Journal Articles

Each year NCAR/UCAR scientists and research staff disseminate the results of their research by publishing hundreds of articles. Our collection of Journal Articles contains peer-reviewed journal articles and published conference proceedings. We provide full text access to article where possible.


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              (Diptera: Culicidae) Longevity and Differential Emergence of Dengue Fever in Two Cities in Sonora, Mexico
(Diptera: Culicidae) Longevity and Differential Emergence of Dengue Fever in Two Cities in Sonora, Mexico
Dengue virus, primarily transmitted by the Aedes aegypti (L.) mosquito, has rapidly expanded in geographic extent over the past several decades. In some areas, however, dengue fever has not emerged despite established Ae. aegypti populations. The reasons for this are unclear and have sometimes been attributed to socioeconomic differences. In 2013 we compared Ae. aegypti adult density and population age structure between two cities in Sonora, Mexico: Hermosillo, which has regular seasonal dengue virus transmission, and Nogales, which has minimal transmission. Larval and pupal abundance was greater in Nogales, and adult density was only higher in Hermosillo during September. Population age structure, however, was consistently older in Hermosillo. This difference in longevity may have been one factor that limited dengue virus transmission in Nogales in 2013, as a smaller proportion of Ae. aegypti females survived past the extrinsic incubation period.

              A GLOBAL VIEW OF VELOCITY FLUCTUATIONS IN THE CORONA BELOW 1.3
              
              
              WITH CoMP
A GLOBAL VIEW OF VELOCITY FLUCTUATIONS IN THE CORONA BELOW 1.3 WITH CoMP
The Coronal Multi-channel Polarimeter (CoMP) has previously demonstrated the presence of Doppler velocity fluctuations in the solar corona. The observed fluctuations are thought to be transverse waves, i.e., highly incompressible motions whose restoring force is dominated by the magnetic tension, some of which demonstrate clear periodicity. We aim to exploit CoMP's ability to provide high cadence observations of the off-limb corona to investigate the properties of velocity fluctuations in a range of coronal features, providing insight into how (whether) the properties of the waves are influenced by the varying magnetic topology in active regions, quiet Sun and open field regions. An analysis of Doppler velocity time-series of the solar corona from the 10747 angstrom Iron XIII line is performe, determining the velocity power spectrum and. using it as a tool to probe wave behavior. Further, the average phase speed and density for each region are estimated and used to compute the spectra for energy density and energy flux. In addition, we assess the noise levels associated with the CoMP data, deriving analytic formulae for the uncertainty on Doppler velocity measurements and providing a comparison by estimating the noise from the data. It is found that the entire corona is replete with transverse wave behavior. The corresponding power spectra indicate that the observed velocity fluctuations are predominately generated by stochastic processes, with the spectral slope of the power varying between the different magnetic regions. Most strikingly, all power spectra reveal the presence of enhanced power occurring at similar to 3 mHz, potentially implying that the excitation of coronal transverse waves by p-modes is a global phenomenon.

              A vision for
A vision for
Water Resources Research (WRR) continues to evolve as the team of international editors begins a new 4 year term of service. In this Editorial we summarize the importance of WRR in the hydrologic sciences, the challenges ahead, and the plans for the future of the journal.

              Alkoxy Radical Bond Scissions Explain the Anomalously Low Secondary Organic Aerosol and Organonitrate Yields From α-Pinene + NO
Alkoxy Radical Bond Scissions Explain the Anomalously Low Secondary Organic Aerosol and Organonitrate Yields From α-Pinene + NO
Oxidation of monoterpenes (C10H16) by nitrate radicals (NO3) constitutes an important source of atmospheric secondary organic aerosol (SOA) and organonitrates. However, knowledge of the mechanisms of their formation is incomplete and differences in yields between similar monoterpenes are poorly understood. In particular, yields of SOA and organonitrates from alpha-pinene + NO3 are low, while those from Delta(3)-carene + NO3 are high. Using computational methods, we suggest that bond scission of the nitrooxy alkoxy radicals from Delta(3)-carene lead to the formation of reactive keto-nitrooxy-alkyl radicals, which retain the nitrooxy moiety and can undergo further reactions to form SOA. By contrast, bond scissions of the nitrooxy alkoxy radicals from alpha-pinene lead almost exclusively to the formation of the relatively unreactive and volatile product pinonaldehyde (C10H16O2), thereby limiting organonitrate and SOA formation. This hypothesis is supported by laboratory experiments that quantify products of the reaction of alpha-pinene + NO3 under atmospherically relevant conditions.

