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Nathan Magee, Kayla Spector, Yi-Hsuan Lin, Corey Tong, and John Beatty

Abstract

Initial ice particle sublimation data are presented from the new Levitating Upper-Tropospheric Environmental Simulator (LUTES) at The College of New Jersey. This experimental system mimics the conditions of a typical cirrus cloud in order to evaluate the phase-change kinetics of single ice particles. These ice particles are charged and then trapped in a levitating electrodynamic balance where they can be observed as they sublimate in a subsaturated atmosphere. Levitation and sublimation take place within a vacuum chamber, which is contained in a freezer at a temperature of −40° to −80°C and is capable of a reduced pressure of 10 mb. The sublimation rates of the ice particles are observed at a variety of temperature, humidity, and pressure conditions and are compared to sublimation rates predicted by particle-scale diffusion models. Initial measurements suggest that the diffusion models are capturing the essential sublimation behavior of the particles, but further measurements promise to inform lingering questions about the fundamental thermodynamics and surface processes of sublimating and growing ice particles under cirrus conditions.

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Huiwen Xue, Alfred M. Moyle, Nathan Magee, Jerry Y. Harrington, and Dennis Lamb

Abstract

Experiments were conducted with an electrodynamic levitation system to study the kinetics of droplet evaporation under chemically rich conditions. Single solution droplets of known composition (HNO3/H2O or H2SO4/HNO3/H2O) were introduced into an environmentally controlled cubic levitation cell. The gaseous environment was set intentionally out of equilibrium with the droplet properties, thus permitting the HNO3 mass accommodation coefficient to be determined. Measurements were performed at room temperature and various pressures (200–1000 hPa). Droplet sizes (initial radii in the range 12–26 μm) were measured versus time to high precision (±0.03 μm) via Mie scattering and compared with sizes computed by different models for mass and heat transfer in the transition regime. The best agreement between the theoretical calculations and experimental results was obtained for an HNO3 mass accommodation coefficient of 0.11 ± 0.03 at atmospheric pressure, 0.17 ± 0.05 at 500 hPa, and 0.33 ± 0.08 at 200 hPa. The determination of the mass accommodation coefficient was not sensitive to the transport model used. The results show that droplet evaporation is strongly limited by HNO3 and occurs in two stages, one characterized by rapid H2O mass transfer and the other by HNO3 mass transfer. The presence of a nonvolatile solute (SO2− 4) affects the activities of the volatile components (HNO3 and H2O) and prevents complete evaporation of the solution droplets. These findings validate recent attempts to include the effects of soluble trace gases in cloud models, as long as suitable model parameters are used.

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Nathan B. Magee, Eli Melaas, Peter M. Finocchio, Melissa Jardel, Anthony Noonan, and Michael J. Iacono

The Blue Hill Meteorological Observatory occupies a unique place in the history of the American Meteorological Society and the development of atmospheric science. Through its 129-yr history, the observatory has been operated by founder Abbott Lawrence Rotch (1861–1912), Harvard University, and the National Weather Service, and it is presently run by the nonprofit Blue Hill Observatory Science Center. While daily temperature and precipitation records are available through the National Climatic Data Center, they do not include the full record of sunshine duration data that were measured using a Campbell–Stokes sunshine recorder. We have recently digitized the observatory's original daily sunshine archives, and now present the first full collection and analysis of sunshine records extending from 1889 to the present. This dataset is unique and salient to modern climate research because the collection represents the earliest and longest continuous measurements of insolation outside of western Europe. This record provides an unprecedented glimpse into regional climate features as well as important links between global phenomena and regional climate. Analysis reveals long-term fluctuations of cloud cover and solar radiation, including signals of regional industrialization, global dimming, volcanic eruptions, and the 11-yr solar cycle. Shorter-period fluctuations include evidence of an intricate annual pattern of sunshine duration and correlations with the Arctic Oscillation, the North Atlantic Oscillation, and galactic cosmic rays.

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