bluuebunny/crossref_metadata_2025_split huggingface dataset:
Multi‐MeV electron loss in the heart of the radiation belts
Authors: Shprits Yuri Y. , Kellerman Adam , Aseev Nikita , Drozdov Alexander Y. , Michaelis Ingo 
Published: January 2017

AbstractSignificant progress has been made in recent years in understanding acceleration mechanisms in the Earth's radiation belts. In particular, a number of studies demonstrated the importance of the local acceleration by analyzing the radial profiles of phase space density (PSD) and observing building up peaks in PSD. In this study, we focus on understanding of the local loss using very similar tools. The profiles of PSD for various values of the first adiabatic invariants during the previously studied 17 January 2013 storm are presented and discussed. The profiles of PSD show clear deepening minimums consistent with the scattering by electromagnetic ion cyclotron waves. Long‐term evolution shows that local minimums in PSD can persist for relatively long times. During considered interval of time the deepening minimums were observed around L* = 4 during 17 January 2013 storm and around L* = 3.5 during 1 March 2013 storm. This study shows a new method that can help identify the location, magnitude, and time of the local loss and will help quantify local loss in the future. This study also provides additional clear and definitive evidence that local loss plays a major role for the dynamics of the multi‐MeV electrons.
Morphology of Ganymede's FUV auroral ovals
Authors: Musacchio Fabrizio , Saur Joachim , Roth Lorenz , Retherford Kurt D. , McGrath Melissa A. , Feldman Paul D. , Strobel Darrell F. 
Published: January 2017

AbstractWe study the morphology of Ganymede's FUV aurora by analyzing spectral images obtained over the past two decades by the Space Telescope Imaging Spectrograph on board the Hubble Space Telescope. The observations cover the eastern and western elongation as well as various magnetic latitudes of Ganymede within the Jovian plasma sheet. We find both asymmetries in the spatial distribution of auroral brightness on the observed moon disk and temporal variation correlated to Ganymede's changing magnetic latitude. The total disk brightness is on average 1.42 ± 0.07 times brighter on the leading side (95.4 ± 2.1 R) than on the trailing side (67.2 ± 2.9 R). The brightness ratio of the sub‐Jovian hemisphere to the anti‐Jovian hemisphere is 1.81 ± 0.06 on the leading side and 1.41 ± 0.14 on the trailing side, respectively. Inside the Jovian current sheet, the brightness of the auroral ovals increases by a factor of 1.45 ± 0.02 on the leading side and decreases by a factor of 0.80 ± 0.02 on the trailing side. At the current sheet center, the auroral ovals shift 4.1° ± 0.7°latitude toward Ganymede's planetographic equator on the leading side and 2.9° ± 1.5° toward the poles on the trailing side. Both effects, the variation of brightness and the movement of the ovals are correlated to a stronger interaction of Jupiter's magnetospheric plasma with Ganymede's minimagnetosphere inside the current sheet. Finally, we calculate the latitudinal difference of the northern and southern ovals from Ganymede's magnetic equator. The result suggests a farther westward orientation of Ganymede's dipole magnetic moment at approximately 47° + 58°/−43°west longitude compared to previous estimates.
Energy transfer from lower energy to higher‐energy electrons mediated by whistler waves in the radiation belts
Authors: Shklyar D. R. 
Published: January 2017

AbstractWe study the problem of energy exchange between waves and particles, which leads to energization of the latter, in an unstable plasma typical of the radiation belts. The ongoing Van Allen Probes space mission brought this problem among the most discussed in space physics. A free energy which is present in an unstable plasma provides the indispensable condition for energy transfer from lower energy particles to higher‐energy particles via resonant wave‐particle interaction. This process is studied in detail by the example of electron interactions with whistler mode wave packets originated from lightning‐induced emission. We emphasize that in an unstable plasma, the energy source for electron energization is the energy of other particles, rather than the wave energy as is often assumed. The way by which the energy is transferred from lower energy to higher‐energy particles includes two processes that operate concurrently, in the same space‐time domain, or sequentially, in different space‐time domains, in which a given wave packet is located. In the first process, one group of resonant particles gives the energy to the wave. The second process consists in wave absorption by another group of resonant particles, whose energy therefore increases. We argue that this mechanism represents an efficient means of electron energization in the radiation belts.
Io plasma torus ion composition: Voyager, Galileo, and Cassini
Authors: Nerney Edward G. , Bagenal Fran , Steffl Andrew J. 
Published: January 2017

