Long time convergence of magnetohydrodynamic flows to alfvénic states

AbstractAlfvénic states of a plasma, where velocity and magnetic field coincide, form a particular simple class of ideal equilibria and are also found in certain astrophysical phenomena. While transient processes of alignment in turbulent plasmas are well known and due to preferential spectral transfer, the possible long-term evolution of a magnetohydrodynamic plasma towards an alfvénic state has been rarely studied. It is shown that this tendency does not exist: neither specific ideal alfvénic equilibria nor the whole set of such states attract trajectories in any functional sense. Another possibility is that the perturbations of a static equilibrium could tend to become alfvénic, such as the classical Alfvén waves. We find that if these equilibria are current free, when a perturbation approaches an alfvénic state it immediately bounces away from it.

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Long-term evolution of the heliospheric magnetic field inferred from cosmogenic 44Ti activity in meteorites

Astronomy and Astrophysics ◽

10.1051/0004-6361/201730392 ◽

2018 ◽

Vol 610 ◽

pp. A28 ◽

Cited By ~ 2

Author(s):

S. Mancuso ◽

C. Taricco ◽

P. Colombetti ◽

S. Rubinetti ◽

N. Sinha ◽

...

Keyword(s):

Magnetic Field ◽

Ice Cores ◽

Long Term Evolution ◽

Galactic Cosmic Rays ◽

Sunspot Activity ◽

Cosmogenic Isotopes ◽

Heliospheric Magnetic Field ◽

The Past ◽

Term Evolution

Typical reconstructions of historic heliospheric magnetic field (HMF) BHMF are based on the analysis of the sunspot activity, geomagnetic data or on measurement of cosmogenic isotopes stored in terrestrial reservoirs like trees (14C) and ice cores (10Be). The various reconstructions of BHMF are however discordant both in strength and trend. Cosmogenic isotopes, which are produced by galactic cosmic rays impacting on meteoroids and whose production rate is modulated by the varying HMF convected outward by the solar wind, may offer an alternative tool for the investigation of the HMF in the past centuries. In this work, we aim to evaluate the long-term evolution of BHMF over a period covering the past twenty-two solar cycles by using measurements of the cosmogenic 44Ti activity (τ1∕2 = 59.2 ± 0.6 yr) measured in 20 meteorites which fell between 1766 and 2001. Within the given uncertainties, our result is compatible with a HMF increase from 4.87-0.30+0.24 nT in 1766 to 6.83-0.11+0.13 nT in 2001, thus implying an overall average increment of 1.96-0.35+0.43 nT over 235 years since 1766 reflecting the modern Grand maximum. The BHMF trend thus obtained is then compared with the most recent reconstructions of the near-Earth HMF strength based on geomagnetic, sunspot number, and cosmogenic isotope data.

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Long-term Evolution of the Sun’s Magnetic Field during Cycles 15–19 Based on Their Proxies from Kodaikanal Solar Observatory

The Astrophysical Journal ◽

10.3847/2041-8213/abba80 ◽

2020 ◽

Vol 902 (1) ◽

pp. L15

Author(s):

Alexander V. Mordvinov ◽

Bidya Binay Karak ◽

Dipankar Banerjee ◽

Subhamoy Chatterjee ◽

Elena M. Golubeva ◽

...

Keyword(s):

Magnetic Field ◽

Long Term Evolution ◽

Solar Observatory ◽

Term Evolution

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Reconstructing solar magnetic fields from historical observations

Astronomy and Astrophysics ◽

10.1051/0004-6361/201935606 ◽

2019 ◽

Vol 627 ◽

pp. A11

Author(s):

I. O. I. Virtanen ◽

I. I. Virtanen ◽

A. A. Pevtsov ◽

L. Bertello ◽

A. Yeates ◽

...

Keyword(s):

Magnetic Field ◽

Magnetic Fields ◽

Large Scale ◽

Active Regions ◽

Long Term Evolution ◽

Photospheric Magnetic Field ◽

Solar Magnetic Fields ◽

Term Evolution ◽

Large Scale Field

Aims. The evolution of the photospheric magnetic field has only been regularly observed since the 1970s. The absence of earlier observations severely limits our ability to understand the long-term evolution of solar magnetic fields, especially the polar fields that are important drivers of space weather. Here, we test the possibility to reconstruct the large-scale solar magnetic fields from Ca II K line observations and sunspot magnetic field observations, and to create synoptic maps of the photospheric magnetic field for times before modern-time magnetographic observations. Methods. We reconstructed active regions from Ca II K line synoptic maps and assigned them magnetic polarities using sunspot magnetic field observations. We used the reconstructed active regions as input in a surface flux transport simulation to produce synoptic maps of the photospheric magnetic field. We compared the simulated field with the observed field in 1975−1985 in order to test and validate our method. Results. The reconstruction very accurately reproduces the long-term evolution of the large-scale field, including the poleward flux surges and the strength of polar fields. The reconstruction has slightly less emerging flux because a few weak active regions are missing, but it includes the large active regions that are the most important for the large-scale evolution of the field. Although our reconstruction method is very robust, individual reconstructed active regions may be slightly inaccurate in terms of area, total flux, or polarity, which leads to some uncertainty in the simulation. However, due to the randomness of these inaccuracies and the lack of long-term memory in the simulation, these problems do not significantly affect the long-term evolution of the large-scale field.

