scholarly journals Southward shift of the coronal neutral line and the heliospheric current sheet: Evidence for radial evolution of hemispheric asymmetry

2018 ◽  
Vol 618 ◽  
pp. A105 ◽  
Author(s):  
J. S. Koskela ◽  
I. I. Virtanen ◽  
K. Mursula
Keyword(s):  
Magnetic Field ◽  
Current Sheet ◽  
Neutral Line ◽  
Heliospheric Current Sheet ◽  
Solar Observatory ◽  
Source Surface ◽  
Field Source ◽  
Southward Shift ◽  
Radial Evolution ◽  
The Magnetic Field

Aims. The heliospheric current sheet (HCS) has been observed to be southward shifted in the late declining to minimum phase of the solar cycle. Here we study the existence of a simultaneous shift in the heliosphere and in the corona using a robust new method. Methods. We use the synoptic maps of the photospheric field of the Wilcox Solar Observatory (WSO) and the Mount Wilson Observatory (MWO) together with the potential field source surface (PFSS) model to calculate the coronal magnetic field and compare it with the simultaneous heliospheric magnetic field of the NASA/NSSDC OMNI 2 dataset. We divide the magnetic field into the two sectors, towards (T) and away (A) from the Sun, and calculate how often the sector polarities at 1 AU and in the corona match each other. We divide the sectors both at 1 AU and in the corona. We also calculate the annual (T − A)/(T + A) ratios of sector occurrence both at 1 AU and in the corona. Results. We verify that the HCS/neutral line is southward shifted both in the corona and heliosphere. We find that the coronal shift is systematically larger than the simultaneous heliospheric shift. Conclusions. The fact that the southward shift of the coronal neutral line is larger than the simultaneous shift of the heliospheric current sheet at 1 AU implies that the radial evolution of the magnetic field between the two sites is different between the northern and southern hemispheres.

scholarly journals Revisiting the coronal current sheet model: Parameter range analysis and comparison with the potential field model

2019 ◽  
Vol 631 ◽  
pp. A17 ◽  
Author(s):  
Jennimari Koskela ◽  
Ilpo Virtanen ◽  
Kalevi Mursula
Keyword(s):  
Magnetic Field ◽  
Current Sheet ◽  
Potential Field ◽  
Neutral Line ◽  
Coronal Magnetic Field ◽  
Solar Observatory ◽  
Latitudinal Variation ◽  
Source Surface ◽  
Current Parameter ◽  
Cusp Surface

Aims. We study the properties of the coronal magnetic field according to the current sheet source surface (CSSS) model in 1976–2017 for all physically reasonable values of the three model parameters (cusp surface radius Rcs, source surface radius Rss, and current parameter a), and compare the CSSS field with the potential field source surface (PFSS) model field. Methods. We used the synoptic maps of the photospheric magnetic field from the Wilcox Solar Observatory (WSO), National Solar Observatory/Kitt Peak (NSO/KP), and the NSO Synoptic Optical Long-term Investigations of the Sun Vector Spectromagnetograph (SOLIS/VSM) in order to calculate the coronal magnetic field according to the CSSS and PFSS models. We calculated the coronal field strength, its latitudinal variation and neutral line location, as well as its polarity match with the heliospheric magnetic field. Results. The CSSS model can correct the erroneous latitudinal variation of the PFSS model if the source surface is sufficiently far out with respect to the cusp surface (Rss ≥ 3 ⋅ Rcs). The topology of the neutral line only slightly depends on source surface radius or current parameter, but excludes very low values of the cusp surface (Rcs ≤ 1.5). A comparison of the polarities gives an optimum cusp surface radius that varies in time between 2 and 5; a stronger current yields a larger optimum Rcs. Interestingly, the optimum polarity match percentages and optimum radii vary very similarly in the two models over the four solar cycles we studied. Conclusions. The CSSS model can produce a stronger total coronal flux than the PFSS model and correct its latitudinal variation. However, the topology of the CSSS model is rather independent of horizontal currents and remains very similar to that of the PFSS model. Therefore, the CSSS model cannot improve the match of field polarities between corona and heliosphere.

scholarly journals THE STRUCTURE OF THE SOLAR WIND IN THE HELIOSPHERE DEPENDING ON THE PHASE OF THE SOLAR CYCLE: LARGE-SCALE DYNAMICS OF THE HELIOSPHERIC CURRENT SHEET

