scholarly journals Properties and geoeffectiveness of magnetic clouds in the rising, maximum and early declining phases of solar cycle 23

2005 ◽  
Vol 23 (2) ◽  
pp. 625-641 ◽  
Author(s):  
K. E. J. Huttunen ◽  
R. Schwenn ◽  
V. Bothmer ◽  
H. E. J. Koskinen
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Solar Cycle ◽  
Solar Maximum ◽  
Magnetic Storms ◽  
Magnetic Clouds ◽  
Solar Cycles ◽  
The North ◽  
Solar Cycle 23 ◽  
The Magnetic Field

Abstract. The magnetic structure and geomagnetic response of 73 magnetic clouds (MC) observed by the WIND and ACE satellites in solar cycle 23 are examined. The results have been compared with the surveys from the previous solar cycles. The preselected candidate MC events were investigated using the minimum variance analysis to determine if they have a flux-rope structure and to obtain the estimation for the axial orientation (θC, φC). Depending on the calculated inclination relative to the ecliptic we divided MCs into "bipolar" (θC<45°) and "unipolar" (θC>45°). The number of observed MCs was largest in the early rising phase, although the halo CME rate was still low. It is likely that near solar maximum we did not identify all MCs at 1AU, as they were crossed far from the axis or they had interacted strongly with the ambient solar wind or with other CMEs. The occurrence rate of MCs at 1AU is also modified by the migration of the filament sites on the Sun towards the poles near solar maximum and by the deflection of CMEs towards the equator due to the fast solar wind flow from large polar coronal holes near solar minimum. In the rising phase nearly all bipolar MCs were associated with the rotation of the magnetic field from the south at the leading edge to the north at the trailing edge. The results for solar cycles 21-22 showed that the direction of the magnetic field in the leading portion of the MC starts to reverse at solar maximum. At solar maximum and in the declining phase (2000-2003) we observed several MCs with the rotation from the north to the south. We observed unipolar (i.e. highly inclined) MCs frequently during the whole investigated period. For solar cycles 21-22 the majority of MCs identified in the rising phase were bipolar while in the declining phase most MCs were unipolar. The geomagnetic response of a given MC depends greatly on its magnetic structure and the orientation of the sheath fields. For each event we distinguished the effect of the sheath fields and the MC fields. All unipolar MCs with magnetic field southward at the axis were geoeffective (Dst<-50nT) while those with the field pointing northward did not cause magnetic storms at all. About half of the all identified MCs were not geoffective or the sheath fields preceding the MC caused the storm. MCs caused more intense magnetic storms (Dst<-100nT) than moderate magnetic storms (-50nT ≥Dst≥-100nT).

scholarly journals Magnetic clouds' structure in the magnetosheath as observed by Cluster and Geotail: four case studies

2014 ◽  
Vol 32 (10) ◽  
pp. 1247-1261 ◽  
Author(s):  
L. Turc ◽  
D. Fontaine ◽  
P. Savoini ◽  
E. K. J. Kilpua
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Magnetic Fields ◽  
Bow Shock ◽  
Field Direction ◽  
Magnetic Clouds ◽  
Magnetic Field Direction ◽  
Field Orientation ◽  
The Impact ◽  
The Magnetic Field

