scholarly journals The Dipolar Solar Minimum Corona

Universe ◽  
2021 ◽  
Vol 7 (12) ◽  
pp. 507
Author(s):  
Daniele Telloni
Keyword(s):  
Solar Wind ◽  
Solar Minimum ◽  
Large Scale ◽  
Slow Solar Wind ◽  
Kinetic Temperature ◽  
Solar Cycles ◽  
Heliospheric Observatory ◽  
Oxygen Ions ◽  
Uv Emission ◽  
The Magnetic Field

The large-scale configuration of the UV solar corona at the minimum activity between solar cycles 22 and 23 is explored in this paper. Exploiting a large sample of spectroscopic observations acquired by the Ultraviolet Coronagraph Spectrometer aboard the Solar and Heliospheric Observatory in the two-year period of 1996–1997, this work provides the first-ever monochromatic O vi 1032 Å image of the extended corona, and the first-ever two-dimensional maps of the kinetic temperature of oxygen ions and the O vi 1037/1032 Å doublet intensity ratio (a proxy for the outflow velocity of the oxygen component of the solar wind), statistically representative of solar minimum conditions. A clear dipolar magnetic structure, both equator- and axis-symmetric, is distinctly shown to shape the solar minimum corona, both in UV emission and in temperature and expansion rate. This statistical approach allows for robust establishment of the key role played by the magnetic field divergence in modulating the speed and temperature of the coronal flows, and identification of the coronal sources of the fast and slow solar wind.

scholarly journals Peculiar Current Solar-Minimum Structure of the Heliosphere

2009 ◽  
Vol 5 (H15) ◽  
pp. 484-487
Author(s):  
P. K. Manoharan
Keyword(s):  
Solar Wind ◽  
Wind Speed ◽  
Solar Minimum ◽  
Large Scale ◽  
Solar Wind Speed ◽  
Heliospheric Current Sheet ◽  
Coronal Density ◽  
Current Minimum ◽  
Similar Phase ◽  
The Magnetic Field

AbstractIn this paper, I review the results of 3-D evolution of the inner heliosphere over the solar cycle 23, based on observations of interplanetary scintillation (IPS) made at 327 MHz using the Ooty Radio Telescope. The large-scale features of solar wind speed and density turbulence of the current minimum are remarkably different from that of the previous cycle. The results on the solar wind density turbulence show that (1) the current solar minimum is experiencing a low level of coronal density turbulence, to a present value of ~50% lower than the previous similar phase, and (2) the scattering diameter of the corona has decreased steadily after the year 2003. The results on solar wind speed are consistent with the magnetic field strength at the poles and the warping of heliospheric current sheet.

scholarly journals Solar wind ion trends and signatures: STEREO PLASTIC observations approaching solar minimum

2009 ◽  
Vol 27 (10) ◽  
pp. 3909-3922 ◽  
Author(s):  
A. B. Galvin ◽  
M. A. Popecki ◽  
K. D. C. Simunac ◽  
L. M. Kistler ◽  
L. Ellis ◽  
...  
Keyword(s):  
Solar Wind ◽  
Solar Minimum ◽  
Large Scale ◽  
Slow Solar Wind ◽  
Transient Event ◽  
Large Scale Structures ◽  
Close Proximity ◽  
Scale Structures

Abstract. STEREO has now completed the first two years of its mission, moving from close proximity to Earth in 2006/2007 to more than 50 degrees longitudinal separation from Earth in 2009. During this time, several large-scale structures have been observed in situ. Given the prevailing solar minimum conditions, these structures have been predominantly coronal hole-associated solar wind, slow solar wind, their interfaces, and the occasional transient event. In this paper, we extend earlier solar wind composition studies into the current solar minimum using high-resolution (1-h) sampling times for the charge state analysis. We examine 2-year trends for iron charge states and solar wind proton speeds, and present a case study of Carrington Rotation 2064 (December 2007) which includes minor ion (He, Fe, O) kinetic and Fe composition parameters in comparison with proton and magnetic field signatures at large-scale structures observed during this interval.

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.

