scholarly journals The Role of Mesoscale Plasma Sheet Dynamics in Ring Current Formation

2021 ◽  
Vol 8 ◽  
Author(s):  
K. A. Sorathia ◽  
A. Michael ◽  
V.G. Merkin ◽  
A.Y. Ukhorskiy ◽  
D. L. Turner ◽  
...  
Keyword(s):  
Ion Transport ◽  
Ring Current ◽  
Identical Particle ◽  
Kinetic Equations ◽  
Plasma Pressure ◽  
Mixed Composition ◽  
Data Set ◽  
Important Species ◽  
Inner Magnetosphere ◽  
Spatial And Temporal Scales

During geomagnetically active periods ions are transported from the magnetotail into the inner magnetosphere and accelerated to energies of tens to hundreds of keV. These energetic ions, of mixed composition with the most important species being H+ and O+, become the dominant source of plasma pressure in the inner magnetosphere. Ion transport and acceleration can occur at different spatial and temporal scales ranging from global quasi-steady convection to localized impulsive injection events and may depend on the ion gyroradius. In this study we ascertain the relative importance of mesoscale flow structures and the effects of ion non-adiabaticity on the produced ring current. For this we use: global magnetohydrodynamic (MHD) simulations to generate self-consistent electromagnetic fields under typical driving conditions which exhibit bursty bulk flows (BBFs); and injected test particles, initialized to match the plasma moments of the MHD simulation, and subsequently evolved according to the kinetic equations of motion. We show that the BBFs produced by our simulation reproduce thermodynamic and magnetic statistics from in situ measurements and are numerically robust. Mining the simulation data we create a data set, over a billion points, connecting particle transport to characteristics of the MHD flow. From this we show that mesoscale bubbles, localized depleted entropy regions, and particle gradient drifts are critical for ion transport. Finally we show, using identical particle ensembles with varying mass, that O+ non-adiabaticity creates qualitative differences in energization and spatial distribution while H+ non-adiabaticity has non-negligible implications for loss timescales.

scholarly journals Another way of deriving the ring current decay time during disturbed periods

1995 ◽  
Vol 38 (2) ◽  
Author(s):  
M. M. Zossi de Artigas ◽  
J. R. Manzano
Keyword(s):  
Ring Current ◽  
Coupling Parameter ◽  
Life Time ◽  
Recovery Phase ◽  
Main Phase ◽  
Physical Analysis ◽  
Inner Magnetosphere ◽  
Current Decay ◽  
The Many ◽  
Energy Dissipated

Coupling parameter, E, and the total energy dissipated by the magnetosphere, UT, are determined for six disturbed periods, following three known criteria for UT computation. It is observed that UT exceeds E for Dst < -90 nT, for alI models. Differences between models reside on the estimated valnes for the particles' life time il1 the equatorial ring current. The values of TR, used in the models, are small during the main phase of the di."turbance, in disagreement with the charge exchange life time of the majority species, H+ and O'-. Based on this conclusion, a different criterion to calculate TR is proposed, differentiating the different stages of the perturbation. TR is calculated, for the main phase of the storm, from the rate of energy deposition estimation, Q, in the ring current. For Dst recovery phase, the vallles are obtained from a ring current decay law computation. The UTvu calculated, physically more coherent with the processes occurring during the event, is now smaller than expected. In this sense, it is understood that the power generated by the solar wind-magnetosphere dy- namo, should also be distributed in the inner magnetosphere, auroral zones and equatorial ring current, as in the outer magnetosphere, plasmoids in the tail shot in antisolar direction. A further adjustment of E, with the Chapman-Ferraro distance, 10' variable, has been made. Although the reslllts, improve the estimation of E, they are sti!l smaller than UT, except UTNU, for some disturbed periods. This result indicates the uncertainty in the computation of the input energy, by using the many expressions proposed in the literature, which are always presented as laws proportional to a given group of parameters, with an unknown factor of proportionality, which deserves more detailed physical analysis.

scholarly journals Storm time dynamics of ring current protons: Implications for the long‐term energy budget in the inner magnetosphere

2016 ◽  
Vol 43 (10) ◽  
pp. 4736-4744 ◽  
Author(s):  
Matina Gkioulidou ◽  
A. Y. Ukhorskiy ◽  
D. G. Mitchell ◽  
L. J. Lanzerotti
Keyword(s):  
Energy Budget ◽  
Ring Current ◽  
Inner Magnetosphere ◽  
Time Dynamics ◽  
Term Energy

PROBLEMS OF THE OUTER RADIATION BELT FORMATION AND TOPOLOGICAL FEATURES OF HIGH LATITUDE MAGNETOSPHERE

2021 ◽  
Vol 44 ◽  
pp. 7-11
Author(s):  
Elena Antonova ◽  
Keyword(s):  
Geomagnetic Storm ◽  
High Latitude ◽  
Radiation Belt ◽  
Ring Current ◽  
Outer Part ◽  
Auroral Oval ◽  
Plasma Pressure ◽  
Relativistic Electrons ◽  
Outer Radiation Belt ◽  
Topological Features

