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James D. Klett

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James D. Klett

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James D. Klett

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The standard boundary layer model for the flow past a circulating drop neglects the stress reduction caused by motion of the drop surface. A modified boundary layer model which incorporates this effect is presented, and is shown to yield good agreement with a numerical solution for the strength of the drop internal circulation.

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James D. Klett

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Analytical solutions to the steady-state kinetic coagulation equation, including sources, are presented for the case in which the collection kernel is of the form K = K 0 u β v β, where K 0 and β am constants (0 ≤ β < 1), and u and v represent aerosol particle volumes. Particle sources are represented by gamma distributions. The solutions look like modulated power law spectra, and rapidly approach their asymptotic power law form with increasing size. For, β = 0 the solution is equivalent to Friedlander's quasi-stationary distribution in the Brownian coagulation regime, and for the case of a constant input rate of single particles with beta; = 0 it is in excellent agreement with the corresponding numerical solution of Quon and Mockros. For β = 2/3 the collection kernel provides an approximate description of gravitational collection, and the corresponding power law solution conforms fairly well with observations of the tropospheric aerosol spectrum under clear air conditions for 1 ≲ r ≲ 102 μm. The characteristic time to approach this solution is investigated, and appears to he short enough for the solution to he applicable to the real atmosphere. Finally, an approximate analysis is provided to give an indication of the effect of truncating the spectra at some specified maximum size. The truncated spectra are found to be little changed from the original forms.

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James D. Klett

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The problem of predicting the orientations of falling nonspherical particles has been addressed by the construction of a heuristic model that assumes the particles are subject to isotropic turbulence within or below the inertial subrange, that is, the Kolmogorov spectrum of eddies, depending on the particle dimensions. The rms tilt angle of a spheroidal particle of small eccentricity is determined by Langevin-type averaging over its equation of motion, taking into account the first-order restoring torque that arises when the stable fall mode is perturbed by either thermal or turbulent fluctuations. By invoking dimensional constraints concerning the nature of the main flow and turbulent stresses and by assuming the thermal and turbulent fluctuations are uncorrelated, an approximate expression for the variance of an assumed Gaussian orientation distribution for small tilt angles and small flow Reynolds numbers is obtained. The expression is then generalized to provide a semiquantitative, nearly Gaussian probability distribution for arbitrary tilt angles, particle aspect ratios, Reynolds numbers, and particle sizes relative to the Kolmogorov microscale length for particles that can be modeled as spheroids, disks, and cylinders, as well as hexagonal plug and columns such as ice crystals.

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James D. Klett

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The influence of an electric field on the diffusion of ions to cloud droplets is calculated by the method of matched asymptotic expansions. The model assumes the droplet suspension is disperse and stationary in the ionic gas, ignores space charge and selective adsorption of ions, and regards each droplet as a perfectly conducting sphere. The resulting mean charge and dispersion of an assumed normal distribution of charge among a set of equal-sized droplets are determined. It is found that the dispersion increases with electric field strength, as does the mean charge for a fixed ratio of polar conductivities.

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Petr Chylek, Timothy J. Vogelsang, James D. Klett, Nicholas Hengartner, Dave Higdon, Glen Lesins, and Manvendra K. Dubey

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Phase 5 of the Coupled Model Intercomparison Project (CMIP5) climate models’ projections of the 2014–2100 Arctic warming under radiative forcing from representative concentration pathway 4.5 (RCP4.5) vary from 0.9° to 6.7°C. Climate models with or without a full indirect aerosol effect are both equally successful in reproducing the observed (1900–2014) Arctic warming and its trends. However, the 2014–2100 Arctic warming and the warming trends projected by models that include a full indirect aerosol effect (denoted here as AA models) are significantly higher (mean projected Arctic warming is about 1.5°C higher) than those projected by models without a full indirect aerosol effect (denoted here as NAA models). The suggestion is that, within models including full indirect aerosol effects, those projecting stronger future changes are not necessarily distinguishable historically because any stronger past warming may have been partially offset by stronger historical aerosol cooling. The CMIP5 models that include a full indirect aerosol effect follow an inverse radiative forcing to equilibrium climate sensitivity relationship, while models without it do not.

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