scholarly journals Magnetic helicity transported by flux emergence and shuffling motions

2012 ◽  
Vol 8 (S294) ◽  
pp. 319-320
Author(s):  
Y. Zhang ◽  
R. Kitai ◽  
K. Takizawa
Keyword(s):  
Magnetic Helicity ◽  
Doppler Velocity ◽  
Similar Distribution ◽  
Normal Velocity ◽  
Flux Emergence ◽  
Helicity Injection ◽  
Field Lines ◽  
Pass Through ◽  
Helical Magnetic Field ◽  
Coronal Field

AbstractMagnetic helicity can be transported from sub-photosphere into corona by the emergence of helical magnetic field lines and the shuffling motions of foot-points of pre-existing coronal field lines. Active region NOAA 10930 was observed by SP and NFI of SOT on board Hinode when it pass through the solar meridian. Based on these observations, we calculate magnetic helicity flow of both terms, by regarding Doppler velocity as normal velocity. The results are compared with which calculated by method proposed by Zhang et. al. (2012). Our results show that helicity injection maps calculated by both methods have similar distribution and the integration values have the same magnitude.

scholarly journals Hemispheric injection of magnetic helicity by surface flux transport

2019 ◽  
Vol 631 ◽  
pp. A138 ◽  
Author(s):  
G. Hawkes ◽  
A. R. Yeates
Keyword(s):  
Magnetic Field ◽  
Solar Cycle ◽  
Solar Rotation ◽  
Surface Flux ◽  
Magnetic Helicity ◽  
Solar Cycles ◽  
Flux Transport ◽  
Transport Models ◽  
Radial Magnetic Field ◽  
Helicity Injection

Aims. We estimate the injection of relative magnetic helicity into the solar atmosphere by surface flux transport over 27 solar cycles (1700–2009). Methods. We determine the radial magnetic field evolution using two separate surface flux transport models: one driven by magnetogram inputs and another by statistical active region insertion guided by the sunspot number record. The injection of relative magnetic helicity is then computed from this radial magnetic field together with the known electric field in the flux transport models. Results. Neglecting flux emergence, solar rotation is the dominant contributor to the helicity injection. At high latitudes, the injection is always negative/positive in the northern/southern hemisphere, while at low latitudes the injection tends to have the opposite sign when integrated over the full solar cycle. The overall helicity injection in a given solar cycle depends on the balance between these two contributions. This net injected helicity correlates well with the end-of-cycle axial dipole moment.

RF current drive with magnetic helicity injection

1985 ◽  
Vol 33 (2) ◽  
pp. 257-264 ◽  
Author(s):  
D. K. Bhadra ◽  
C. Chu
Keyword(s):  
Steady State ◽  
Plasma Density ◽  
Electromagnetic Waves ◽  
Current Drive ◽  
Magnetic Helicity ◽  
Finite Frequency ◽  
Helicity Injection ◽  
Steady State Current ◽  
External Injection ◽  
Frequency Current

External injection of magnetic helicity into a plasma may be possible through the introduction of appropriately polarized electromagnetic waves. A concept of steady-state current-drive is presented, based on the validity of conservation of helicity (appropriately defined for finite frequency processes). It is shown that such external injection of helicity can maintain a steady-state current by compensating the volt-seconds consumed through plasma resistivity. Such a mechanism, if experimentally successful, is particularly interesting at high densities because the efficiency of the process does not depend on plasma density, as opposed to other radio-frequency current-drive techniques.

scholarly journals Dynamical critical scaling of electric field fluctuations in the greater cusp and magnetotail implied by HF radar observations of F-region Doppler velocity

2006 ◽  
Vol 24 (2) ◽  
pp. 689-705 ◽  
Author(s):  
M. L. Parkinson
Keyword(s):  
Solar Wind ◽  
Open Field ◽  
Electric Fields ◽  
Spectral Width ◽  
Hf Radar ◽  
Doppler Velocity ◽  
Closed Field ◽  
Scaling Exponent ◽  
Central Plasma ◽  
Field Lines

