Large-scale solar wind fluctuations in the inner heliosphere at low solar activity

1989 ◽  
Vol 94 (A1) ◽  
pp. 168 ◽  
Author(s):  
B. Bavassano ◽  
R. Bruno
Keyword(s):  
Solar Wind ◽  
Solar Activity ◽  
Large Scale ◽  
Inner Heliosphere

scholarly journals Solar cycle changes of large-scale solar wind structure

2009 ◽  
Vol 5 (S264) ◽  
pp. 356-358 ◽  
Author(s):  
P. K. Manoharan
Keyword(s):  
Solar Wind ◽  
Solar Cycle ◽  
Large Scale ◽  
Interplanetary Space ◽  
The Sun ◽  
Wind Structure ◽  
Level Of Activity ◽  
Solar Wind Structure ◽  
Current Minimum ◽  
Inner Heliosphere

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.

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

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

<p>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.</p><p>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.</p>

Investigation of the coronal heating through phase relation of solar activity indexes

2020 ◽  
Vol 37 ◽  
Author(s):  
K. J. Li ◽  
J. C. Xu ◽  
Z. Q. Yin ◽  
J. L. Xie ◽  
W. Feng
Keyword(s):  
Solar Wind ◽  
Solar Activity ◽  
Phase Relation ◽  
Large Scale ◽  
Solar Rotation ◽  
Rotation Period ◽  
Magnetic Activity ◽  
Coronal Heating ◽  
Small Scale

Abstract The coronal heating problem is a long-standing perplexing issue. In this study, 13 solar activity indexes are used to investigate their phase relation with the sunspot number (SSN). Only three of them are found to statistically significantly lag the SSN (large-scale magnetic activity) by about one solar rotation period; the three indexes are total solar irradiance (TSI), the modified coronal index, and the solar wind velocity; the former two indexes may represent the long-term variation of energy quantity of the heated photosphere and corona, respectively. The Mount Wilson Sunspot Index (MWSI) and the Magnetic Plage Strength Index (MPSI), which reflect the large- and small-scale magnetic field activities, respectively, are also utilised to investigate their phase relations with the three indexes. The three indexes are found to be much more intimately related to MPSI than to MWSI, and MWSI statistically significantly leads TSI by about one rotation period. The heated corona is found to pulse perfectly in step with the small-scale magnetic activity rather than the large-scale magnetic activity; furthermore, combined with observations, our statistical evidence should thus attribute coronal heating firmly to small-scale magnetic activity phenomena, such as spicules, micro-flares, nano-flares, and others. The photosphere and the corona are synchronously heated, which should seemingly prefer magnetic reconnection heating to wave heating. In the long term, such a coronal heating way is inferred effective. Statistically, it is also small-scale magnetic activity phenomena that produce TSI enhancement. Coronal heating and solar wind acceleration are found to be synchronous, as standard models require.

scholarly journals Large-scale velocity fluctuations in polar solar wind

2005 ◽  
Vol 23 (3) ◽  
pp. 1025-1031 ◽  
Author(s):  
B. Bavassano ◽  
R. Bruno ◽  
R. D'Amicis
Keyword(s):  
Solar Wind ◽  
Solar Activity ◽  
High Latitude ◽  
Large Scale ◽  
Activity Cycle ◽  
High Solar Activity ◽  
Time Lags ◽  
Polar Wind ◽  
Frequency Distributions ◽  
Long Range Correlations

Abstract. The 3-D structure of the solar wind varies dramatically along the Sun's activity cycle. In the present paper we focus on some properties of the polar solar wind. This is a fast, teneous, and steady flow (as compared to low-latitude conditions) that fills the high-latitude heliosphere at low solar activity. The polar wind has been extensively investigated by Ulysses, the first spacecraft to perform in-situ measurements in the high-latitude heliosphere. Though the polar wind is quite a uniform flow, fluctuations in its velocity do not appear negligible. A simple way to characterize the solar wind structure is that of performing a multi-scale statistical analysis of the wind velocity differences. The occurrence frequency distributions of velocity differences at time lags from 1 to 1024h and the corresponding values of mean, standard deviation, skewness, and kurtosis have been obtained. A comparison with previous results in ecliptic wind at both low and high solar activity has been performed. It comes out that the kind of trend observed in the distributions for changing scale is the same for the different solar wind regimes. Differences between different flows just have an effect on the values of the distribution moments and the scales at which the transition from non-Gaussian to Gaussian-like behaviours occurs. This is typical of systems in which random fluctuations are mixed to coherent structures of some characteristic size, in other words, systems where long-range correlations cannot be neglected.

