497 Works

Global hybrid simulation of the dayside reconnection layer and associated field-aligned currents

Y Lin
A two-dimensional global hybrid simulation is carried out to study the structure of the magnetopause boundary layer in the noon-midnight meridian plane associated with the dayside reconnection. In the simulation the bow shock, magnetosheath, and magnetopause are formed self-consistently by supersonic solar wind passing the geomagnetic field. The dayside reconnection is triggered by imposing a current-dependent resistivity at the subsolar magnetopause. A large-amplitude rotational discontinuity is formed in the quasi-steady reconnection layer in the northern...

Increasing Mississippi river discharge throughout the 21st century influenced by changes in climate, land use, and atmospheric CO2

Bo Tao, Hanqin Tian, Wei Ren, Jia Yang, Qichun Yang, Ruoying He, Weijun Cai & Steven Lohrenz
Previous studies have demonstrated that changes in temperature and precipitation (hereafter climate change) would influence river discharge, but the relative importance of climate change, land use, and elevated atmospheric CO2 have not yet been fully investigated. A process-based projection for the Mississippi River basin suggests that river discharge would be substantially enhanced (10.7–59.8%) by the 2090s compared to the recent decade (2000s), although large discrepancies exist among different climate, atmospheric CO2, and land use change...

Are we underestimating the genetic variances of dimorphic traits?

Mathew E. Wolak, Derek A. Roff & Daphne J. Fairbairn
Populations often contain discrete classes or morphs (e.g., sexual dimorphisms, wing dimorphisms, trophic dimorphisms) characterized by distinct patterns of trait expression. In quantitative genetic analyses, the different morphs can be considered as different environments within which traits are expressed. Genetic variances and covariances can then be estimated independently for each morph or in a combined analysis. In the latter case, morphs can be considered as separate environments in a bivariate analysis or entered as fixed...

Long-Term Decrease in Coloration: A Consequence of Climate Change?

David López-Idiáquez, Céline Teplitsky, Arnaud Grégoire, Amélie Fargevieille, María Del Rey, Christophe De Franceschi, Anne Charmantier & Claire Doutrelant
Climate change has been shown to affect fitness-related traits in a wide range of taxa; for instance, warming leads to phenological advancements in many plant and animal species. The influence of climate change on social and secondary sexual traits, which are associated with fitness because of their role as quality signals, is, however, unknown. Here, we use more than 5,800 observations collected on two Mediterranean blue tit subspecies (Cyanistes caeruleus caeruleus and Cyanistes caeruleus ogliastrae)...

The Silurian to Permian history of a metamorphic core complex in Lofoten, northern Scandinavian Caledonides

Mark Steltenpohl, Willis Hames & Arild Andresen
[1] The Lofoten archipelago exposes Precambrian Baltic basement and Caledonian allochthonous sequences within a 1000 km long chain of gravity and magnetic highs and structural culminations along the extended, British and Norwegian continental shelf. Previous regional geophysical studies indicate that post-Caledonian extension and development of the northern Norwegian shelf occurred during broadly defined Carboniferous-Permian, Cretaceous-Jurassic, and early Tertiary events. Structures related to these events are known to young westward. We report field, structural, and Ar-40/Ar-39...

LOW-ALTITUDE OBSERVATIONS AND MODELING OF QUASI-STEADY MAGNETOPAUSE RECONNECTION

T Onsager, Shen-Wu Chang, J PEREZ, J AUSTIN & L JANOO
Data from two near-conjugate passes of DE 1 and DE 2 through the cusp/cleft region of the Earth's magnetosphere are presented and compared with model calculations of particle transport from the solar wind to spacecraft locations in the magnetosphere. Comparison of the observed and calculated particle spectra shows that the model can successfully match the spectra at both spacecraft using the same model parameters. This demonstrates that the modeling technique is applicable at both high...

Scalings of Alfven-cyclotron and ion Bernstein instabilities on temperature anisotropy of a ring-like velocity distribution in the inner magnetosphere

Peter Gary, Kyungguk Min & Kaijun Liu
A ring-like proton velocity distribution with f(p)(v)/v>0 and which is sufficiently anisotropic can excite two distinct types of growing modes in the inner magnetosphere: ion Bernstein instabilities with multiple ion cyclotron harmonics and quasi-perpendicular propagation and an Alfven-cyclotron instability at frequencies below the proton cyclotron frequency and quasi-parallel propagation. Recent particle-in-cell simulations have demonstrated that even if the maximum linear growth rate of the latter instability is smaller than the corresponding growth of the former...

