bluuebunny/crossref_metadata_2025_split huggingface dataset:
Do cosmic ray air showers initiate lightning?: A statistical analysis of cosmic ray air showers and lightning mapping array data
Authors: Hare B. M. , Dwyer J. R. , Winner L. H. , Uman M. A. , Jordan D. M. , Kotovsky D. A. , Caicedo J. A. , Wilkes R. A. , Carvalho F. L. , Pilkey J. T. , Ngin T. K. , Gamerota W. R. , Rassoul H. K. 
Published: July 2017

AbstractIt has been argued in the technical literature, and widely reported in the popular press, that cosmic ray air showers (CRASs) can initiate lightning via a mechanism known as relativistic runaway electron avalanche (RREA), where large numbers of high‐energy and low‐energy electrons can, somehow, cause the local atmosphere in a thundercloud to transition to a conducting state. In response to this claim, other researchers have published simulations showing that the electron density produced by RREA is far too small to be able to affect the conductivity in the cloud sufficiently to initiate lightning. In this paper, we compare 74 days of cosmic ray air shower data collected in north central Florida during 2013–2015, the recorded CRASs having primary energies on the order of 1016 eV to 1018 eV and zenith angles less than 38°, with Lightning Mapping Array (LMA) data, and we show that there is no evidence that the detected cosmic ray air showers initiated lightning. Furthermore, we show that the average probability of any of our detected cosmic ray air showers to initiate a lightning flash can be no more than 5%. If all lightning flashes were initiated by cosmic ray air showers, then about 1.6% of detected CRASs would initiate lightning; therefore, we do not have enough data to exclude the possibility that lightning flashes could be initiated by cosmic ray air showers.
Effect of grain sorting on gravel bed river evolution subject to cycled hydrographs: Bed load sheets and breakdown of the hydrograph boundary layer
Authors: An Chenge , Fu Xudong , Wang Guangqian , Parker Gary 
Published: July 2017

AbstractThe evolution of gravel bed rivers under cycled hydrographs and constant sediment supply is studied in this paper. With the aid of numerical modeling and flume experiments, previous research has indicated that under such water and sediment supply conditions, a river can reach a mobile‐bed equilibrium characterized by a hydrograph boundary layer (HBL) located near the upstream end of the river. The HBL defines the spatial region within which riverbed topography and grain size respond to the hydrograph, and downstream of which these bed characteristics are invariant. However, neither the governing physical mechanisms nor the general applicability of the HBL is yet well understood. In this paper, we implement a 1‐D morphodynamic model for this problem. The model is first validated with data for both flume experiments and numerical simulations. It is then implemented at field scale with grain size distributions varying from uniform sediment to very poorly sorted sediment mixtures. Our results show that the idea of an HBL is applicable in the case of uniform sediment, but breaks down in the case of poorly sorted sediment mixtures. In such cases, persistent low‐amplitude bed load sheets emerge along the entire channel reach, in addition to HBL‐like upstream boundary effects. Bed load sheets can be described as surface texture or grain size sorting waves in consonance with low‐amplitude elevation variations, and are ascribed to nonlinear advection terms in the governing equations that vanish for uniform sediment, but become significant when sediment is very poorly sorted.
Temporal variations in air permeability and soil CO2 flux in volcanic ash soils (island of Vulcano, Italy)
Authors: Camarda Marco , Prano Vincenzo , Cappuzzo Santo , Gurrieri Sergio , Valenza Mariano 
Published: July 2017