AbstractThe Io torus produces ultraviolet emissions diagnostic of plasma conditions. We revisit data sets obtained by the Voyager 1, Galileo, and Cassini missions at Jupiter. With the latest version (8.0) of the CHIANTI atomic database we analyze UV spectra to determine ion composition. We compare ion composition obtained from observations from these three missions with a theoretical model of the physical chemistry of the torus by Delamere et al. (2005). We find ion abundances from the Voyager data similar to the Cassini epoch, consistent with the dissociation and ionization of SO2, but with a slightly higher average ionization state for sulfur, consistent with the higher electron temperature measured by Voyager. This reanalysis of the Voyager data produces a much lower oxygen:sulfur ratio than earlier analysis by Shemansky (1988), which was also reported by Bagenal (1994). We derive fractional ion compositions in the center of the torus to be S+/Ne ~ 5%, S++/Ne ~ 20%, S+++/Ne ~ 5%, O+/Ne ~ 20%, O++/Ne ~ 3%, and Σ(On+)/Σ(Sn+) ~ 0.8, leaving about 10–15% of the charge as protons. The radial profile of ion composition indicates a slightly higher average ionization state, a modest loss of sulfur relative to oxygen, and Σ(On+)/Σ(Sn+) ~ 1.2 at about 8 RJ, beyond which the composition is basically frozen in. The Galileo observations of UV emissions from the torus suggest that the composition in June 1996 may have comprised a lower abundance of oxygen than usual, consistent with observations made at the same time by the EUVE satellite.
Simulation of the production rates of cosmogenic nuclides on the Moon based on Geant4
Authors: Li Yong , Zhang Xiaoping , Dong Wudong , Ren Zhongzhou , Dong Tiekuang , Xu Aoao 
Published: January 2017

AbstractA numerical simulation model is built to simulate the production of cosmogenic nuclides based on Geant4 (GEometry ANd Tracking). Some modifications have been made for cross sections in Geant4 using the experimental data or the other proper model and the contributions of all secondary particles caused by cosmic rays are included in our simulation model. Our simulation results suggest a substantial contribution of the secondary charged pions to the production rates of 10Be and 14C, as high as 21.04% for 10Be and 21.36% for 14C, respectively. Within one set of self‐consistent parameters, the simulation results of the production rates of the cosmogenic nuclides, 53Mn, 36Cl, 41Ca, 26Al, 10Be, and 14C, agree well with the measured data from Apollo 15 drill core. This model provides users a validated approach to study the production of cosmogenic nuclides on the planet surface and in the meteorites.
A self‐consistent mechanism for electron cyclotron maser emission and its application to type III solar radio bursts
Authors: Chen L. , Wu D. J. , Zhao G. Q. , Tang J. F. 
Published: January 2017

AbstractType III solar radio bursts (SRBs) produced by fast electron beams (FEBs) traveling along solar magnetic fields are the best known and the most important kind of SRBs because of their clearest association with FEBs as well as most frequent observations during solar activities. However, the physics of their emitting mechanism has been a controversial issue. Based on the electron cyclotron maser (ECM) instability driven directly by a magnetized FEB, whose physics is fairly well known from the Earth's auroral kilometric radiation, this paper proposes a self‐consistent mechanism for type III SRBs, in which the Alfvén wave (AW) produced by the current instability of the beam‐return current system associated with the FEB, called the self‐generated AW, plays an important and crucial role. Taking into account the return‐current effect of the FEB, the growth rate and the saturation intensity of the self‐generated AW are estimated. Then the effects of the self‐generated AW on the ECM emission via the ECM instability driven by the magnetized FEB are further investigated. The results show that the self‐generated AW can significantly influence and change the physical properties of the ECM emission. In particular, this novel ECM emission mechanism can effectively overcome the main difficulties of the conventional ECM emission mechanism in application to type III SRBs and may potentially provide a self‐consistent physics scenario for type III SRBs.
The magnetic storms of 3–4 August 2010 and 5–6 August 2011: 1. Ground‐ and space‐based observations
Authors: Valladares C. E. , Eccles J. V. , Basu Su. , Schunk R. W. , Sheehan R. , Pradipta R. , Ruohoniemi J. M. 
Published: January 2017