We analyzed the problems of formation of the outer radiation belt (ORB) taking into consideration the latest changes in our understanding of the high-latitude magnetospheric topology. This includes strong evidence that the auroral oval maps to the outer part of the ring current, meanwhile the ORB polar boundary maps inside the auroral oval. Our analysis also includes the variation of the plasma pressure distribution and the time of the acceleration of relativistic electrons during geomagnetic storm. It is shown that the maximum of ORB is formed after the geomagnetic storm in the region of plasma pressure maximum. The position of this maximum agrees with the prediction of the ORB formation theory based on the analysis of ring current development during storm. We emphasize the role of adiabatic processes in the ORB dynamics and the importance of the substorm injections during storm recovery phase for the formation of enhanced fluxes of ORB electrons after the storm.

scholarly journals Strong Southward and Northward Currents Observed in the Inner Plasma Sheet

2019 ◽  
Author(s):  
Yanyan Yang ◽  
Chao Shen ◽  
Yong Ji
Keyword(s):  
Magnetic Field ◽  
Plasma Sheet ◽  
Ring Current ◽  
Generation Mechanism ◽  
Storm Events ◽  
Current Generation ◽  
Inner Magnetosphere ◽  
Latitude Region ◽  
Field Lines ◽  
The Magnetic Field

Abstract. It is generally believed that field aligned currents (FACs) and the ring current (RC) are two dominant parts of the inner magnetosphere. However, using the Cluster spacecraft crossing of the pre-midnight inner plasma sheet in the latitude region between 10° N and 30° N, it is found that, during large storm events, in addition to FACs and the RC, there also exist strong southward and northward currents, which cannot be FACs, because the magnetic field in these regions is mainly along the XY plane. Detailed investigation shows that both magnetic field lines (MFLs) and currents in these regions highly fluctuate. When the curvature of MFLs changes direction in the XY plane, the current also alternatively switches between southward and northward. Further analysis of the current generation mechanism indicates that the most reasonable candidate for the origin of these southward and northward currents is the curvature drift of energetic particles.

scholarly journals Study of the applicability of the curlometer technique with the four Cluster spacecraft in regions close to Earth

2012 ◽  
Vol 30 (3) ◽  
pp. 597-611 ◽  
Author(s):  
S. Grimald ◽  
I. Dandouras ◽  
P. Robert ◽  
E. Lucek
Keyword(s):  
Magnetic Field ◽  
Current Density ◽  
Ring Current ◽  
Current System ◽  
Sufficient Conditions ◽  
Magnetic Activity ◽  
Inner Magnetosphere ◽  
Good Proxy ◽  
The Magnetic Field ◽  
Magnetospheric Current System

Abstract. Knowledge of the inner magnetospheric current system (intensity, boundaries, evolution) is one of the key elements for the understanding of the whole magnetospheric current system. In particular, the calculation of the current density and the study of the changes in the ring current is an active field of research as it is a good proxy for the magnetic activity. The curlometer technique allows the current density to be calculated from the magnetic field measured at four different positions inside a given current sheet using the Maxwell-Ampere's law. In 2009, the CLUSTER perigee pass was located at about 2 RE allowing a study of the ring current deep inside the inner magnetosphere, where the pressure gradient is expected to invert direction. In this paper, we use the curlometer in such an orbit. As the method has never been used so deep inside the inner magnetosphere, this study is a test of the curlometer in a part of the magnetosphere where the magnetic field is very high (about 4000 nT) and changes over small distances (ΔB = 1nT in 1000 km). To do so, the curlometer has been applied to calculate the current density from measured and modelled magnetic fields and for different sizes of the tetrahedron. The results show that the current density cannot be calculated using the curlometer technique at low altitude perigee passes, but that the method may be accurate in a [3 RE; 5 RE] or a [6 RE; 8.3 RE] L-shell range. It also demonstrates that the parameters used to estimate the accuracy of the method are necessary, but not sufficient conditions.

scholarly journals Evolution of the U.S. Biological Select AgentRathayibacter toxicus

mBio ◽  
2018 ◽  
Vol 9 (4) ◽  
Author(s):  
Edward W. Davis ◽  
Javier F. Tabima ◽  
Alexandra J. Weisberg ◽  
Lucas Dantas Lopes ◽  
Michele S. Wiseman ◽  
...  
Keyword(s):  
Genetic Diversity ◽  
Adaptive Immune System ◽  
The United States ◽  
Genomic Diversity ◽  
Data Set ◽  
Important Species ◽  
Content Type ◽  
Low Genetic Diversity ◽  
History Of ◽  
Short Palindromic Repeat