Abstract. Magnetic clouds (MCs) are large-scale magnetic flux ropes ejected from the Sun into the interplanetary space. They play a central role in solar–terrestrial relations as they can efficiently drive magnetic activity in the near-Earth environment. Their impact on the Earth's magnetosphere is often attributed to the presence of southward magnetic fields inside the MC, as observed in the upstream solar wind. However, when they arrive in the vicinity of the Earth, MCs first encounter the bow shock, which is expected to modify their properties, including their magnetic field strength and direction. If these changes are significant, they can in turn affect the interaction of the MC with the magnetosphere. In this paper, we use data from the Cluster and Geotail spacecraft inside the magnetosheath and from the Advanced Composition Explorer (ACE) upstream of the Earth's environment to investigate the impact of the bow shock's crossing on the magnetic structure of MCs. Through four example MCs, we show that the evolution of the MC's structure from the solar wind to the magnetosheath differs largely from one event to another. The smooth rotation of the MC can either be preserved inside the magnetosheath, be modified, i.e. the magnetic field still rotates slowly but at different angles, or even disappear. The alteration of the magnetic field orientation across the bow shock can vary with time during the MC's passage and with the location inside the magnetosheath. We examine the conditions encountered at the bow shock from direct observations, when Cluster or Geotail cross it, or indirectly by applying a magnetosheath model. We obtain a good agreement between the observed and modelled magnetic field direction and shock configuration, which varies from quasi-perpendicular to quasi-parallel in our study. We find that the variations in the angle between the magnetic fields in the solar wind and in the magnetosheath are anti-correlated with the variations in the shock obliquity. When the shock is in a quasi-parallel regime, the magnetic field direction varies significantly from the solar wind to the magnetosheath. In such cases, the magnetic field reaching the magnetopause cannot be approximated by the upstream magnetic field. Therefore, it is important to take into account the conditions at the bow shock when estimating the impact of an MC with the Earth's environment because these conditions are crucial in determining the magnetosheath magnetic field, which then interacts with the magnetosphere.

scholarly journals Resistive evolution of toroidal field distributions and their relation to magnetic clouds

2019 ◽  
Vol 85 (1) ◽  
Author(s):  
C. B. Smiet ◽  
H. J. de Blank ◽  
T. A. de Jong ◽  
D. N. L. Kok ◽  
D. Bouwmeester
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Field Strength ◽  
Magnetic Field Strength ◽  
Magnetic Clouds ◽  
Twisted Field ◽  
Field Lines ◽  
Rotational Transform ◽  
Universal Pattern ◽  
The Magnetic Field

We study the resistive evolution of a localized self-organizing magnetohydrodynamic equilibrium. In this configuration the magnetic forces are balanced by a pressure force caused by a toroidal depression in the pressure. Equilibrium is attained when this low-pressure region prevents further expansion into the higher-pressure external plasma. We find that, for the parameters investigated, the resistive evolution of the structures follows a universal pattern when rescaled to resistive time. The finite resistivity causes both a decrease in the magnetic field strength and a finite slip of the plasma fluid against the static equilibrium. This slip is caused by a Pfirsch–Schlüter-type diffusion, similar to what is seen in tokamak equilibria. The net effect is that the configuration remains in magnetostatic equilibrium whilst it slowly grows in size. The rotational transform of the structure becomes nearly constant throughout the entire structure, and decreases according to a power law. In simulations this equilibrium is observed when highly tangled field lines relax in a high-pressure (relative to the magnetic field strength) environment, a situation that occurs when the twisted field of a coronal loop is ejected into the interplanetary solar wind. In this paper we relate this localized magnetohydrodynamic equilibrium to magnetic clouds in the solar wind.

scholarly journals Quasi-periodic changes in the 3D solar anisotropy of Galactic cosmic rays for 1965–2014

2017 ◽  
Vol 609 ◽  
pp. A32 ◽  
Author(s):  
R. Modzelewska ◽  
M. V. Alania
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Solar Activity ◽  
Solar Cycle ◽  
Cosmic Rays ◽  
Ecliptic Plane ◽  
Galactic Cosmic Rays ◽  
Magnetic Cycle ◽  
The North ◽  
Solar Magnetic Cycle

