The dynamo-wind feedback loop : Assessing their non-linear interplay

AbstractThough generated deep inside the convection zone, the solar magnetic field has a direct impact on the Earth space environment via the Parker spiral. It strongly modulates the solar wind in the whole heliosphere, especially its latitudinal and longitudinal speed distribution over the years. However the wind also influences the topology of the coronal magnetic field by opening the magnetic field lines in the coronal holes, which can affect the inner magnetic field of the star by altering the dynamo boundary conditions. This coupling is especially difficult to model because it covers a large variety of spatio-temporal scales. Quasi-static studies have begun to help us unveil how the dynamo-generated magnetic field shapes the wind, but the full interplay between the solar dynamo and the solar wind still eludes our understanding.We use the compressible magnetohydrodynamical (MHD) code PLUTO to compute simultaneously in 2.5D the generation and evolution of magnetic field inside the star via an α-Ω dynamo process and the corresponding evolution of a polytropic coronal wind over several activity cycles for a young Sun. A multi-layered boundary condition at the surface of the star connects the inner and outer stellar layers, allowing both to adapt dynamically. Our continuously coupled dynamo-wind model allows us to characterize how the solar wind conditions change as a function of the cycle phase, and also to quantify the evolution of integrated quantities such as the Alfvén radius. We further assess the impact of the solar wind on the dynamo itself by comparing our results with and without wind feedback.

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PFSS-Based Solar Wind Forecast and the Radius of the Source-Surface

Proceedings of the International Astronomical Union ◽

10.1017/s1743921317009875 ◽

2017 ◽

Vol 13 (S335) ◽

pp. 307-309

Author(s):

Ljubomir Nikolić

Keyword(s):

Magnetic Field ◽

Solar Wind ◽

Spherical Surface ◽

Solar Wind Speed ◽

Coronal Holes ◽

Coronal Magnetic Field ◽

Source Surface ◽

Field Source ◽

Forecast Models ◽

Field Lines

AbstractThe potential-field source-surface (PFSS) model of the solar corona is a widely used tool in the space weather research and operations. In particular, the PFSS model is used in solar wind forecast models which empirically associate solar wind properties with the numerically derived coronal magnetic field. In the PFSS model, the spherical surface where magnetic field lines are forced to open is typically placed at 2.5 solar radii. However, the results presented here suggest that setting this surface (the source-surface) to lower heights can provide a better agreement between observed and modelled coronal holes during the current solar cycle. Furthermore, the lower heights of the source-surface provide a better match between observed and forecasted solar wind speed.

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Plasma Flow and Solar Wind Acceleration in Non-Radial Coronal Magnetic Fields

Symposium - International Astronomical Union ◽

10.1017/s0074180900030151 ◽

1983 ◽

Vol 102 ◽

pp. 473-477

Author(s):

H. Biernat ◽

N. Kömle ◽

H. Rucker

Keyword(s):

Magnetic Field ◽

Solar Wind ◽

Plasma Flow ◽

Coronal Holes ◽

Expansion Velocity ◽

The Sun ◽

Solar Wind Acceleration ◽

Coronal Magnetic Fields ◽

Field Lines ◽

The Magnetic Field

In the vicinity of the Sun — especially above coronal holes — the magnetic field lines show strong non-radial divergence and considerable curvature (see e.g. Kopp and Holzer, 1976; Munro and Jackson, 1977; Ripken, 1977). In the following we study the influence of these characteristics on the expansion velocity of the solar wind.

