Solar cycle changes of large-scale solar wind structure

AbstractIn this paper, I present the results on large-scale evolution of density turbulence of solar wind in the inner heliosphere during 1985–2009. At a given distance from the Sun, the density turbulence is maximum around the maximum phase of the solar cycle and it reduces to ~70%, near the minimum phase. However, in the current minimum of solar activity, the level of turbulence has gradually decreased, starting from the year 2005, to the present level of ~30%. These results suggest that the source of solar wind changes globally, with the important implication that the supply of mass and energy from the Sun to the interplanetary space has significantly reduced in the present low level of activity.

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Structure and connectivity of CME-driven shocks and sheaths through the inner heliosphere

10.5194/egusphere-egu21-8141 ◽

2021 ◽

Author(s):

Erika Palmerio ◽

Christina Lee ◽

Dusan Odstrcil ◽

Leila Mays

Keyword(s):

Solar Wind ◽

Large Scale ◽

The Sun ◽

Interplanetary Shocks ◽

Plasma Parameters ◽

Wind Structure ◽

Solar Wind Structure ◽

Magnetohydrodynamic Simulations ◽

Comprehensive Study ◽

Inner Heliosphere

The evolution of coronal mass ejections (CMEs) as they travel away from the Sun is one of the major issues in heliophysics and space weather. During propagation, CMEs and the structures ahead of them (i.e., interplanetary shocks and sheath regions, if present) are significantly affected by the ambient solar wind, which is able to alter their speed, trajectory, and orientation. The scarcity of multi-spacecraft measurements of the same CME, however, implies that little is known about how and where (in terms of distance from the Sun) these various processes exactly come into play.To address this issue, we run a series of 3D magnetohydrodynamic simulations using the coupled solar&#8211;heliospheric WSA&#8211;Enlil model, in which we launch idealised CMEs as hydrodynamic (non-magnetised) structures. This allows us to focus on the evolution of CME-driven shocks and sheath regions through a multi-point study. We launch CMEs of various speeds through different solar wind backgrounds and at different heliolongitudes with respect to the streamer belt position. Then, we investigate the resulting magnetic field and plasma parameters at a series of synthetic spacecraft placed at various longitudes around the CME apex and at various heliocentric distances between 0.5 AU and 2 AU. We also analyse how the magnetic connectivity at these spacecraft evolves as the CME propagates. This work represents a comprehensive study of the interaction of CME-driven shocks and sheath regions with the large-scale solar wind structure throughout the inner heliosphere, with the aim to establish a range of expected behaviours and outcomes useful to interpret real events.

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Large-scale solar-wind structure near the Sun detected by Doppler scintillation

Nature ◽

10.1038/366543a0 ◽

1993 ◽

Vol 366 (6455) ◽

pp. 543-545 ◽

Cited By ~ 24

Author(s):

Richard Woo ◽

Paul Gazis

Keyword(s):

Solar Wind ◽

Large Scale ◽

The Sun ◽

Wind Structure ◽

Solar Wind Structure

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Large-scale electron solar wind parameters of the inner heliosphere with Parker Solar Probe/FIELDS

10.5194/egusphere-egu2020-18573 ◽

2020 ◽

Author(s):

Karine Issautier ◽

Mingzhe Liu ◽

Michel Moncuquet ◽

Nicole Meyer-Vernet ◽

Milan Maksimovic ◽

...

Keyword(s):

Solar Wind ◽

Large Scale ◽

Statistical Study ◽

Solar Wind Speed ◽

The Sun ◽

Solar Wind Parameters ◽

Power Law Index ◽

Probe Mission ◽

Inner Heliosphere

We present in situ properties of electron density and temperature in the inner heliosphere obtained during the three first solar encounters at 35 solar radii of the Parker Solar Probe mission. These preliminary results, recently shown by Moncuquet et al., ApJS, 2020, are obtained from the analysis of the plasma quasi-thermal noise (QTN) spectrum measured by the radio RFS/FIELDS instrument along the trajectories extending between 0.5 and 0.17 UA from the Sun, revealing different states of the emerging solar wind, five months apart. The temperature of the weakly collisional core population varies radially with a power law index of about -0.8, much slower than adiabatic, whereas the temperature of the supra-thermal population exhibits a much flatter radial variation, as expected from its nearly collisionless state. These measured temperatures are close to extrapolations towards the Sun of Helios measurements.We also present a statistical study from these in situ electron solar wind parameters, deduced by QTN spectroscopy, and compare the data to other onboard measurements. In addition, we focus on the large-scale solar wind properties. In particular, from the invariance of the energy flux, a direct relation between the solar wind speed and its density can be deduced, as we have already obtained based on Wind continuous in situ measurements (Le Chat et al., Solar Phys., 2012). We study this anti-correlation during the three first solar encounters of PSP.

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Solar Wind Anomalies at 1 au and Their Associations with Large-scale Structures

The Astrophysical Journal ◽

10.3847/1538-4357/ac2a49 ◽

2021 ◽

Vol 923 (1) ◽

pp. 105

Author(s):

Yan Li ◽

Shaosui Xu ◽

Janet G. Luhmann ◽

Benoit Lavraud

Keyword(s):

Magnetic Field ◽

Solar Wind ◽

Solar Minimum ◽

Large Scale ◽

Spatial Scales ◽

Radial Magnetic Field ◽

Suprathermal Electron ◽

Wind Structure ◽

Solar Wind Structure ◽

Cycle 24

Abstract We study solar wind anomalies and their associations with solar wind structures using the STEREO solar wind and suprathermal electron (STE) data from IMPACT and PLASTIC. We define solar wind anomalies as temporary and local excursions from the average solar wind state, regardless of their origins, for six anomalies: sunward strahls, counterstreaming suprathermal electrons, suprathermal electron depletions, nearly radial magnetic field episodes, anomalously low proton temperatures, and anomalously low proton beta. We first establish the solar wind synoptic contour displays, which show the expected variations in solar wind structure during the solar cycle: recurrent corotating heliospheric magnetic field (HMF) and stream structures are dominant during solar quiet times around the solar minimum (2008 December) preceding cycle 24, while complex structures characterize solar active times around the solar maximum (2014 April). During the declining phase of the cycle (2016–2019), the stream structures remain complex, but the HMF sectors show the structures of the solar minimum. We then systematically study the six anomalies by analyzing the STE data using automated procedures. All anomalies present some degree of dependence on the large-scale solar wind structure, especially around the solar minimum, implying that the solar wind structure plays a role in either the generation or transportation of these anomalies. One common feature of all of the anomalies is that the distributions of the durations of the anomalous episodes all peak at the 1 hr data resolution, but monotonically decrease over longer durations, which may arguably imply that solar anomalies occur on a continuum of temporal and spatial scales.

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