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The long-term evolution project

International Astronomical Union Colloquium ◽

10.1017/s0252921100083925 ◽

1985 ◽

Vol 83 ◽

pp. 203-214 ◽

Cited By ~ 1

Author(s):

A. Carusi ◽

L. Kresák ◽

E. Perozzi ◽

G.B. Valsecchi

Keyword(s):

Dynamical Evolution ◽

Long Term Evolution ◽

Astronomical Institute ◽

Data Set ◽

Future Developments ◽

Term Evolution ◽

Short Period ◽

Long Time ◽

Insight Into

AbstractThe Long-Term Evolution Project (LTEP), realized in collaboration by the IAS-Reparto di Planetologia (Rome, Italy) and the Astronomical Institute of SAV (Bratislava, Czechoslovakia), has been developed with the aim of giving a general insight into the dynamical evolution of short-period comets. The motion of all the known short-period comets has been investigated over a long time span (over 800 years) taking care, as far as possible, to eliminate the sources of possible discrepancies within the computations. An internally consistent data-set and an atlas of orbital evolutions are the first outputs of this project. The main characteristics of the LTEP are discussed, together with some general remarks on its importance for cometary studies, its limitations and the future developments.

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Long-term evolution of magnetic fields in flaring Active Region NOAA 12673

Research in Astronomy and Astrophysics ◽

10.1088/1674-4527/21/12/312 ◽

2022 ◽

Vol 21 (12) ◽

pp. 312

Author(s):

Johan Muhamad ◽

Muhamad Zamzam Nurzaman ◽

Tiar Dani ◽

Arun Relung Pamutri

Keyword(s):

Magnetic Field ◽

Active Region ◽

Solar Flares ◽

Long Term Evolution ◽

Solar Dynamics Observatory ◽

Active Longitude ◽

Term Evolution ◽

Solar Dynamics ◽

Different Characteristics

Abstract During the lifetime of AR 12673, its magnetic field evolved drastically and produced numerous large flares. In this study, using full maps of the Sun observed by the Solar Dynamics Observatory and the Solar Terrestrial Relations Observatory, we identified that AR 12673 emerged in decayed AR 12665, which had survived for two solar rotations. Although both ARs emerged at the same location, they possessed different characteristics and different flare productivities. Therefore, it is important to study the long-term magnetic evolution of both ARs to identify the distinguishing characteristics of an AR that can produce large solar flares. We used the Space-weather Helioseismic and Magnetic Imager Active Region Patch data to investigate the evolution of the photospheric magnetic field and other physical properties of the recurring ARs during five Carrington rotations. All these investigated parameters dynamically evolved through a series of solar rotations. We compared the long-term evolution of AR 12665 and AR 12673 to understand the differences in their flare-producing properties. We also studied the relation of the long-term evolution of these ARs with the presence of active longitude. We found that the magnetic flux and complexity of AR 12673 developed much faster than those of AR 12665. Our results confirmed that a strong emerging flux that emerged in the pre-existing AR near the active longitude created a very strong and complex AR that produced large flares.

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Averting Paging Related Attacks in 4G LTE Communication System

International Journal of Recent Technology and Engineering - 2 ◽

10.35940/ijrte.b1029.0782s419 ◽

2019 ◽

Vol 8 (2S4) ◽

pp. 160-163

Keyword(s):

Communication System ◽

Security Analysis ◽

Long Term Evolution ◽

Data Rate ◽

Security Vulnerabilities ◽

Term Evolution ◽

Long Time ◽

4G Lte ◽

Secured Communication

Long Term Evolution (LTE) objective is to provide secured communication at higher data rate for the users. It’s been long time that the technology is being consumed by the users. However, there are still security vulnerabilities that provides scope for various attacks on the network. One such scenario is that attacks related paging procedure itself. This paper discusses about the possible attacks related to paging and how these attacks affect the security of the network and also propose a scheme to avert these attacks by leveraging the existing LTE communication system and also the simulation of the proposed scheme with the security analysis of the same

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