Variations of interplanetary parameters in different types of large-scale solar-wind phenomena during 21-24 solar cycles

2020 ◽  
Author(s):  
Yuri Yermolaev ◽  
Irina Lodkina ◽  
Alexander Khokhlachev ◽  
Michael Yermolaev ◽  
Natalia Borodkova ◽  
...  
Keyword(s):  
Solar Wind ◽  
Large Scale ◽  
Solar Cycles ◽  
Different Types

Ion-scale break of the plasma fluctuation spectra in different large-scale solar wind streams

2021 ◽  
Author(s):  
Maria Riazantseva ◽  
Liudmila Rakhmanova ◽  
Yuri Yermolaev ◽  
Irina Lodkina ◽  
Georgy Zastenker ◽  
...  
Keyword(s):  
Solar Wind ◽  
Large Scale ◽  
Plasma Heating ◽  
Coronal Holes ◽  
Magnetic Clouds ◽  
Alfven Wave ◽  
Slow Solar Wind ◽  
P Value ◽  
High Temporal Resolution ◽  
Turbulent Cascade

<p>Appearance of measurements of the interplanetary medium parameters with high temporal resolution gave rise to a variety of investigations of turbulent cascade at ion kinetic scales at which processes of plasma heating was believed to operate. Our recent studies based on high frequency plasma measurements at Spektr-R spacecraft have shown that the turbulent cascade was not stable and dynamically changed depending on the plasma conditions in different large-scale solar wind structures. These changes was most significant at the kinetic scales of the turbulent cascade. Slow undisturbed solar wind was characterized by the consistency of the spectra to the predictions of the kinetic Alfven wave turbulence model. On the other hand, the discrepancy between the model predictions and registered spectra were found in stream interaction regions characterized by crucial steepening of spectra at the kinetic scales with slopes having values up to -(4-5). This discrepancy was clearly shown for plasma compression region Sheath in front of the magnetic clouds and CIR in front of high speed streams associated with coronal holes. Present study is focused on the break preceding the kinetic scales. Currently the characteristic plasma parameters associated with the formation of the break is still debated. Number of studies demonstrated that the break was consistent with distinct characteristic frequencies for different values ​​of the plasma proton parameter beta βp. Present study consider the ratio between the break frequency determined for ion flux fluctuation spectra according to Spektr-R data and several characteristic plasma frequencies used traditionally in such cases. The value of this ratio is statistically compared for different large-scale solar wind streams. We analyze both the classical spectrum view with two slopes and one break and the spectrum with flattening between magnetohydrodynamic and kinetic scales.  Our results show that for the Sheath and CIR regions characterized typically by βp ≤1 the break corresponds statistically to the frequency determined by the proton gyroradius. At the same time such correspondence are not observed either for the undisturbed slow solar wind with similar βp value or for disturbed flows associated with interplanetary manifestations of coronal mass ejections, where βp << 1. The results also shows that in slow undisturbed solar wind the break is closer to the frequency determined by the inertial proton length. Thus, apparently the transition between streams of different speeds may result in the change of dissipation regimes and plays role in plasma heating at these areas. This work was supported by the RFBR grant No. 19-02-00177a</p>

scholarly journals Solar cycle changes in the geo-effectiveness of small-scale solar wind turbulence measured by Wind and ACE at 1 AU

2007 ◽  
Vol 25 (5) ◽  
pp. 1183-1197 ◽  
Author(s):  
M. L. Parkinson ◽  
R. C. Healey ◽  
P. L. Dyson
Keyword(s):  
Solar Wind ◽  
Solar Cycle ◽  
Solar Minimum ◽  
Large Scale ◽  
Small Scale ◽  
Scaling Exponent ◽  
Mhd Turbulence ◽  
Scaling Exponents ◽  
Solar Wind Turbulence ◽  
Wind Turbulence

Abstract. Multi-scale structure of the solar wind in the ecliptic at 1 AU undergoes significant evolution with the phase of the solar cycle. Wind spacecraft measurements during 1995 to 1998 and ACE spacecraft measurements during 1997 to 2005 were used to characterise the evolution of small-scale (~1 min to 2 h) fluctuations in the solar wind speed vsw, magnetic energy density B2, and solar wind ε parameter, in the context of large-scale (~1 day to years) variations. The large-scale variation in ε most resembled large-scale variations in B2. The probability density of large fluctuations in ε and B2 both had strong minima during 1995, a familiar signature of solar minimum. Generalized Structure Function (GSF) analysis was used to estimate inertial range scaling exponents aGSF and their evolution throughout 1995 to 2005. For the entire data set, the weighted average scaling exponent for small-scale fluctuations in vsw was aGSF=0.284±0.001, a value characteristic of intermittent MHD turbulence (>1/4), whereas the scaling exponents for corresponding fluctuations in B2 and ε were aGSF=0.395±0.001 and 0.334±0.001, respectively. These values are between the range expected for Gaussian fluctuations (1/2) and Kolmogorov turbulence (1/3). However, the scaling exponent for ε changed from a Gaussian-Kolmogorov value of 0.373±0.005 during 1997 (end of solar minimum) to an MHD turbulence value of 0.247±0.004 during 2003 (recurrent fast streams). Changes in the characteristics of solar wind turbulence may be reproducible from one solar cycle to the next.