AbstractWe have used total electron content (TEC) values from low, middle, and high latitudes recorded over the American continent and density and ion temperature measured in situ by the DMSP‐F15 and F17 satellites during the geomagnetic storms of 3–4 August 2010 and 5–6 August 2011 to study the formation and dynamics of plasma density enhancements that developed during these two storms. Common to both storms are the timing of the main phase that extends between 20 and 24 UT and their seasonality with both storms occurring near the end of the Northern Hemisphere summer solstice. During both storms, TEC data show incipient equatorial anomalies lacking a poleward expansion beyond 20° magnetic latitude. Two large‐scale TEC enhancements were observed at middle latitudes showing a complicated pattern of structuring and merging. The first TEC enhancement corresponds to a storm‐enhanced density (SED) seen between 21 and 01 UT on the following day. The second TEC enhancement was observed over Central America, located equatorward of the SED and apparently moving northward. However, careful analysis of the TEC values indicates that this second TEC enhancement is not transported from lower latitudes through a superfountain effect. Instead, the enhanced plasma has a local origin and is driven by a southward directed meridional wind that moves plasma up the tilted magnetic field lines. DMSP flights passing over the second TEC enhancement show a reduction of the ion temperature, confirming an adiabatic expansion of the plasma as it moves up the field lines. It is concluded that the midlatitude TEC enhancements do not arise from a low‐latitude ionospheric fountain effect.
Particle energization by a substorm dipolarization
Authors: Kabin K. , Kalugin G. , Donovan E. , Spanswick E. 
Published: January 2017

AbstractMagnetotail dipolarizations, often associated with substorms, produce significant energetic particle enhancements in the nighttime magnetosphere. In this paper, we apply our recently developed magnetotail dipolarization model to the problem of energizing electrons and ions. Our model is two‐dimensional in the meridional plane and is characterized by the ability to precisely control the location of the transition from the dipole‐like to tail‐like magnetic fields. Both magnetic and electric fields are calculated, self‐consistently, as the transition zone retreats farther into the tail and the area around the Earth occupied by dipole‐like lines increases in size. These fields are used to calculate the motion of electrons and ions and changes in their energies. We consider the energizing effects of the fields restricted to ±15° and ±30° sectors around the midnight meridian, as well the axisymmetric case. Energies of some electrons increase by a factor of 25, which is more than enough to produce observable ionospheric signatures. Electrons are treated using the Guiding Center approximation, while protons and heavier particles generally require description based on the Lorentz equations.
Topographic controlled forcing of salt flow: Three‐dimensional models of an active salt system, Canyonlands, Utah
Authors: Kravitz Katherine , Upton Phaedra , Mueller Karl , Roy Samuel G. 
Published: January 2017

AbstractThe grabens within Canyonlands, Utah, is an active salt system primarily driven by differential unloading due to incision of the Colorado River. However, many other conditions exist in the region that potentially influence regional deformation, including the gentle dip of the evaporite deposits, unconfined salt within the river canyon, weaknesses in the overburden, and topographic gradients on various scales. Three‐dimensional numerical models were built to test the scale at which salt responds to these parameters individually and as a whole. Topography has a large influence on salt flow on both a regional and local scales and predicts the formation of existing structures in the region on consistent spatial scales without the influence of overburden weakening or salt geometry. Topography also has a large influence on the direction of salt flow, which acts to divert salt away from the canyon at the edge of the grabens and enhance salt flow within the grabens. Unconfined salt within the canyon regionally alters displacement rates and patterns, indicating a clear shift in strain before and after incision of the river into the Paradox Formation. On a local scale, there is a strong coupling between overburden weakening and salt flow patterns, where salt responds to individual structures and less to regional drivers. All these driving forces create an ensemble of feedback that alters the strain field and structural development through time.
Quantifying uncertainties in radar forward models through a comparison between CloudSat and SPartICus reflectivity factors
Authors: Mascio Jeana , Mace Gerald G. 
Published: January 2017