Aims. We study features of the 3D solar anisotropy of Galactic cosmic rays (GCR) for 1965−2014 (almost five solar cycles, cycles 20−24). We analyze the 27-day variations of the 2D GCR anisotropy in the ecliptic plane and the north-south anisotropy normal to the ecliptic plane. We study the dependence of the 27-day variation of the 3D GCR anisotropy on the solar cycle and solar magnetic cycle. We demonstrate that the 27-day variations of the GCR intensity and anisotropy can be used as an important tool to study solar wind, solar activity, and heliosphere. Methods. We used the components Ar, Aϕ and At of the 3D GCR anisotropy that were found based on hourly data of neutron monitors (NMs) and muon telescopes (MTs) using the harmonic analyses and spectrographic methods. We corrected the 2D diurnal (~24-h) variation of the GCR intensity for the influence of the Earth magnetic field. We derived the north-south component of the GCR anisotropy based on the GG index, which is calculated as the difference in GCR intensities of the Nagoya multidirectional MTs. Results. We show that the behavior of the 27-day variation of the 3D anisotropy verifies a stable long-lived active heliolongitude on the Sun. This illustrates the usefulness of the 27-day variation of the GCR anisotropy as a unique proxy to study solar wind, solar activity, and heliosphere. We distinguish a tendency of the 22-yr changes in amplitude of the 27-day variation of the 2D anisotropy that is connected with the solar magnetic cycle. We demonstrate that the amplitudes of the 27-day variation of the north-south component of the anisotropy vary with the 11-yr solar cycle, but a dependence of the solar magnetic polarity can hardly be recognized. We show that the 27-day recurrences of the GG index and the At component are highly positively correlated, and both are highly correlated with the By component of the heliospheric magnetic field.

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 cycle variations in differential instrumental responses from ground‑based geomagnetic records

2020 ◽  
Author(s):  
Stuart Gilder ◽  
Michael Wack ◽  
Elena Kronberg ◽  
Ameya Prabhu
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Solar Cycle ◽  
High Speed ◽  
Magnetic Measurements ◽  
Solar Wind Speed ◽  
Maximum Amplitude ◽  
Auroral Oval ◽  
Wide Frequency Range ◽  
The Magnetic Field

&lt;p&gt;We developed a new technique based on differences in instrument responses from ground-based magnetic measurements that extracts the frequency content of the magnetic field with periods ranging from 0.1 to 100 seconds. By stacking hourly averages over an entire year, we found that the maximum amplitude of the magnetic field oscillations occurred near solar noon over diurnal periods at all latitudes except in the auroral oval. Seasonal variability was identified only at high latitude. Long-term trends in field oscillations followed the solar cycle, yet the maxima occurred during the declining phase when high-speed streams in the solar wind dominated. A parameter based on solar wind speed and the relative variability of the interplanetary magnetic field correlated robustly with the ground-based measurements. Our findings suggest that turbulence in the solar wind, its interaction at the magnetopause, and its propagation into the magnetosphere stimulate magnetic field fluctuations at the ground on the dayside over a wide frequency range. Our method enables the study of field line oscillations using the publicly available, worldwide database of geomagnetic observatories.&lt;/p&gt;

scholarly journals Solar Cycle Variation of Cosmic ray Intensity along with Interplanetary and Solar Wind Plasma Parameters

2008 ◽  
Vol 45 (3) ◽  
pp. 63-68 ◽  
Author(s):  
Rajesh Mishra ◽  
Rekha Agarwal ◽  
Sharad Tiwari
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Solar Cycle ◽  
Interplanetary Magnetic Field ◽  
Cosmic Ray ◽  
Solar Wind Plasma ◽  
Solar Cycles ◽  
Plasma Parameters ◽  
Solar Cycle Variation ◽  
Cosmic Ray Intensity