              Characterizing solar-type stars from full-length
              
              data sets using the Asteroseismic Modeling Portal
Characterizing solar-type stars from full-length data sets using the Asteroseismic Modeling Portal
The Kepler space telescope yielded unprecedented data for the study of solar-like oscillations in other stars. The large samples of multi-year observations posed an enormous data analysis challenge that has only recently been surmounted. Asteroseismic modeling has become more sophisticated over time, with better methods gradually developing alongside the extended observations and improved data analysis techniques. We apply the latest version of the Asteroseismic Modeling Portal (AMP) to the full-length Kepler data sets for 57 stars, comprising planetary hosts, binaries, solar-analogs, active stars, and for validation purposes, the Sun. From an analysis of the derived stellar properties for the full sample, we identify a variation of the mixing-length parameter with atmospheric properties. We also derive a linear relation between the stellar age and a characteristic frequency separation ratio. In addition, we find that the empirical correction for surface effects suggested by Kjeldsen and coworkers is adequate for solar-type stars that are not much hotter (T-eff less than or similar to 6200 K) or significantly more evolved (log g greater than or similar to 4.2, (Delta v) greater than or similar to 80 mu Hz) than the Sun. Precise parallaxes from the Gaia mission and future observations from TESS and PLATO promise to improve the reliability of stellar properties derived from asteroseismology.

              Commentary on “O
              
              variability in the troposphere as observed by IASI over 2008-2016: Contribution of atmospheric chemistry and dynamics” by Wespes et al.
Commentary on “O variability in the troposphere as observed by IASI over 2008-2016: Contribution of atmospheric chemistry and dynamics” by Wespes et al.
Evaluation and attribution of variability and trends in tropospheric ozone requires consideration not only of the spatial distribution of ozone precursor emissions and their changes in time but also of variations in transport at regional and global scales. Satellite measurements of tropospheric ozone are now beginning to provide the vertical resolution, length of record, and density of coverage needed for disentangling the factors that influence variability and trends. A recent study by Wespes et al. (2017), utilizing an 8year data set from the Infrared Atmospheric Sounding Instrument (IASI) satellite instrument to perform a global scale, spatially resolved analysis of influences of geophysical drivers on tropospheric ozone variability, represents a key step toward understanding long-term changes in the distribution of tropospheric ozone and its corresponding impacts on air quality, chemistry, and climate.

              DETECTION OF SOLAR-LIKE OSCILLATIONS, OBSERVATIONAL CONSTRAINTS, AND STELLAR MODELS FOR
              
              CYG, THE BRIGHTEST STAR OBSERVED BY THE
              
              MISSION
DETECTION OF SOLAR-LIKE OSCILLATIONS, OBSERVATIONAL CONSTRAINTS, AND STELLAR MODELS FOR CYG, THE BRIGHTEST STAR OBSERVED BY THE MISSION
theta Cygni is an F3 spectral type magnitude V = 4.48 main-sequence star that was the brightest star observed by the original Kepler spacecraft mission. Short-cadence (58.8 s) photometric data using a custom aperture were first obtained during Quarter 6 ( 2010 June-September). and subsequently in Quarters 8 and 12-17. We present analyses of solar-like oscillations based on Q6 and Q8 data, identifying angular degree l = 0, 1, and 2 modes with frequencies of 1000-2700 mu Hz, a large frequency separation of 83.9 +/- 0.4 mu Hz, and maximum oscillation amplitude at frequency nu(max) = 1829 +/- 54 mu Hz. We also present analyses of new ground-based spectroscopic observations, which, combined with interferometric angular diameter measurements, give T-eff = 6697 +/- 78 K, radius 1.49 +/- 0.03 Re-circle dot, [Fe/H] = -0.02 +/- 0.06 dex, and log g = 4.23 +/- 0.03. We calculate stellar models matching these constraints using the Yale Rotating Evolution Code and the Asteroseismic Modeling Portal. The best-fit models have masses of 1.35-1.39 M-circle dot and ages of 1.0-1.6 Gyr. theta Cyg's T-eff and log g place it cooler than the red edge of the gamma Doradus instability region established from pre-Kepler ground-based observations, but just at the red edge derived from pulsation modeling. The pulsation models show gamma Dor gravity modes driven by the convective blocking mechanism, with frequencies of 1-3 cycles per day (11 to 33 mu Hz). However, gravity modes were not seen in Kepler data; one signal at 1.776 cycles per day (20.56 mu Hz) may be attributable to a faint, possibly background, binary.