AbstractInterpretations of remote sensing measurements collected in sample volumes containing ice‐phase hydrometeors are very sensitive to assumptions regarding the distributions of mass with ice crystal dimension, otherwise known as mass‐dimensional or m‐D relationships. How these microphysical characteristics vary in nature is highly uncertain, resulting in significant uncertainty in algorithms that attempt to derive bulk microphysical properties from remote sensing measurements. This uncertainty extends to radar reflectivity factors forward calculated from model output because the statistics of the actual m‐D in nature is not known. To investigate the variability in m‐D relationships in cirrus clouds, reflectivity factors measured by CloudSat are combined with particle size distributions (PSDs) collected by coincident in situ aircraft by using an optimal estimation‐based (OE) retrieval of the m‐D power law. The PSDs were collected by 12 flights of the Stratton Park Engineering Company Learjet during the Small Particles in Cirrus campaign. We find that no specific habit emerges as preferred, and instead, we find that the microphysical characteristics of ice crystal populations tend to be distributed over a continuum‐defying simple categorization. With the uncertainties derived from the OE algorithm, the uncertainties in forward‐modeled backscatter cross section and, in turn, radar reflectivity is calculated by using a bootstrapping technique, allowing us to infer the uncertainties in forward‐modeled radar reflectivity that would be appropriately applied to remote sensing simulator algorithms.
Boundaries of tropical tropopause layer (TTL): A new perspective based on thermal and stability profiles
Authors: Sunilkumar S. V. , Muhsin M. , Venkat Ratnam M. , Parameswaran K. , Krishna Murthy B. V. , Emmanuel Maria 
Published: January 2017

AbstractThe structure of tropical tropopause layer (TTL) is delineated based on static stability criteria. It is defined as the region extending from the level of minimum static stability to the level of maximum static stability. The static stability and dynamic instability steadily increase from the base to the top of the TTL. Radiosonde data from three tropical stations and Constellation Observing System for Meteorology, Ionosphere, and Climate GPS radio occultation (COSMIC) data over the tropics are used for this investigation. This study suggests that in terms of stability, the TTL can further be considered as a composite of three sublayers: a bottom layer (BL), a middle layer (ML), and an upper layer (UL) embedded between the potential temperatures ~350–360 K, ~360–380 K, and 380–420 K, respectively. While the BL is significantly influenced by frequent convective outflows, the influence of convection declines across the ML. Ozone and water vapor mixing ratios show a discernible change in their gradients across these sublayers. Occurrences of small‐scale turbulence and cirrus are maximum in the BL and decrease in the ML and UL. Longitudinally, the BL is broad and the ML and UL are narrow over the deep convective cores. Strength of static stability in the UL (BL) is relatively strong (weak) centered about the equator, with pronounced features over the deep convective regions. These features of static stability centered about the equator in the BL could be attributed to the convective outflows in the troposphere and that in the UL to the dynamic and radiative processes in the upper troposphere and lower stratosphere.
Radiative effects of absorbing aerosols over northeastern India: Observations and model simulations
Authors: Gogoi Mukunda M. , Babu S. Suresh , Moorthy K. Krishna , Bhuyan Pradip Kumar , Pathak Binita , Subba Tamanna , Chutia Lakhima , Kundu Shyam Sundar , Bharali Chandrakala , Borgohain Arup , Guha Anirban , De Barin Kumar , Singh Brajamani , Chin Mian 
Published: January 2017