Magnetic field rotation and transition width in rotational discontinuities and Alfven wave trains

Yu Lin & L Lee
A hybrid simulation is carried out to study the evolution of magnetic field rotations in rotational discontinuities (RDs) and large-amplitude Alfven wave trains (AWTs) whose initial field rotation angle \Delta Phi\ > 180 degrees. For a given initial half width D, the RDs or AWTs lose a multiple of +/-360 degrees field rotation at a critical time, until a smallest rotation angle \Delta Phi\ < 180 degrees is reached. The critical time t(c) for losing...

The demographic basis of population regulation in Columbian ground squirrels

Stephen Dobson & Madan Oli
Environmental factors influence the dynamics and regulation of biological populations through their influences on demographic variables, but demographic mechanisms of population regulation have received little attention. We investigated the demographic basis of regulation of Columbian ground squirrel (Spermophilus columbianus) populations under natural and experimentally food-supplemented conditions. Food supplementation caused substantial increases in population density, and population densities returned to pretreatment levels when the supplementation ended. Control (untreated) populations remained relatively stable throughout the study period...

TESTING THE STOCHASTICITY OF PATTERNS OF ORGANISMAL DIVERSITY - AN IMPROVED NULL MODEL

Joseph Slowinski & Craig Guyer

An Overlooked Hotspot? Rapid Biodiversity Assessment Reveals a Region of Exceptional Herpetofaunal Richness in the Southeastern United States

Sean P. Graham, David A. Steen, Kerry T. Nelson, Andrew M. Durso & John C Maerz
We conducted a competitive bioblitz survey in four Georgia counties to raise awareness of a unique and species rich herpetofauna in the Pine Mountain/ Fall Line Sandhills Region of Georgia, and compared documented species of these counties to other herpetofaunas of the southeast that have known high richness and/ or were subject to thorough collection efforts. Our results demonstrate the efficacy of bioblitzes for documenting large numbers of species in a limited amount of time...

The U.S. educational effort in unsaturated zone hydrology

James Davidson, George Hornberger & Fred Molz
The region of the earth below the land surface and above the water-saturated zone plays a major role in determining the behavior of hydrologic systems. To help educators and other interested individuals evaluate and continue molding the U.S. educational effort in the hydrology of the unsaturated zone, the AGU Hydrology Section Committee on Water in the Unsaturated Zone conducted a study of the number and level of university educational programs involved in unsaturated zone hydrology....

Magma-facilitated transpressional strain partitioning within the Sawtooth metamorphic complex, Idaho: A zone accommodating Cretaceous orogen-parallel translation in the Idaho batholith

Chong Ma, David A. Foster, Paul A. Mueller & Barbara L. Dutrow
Structural data from metasedimentary rocks and geochronologic data from intrusive rocks in the Idaho batholith provide evidence for the relationship between deformation and magmatism in the northern U.S. Cordillera. The Sawtooth metamorphic complex (SMC), Idaho, is exposed as an inlier in the central Idaho batholith and contains strongly deformed metasedimentary and intrusive rocks. Geologic mapping reveals north-south-striking, alternating contraction- and shear-dominated domains across strike. The contraction-dominated domains consist of centimeter- to tens of meter-scale, shallowly...

Statistically Determining the Spatial Extent of Relativistic Electron Precipitation Events Using 2-s Polar-Orbiting Satellite Data

L. Claire Gasque, Robyn Millan & Sapna Shekhar
Relativistic electron precipitation (REP) from the outer radiation belt into Earth's atmosphere poses risks for satellites and affects Earth's climate, producing ozone-destroying compounds. Characterizing the spatial extent of REP events, which are periods of precipitation localized in space and time, is important for quantifying these effects and improving understanding of outer radiation belt dynamics, allowing quantification of the relative roles of atmospheric and magnetopause particle loss. Following Shekhar et al. (2017, https://doi.org/10.1002/2017JA024716), who used 16...

Scalings for the Alfven-cyclotron instability: Linear dispersion theory and hybrid particle-in-cell simulations

S. Peter Gary, Xiangrong Fu, Misa M. Cowee, Dan Winske & Kaijun Liu
The Alfven-cyclotron instability is driven by an ion temperature anisotropy such that T-perpendicular to/T-|| >1 where and || denote directions perpendicular and parallel to a uniform background magnetic field B-o, respectively. The computations presented here consider a model of a magnetized, homogeneous, collisionless plasma. Two representations of the proton velocity distribution are considered: a single bi-Maxwellian and a magnetospheric-like configuration of two components, a more dense, relatively cool, isotropic component and a less dense, relatively...

The ion temperature gradient: An intrinsic property of Earth's magnetotail

San Lu, A Artemyev, V Angelopoulos, Y Lin & X Wang
Although the ion temperature gradient along (X-GSM) and across (Z(GSM)) the Earth's magnetotail, which plays a key role in generating the cross-tail current and establishing pressure balance with the lobes, has been extensively observed by spacecraft, the mechanism responsible for its formation is still unknown. We use multispacecraft observations and three-dimensional (3-D) global hybrid simulations to reveal this mechanism. Using THEMIS (Time History of Events and Macroscale Interactions during Substorms), Geotail, and ARTEMIS (Acceleration, Reconnection,...