AbstractAir permeability is a major physical factor affecting the advective transport of a gas through the soil, and variations in this parameter can strongly influence the emission of endogenous gases from the soil to the atmosphere. In this paper, we illustrated a new and simple method for measuring in situ air permeability based on the measurement of air pressure inside a special probe inserted into the soil. The method was designed and developed primarily to study the relationship between air permeability and the soil CO2 flux in an active volcanic area. The method was used for continuous monitoring of the air permeability at two different locations on the island of Vulcano. At the same time, the values of the atmospheric pressure, temperature, rain, and volumetric water content of the soil were also acquired to investigate their effect on soil air permeability and soil CO2 flux. The results showed that during the monitoring period, soil air permeability exhibited minor variations at each site, while larger variations in the soil CO2 flux were recorded. The effect of soil air permeability on soil CO2 flux was negligible at both sites, whereas a strong dependence of soil CO2 flux on volumetric water content and on atmospheric pressure was found. Furthermore, the variation in air permeability recorded at both sites was much lower than that predicted using some well‐known predictive models, showing that the relationship among different soil transport parameters is more complex in real field conditions than would be expected by semiempirical models.
Electron density extrapolation above F2 peak by the linear Vary‐Chap model supporting new Global Navigation Satellite Systems‐LEO occultation missions
Authors: Hernández‐Pajares Manuel , Garcia‐Fernàndez Miquel , Rius Antonio , Notarpietro Riccardo , von Engeln Axel , Olivares‐Pulido Germán , Aragón‐Àngel Àngela , García‐Rigo Alberto 
Published: July 2017

AbstractThe new radio‐occultation (RO) instrument on board the future EUMETSAT Polar System‐Second Generation (EPS‐SG) satellites, flying at a height of 820 km, is primarily focusing on neutral atmospheric profiling. It will also provide an opportunity for RO ionospheric sounding, but only below impact heights of 500 km, in order to guarantee a full data gathering of the neutral part. This will leave a gap of 320 km, which impedes the application of the direct inversion techniques to retrieve the electron density profile. To overcome this challenge, we have looked for new ways (accurate and simple) of extrapolating the electron density (also applicable to other low‐Earth orbiting, LEO, missions like CHAMP): a new Vary‐Chap Extrapolation Technique (VCET). VCET is based on the scale height behavior, linearly dependent on the altitude above hmF2. This allows extrapolating the electron density profile for impact heights above its peak height (this is the case for EPS‐SG), up to the satellite orbital height. VCET has been assessed with more than 3700 complete electron density profiles obtained in four representative scenarios of the Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) in the United States and the Formosa Satellite Mission 3 (FORMOSAT‐3) in Taiwan, in solar maximum and minimum conditions, and geomagnetically disturbed conditions, by applying an updated Improved Abel Transform Inversion technique to dual‐frequency GPS measurements. It is shown that VCET performs much better than other classical Chapman models, with 60% of occultations showing relative extrapolation errors below 20%, in contrast with conventional Chapman model extrapolation approaches with 10% or less of the profiles with relative error below 20%.
Sixteen year variation of horizontal phase velocity and propagation direction of mesospheric and thermospheric waves in airglow images at Shigaraki, Japan
Authors: Takeo D. , Shiokawa K. , Fujinami H. , Otsuka Y. , Matsuda T. S. , Ejiri M. K. , Nakamura T. , Yamamoto M. 
Published: July 2017

AbstractWe analyzed the horizontal phase velocity of gravity waves and medium‐scale traveling ionospheric disturbances (MSTIDs) by using the three‐dimensional fast Fourier transform method developed by Matsuda et al. (2014) for 557.7 nm (altitude: 90–100 km) and 630.0 nm (altitude: 200–300 km) airglow images obtained at Shigaraki MU Observatory (34.8°N, 136.1°E, dip angle: 49°) over ∼16 years from 16 March 1999 to 20 February 2015. The analysis of 557.7 nm airglow images shows clear seasonal variation of the propagation direction of gravity waves in the mesopause region. In spring, summer, fall, and winter, the peak directions are northeastward, northeastward, northwestward, and southwestward, respectively. The difference in east‐west propagation direction between summer and winter is probably caused by the wind filtering effect due to the zonal mesospheric jet. Comparison with tropospheric reanalysis data shows that the difference in north‐south propagation direction between summer and winter is caused by differences in the latitudinal location of wave sources due to convective activity in the troposphere relative to Shigaraki. The analysis of 630.0 nm airglow images shows that the propagation direction of MSTIDs is mainly southwestward with a minor northeastward component throughout the 16 years. A clear negative correlation is seen between the yearly power spectral density of MSTIDs and F10.7 solar flux. This negative correlation with solar activity may be explained by the linear growth rate of the Perkins instability and secondary wave generation of gravity waves in the thermosphere.
Peculiarities of VLF wave propagation in the Earth's magnetosphere in the presence of artificial large‐scale inhomogeneity
Authors: Pasmanik D. L. , Demekhov A. G. 
Published: July 2017