The effect of stream interaction regions on CME structures: observations in longitudinal conjunction at Mercury and 1 AU

2021 ◽  
Author(s):  
Camilla Scolini ◽  
Reka M. Winslow ◽  
Noé Lugaz ◽  
Antoinette B. Galvin
Keyword(s):  
Solar Wind ◽  
Large Scale ◽  
Flux Rope ◽  
Solar Wind Plasma ◽  
In Situ Data ◽  
Earth Environment ◽  
Size Evolution ◽  
Interaction Regions ◽  
Plasma Measurements ◽  
Inner Heliosphere

<p>We present a study of two CMEs observed at Mercury and 1 AU by spacecraft in longitudinal conjunction. Of the two CMEs, one propagated relatively self-similarly, while the other one underwent significant changes in its properties, making them excellent case studies to investigate the following question: what causes the drastic alterations observed in some CMEs during propagation, while other CMEs remain relatively unchanged? Answering this question will also help us better understand the potential impact of CMEs on the near-Earth environment. </p><p>In this work we focus on the presence or absence of large-scale corotating structures in the propagation space between Mercury and 1 AU, that have been shown in the past to influence  the orientation  of  CME  magnetic  structures  and  the  properties  of  CME  sheaths. At both locations, we determine the CME flux rope orientation and characteristics using different fitting and classification methods. Our analysis is complemented by solar wind plasma measurements near 1 AU, by estimates of the size evolution of the sheaths and magnetic ejecta with heliocentric distance, and by the identification of solar wind structures in the CME propagation space based on in situ data, remote-sensing observations, and numerical simulations of the solar wind conditions in the inner heliosphere.</p><p>Results indicate that the changes observed in one CME were likely caused by a stream interaction region, while the CME exhibiting little change did not interact with any large-scale structure between Mercury and 1 AU. This work provides end-member examples of CME propagation in the inner heliosphere, exemplifying how interactions  with  corotating  structures  in  the  solar  wind  can  induce  essential  changes  in  CME structures. Our findings provide new fundamental insights on the propagation and evolution of CMEs, and can help lay the foundation for improved predictions of CME properties at 1 AU.</p>

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

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

<p>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.</p><p>To address this issue, we run a series of 3D magnetohydrodynamic simulations using the coupled solar–heliospheric WSA–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.</p>

scholarly journals Solar-wind predictions for the Parker Solar Probe orbit

2018 ◽  
Vol 611 ◽  
pp. A36 ◽  
Author(s):  
M. S. Venzmer ◽  
V. Bothmer
Keyword(s):  
Solar Wind ◽  
Solar Activity ◽  
Solar Corona ◽  
Wind Model ◽  
Wind Environment ◽  
Frequency Distributions ◽  
Solar Wind Model ◽  
Solar Wind Parameters ◽  
Inner Heliosphere