2019 ◽  
Vol 47 (1) ◽  
pp. 85-87
Author(s):  
E.V. Maiewski ◽  
R.A. Kislov ◽  
H.V. Malova ◽  
O.V. Khabarova ◽  
V.Yu. Popov ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Solar Activity ◽  
Solar Cycle ◽  
Current Sheet ◽  
Heliospheric Current Sheet ◽  
High Solar Activity ◽  
The Sun ◽  
High Latitudes ◽  
The Magnetic Field

A stationary axisymmetric MHD model of the solar wind has been constructed, which allows us to study the spatial distribution of the magnetic field and plasma characteristics at radial distances from 20 to 400 radii of the Sun at almost all heliolatitudes. The model takes into account the changes in the magnetic field of the Sun during a quarter of the solar cycle, when the dominant dipole magnetic field is replaced by a quadrupole. Selfconsistent solutions for the magnetic and velocity fields, plasma concentration and current density of the solar wind depending on the phase of the solar cycle are obtained. It is shown that during the domination of the dipole magnetic component in the solar wind heliospheric current sheet (HCS) is located in the equatorial plane, which is a part of the system of radial and transverse currents, symmetrical in the northern and southern hemispheres. As the relative contribution of the quadrupole component to the total magnetic field increases, the shape of the HCS becomes conical; the angle of the cone gradually decreases, so that the current sheet moves entirely to one of the hemispheres. At the same time, at high latitudes of the opposite hemisphere, a second conical HCS arises, the angle of which increases. When the quadrupole field becomes dominant (at maximum solar activity), both HCS lie on conical surfaces inclined at an angle of 35 degrees to the equator. The model describes the transition from the fast solar wind at high latitudes to the slow solar wind at low latitudes: a relatively gentle transition in the period of low solar activity gives way to more drastic when high solar activity. The model also predicts an increase in the steepness of the profiles of the main characteristics of the solar wind with an increase in the radial distance from the Sun. Comparison of the obtained dependences with the available observational data is discussed.

Solar wind velocity distribution on the heliospheric current sheet during Carrington rotations 1787-1795

1995 ◽  
Vol 13 (8) ◽  
pp. 807-814
Author(s):  
B. Bala ◽  
S. R. Prabhakaran Nayar
Keyword(s):  
Solar Wind ◽  
Velocity Distribution ◽  
Current Sheet ◽  
Wind Velocity ◽  
Solar Wind Velocity ◽  
Neutral Line ◽  
Coronal Magnetic Field ◽  
Heliospheric Current Sheet ◽  
Source Surface ◽  
Low Speed

Abstract. The solar wind velocity distribution in the heliosphere is best represented using a v-map, where velocity contours are plotted in heliographic latitude-longitude coordinates. It has already been established that low-speed regions of the solar wind on the source surface correspond to the maximum bright regions of the K-corona and the neutral line of the coronal magnetic field. In this analysis, v-maps on the source surface for Carrington rotations (CRs) 1787–1795, during 1987, have been prepared using the interplanetary scintillation measurements at Research Institute of Atmospherics (RIA), Nagoya Univ., Japan. These v-maps were then used to study the time evolution of the low-speed (\\leq450 km s–1) belt of the solar wind and to deduce the distribution of solar wind velocity on the heliospheric current sheet. The low-speed belt of the solar wind on the source surface was found to change from one CR to the next, implying a time evolution. Instead of a slow and systematic evolution, the pattern of distribution of solar wind changed dramatically at one particular solar rotation (CR 1792) and the distributions for the succeeding rotations were similar to this pattern. The low-speed region, in most cases, was found to be close to the solar equator and almost parallel to it. However, during some solar rotations, they were found to be organised in certain longitudes, leaving regions with longitudinal width greater than 30° free of low-speed solar wind, i.e. these regions were occupied by solar wind with velocities greater than 450 km s–1. It is also noted from this study that the low-speed belt, in general, followed the neutral line of the coronal magnetic field, except in certain cases. The solar wind velocity on the heliospheric current sheet (HCS) varied in the range 300–585 km s–1 during the period of study, and the pattern of velocity distribution varied from rotation to rotation.

