E-Print Archive

There are 4236 abstracts currently viewable.


Advanced Search
Main Page Add New E-Print Submitter
News Help/FAQ About Preferences
Manage Key Phrase
* News 04/04/20 * The archive is using a new backend database. This has thrown up a few SQL errors in the last few days. If you have any issues please email adavey@nso.edu with either the number of eprint you are trying to edit or a link to your preprint.

A global two-scale helicity proxy from pi-ambiguous solar magnetic fields View all abstracts by submitter

Axel Brandenburg   Submitted: 2019-10-15 22:42

If the α effect plays a role in the generation of the Sun's magnetic field, the field should show evidence of magnetic helicity of opposite signs at large and small length scales. Measuring this faces two challenges: (i) in weak-field regions, horizontal field measurements are unreliable because of the pi ambiguity, and (ii) one needs a truly global approach to computing helicity spectra in the case where one expects a sign reversal across the equator at all wavenumbers. Here we develop such a method using spin-2 spherical harmonics to decompose the linear polarization in terms of the parity-even and parity-odd E and B polarizations, respectively. Using simple one- and two-dimensional models, we show that the product of the spectral decompositions of E and B, taken at spherical harmonic degrees that are shifted by one, can act as a proxy of the global magnetic helicity with a sign that represents that in the northern hemisphere. We then apply this method to the analysis of solar synoptic vector magnetograms, from which we extract a pseudo-polarization corresponding to a "pi-ambiguated" magnetic field, i.e., a magnetic field vector that has no arrow. We find a negative sign of the global EB helicity proxy at spherical harmonic degrees of around 6. This could indicate a positive magnetic helicity at large length scales, but the spectrum fails to capture clear evidence of the well-known negative magnetic helicity at smaller scales. This method might also be applicable to stellar and Galactic polarization data.

Authors: Axel Brandenburg

Publication Status: Astrophys. J. 883, 119 (2019)
Last Modified: 2019-10-16 12:42
Go to main E-Print page  Round-Trip Slipping Magnetic Reconnection Observed in a Fan-Spine Jet  Multi-layered Kelvin-Helmholtz Instability in the Solar Corona  Edit Entry  Download Preprint  Submitter's Homepage Delete Entry 

Go to main E-Print pageGo to main E-Print page.
Previous AbstractPrevious Abstract.
Next AbstractNext Abstract.
Download PreprintDownload Preprint.
Submitter's HomepageSubmitters Homepage.
Edit EntryEdit Entry.
View All Abstracts By SubmitterView all abstracts by submitter.
Delete AbstractDelete abstract.

Latest Entries
Sunquake with a second-bounce, other sunquakes and emission associated with X9.3 flare of 6 September 2017. II. Proposed interpretation
f-mode strengthening from a localized bipolar subsurface magnetic field
Imaging and spectral study on the null point of a fan-spine structure during a solar flare
Forecasting Solar Cycle 25 Using Deep Neural Networks
An Observational Test of Solar Plasma Heating by Magnetic Flux Cancellation
The Drivers of Active Region Outflows into the Slow Solar Wind
HXR emission from an activated flux rope and subsequent evolution of an eruptive long duration solar flare
A Survey of Computational Tools in Solar Physics
Sunquake with a second bounce, other sunquakes, and emission associated with the X9.3 flare of 6 September 2017. I. Observations
The PDFI_SS Electric Field Inversion Software
Spatial Distribution of Origin of Umbral Waves in a Sunspot Umbra
A Unique Resource for Solar Flare Diagnostic Studies: the SMM Bent Crystal Spectrometer
Inferring Vector Magnetic Fields from Stokes Profiles of GST/NIRIS Using a Convolutional Neural Network
Global Energetics of Solar Flares, X. Petschek Reconnection Rate and Alfvén Mach Number of Magnetic Reconnection Outflows
Transverse coronal loop oscillations excited by homologous circular-ribbon flares
Temporal evolution of oscillating coronal loops
Intrusion of Magnetic Peninsula toward the Neighboring Opposite-polarity Region That Triggers the Largest Solar Flare in Solar Cycle 24
On the Relationship Between Transit Time of ICMEs and Strength of the Initiated Geomagnetic Storms
Standing kink waves in sigmoid solar coronal loops: implications for coronal seismology
Excitation of negative energy surface magnetohydrodynamic waves in an incompressible cylindrical plasma

Related Pages
MSU Solar Physics.
Max Millennium Science Mail Archive.
Max Millennium Message of the Day Mail Archive.
Max Millennium Flare Catalog

Archive Maintainer
Alisdair Davey

© 2000-2020 Solar Physics Group - Montana State University