AbstractWe study specific features of VLF waves propagation in the Earth's ionosphere and magnetosphere in the presence of large‐scale field‐aligned plasma inhomogeneities (ducts). These inhomogeneities can, e.g., be formed during the ionosphere heating by high‐power HF facilities such as High Frequency Active Auroral Research Program and “Sura.” They can extend up to altitudes of several thousand kilometers along geomagnetic field lines and have transverse scales of about 1° determined by the heated region scale. We analyze ray trajectories of VLF waves with frequencies of 1 to 15 kHz starting from about 100 km altitude and use the plasma parameters obtained within the framework of the SAMI2 simulation model (Huba et al., 2000). This model employs MHD equations for thermal plasma and allows one to obtain the plasma parameters along the entire magnetic flux tube in a fixed meridional plane. By knowing the ray trajectories, we calculate and compare the amplitude variation along the ray paths for the cases of unperturbed and heated ionosphere. We show that the presence of a large‐scale density disturbance produced by the HF heating can lead to significant changes of wave propagation trajectories. In particular, efficient guiding of VLF waves in this region can take place, which in turn can result in the appearance of several wave focusing regions and a drastic local increase of the VLF wave amplitude in these regions (up to ∼10 times as compared to the case of unperturbed plasma). The number of focusing regions is determined by an extension of an artificial duct along the geomagnetic field.
Ionospheric electron heating associated with pulsating auroras: A Swarm survey and model simulation
Authors: Liang Jun , Yang B. , Donovan E. , Burchill J. , Knudsen D. 
Published: July 2017

AbstractIn this paper we report a study on the plasma signatures (electron temperature, plasma density, and field‐aligned current) of patchy pulsating auroras in the upper F region ionosphere using Swarm satellite data. Via a survey of 38 patch crossing events, we repeatedly identify a strong electron temperature enhancement associated with the pulsating aurora. On average, the electron temperature at Swarm satellite altitudes (~460 km) increases from ~2200 K at subauroral latitudes to a peak of ~3000 K within the pulsating auroral patch. This indicates that pulsating auroras may act as an important heating source for the nightside ionosphere. On the other hand, no well‐defined trend of plasma density variations associated with pulsating auroras is identified at Swarm altitudes. The field‐aligned currents within the pulsating aurora patch are mostly upward, with mean magnitudes on order of ~1 μA/m2. We then perform a numerical simulation to explore the potential mechanisms underlying the strong electron heating associated with the pulsating aurora. Via simulations we find that to account for the realistic electron temperature observation in a major portion of our events, pulsating auroras are likely accompanied by substantial magnetospheric heat fluxes around the order of ~1010 eV/cm2. We propose that such magnetospheric heat fluxes may be pertinent to one long‐hypothesized feature of pulsating auroras, namely, the coexistence of an enhanced low‐energy plasma population in magnetic flux tubes threading the pulsating aurora, in addition to the energetic electron precipitation. Via a Swarm survey we repeatedly find a strong electron temperature enhancement associated with the pulsating aurora The field‐aligned currents within pulsating auroras are moderately upward, with mean magnitudes on the order of ~1e−6 A/m2 To explain the observed electron heating, pulsating auroras are likely accompanied by magnetospheric heat fluxes around ~1E+10 eV/cm2/s.
Flux ropes in the Hermean magnetotail: Distribution, properties, and formation
Authors: Smith A. W. , Slavin J. A. , Jackman C. M. , Poh G.‐K. , Fear R. C. 
Published: July 2017