scholarly journals The evolution of inverted magnetic fields through the inner heliosphere

2020 ◽  
Vol 494 (3) ◽  
pp. 3642-3655 ◽  
Author(s):  
Allan R Macneil ◽  
Mathew J Owens ◽  
Robert T Wicks ◽  
Mike Lockwood ◽  
Sarah N Bentley ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Radial Distance ◽  
Occurrence Rate ◽  
Slow Solar Wind ◽  
The Sun ◽  
Radial Evolution ◽  
In Transit ◽  
The Magnetic Field ◽  
Inner Heliosphere

ABSTRACT Local inversions are often observed in the heliospheric magnetic field (HMF), but their origins and evolution are not yet fully understood. Parker Solar Probe has recently observed rapid, Alfvénic, HMF inversions in the inner heliosphere, known as ‘switchbacks’, which have been interpreted as the possible remnants of coronal jets. It has also been suggested that inverted HMF may be produced by near-Sun interchange reconnection; a key process in mechanisms proposed for slow solar wind release. These cases suggest that the source of inverted HMF is near the Sun, and it follows that these inversions would gradually decay and straighten as they propagate out through the heliosphere. Alternatively, HMF inversions could form during solar wind transit, through phenomena such velocity shears, draping over ejecta, or waves and turbulence. Such processes are expected to lead to a qualitatively radial evolution of inverted HMF structures. Using Helios measurements spanning 0.3–1 au, we examine the occurrence rate of inverted HMF, as well as other magnetic field morphologies, as a function of radial distance r, and find that it continually increases. This trend may be explained by inverted HMF observed between 0.3 and 1 au being primarily driven by one or more of the above in-transit processes, rather than created at the Sun. We make suggestions as to the relative importance of these different processes based on the evolution of the magnetic field properties associated with inverted HMF. We also explore alternative explanations outside of our suggested driving processes which may lead to the observed trend.

Statistical Differences of Magnetic Field Kinks Observed by PSP and WIND

2021 ◽  
Author(s):  
Chuanpeng Hou ◽  
Xingyu Zhu ◽  
Rui Zhuo ◽  
Jiansen He
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Radial Velocity ◽  
Slow Solar Wind ◽  
Number Density ◽  
Ion Temperature ◽  
Group I ◽  
Rotational Discontinuity ◽  
Background Magnetic Field ◽  
The Magnetic Field

<p>Parker Solar Probe’s (PSP) observations near the sun show the extensive presence of magnetic field kinks (switchback for large kinks) in the slow solar wind. These kinks are usually accompanied by the enhancement of radial solar wind velocity and ion temperature, increasing or decreasing of number density. The magnetic field kinks have also been observed by WIND and Ulysses to exist near and beyond 1 AU, respectively. In this study, we statistically analyze the property difference of magnetic field kinks observed by PSP and WIND. We obtain the following four points of results. (1) Inside the PSP-kinks, the radial velocity and protons’ temperature increase while density shows enhancement or descent. However, inside the WIND-kinks, besides the slight enhancement of radial velocity, the density and temperature show no obvious change compared with the outside plasma. (2) By employing the Walen-test of kinks, we find that, R components of some PSP-kinks but not all satisfy the rotational discontinuity (RD) features, while the three components of most WIND-kinks well match the RD features. (3) The correlation between magnetic field and velocity inside the PSP-kinks and WIND-kinks does not show significant differences. (4) Both the PSP-kinks and WIND-kinks can be divided into two groups based on the histograms of θ<sub>Bn</sub>, where B is the background magnetic field, and n is the normal direction of kink. The first group (group-I) has θ<sub>Bn</sub> concentrating around 20° for PSP-kinks and 30° for WIND-kinks, indicating that the satellites were crossing the same kinked interplanetary magnetic field (IMF) from the upstream to the downstream. The second group (group-II) has θ<sub>Bn</sub> concentrating around 90° for PSP-kinks and WIND-kinks, suggesting that the satellites were crossing an interface between the unkinked and kinked IMF regions. Our findings help better understanding the nature of kinks and provide the observational basis for testifying models about radial propagation and evolution of magnetic field kinks.</p>

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

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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