Context. The Parker Solar Probe (PSP; formerly Solar Probe Plus) mission will be humanitys first in situ exploration of the solar corona with closest perihelia at 9.86 solar radii (R⊙) distance to the Sun. It will help answer hitherto unresolved questions on the heating of the solar corona and the source and acceleration of the solar wind and solar energetic particles. The scope of this study is to model the solar-wind environment for PSPs unprecedented distances in its prime mission phase during the years 2018 to 2025. The study is performed within the Coronagraphic German And US SolarProbePlus Survey (CGAUSS) which is the German contribution to the PSP mission as part of the Wide-field Imager for Solar PRobe.Aim. We present an empirical solar-wind model for the inner heliosphere which is derived from OMNI and Helios data. The German-US space probes Helios 1 and Helios 2 flew in the 1970s and observed solar wind in the ecliptic within heliocentric distances of 0.29 au to 0.98 au. The OMNI database consists of multi-spacecraft intercalibrated in situ data obtained near 1 au over more than five solar cycles. The international sunspot number (SSN) and its predictions are used to derive dependencies of the major solar-wind parameters on solar activity and to forecast their properties for the PSP mission.Methods. The frequency distributions for the solar-wind key parameters, magnetic field strength, proton velocity, density, and temperature, are represented by lognormal functions. In addition, we consider the velocity distributions bi-componental shape, consisting of a slower and a faster part. Functional relations to solar activity are compiled with use of the OMNI data by correlating and fitting the frequency distributions with the SSN. Further, based on the combined data set from both Helios probes, the parameters frequency distributions are fitted with respect to solar distance to obtain power law dependencies. Thus an empirical solar-wind model for the inner heliosphere confined to the ecliptic region is derived, accounting for solar activity and for solar distance through adequate shifts of the lognormal distributions. Finally, the inclusion of SSN predictions and the extrapolation down to PSPs perihelion region enables us to estimate the solar-wind environment for PSPs planned trajectory during its mission duration.Results. The CGAUSS empirical solar-wind model for PSP yields dependencies on solar activity and solar distance for the solar-wind parameters’ frequency distributions. The estimated solar-wind median values for PSPs first perihelion in 2018 at a solar distance of 0.16 au are 87 nT, 340 km s−1, 214 cm−3, and 503 000 K. The estimates for PSPs first closest perihelion, occurring in 2024 at 0.046 au (9.86 R⊙), are 943 nT, 290 km s−1, 2951 cm−3, and 1 930 000 K. Since the modeled velocity and temperature values below approximately 20 R⊙appear overestimated in comparison with existing observations, this suggests that PSP will directly measure solar-wind acceleration and heating processes below 20 R⊙ as planned.

scholarly journals Dynamics of interplanetary CMEs and associated type II bursts

2008 ◽  
Vol 4 (S257) ◽  
pp. 287-290 ◽  
Author(s):  
Alejandro Lara ◽  
Andrea I. Borgazzi
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Large Scale ◽  
Interplanetary Medium ◽  
Hydrodynamic Theory ◽  
Type Ii ◽  
Large Scale Structures ◽  
Scale Structures ◽  
Ambient Solar Wind ◽  
Inner Heliosphere

AbstractCoronal mass ejections (CMEs) are large scale structures of plasma (~1016g) and magnetic field expelled from the solar corona to the interplanetary medium. During their travel in the inner heliosphere, these “interplanetary CMEs” (ICMEs), suffer acceleration due to the interaction with the ambient solar wind. Based on hydrodynamic theory, we have developed an analytical model for the ICME transport which reproduce well the observed deceleration of fast ICMEs. In this work we present the results of the model and its application to the CME observed on May 13, 2005 and the associated interplanetary type II burst.

scholarly journals EUHFORIA: European heliospheric forecasting information asset

2018 ◽  
Vol 8 ◽  
pp. A35 ◽  
Author(s):  
Jens Pomoell ◽  
S. Poedts
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Large Scale ◽  
Weather Forecasting ◽  
Mass Density ◽  
Solar Wind Speed ◽  
Plasma Parameters ◽  
Cone Model ◽  
Plasma State ◽  
Inner Heliosphere

The implementation and first results of the new space weather forecasting-targeted inner heliosphere model “European heliospheric forecasting information asset” (EUHFORIA) are presented. EUHFORIA consists of two major components: a coronal model and a heliosphere model including coronal mass ejections. The coronal model provides data-driven solar wind plasma parameters at 0.1 AU by constructing a magnetic field model of the coronal large-scale magnetic field and employing empirical relations to determine the plasma state such as the solar wind speed and mass density. These are then used as boundary conditions to drive a three-dimensional time-dependent magnetohydrodynamics model of the inner heliosphere up to 2 AU. CMEs are injected into the ambient solar wind modeled using the cone model, with their parameters obtained from fits to imaging observations. In addition to detailing the modeling methodology, an initial validation run is presented. The results feature a highly dynamic heliosphere that the model is able to capture in good agreement with in situ observations. Finally, future horizons for the model are outlined.

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