AbstractAn automated method was applied to identify magnetotail flux rope encounters in MESSENGER (MErcury Surface, Space ENvironment, GEochemistry, and Ranging) magnetometer data. The method identified significant deflections of the north‐south component of the magnetic field coincident with enhancements in the total field or dawn‐dusk component. Two hundred forty‐eight flux ropes are identified that possess well‐defined minimum variance analysis (MVA) coordinate systems, with clear rotations of the field. Approximately 30% can be well approximated by the cylindrically symmetric, linearly force‐free model. Flux ropes are most common moving planetward, in the postmidnight sector. Observations are intermittent, with the majority (61%) of plasma sheet passages yielding no flux ropes; however, the peak rate of flux ropes during a reconnection episode is ∼5 min−1. Overall, the peak postmidnight rate is ∼0.25 min−1. Only 25% of flux ropes are observed in isolation. The radius of flux ropes is comparable to the ion inertial length within Mercury's magnetotail plasma sheet. No clear statistical separation is observed between tailward and planetward moving flux ropes, suggesting the near‐Mercury neutral line (NMNL) is highly variable. Flux ropes are more likely to be observed if the preceding lobe field is enhanced over background levels. A very weak correlation is observed between the flux rope core field and the preceding lobe field orientation; a stronger relationship is found with the orientation of the field within the plasma sheet. The core field strength measured is ∼6 times stronger than the local dawn‐dusk plasma sheet magnetic field.
Climatology of semidiurnal lunar and solar tides at middle and high latitudes: Interhemispheric comparison
Authors: Conte J. Federico , Chau Jorge L. , Stober Gunter , Pedatella Nicholas , Maute Astrid , Hoffmann Peter , Janches Diego , Fritts David , Murphy Damian J. 
Published: July 2017

AbstractThe semidiurnal lunar and solar tides obtained from meteor radar measurements spanning from 2009 to 2013 observed at Davis (69°S) and Rio Grande (54°S) are presented and compared to the Northern Hemisphere ones at Andenes (69°N) and Juliusruh (54°N). Mean tidal differences for both intrahemispheric and interhemispheric scenarios are analyzed. Tidal behavior is also compared against numerical simulations during 2009 and 2013 sudden stratospheric warming (SSW) time periods. Possible influences in the Southern Hemisphere from the local stratosphere are also investigated using Modern Era Retrospective analysis for Research and Applications, version 2 (MERRA 2) data sets. The main features of the mean zonal wind are similar in both hemispheres, i.e., stronger amplitudes over midlatitude locations, eastward winds during winter and westward below 90 km with eastward higher up during corresponding summer times. On the other hand, the semidiurnal solar tides observed in the Southern Hemisphere show clear differences when compared to the Northern Hemisphere and between middle‐ and high‐latitude locations at the same hemisphere. These differences are even larger for the semidiurnal lunar tide, which shows stronger amplitudes from October to March and March to October, over Davis and Rio Grande, respectively. Our results indicate that the lunar tides over the Southern Hemisphere midlatitudes are more prone to react to the Northern Hemisphere stratospheric polar vortex influences, in agreement with numerical simulations, particularly for the time of the 2013 SSW.
Characterizing the information content of cloud thermodynamic phase retrievals from the notional PACE OCI shortwave reflectance measurements
Authors: Coddington O. M. , Vukicevic T. , Schmidt K. S. , Platnick S. 
Published: July 2017

AbstractWe rigorously quantify the probability of liquid or ice thermodynamic phase using only shortwave spectral channels specific to the National Aeronautics and Space Administration's Moderate Resolution Imaging Spectroradiometer, Visible Infrared Imaging Radiometer Suite, and the notional future Plankton, Aerosol, Cloud, ocean Ecosystem imager. The results show that two shortwave‐infrared channels (2135 and 2250 nm) provide more information on cloud thermodynamic phase than either channel alone; in one case, the probability of ice phase retrieval increases from 65 to 82% by combining 2135 and 2250 nm channels. The analysis is performed with a nonlinear statistical estimation approach, the GEneralized Nonlinear Retrieval Analysis (GENRA). The GENRA technique has previously been used to quantify the retrieval of cloud optical properties from passive shortwave observations, for an assumed thermodynamic phase. Here we present the methodology needed to extend the utility of GENRA to a binary thermodynamic phase space (i.e., liquid or ice). We apply formal information content metrics to quantify our results; two of these (mutual and conditional information) have not previously been used in the field of cloud studies.
An influence of extreme southern hemisphere cold surges on the North Atlantic Subtropical High through a shallow atmospheric circulation
Authors: Bowerman A. R. , Fu R. , Yin L. , Fernando D. N. , Arias P. A. , Dickinson R. E. 
Published: July 2017