Abstract. Akasofu's solar wind ε parameter describes the coupling of solar wind energy to the magnetosphere and ionosphere. Analysis of fluctuations in ε using model independent scaling techniques including the peaks of probability density functions (PDFs) and generalised structure function (GSF) analysis show the fluctuations were self-affine (mono-fractal, single exponent scaling) over 9 octaves of time scale from ~46 s to ~9.1 h. However, the peak scaling exponent α0 was a function of the fluctuation bin size, so caution is required when comparing the exponents for different data sets sampled in different ways. The same generic scaling techniques revealed the organisation and functional form of concurrent fluctuations in azimuthal magnetospheric electric fields implied by SuperDARN HF radar measurements of line-of-sight Doppler velocity, vLOS, made in the high-latitude austral ionosphere. The PDFs of vLOS fluctuation were calculated for time scales between 1 min and 256 min, and were sorted into noon sector results obtained with the Halley radar, and midnight sector results obtained with the TIGER radar. The PDFs were further sorted according to the orientation of the interplanetary magnetic field, as well as ionospheric regions of high and low Doppler spectral width. High spectral widths tend to occur at higher latitude, mostly on open field lines but also on closed field lines just equatorward of the open-closed boundary, whereas low spectral widths are concentrated on closed field lines deeper inside the magnetosphere. The vLOS fluctuations were most self-affine (i.e. like the solar wind ε parameter) on the high spectral width field lines in the noon sector ionosphere (i.e. the greater cusp), but suggested multi-fractal behaviour on closed field lines in the midnight sector (i.e. the central plasma sheet). Long tails in the PDFs imply that "microbursts" in ionospheric convection occur far more frequently, especially on open field lines, than can be captured using the effective Nyquist frequency and volume resolution of SuperDARN radars.

Transport implications of current drive by magnetic helicity injection

2001 ◽  
Vol 8 (11) ◽  
pp. 4839-4848 ◽  
Author(s):  
Ronald W. Moses ◽  
Richard A. Gerwin ◽  
Kurt F. Schoenberg
Keyword(s):  
Current Drive ◽  
Magnetic Helicity ◽  
Helicity Injection

Preliminary investigation of the structure of the upper ionosphere as observed by the topside sounder satellite, Alouette

1964 ◽  
Vol 281 (1387) ◽  
pp. 464-487 ◽  
Keyword(s):  
Magnetic Field ◽  
Preliminary Investigation ◽  
Radiation Belts ◽  
Local Times ◽  
Topside Ionosphere ◽  
Equatorial Anomaly ◽  
Electron Distributions ◽  
Field Lines ◽  
Pass Through ◽  
Upper Ionosphere

Results are presented which illustrate the shape of the topside electron distributions at different local times and different latitudes. It is shown that the ionosphere appears to cool and contract during the night. The morphology and diurnal variation of the geomagnetic equatorial anomaly has been investigated; the structure of the equatorial topside ionosphere appears to be determined by the Earth’s magnetic field, and the geomagnetic anomaly is shown to exist in the topside only between 10.00 and 22.00 local time. Deductions about the composition or temperature of the atmosphere are shown to be complicated because diffusion occurs along field lines only and also because the temperature increases with height above ground. The scale height of the electron density distributions is found to increase with latitude, and it is shown that this effect is probably related to an increase of electron temperature with latitude. Five different localized phenomena have been observed in the ionosphere by the topside sounder, and three of these are shown to occur at the latitudes at which the magnetic field lines which pass through the hearts of the three radiation belts enter the Earth’s atmosphere. Other results are presented which also constitute important evidence that particles dumped from the radiation belts may be important sources of heat or ionization in the atmosphere. Observations made at sunrise and also during an eclipse indicate that the effects of electromagnetic movements and/or movements produced by temperature changes are very important in the upper ionosphere.

scholarly journals Flux emergence and interaction with a coronal field: 3D MHD simulations

2006 ◽  
Vol 2 (S233) ◽  
pp. 53 ◽  
Author(s):  
V. Archontis ◽  
F. Moreno-Insertis ◽  
K. Galsgaard ◽  
A. W. Hood
Keyword(s):  
Flux Emergence ◽  
Mhd Simulations ◽  
Coronal Field
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