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Analysis of the distribution, rotation and scale characteristics of solar wind switchbacks: comparison between the first and second encounters of Parker Solar Probe

Research in Astronomy and Astrophysics ◽

10.1088/1674-4527/ac49e4 ◽

2022 ◽

Author(s):

Mingming Meng ◽

Ying Liu ◽

Chong Chen ◽

Rui Wang

Keyword(s):

Magnetic Field ◽

Solar Wind ◽

Coronal Holes ◽

Minimum Variance ◽

Tangential Component ◽

Magnetic Field Rotation ◽

Anticlockwise Rotation ◽

Scale Characteristics ◽

Field Lines ◽

The Magnetic Field

Abstract The S-shaped magnetic structure in the solar wind formed by the twisting of magnetic field lines is called a switchback, whose main characteristics are the reversal of the magnetic field and the significant increase in the solar wind radial velocity. We identify 242 switchbacks during the first two encounters of Parker Solar Probe (PSP). Statistics methods are applied to analyze the distribution and the rotation angle and direction of the magnetic field rotation of the switchbacks. The diameter of switchbacks is estimated with a minimum variance analysis (MVA) method based on the assumption of a cylindrical magnetic tube. We also make a comparison between switchbacks from inside and the boundary of coronal holes. The main conclusions are as follows: (1) the rotation angles of switchbacks observed during the first encounter seem larger than those of the switchbacks observed during the second encounter in general; (2) the tangential component of the velocity inside the switchbacks tends to be more positive (westward) than in the ambient solar wind; (3) switchbacks are more likely to rotate clockwise than anticlockwise, and the number of switchbacks with clockwise rotation is 1.48 and 2.65 times of those with anticlockwise rotation during the first and second encounters, respectively; (4) the diameter of switchbacks is about 10^5 km on average and across five orders of magnitude (10^3 – 10^7 km).

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Energy Balance in Coronal Holes and Solar Wind Streams

International Astronomical Union Colloquium ◽

10.1017/s0252921100053410 ◽

1977 ◽

Vol 36 ◽

pp. 421-445 ◽

Cited By ~ 2

Author(s):

J.B. Zirker

Keyword(s):

Magnetic Field ◽

Solar Wind ◽

Energy Balance ◽

Coronal Holes ◽

Early History ◽

Satellite Observations ◽

History Of Research ◽

History Of ◽

Field Lines ◽

Open Magnetic Field

Coronal holes are regions of depressed density and temperature in the inner corona that coincide with open magnetic field lines. They were recognized for many years on eclipse photographs, but real understanding of their importance began to emerge only after data from rocket and satellite observations were analyzed. Wilson (1976) has summarized the early history of research on coronal holes.

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Fractionation of the Solar Wind

Highlights of Astronomy ◽

10.1017/s153929960001131x ◽

1995 ◽

Vol 10 ◽

pp. 310-312 ◽

Cited By ~ 1

Author(s):

R. Von Steiger

Keyword(s):

Magnetic Field ◽

Solar Wind ◽

Coronal Holes ◽

Step Function ◽

Solar Photosphere ◽

Ion Separation ◽

Solar Composition ◽

Solar Abundances ◽

Field Lines ◽

First Ionization Potential

The composition of the solar wind (SW) is not a true sample of the solar composition, but it is fractionated with respect to the solar photosphere. This fractionation follows the well-known first ionization potential (FIP) pattern: When plotting the SW abundances with respect to the solar abundances as a function of FIP, a step function is obtained (Fig. 1). The step at ∼ 10eV has a height of 3-5 in the slow SW, but this is reduced to 1.5-2 in the fast streams, which originate in the coronal holes. The data given in Fig. 1 are collected and discussed in von Steiger & Geiss (1994), including the “FIP exceptions”, Kr and Xe.The process leading to the observed overabundance of the low-FIPs has been located to operate by atom-ion separation across magnetic field lines in the chromosphere (Geiss, 1982), because this is the only region of the solar atmosphere where a significant fraction of the gas is neutral. The fractionated abundances observed in the S W are thus important tracers for processes and conditions at this site.