AbstractPrevious studies have attributed interhemisphere influences of the atmosphere to the latitudinal propagation of planetary waves crossing the equator, to the triggering of equatorial Kelvin waves, or to monsoonal circulation. Over the American‐Atlantic sector, such cross‐equatorial influences rarely occur during boreal summer due to unfavorable atmospheric conditions. We have observed that an alternative mechanism provides an interhemisphere influence. When episodes of extreme cold surges and upper tropospheric westerly winds occur concurrently over southern hemisphere Amazonia, cold surges from extratropical South America can penetrate deep into southern Amazonia. Although they do not appear to influence upper tropospheric circulation of the northern hemisphere, extremely strong southerly cross‐equatorial advection (>2σ standard deviations, or 2) of cold and dense air in the lower troposphere can reach as least 10°N. Such cold advection increases the northward cross‐equatorial pressure gradient in the lower to middle troposphere, thus shallow northerly return flow below 500 hPa. This return flow and the strong lower tropospheric southerly cross‐equatorial flow form an anomalous shallow meridional circulation spanning from southern Amazonia to the subtropical North Atlantic, with increased geopotential height anomalies exceeding +1σ to at least 18°N. It projects onto the southern edge of the North Atlantic Subtropical High (NASH), increasing its pressure and leading to equatorward expansion of NASH's southern boundary. These anomalies enhance the NASH, leading to its equatorward expansion. These extreme cold surges can potentially improving the predictability of weather patterns of the tropical and subtropical Atlantic, including the variability of the NASH's southern edge.
Evaluation of NASA Deep Blue/SOAR aerosol retrieval algorithms applied to AVHRR measurements
Authors: Sayer A. M. , Hsu N. C. , Lee J. , Carletta N. , Chen S.‐H. , Smirnov A. 
Published: July 2017

AbstractThe Deep Blue (DB) and Satellite Ocean Aerosol Retrieval (SOAR) algorithms have previously been applied to observations from sensors like the Moderate Resolution Imaging Spectroradiometers (MODIS) and Sea‐viewing Wide Field‐of‐view Sensor (SeaWiFS) to provide records of midvisible aerosol optical depth (AOD) and related quantities over land and ocean surfaces, respectively. Recently, DB and SOAR have also been applied to Advanced Very High Resolution Radiometer (AVHRR) observations from several platforms (NOAA11, NOAA14, and NOAA18), to demonstrate the potential for extending the DB and SOAR AOD records. This study provides an evaluation of the initial version (V001) of the resulting AVHRR‐based AOD data set, including validation against Aerosol Robotic Network (AERONET) and ship‐borne observations, and comparison against both other AVHRR AOD records and MODIS/SeaWiFS products at select long‐term AERONET sites. Although it is difficult to distil error characteristics into a simple expression, the results suggest that one standard deviation confidence intervals on retrieved AOD of ±(0.03 + 15%) over water and ±(0.05 + 25%) over land represent the typical level of uncertainty, with a tendency toward negative biases in high‐AOD conditions, caused by a combination of algorithmic assumptions and sensor calibration issues. Most of the available validation data are for NOAA18 AVHRR, although performance appears to be similar for the NOAA11 and NOAA14 sensors as well.
Mechanically Tunable Bioink for 3D Bioprinting of Human Cells
Authors: Forget Aurelien , Blaeser Andreas , Miessmer Florian , Köpf Marius , Campos Daniela F. Duarte , Voelcker Nicolas H. , Blencowe Anton , Fischer Horst , Shastri V. Prasad 
Published: July 2017

AbstractThis study introduces a thermogelling bioink based on carboxylated agarose (CA) for bioprinting of mechanically defined microenvironments mimicking natural tissues. In CA system, by adjusting the degree of carboxylation, the elastic modulus of printed gels can be tuned over several orders of magnitudes (5–230 Pa) while ensuring almost no change to the shear viscosity (10–17 mPa) of the bioink solution; thus enabling the fabrication of 3D structures made of different mechanical domains under identical printing parameters and low nozzle shear stress. Human mesenchymal stem cells printed using CA as a bioink show significantly higher survival (95%) in comparison to when printed using native agarose (62%), a commonly used thermogelling hydrogel for 3D‐bioprinting applications. This work paves the way toward the printing of complex tissue‐like structures composed of a range of mechanically discrete microdomains that could potentially reproduce natural mechanical aspects of functional tissues.