ABSTRACTRathayibacter toxicusis a species of Gram-positive, corynetoxin-producing bacteria that causes annual ryegrass toxicity, a disease often fatal to grazing animals. A phylogenomic approach was employed to model the evolution ofR. toxicusto explain the low genetic diversity observed among isolates collected during a 30-year period of sampling in three regions of Australia, gain insight into the taxonomy ofRathayibacter, and provide a framework for studying these bacteria. Analyses of a data set of more than 100 sequencedRathayibactergenomes indicated thatRathayibacterforms nine species-level groups.R. toxicusis the most genetically distant, and evidence suggested that this species experienced a dramatic event in its evolution. Its genome is significantly reduced in size but is colinear to those of sister species. Moreover,R. toxicushas low intergroup genomic diversity and almost no intragroup genomic diversity between ecologically separated isolates.R. toxicusis the only species of the genus that encodes a clustered regularly interspaced short palindromic repeat (CRISPR) locus and that is known to host a bacteriophage parasite. The spacers, which represent a chronological history of infections, were characterized for information on past events. We propose a three-stage process that emphasizes the importance of the bacteriophage and CRISPR in the genome reduction and low genetic diversity of theR. toxicusspecies.IMPORTANCERathayibacter toxicusis a toxin-producing species found in Australia and is often fatal to grazing animals. The threat of introduction of the species into the United States led to its inclusion in the Federal Select Agent Program, which makesR. toxicusa highly regulated species. This work provides novel insights into the evolution ofR. toxicus.R. toxicusis the only species in the genus to have acquired a CRISPR adaptive immune system to protect against bacteriophages. Results suggest that coexistence with the bacteriophage NCPPB3778 led to the massive shrinkage of theR. toxicusgenome, species divergence, and the maintenance of low genetic diversity in extant bacterial groups. This work contributes to an understanding of the evolution and ecology of an agriculturally important species of bacteria.

Modeling Abiotic Niches of Crops and Wild Ancestors Using Deep Learning: A Generalized Approach

2019 ◽  
Author(s):  
W. G. Hulleman ◽  
R. A. Vos
Keyword(s):  
Deep Learning ◽  
Species Distribution ◽  
Habitat Suitability ◽  
Species Interactions ◽  
Method Development ◽  
Species Distribution Modeling ◽  
Crop Species ◽  
Data Set ◽  
Important Species ◽  
Distribution Modeling

AbstractIntroductionUnderstanding what interactions and environmental factors shape the geographic distribution of species is one of the fundamental questions in ecology and evolution. Insofar as the focus is on agriculturally important species, insight into this is also of applied importance. Species Distribution Modeling (SDM) comprises a spectrum of approaches for establishing correlative models of species (co-)occurrences and geospatial patterns of abiotic environmental variables.MethodsHere, we contribute to this field by presenting a generalized approach for SDM that utilizes deep learning, which offers some improvements over current methods, and by presenting a case study on the habitat suitability of staple crops and their wild ancestors. The approach we present is implemented in a reusable software toolkit, which we apply to an extensive data set of geo-referenced occurrence records for 52 species and 59 GIS layers. We compare the habitat suitability projections for selected, major crop species with the actual extent of their current cultivation.ResultsOur results show that the approach yields especially plausible projections for species with large numbers of occurrences (>500). For the analysis of such data sets, the toolkit provides a convenient interface for using deep neural networks in SDM, a relatively novel application of deep learning. The toolkit, the data, and the results are available as open source / open access packages.ConclusionsSpecies Distribution Modeling with deep learning is a promising avenue for method development. The niche projections that can be produced are plausible, and the general approach provides great flexibility for incorporating additional data such as species interactions.

The phylogenomics of diversification on an island: applying anchored hybrid enrichment to New Zealand Leptospermum scoparium (Myrtaceae)

2019 ◽  
Vol 191 (1) ◽  
pp. 1-17 ◽  
Author(s):  
Matt H Buys ◽  
Richard C Winkworth ◽  
Peter J de Lange ◽  
Peter G Wilson ◽  
Nora Mitchell ◽  
...  
Keyword(s):  
Genetic Diversity ◽  
New Zealand ◽  
Sequence Data ◽  
Large Data ◽  
Data Matrix ◽  
Data Set ◽  
Important Species ◽  
Anchored Hybrid Enrichment ◽  
Data Signal ◽  
Leptospermum Scoparium

Abstract Leptospermum scoparium (Myrtaceae) is a morphologically highly variable species found in mainland Australia, Tasmania and New Zealand. For example, in New Zealand up to six morphologically distinct varieties of this species have been described, although only two (var. scoparium and var. incanum) are now formally recognized. In the present study we provide a first examination of genetic diversity in this culturally and commercially important species with the aim of gaining insights into its origins and evolution. We used anchored hybrid enrichment to acquire sequence data from 485 orthologous low-copy nuclear loci for 27 New Zealand and three Australian accessions of L. scoparium and representatives of several other Leptospermum spp. The final concatenated data matrix contained 421 687 nucleotide positions of which 55 102 were potentially informative. Despite the relative large data set, our analyses suggest that a combination of low and incompatible data signal limits the resolution of relationships among New Zealand populations of L. scoparium. Nevertheless, our analyses are consistent with genetic diversity being geographically structured, with three groups of L. scoparium recovered. We discuss the evolutionary and taxonomic implications of our findings.

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