Solar Cycle Variation of Cosmic ray Intensity along with Interplanetary and Solar Wind Plasma ParametersGalactic cosmic rays are modulated at their propagation in the heliosphere by the effect of the large-scale structure of the interplanetary medium. A comparison of the variations in the cosmic ray intensity data obtained by neutron monitoring stations with those in geomagnetic disturbance, solar wind velocity (V), interplanetary magnetic field (B), and their product (V' B) near the Earth for the period 1964-2004 has been presented so as to establish a possible correlation between them. We used the hourly averaged cosmic ray counts observed with the neutron monitor in Moscow. It is noteworthy that a significant negative correlation has been observed between the interplanetary magnetic field, product (V' B) and cosmic ray intensity during the solar cycles 21 and 22. The solar wind velocity has a good positive correlation with cosmic ray intensity during solar cycle 21, whereas it shows a weak correlation during cycles 20, 22 and 23. The interplanetary magnetic field shows a weak negative correlation with cosmic rays for solar cycle 20, and a good anti-correlation for solar cycles 21-23 with the cosmic ray intensity, which, in turn, shows a good positive correlation with disturbance time index (Dst) during solar cycles 21 and 22, and a weak correlation for cycles 20 and 23.

What epoch and space region at the heliospheric boundaries are probing IBEX and IMAP observations of interstellar neutral gas populations?

2020 ◽  
Author(s):  
Maciej Bzowski ◽  
Marzena Kubiak ◽  
Jacob Heerikhuisen
Keyword(s):  
Magnetic Field ◽  
Remote Sensing ◽  
Solar Wind ◽  
Solar Cycle ◽  
Plasma Flow ◽  
Solar Cycles ◽  
Neutral Atoms ◽  
Neutral Gas ◽  
Direct Sampling

&lt;p&gt;Interaction between the solar wind and the local interstellar environment has been studied using several observation techniques, including in-situ sampling of the plasma, magnetic field,&amp;#160; energetic ions by the Voyager spacecraft; remote-sensing observations of energetic neutral atoms (IBEX, Cassini); and the primary and secondary populations of interstellar neutral gas (IBEX-Lo). Understanding the processes at the heliospheric boundary and of the conditions outside the heliosphere is typically&amp;#160; done by fitting parameters used in models of this interaction to various observables, including the Voyager crossing distances of the termination shock and the heliopause, the size of the IBEX ribbon and its center directions, the sky distribution of the Lyman-alpha helioglow, and the flux of interstellar gas at 1 au from direct-sampling observations. Typically, it is expected that all or most of these observables are successfully reproduced. Even though the interaction of interstellar neutral gas with the solar wind and solar EUV output is sometimes taken into account, the global heliosphere is usually simulated as a stationary structure, with the solar wind flux, density, and magnetic field variation ignored. However, solar wind is a dynamic phenomenon, which results in variations in the plasma flow both inside and outside the heliopause and in variations of the distance to the heliopause. Based on in-situ solar wind observations, dynamic pressure of the solar wind may change by a factor of 2, which may result in a heliopause distance change by 50%, counting from the lowest-pressure conditions.&lt;/p&gt;&lt;p&gt;Interstellar neutral atoms reaching detectors at 1 au or contributing to the helioglow observed from 1 au need very different times to travel from the interaction&amp;#160; region , typically located at ~1.75 of the heliopause distance to 1 au. While the primary ISN atoms take 3&amp;#8212;4 solar cycles to travel from this region to 1 au, with a physical time spread (not an uncertainty!) of about one solar cycle, the atoms from secondary population take as much as 15 solar cycles, with a large spread of 7 solar cycles. This implies that ISN He atoms sampled by IBEX-Lo, as well as those observed as the helioglow, originate from two different and disparate epochs. While it may be expected that the interstellar conditions at a time scale of 200 years are little variable, solar wind is definitely varying, with secular changes superimposed on the solar cycle variation.&lt;/p&gt;&lt;p&gt;Direct-sampling observations provide information on the plasma flow in the OHS inside ~60&amp;#176; around the inflow direction, with well-defined regions of the OHS contributing atoms to individual pixels observed by IBEX and IMAP at different orbits. However, the information obtained is heavily averaged over time, and the epoch&amp;#160; imprinted on these population is very different to the epochs characteristic for in-situ observations from the Voyagers (by 50 to 170 years!)&amp;#160; and remote-sensing observations of the much faster-running energetic neutral atoms.&lt;/p&gt;

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