AbstractMultiyear measurements of spectral properties of aerosol absorption are examined over four geographically distinct locations of northeastern India. Results indicated significant spatiotemporal variation in aerosol absorption coefficients (σabs) with highest values in winter and lowest in monsoon. The western parts of the region, close to the outflow of Indo‐Gangetic Plains, showed higher values of σabs and black carbon (BC) concentration—mostly associated with fossil fuel combustion. But, the eastern parts showed higher contributions from biomass‐burning aerosols, as much as 20–25% to the total aerosol absorption, conspicuously during premonsoon season. This is attributed to a large number of burning activities over the Southeast Asian region, as depicted from Moderate Resolution Imaging Spectroradiometer fire count maps, whose spatial extent and magnitude peaks during March/April. The nearly consistent high values of aerosol index (AI) and layer height from Ozone Monitoring Instrument indicate the presence of absorbing aerosols in the upper atmosphere. The observed seasonality has been captured fairly well by Goddard Chemistry Aerosol Radiation and Transport (GOCART) as well as Weather Research and Forecasting–Chemistry (WRF‐Chem) model simulations. The ratio of column‐integrated optical depths due to particulate organic matter and BC from GOCART showed good coincidence with satellite‐based observations, indicating the increased vertical dispersion of absorbing aerosols, probably by the additional local convection due to higher fire radiative power caused by the intense biomass‐burning activities. In the WRF‐Chem though underperformed by different magnitude in winter, the values are closer or overestimated near the burnt areas. Atmospheric forcing due to BC was highest (~30 Wm−2) over the western part associated with the fossil fuel combustion.
An improved ray theory and transfer matrix method‐based model for lightning electromagnetic pulses propagating in Earth‐ionosphere waveguide and its applications
Authors: Qin Zilong , Chen Mingli , Zhu Baoyou , Du Ya‐ping 
Published: January 2017

AbstractAn improved ray theory and transfer matrix method‐based model for a lightning electromagnetic pulse (LEMP) propagating in Earth‐ionosphere waveguide (EIWG) is proposed and tested. The model involves the presentation of a lightning source, parameterization of the lower ionosphere, derivation of a transfer function representing all effects of EIWG on LEMP sky wave, and determination of attenuation mode of the LEMP ground wave. The lightning source is simplified as an electric point dipole standing on Earth surface with finite conductance. The transfer function for the sky wave is derived based on ray theory and transfer matrix method. The attenuation mode for the ground wave is solved from Fock's diffraction equations. The model is then applied to several lightning sferics observed in central China during day and night times within 1000 km. The results show that the model can precisely predict the time domain sky wave for all these observed lightning sferics. Both simulations and observations show that the lightning sferics in nighttime has a more complicated waveform than in daytime. Particularly, when a LEMP propagates from east to west (Φ = 270°) and in nighttime, its sky wave tends to be a double‐peak waveform (dispersed sky wave) rather than a single peak one. Such a dispersed sky wave in nighttime may be attributed to the magneto‐ionic splitting phenomenon in the lower ionosphere. The model provides us an efficient way for retrieving the electron density profile of the lower ionosphere and hence to monitor its spatial and temporal variations via lightning sferics.
Projecting regional climate and cropland changes using a linked biogeophysical‐socioeconomic modeling framework: 1. Model description and an equilibrium application over West Africa
Authors: Wang Guiling , Ahmed Kazi Farzan , You Liangzhi , Yu Miao , Pal Jeremy , Ji Zhenming 
Published: January 2017

AbstractAgricultural land use alters regional climate through modifying the surface mass, energy, and momentum fluxes; climate influences agricultural land use through their impact on crop yields. These interactions are not well understood and have not been adequately considered in climate projections. This study tackles the critical linkages within the coupled natural‐human system of West Africa in a changing climate based on an equilibrium application of a modeling framework that asynchronously couples models of regional climate, crop yield, multimarket agricultural economics, and cropland expansion. Using this regional modeling framework driven with two global climate models, we assess the contributions of land use change (LUC) and greenhouse gas (GHGs) concentration changes to regional climate changes and assess the contribution of climate change and socioeconomic factors to agricultural land use changes. For future cropland expansion in West Africa, our results suggest that socioeconomic development would be the dominant driver in the east (where current cropland coverage is already high) and climate changes would be the primary driver in the west (where future yield drop is severe). For future climate, it is found that agricultural expansion would cause a dry signal in the west and a wet signal in the east downwind, with an east‐west contrast similar to the GHG‐induced changes. Over a substantial portion of West Africa, the strength of the LUC‐induced climate signals is comparable to the GHG‐induced changes. Uncertainties originating from the driving global models are small; human decision making related to land use and international trade is a major source of uncertainty.