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A porcupine Sun? Implications for the solar wind and Earth

Proceedings of the International Astronomical Union ◽

10.1017/s1743921312004851 ◽

2011 ◽

Vol 7 (S286) ◽

pp. 210-214 ◽

Cited By ~ 2

Author(s):

Sarah E. Gibson ◽

Liang Zhao

Keyword(s):

Magnetic Field ◽

Solar Wind ◽

Spatial Scales ◽

Coronal Magnetic Field ◽

Heliospheric Current Sheet ◽

Magnetic Structures ◽

Fast Wind ◽

Global Configuration ◽

Slow Wind ◽

The Impact

AbstractThe recent minimum was unusually long, and it was not just the case of the “usual story” slowed down. The coronal magnetic field never became completely dipolar as in recent Space Age minima, but rather gradually evolved into an (essentially axisymmetric) global configuration possessing mixed open and closed magnetic structures at many latitudes. In the process, the impact of the solar wind at the Earth went from resembling that from a sequence of rotating “fire-hoses” to what might be expected from a weak, omnidirectional “lawn-sprinkler”. The previous (1996) solar minimum was a more classic dipolar configuration, and was characterized by slow wind of hot origin localized to the heliospheric current sheet, and fast wind of cold origin emitted from polar holes, but filling most of the heliosphere. In contrast, the more recent minimum solar wind possessed a broad range of speeds and source temperatures (although cooler overall than the prior minimum). We discuss possible connections between these observations and the near-radial expansion and small spatial scales characteristic of the recent minimum's porcupine-like magnetic field.

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Active Region Contributions to the Solar Wind over Multiple Solar Cycles

Solar Physics ◽

10.1007/s11207-021-01861-x ◽

2021 ◽

Vol 296 (8) ◽

Author(s):

David Stansby ◽

Lucie M. Green ◽

Lidia van Driel-Gesztelyi ◽

Timothy S. Horbury

Keyword(s):

Magnetic Field ◽

Solar Wind ◽

Coronal Holes ◽

Active Regions ◽

Coronal Magnetic Field ◽

Solar Cycles ◽

Fractional Contribution ◽

Source Regions ◽

Mass Ejection ◽

Coronal Structures

AbstractBoth coronal holes and active regions are source regions of the solar wind. The distribution of these coronal structures across both space and time is well known, but it is unclear how much each source contributes to the solar wind. In this study we use photospheric magnetic field maps observed over the past four solar cycles to estimate what fraction of magnetic open solar flux is rooted in active regions, a proxy for the fraction of all solar wind originating in active regions. We find that the fractional contribution of active regions to the solar wind varies between 30% to 80% at any one time during solar maximum and is negligible at solar minimum, showing a strong correlation with sunspot number. While active regions are typically confined to latitudes ±30∘ in the corona, the solar wind they produce can reach latitudes up to ±60∘. Their fractional contribution to the solar wind also correlates with coronal mass ejection rate, and is highly variable, changing by ±20% on monthly timescales within individual solar maxima. We speculate that these variations could be driven by coronal mass ejections causing reconfigurations of the coronal magnetic field on sub-monthly timescales.

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The origin of slow Alfvénic solar wind at solar minimum

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stz3422 ◽

2019 ◽

Vol 492 (1) ◽

pp. 39-44 ◽

Cited By ~ 10

Author(s):

D Stansby ◽

L Matteini ◽

T S Horbury ◽

D Perrone ◽

R D’Amicis ◽

...

Keyword(s):

Magnetic Field ◽

Solar Wind ◽

Alpha Particle ◽

Coronal Holes ◽

Slow Solar Wind ◽

Kinetic Properties ◽

Fast Solar Wind ◽

Lower Corona ◽

Field Lines ◽

Slow Wind

ABSTRACT Although the origins of slow solar wind are unclear, there is increasing evidence that at least some of it is released in a steady state on overexpanded coronal hole magnetic field lines. This type of slow wind has similar properties to the fast solar wind, including strongly Alfvénic fluctuations. In this study, a combination of proton, alpha particle, and electron measurements are used to investigate the kinetic properties of a single interval of slow Alfvénic wind at 0.35 au. It is shown that this slow Alfvénic interval is characterized by high alpha particle abundances, pronounced alpha–proton differential streaming, strong proton beams, and large alpha-to-proton temperature ratios. These are all features observed consistently in the fast solar wind, adding evidence that at least some Alfvénic slow solar wind also originates in coronal holes. Observed differences between speed, mass flux, and electron temperature between slow Alfvénic and fast winds are explained by differing magnetic field geometry in the lower corona.

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