Modulation of Magnetosonic Waves by Background Plasma Density in a Dipole Magnetic Field: 2-D PIC Simulation

Jicheng Sun, Quanming Lu, Xueyi Wang, Xu Liu, Xinliang Gao & Huigen Yang
Recent satellite observations, combined with instability analyses, have shown that the background plasma density variation can modulate the magnetosonic (MS) waves by controlling the wave excitation. However, the detailed modulation process needs to be identified since the MS waves propagate nearly perpendicular to the background magnetic field. In this study, we investigate the MS wave modulation by background plasma density using a 2-D general curvilinear particle-in-cell simulation in the meridian plane of a dipole magnetic...

Large-Scale High-Speed Jets in Earth's Magnetosheath: Global Hybrid Simulations

Jin Guo, San Lu, Quanming Lu, Yu Lin, Xueyi Wang, Junyi Ren, Yufei Hao, Kai Huang, Rongsheng Wang & Xinliang Gao
High-speed jets (HSJs) occur frequently in Earth's magnetosheath downstream of the quasiparallel bow shock. They have great impacts on the magnetosheath and the magnetosphere. Using two-dimensional global hybrid simulations, we investigate the formation and evolution of HSJs with different solar wind conditions. When the quasi-parallel shock is formed, HSJs begin to appear in the quasi-parallel magnetosheath. Some elongated HSJs formed at the quasi-parallel bow shock extend toward the quasi-perpendicular magnetosheath along with the background magnetosheath...

Experimental and numerical investigation of saltwater intrusion dynamics in flux-controlled groundwater systems

Sun Woo Chang & T. Prabhakar Clement
Sea level rise and reduction of groundwater fluxes due to changes in rainfall patterns are the two major climate change–induced hydrological variables that can severely affect saltwater intrusion in coastal aquifers. In this study we use a combination of laboratory experiments and numerical simulations to study the impacts of changes in one of these climate change–induced hydrological variables, groundwater flux, on saltwater intrusion process. We have completed experiments in a laboratory-scale model to study the...

Performance of soybean cultivars in Alabama, 2014

Kathryn M. Glass, , & Jon H. Brasher
"December 2014."

Surface Green’s function calculations: A nonrecursive scheme with an infinite number of principal layers

Aleksey Kletsov, Yuri Dahnovsky & J.V. Ortiz
A novel computational method for a surface Green’s function matrix is introduced for the calculation of electrical current in molecular wires. The proposed nonrecursive approach includes an infinite number of principal layers and yields the second-order matrix equation for the transformed Green’s function matrix. The solution is found by the direct diagonalization of the auxiliary matrix without any iteration process. As soon as complex roots of the auxiliary matrix Gˆ S are calculated, the gaps...

Electron propagator calculations on C-60 and C-70 photoelectron spectra

V. G. Zakrzewski, O. Dolgounitcheva & J.V. Ortiz
Vertical ionization energies of C60 and C70 fullerenes are calculated with semidirect implementations of electron propagator methods and a triple- plus polarization basis set. These predictions are in close agreement with photoelectron spectra for final states in which the Koopmans description is qualitatively valid. Many correlation states, where the latter description fails, are predicted by methods with nondiagonal self-energies.

Second-order, two-electron Dyson propagator theory: Comparisons for vertical double ionization potentials

T. Ida & J.V. Ortiz
The second-order, two-electron Dyson propagator is derived using superoperator theory with a spin-adapted formulation. To include certain ladder diagrams to all orders, the shifted-denominator SD2 approximation is made. Formal and computational comparisons with other approximations illustrate the advantages of the SD2 procedure. Vertical double ionization potentials DIPs for a set of closed-shell molecules are evaluated with the second-order propagator and the SD2 method. The results of the SD2 approximation are in good agreement with experiment....

Partial photoionization cross sections of and Rydberg radicals

A.M. Velasco, C. Lavin, I. Martin, J. Melin & J.V. Ortiz
ammonium and oxonium Rydberg radicals from the outermost, occupied orbitals of their respective ground states are reported. These properties are known to be relevant in photoelectron dynamics studies. For the present calculations, the molecular-adapted quantum defect orbital method has been employed. A Cooper minimum has been found in the 3sa1-kpt2 Rydberg channel of NH4 beyond the ionization threshold, which provides the main contribution to the photoionization of this radical. However, no net minimum is found...

Preliminary performance of soybeans in Alabama, 2020

Henry G. Jordan
Caption title. "January 13, 2021."

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