response to CO2 forcing. While the effects of an increasing tropical large-scale rain fraction are opposite in some ways in the two ensembles—for example, the Hadley circulation weakens with the large-scale rainfall fraction in the CAM3.1 ensemble while strengthening in the CAM5.3 ensemble—we can nonetheless understand these different effects in terms of the relationship between latent heating and circulation, and we propose explanations for each ensemble. We compare these results with data from phase 5 of the Coupled Model Intercomparison Project (CMIP5), for which some of the same patterns hold. Given the importance of this partitioning, there is a need for constraining this source of uncertainty using observations. However, since a “large-scale rainfall fraction” is a modeling construct, it is not clear how observations may be used to test various modeling assumptions determining this fraction.

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Benjamin M. Herman and Douglas N. Yarger

Abstract

A method of estimating the vertical distribution of ozone by inverting the equation of radiative transfer is presented. The method allows for all orders of scattering as well as polarization of the diffusely reflected sunlight. The information content of the reflected sunlight as a function of observation angle is examined for the case where perfect measurements are assumed, and also for the case where a 1% random error is introduced into the measurements. Inversion results utilizing simulated satellite measurements are presented for several different ozone soundings.

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Benjamin M. Herman and Douglas N. Yarger

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The effects of multiple scattering on the heating rates in the ozone layer are investigated. Computations are performed for two wavelengths, one rather highly absorbing, λ=3112 Å, and one rather weakly absorbing, λ=3323 Å, and for three solar elevation angles. These results are compared with heating rates computed on the basis of a Beer's law type of exponential absorption, neglecting all scattering. It is shown that, at the weakly absorbing wavelength, and for small zenith angles, the effect of scattering is such as to increase the heating rate by about 40 per cent. At the more highly absorbing wavelength, scattering effects are small and may safely be neglected.

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Benjamin M. Herman and Louis J. Battan

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Calculations of the normalized back-scattering cross-section, σb, of ice spheres surrounded by shells of liquid water have been made from an extension of the Mie theory to a two-layer model. Curves of σb as a function of the thickness of the liquid-water shell are presented for various-sized spheres for 3.21, 4.67 and 10.0 cm radiation. It is shown that, depending upon the size of the sphere and the wavelength of the incident radiation, the back-scattering may either increase or decrease as the ice acquires a liquid-water shell. For certain-sized spheres, interference phenomena, which in some instances may lower the value of σb by several orders of magnitude, are in evidence during the course of melting.Comparisons are made between the theoretical results presented here and experimental measurements of σb for melting ice spheres performed by Atlas et al (1960).

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Prof. Benjamin F. Sharpe

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No Abstract Available.

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Benjamin M. Herman and Farid F. Abraham

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