Three-dimensional reconstruction of an expanding shock associated with a Solar particle event

2021 ◽  
Author(s):  
Federica Frassati ◽  
Monica Laurenza ◽  
Alessandro Bemporad ◽  
Matthew J. West ◽  
Salvatore Mancuso ◽  
...  
Keyword(s):  
Magnetic Field ◽  
3D Reconstruction ◽  
Ultra Violet ◽  
Coronal Magnetic Field ◽  
Release Time ◽  
Shock Acceleration ◽  
Source Surface ◽  
Type Ii ◽  
Field Source ◽  
The Magnetic Field

<p><span>On 2013 June 21st an eruption occurred in the active region NOAA 1177 (14S73E), </span><span>giving rise to</span> <span>a M2.9 class flare starting at 02:30 UT, a fast partial halo coronal mass ejection (CME), and a type II radio burst. The concomitant emission of solar energetic particles (SEPs) produced a significant increase in the proton fluxes measured by LET and HET aboard STEREO-B. By using stereoscopic observations in extreme ultra violet (EUV) and white light (WL) spectral intervals, we performed a 3D reconstruction of the expanding front by processing SDO/AIA, STEREO/EUVI, COR1 and COR2, and SOHO/LASCO data assuming a spheroidal model. By using the 3D reconstruction, we estimated the temporal evolution of θ</span><span><sub>Bn,</sub></span><span> </span><span>i.e.,</span> <span>the angle between the normal to the expanding front and the coronal magnetic field computed by the Potential-Field Source-Surface (PFSS) approximation, within 2.5 R</span><span><sub>ʘ</sub></span><span>. The front </span><span>of the CME</span><span>was found to be quasi-parallel to the magnetic field almost everywhere</span><span><sub>.</sub></span><span> Above 2.5 R</span><span><sub>ʘ</sub></span><span>, where the front was identified as a shock, we projected the 3D expanding surface </span><span>reconstructed for </span><span>different times on the ecliptic plane and</span><span> </span><span>we calculated the θ</span><span><sub>Bn </sub></span><span>between the normal to the front and Parker spiral arms. In this case the shock was almost perpendicular to the magnetic field (quasi-parallel shock). During the expansion the region located between the nose and the eastern flank of the shock was magnetically connected with ST-B in agreement with the significant SEP flux measured on-board this spacecraft.</span> <span>W</span><span>hile</span> <span>the shock was only marginally connected with ST-A and GOES-15. </span><span>T</span><span>he SEP release time was estimated to be 10 minutes after the Type II onset, when the shock front was already above 2.5 R</span><span><sub>ʘ</sub></span><span> with a quasi-parallel configuration. Our results are discussed in the framework of the shock acceleration scenario, even if quasi-parallel shocks are expected to have a reduced acceleration efficiency.</span></p>

Evolution of Large-Scale Coronal Structures

1994 ◽  
Vol 144 ◽  
pp. 29-33
Author(s):  
P. Ambrož
Keyword(s):  
Magnetic Field ◽  
Field Line ◽  
Large Scale ◽  
Coronal Magnetic Field ◽  
Source Surface ◽  
Solar Cycles ◽  
Characteristic Relationship ◽  
The Magnetic Field ◽  
Coronal Structures

AbstractThe large-scale coronal structures observed during the sporadically visible solar eclipses were compared with the numerically extrapolated field-line structures of coronal magnetic field. A characteristic relationship between the observed structures of coronal plasma and the magnetic field line configurations was determined. The long-term evolution of large scale coronal structures inferred from photospheric magnetic observations in the course of 11- and 22-year solar cycles is described.Some known parameters, such as the source surface radius, or coronal rotation rate are discussed and actually interpreted. A relation between the large-scale photospheric magnetic field evolution and the coronal structure rearrangement is demonstrated.

scholarly journals Solar wind and substorm excitation of the wavy current sheet

2009 ◽  
Vol 27 (6) ◽  
pp. 2457-2474 ◽  
Author(s):  
C. Forsyth ◽  
M. Lester ◽  
R. C. Fear ◽  
E. Lucek ◽  
I. Dandouras ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Current Sheet ◽  
Pressure Pulse ◽  
Wind Pressure ◽  
Expansion Velocity ◽  
Solar Wind Pressure ◽  
Wave Models ◽  
Best Fit ◽  
The Magnetic Field

Abstract. Following a solar wind pressure pulse on 3 August 2001, GOES 8, GOES 10, Cluster and Polar observed dipolarizations of the magnetic field, accompanied by an eastward expansion of the aurora observed by IMAGE, indicating the occurrence of two substorms. Prior to the first substorm, the motion of the plasma sheet with respect to Cluster was in the ZGSM direction. Observations following the substorms show the occurrence of current sheet waves moving predominantly in the −YGSM direction. Following the second substorm, the current sheet waves caused multiple current sheet crossings of the Cluster spacecraft, previously studied by Zhang et al. (2002). We further this study to show that the velocity of the current sheet waves was similar to the expansion velocity of the substorm aurora and the expansion of the dipolarization regions in the magnetotail. Furthermore, we compare these results with the current sheet wave models of Golovchanskaya and Maltsev (2005) and Erkaev et al. (2008). We find that the Erkaev et al. (2008) model gives the best fit to the observations.

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