              Dependence of Pedersen conductance in the
              
              and
              
              regions and their ratio on the solar and geomagnetic activities
Dependence of Pedersen conductance in the and regions and their ratio on the solar and geomagnetic activities
Ionospheric conductivity plays an important role in the magnetosphere-ionosphere coupling. The altitudinal distribution of Pedersen conductivity gives us a rough idea about the altitudinal distribution of Joule heating at high latitudes, which is of great significance regarding the response of upper atmosphere to geomagnetic energy inputs. Based on the electron density profiles derived from the Constellation Observing System for Meteorology, Ionosphere, and Climate measurements during 2009-2014, Pedersen conductivity has been estimated. A climatologic study of the height-integrated Pedersen conductivity in both E (100-150 km) and F (150-600km) regions, i.e., Sigma(PE) and Sigma(PF), and their ratio (gamma(P)=Sigma(PE)/Sigma(PF)) under different solar and geomagnetic conditions has been conducted. Both Sigma(PE) and Sigma(PF) increase with F-10.7 and Ap indices. Their ratio is smaller at higher solar flux but larger under more disturbed geomagnetic conditions. Meanwhile, an interhemispheric asymmetry has been identified in the Ap and F-10.7 dependencies of gamma(P), which also varies with local time. These results will help to improve our understanding of the variations of the altitudinal energy distribution under different solar and geomagnetic conditions and the interhemispheric asymmetry of the high-latitude electrodynamics.

              Discovery of Scattering Polarization in the Hydrogen Ly
              
              Line of the Solar Disk Radiation
Discovery of Scattering Polarization in the Hydrogen Ly Line of the Solar Disk Radiation
There is a thin transition region (TR) in the solar atmosphere where the temperature rises from 10,000 K in the chromosphere to millions of degrees in the corona. Little is known about the mechanisms that dominate this enigmatic region other than the magnetic field plays a key role. The magnetism of the TR can only be detected by polarimetric measurements of a few ultraviolet (UV) spectral lines, the Ly alpha line of neutral hydrogen at 121.6. nm (the strongest line of the solar UV spectrum) being of particular interest given its sensitivity to the Hanle effect (the magnetic-field-induced modification of the scattering line polarization). We report the discovery of linear polarization produced by scattering processes in the Ly alpha line, obtained with the Chromospheric Lyman-Alpha Spectro-Polarimeter (CLASP) rocket experiment. The Stokes profiles observed by CLASP in quiet regions of the solar disk show that the Q/I and U/I linear polarization signals are of the order of 0.1% in the line core and up to a few percent in the nearby wings, and that both have conspicuous spatial variations with scales of similar to 10. arcsec. These observations help constrain theoretical models of the chromosphere-corona TR and extrapolations of the magnetic field from photospheric magnetograms. In fact, the observed spatial variation from disk to limb of polarization at the line core and wings already challenge the predictions from three-dimensional magnetohydrodynamical models of the upper solar chromosphere.

              Effect of increasing CO
              
              on the terrestrial carbon cycle
Effect of increasing CO on the terrestrial carbon cycle
Feedbacks from the terrestrial carbon cycle significantly affect future climate change. The CO2 concentration dependence of global terrestrial carbon storage is one of the largest and most uncertain feedbacks. Theory predicts the CO2 effect should have a tropical maximum, but a large terrestrial sink has been contradicted by analyses of atmospheric CO2 that do not show large tropical uptake. Our results, however, show significant tropical uptake and, combining tropical and extratropical fluxes, suggest that up to 60% of the present-day terrestrial sink is caused by increasing atmospheric CO2. This conclusion is consistent with a validated subset of atmospheric analyses, but uncertainty remains. Improved model diagnostics and new space-based observations can reduce the uncertainty of tropical and temperate zone carbon flux estimates. This analysis supports a significant feedback to future atmospheric CO2 concentrations from carbon uptake in terrestrial ecosystems caused by rising atmospheric CO2 concentrations. This feedback will have substantial tropical contributions, but the magnitude of future carbon uptake by tropical forests also depends on how they respond to climate change and requires their protection from deforestation.

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