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Oak Ridge, TN, United States

Sullivan J.T.,NASA | Sullivan J.T.,Oak Ridge Assoc Universities | McGee T.J.,NASA | Thompson A.M.,NASA | And 6 more authors.
Journal of Geophysical Research: Atmospheres | Year: 2015

The evolution of a Stratospheric-Tropospheric Exchange (STE) event from 4 to 8 August 2014 at Fort Collins, Colorado, is described. The event is characterized with observations from the Goddard Space Flight Center TROPospheric OZone (TROPOZ) Differential Absorption Lidar, the University of Wisconsin High Spectral Resolution Lidar, and multiple ozonesondes during NASA's Deriving Information on Surface Conditions from Column and Vertically Resolved Observations Relevant to Air Quality and the Front Range Air Pollution and Photochemistry Experiment (FRAPPE) campaigns. Based on the extended TROPOZ observations throughout the entire campaign, it was found that STE events have largely contributed to an additional 10-30 ppbv of ozone at Fort Collins. Additional measurements of ozone and relative humidity from the Atmospheric Infrared Sounder are characterize the transport of the intrusion. The Real-time Air Quality Modeling System simulated ozone agrees well with the TROPOZ ozone concentrations and altitude during the STE event. To extend the analysis into other seasons and years, the modeled ozone to potential vorticity ratio is used as a tracer for stratospheric air residing below the tropopause. It is found that at Fort Collins, CO, and depending on season from 2012 to 2014, between 18 and 31% of tropospheric ozone corresponds to stratospheric air. A relationship to determine the lifetime of stratospheric air below the tropopause is derived using the simulated ratio tracer. Results indicate that throughout summer 2014, 43% of stratospheric air resided below the tropopause for less than 12 h. However, nearly 39% persisted below the tropopause for 12-48 h and likely penetrated deeper in the troposphere. © 2015. American Geophysical Union. All Rights Reserved. Source

Zamora L.M.,NASA | Zamora L.M.,Oak Ridge Assoc Universities | Kahn R.A.,NASA | Cubison M.J.,University of Colorado at Boulder | And 11 more authors.
Atmospheric Chemistry and Physics | Year: 2016

The incidence of wildfires in the Arctic and subarctic is increasing; in boreal North America, for example, the burned area is expected to increase by 200-300g% over the next 50-100 years, which previous studies suggest could have a large effect on cloud microphysics, lifetime, albedo, and precipitation. However, the interactions between smoke particles and clouds remain poorly quantified due to confounding meteorological influences and remote sensing limitations. Here, we use data from several aircraft campaigns in the Arctic and subarctic to explore cloud microphysics in liquid-phase clouds influenced by biomass burning. Median cloud droplet radii in smoky clouds were g1/4 g40-60g% smaller than in background clouds. Based on the relationship between cloud droplet number (Nliq) and various biomass burning tracers (BBt) across the multi-campaign data set, we calculated the magnitude of subarctic and Arctic smoke aerosol-cloud interactions (ACIs, where ACI Combining double low line (1g•3) × dln(Nliq)g•dln(BBt)) to be g1/4 g0.16 out of a maximum possible value of 0.33 that would be obtained if all aerosols were to nucleate cloud droplets. Interestingly, in a separate subarctic case study with low liquid water content ( g1/4 g0.02gggmg'3) and very high aerosol concentrations (2000-3000gcmg'3) in the most polluted clouds, the estimated ACI value was only 0.05. In this case, competition for water vapor by the high concentration of cloud condensation nuclei (CCN) strongly limited the formation of droplets and reduced the cloud albedo effect, which highlights the importance of cloud feedbacks across scales. Using our calculated ACI values, we estimate that the smoke-driven cloud albedo effect may decrease local summertime short-wave radiative flux by between 2 and 4gWgmg'2 or more under some low and homogeneous cloud cover conditions in the subarctic, although the changes should be smaller in high surface albedo regions of the Arctic. We lastly explore evidence suggesting that numerous northern-latitude background Aitken particles can interact with combustion particles, perhaps impacting their properties as cloud condensation and ice nuclei. © Author(s) 2016. Source

Chrystal C.,Oak Ridge Assoc Universities | Burrell K.H.,General Atomics | Grierson B.A.,Princeton Plasma Physics Laboratory | Pace D.C.,General Atomics
Review of Scientific Instruments | Year: 2015

Neutral beam injection is used in tokamaks to heat, apply torque, drive non-inductive current, and diagnose plasmas. Neutral beam diagnostics need accurate spatial calibrations to benefit from the measurement localization provided by the neutral beam. A new technique has been developed that uses in situ measurements of neutral beam emission to determine the spatial location of the beam and the associated diagnostic views. This technique was developed to improve the charge exchange recombination (CER) diagnostic at the DIII-D tokamak and uses measurements of the Doppler shift and Stark splitting of neutral beam emission made by that diagnostic. These measurements contain information about the geometric relation between the diagnostic views and the neutral beams when they are injecting power. This information is combined with standard spatial calibration measurements to create an integrated spatial calibration that provides a more complete description of the neutral beam-CER system. The integrated spatial calibration results are very similar to the standard calibration results and derived quantities from CER measurements are unchanged within their measurement errors. The methods developed to perform the integrated spatial calibration could be useful for tokamaks with limited physical access. © 2015 AIP Publishing LLC. Source

Pain S.D.,Oak Ridge National Laboratory | Bardayan D.W.,Oak Ridge National Laboratory | Bardayan D.W.,University of Notre Dame | Blackmon J.C.,Louisiana State University | And 23 more authors.
Physical Review Letters | Year: 2015

The Galactic 1.809-MeV γ-ray signature from the β decay of Al26g is a dominant target of γ-ray astronomy, of which a significant component is understood to originate from massive stars. The Al26g(p,γ)Si27 reaction is a major destruction pathway for Al26g at stellar temperatures, but the reaction rate is poorly constrained due to uncertainties in the strengths of low-lying resonances in Si27. The Al26g(d,p)Al27 reaction has been employed in inverse kinematics to determine the spectroscopic factors, and hence resonance strengths, of proton resonances in Si27 via mirror symmetry. The strength of the 127-keV resonance is found to be a factor of 4 higher than the previously adopted upper limit, and the upper limit for the 68-keV resonance has been reduced by an order of magnitude, considerably constraining the Al26g destruction rate at stellar temperatures. © 2015 American Physical Society. Source

Pace D.C.,General Atomics | Cooper C.M.,Oak Ridge Assoc Universities | Taussig D.,General Atomics | Eidietis N.W.,General Atomics | And 4 more authors.
Review of Scientific Instruments | Year: 2016

A gamma ray camera is built for the DIII-D tokamak [J. Luxon, Nucl. Fusion 42, 614 (2002)] that provides spatial localization and energy resolution of gamma flux by combining a lead pinhole camera with custom-built detectors and optimized viewing geometry. This diagnostic system is installed on the outer midplane of the tokamak such that its 123 collimated sightlines extend across the tokamak radius while also covering most of the vertical extent of the plasma volume. A set of 30 bismuth germanate detectors can be secured in any of the available sightlines, allowing for customizable coverage in experiments with runaway electrons in the energy range of 1-60 MeV. Commissioning of the gamma ray imager includes the quantification of electromagnetic noise sources in the tokamak machine hall and a measurement of the energy spectrum of background gamma radiation. First measurements of gamma rays coming from the plasma provide a suitable testbed for implementing pulse height analysis that provides the energy of detected gamma photons. © 2016 AIP Publishing LLC. Source

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