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.

scholarly journals Interplanetary conditions: lessons from this minimum

2011 ◽  
Vol 7 (S286) ◽  
pp. 168-178 ◽  
Author(s):  
J. Luhmann ◽  
C. O. Lee ◽  
P. Riley ◽  
L. K. Jian ◽  
C. T. Russell ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Solar Minimum ◽  
Large Scale ◽  
Coronal Magnetic Field ◽  
Source Surface ◽  
Field Source ◽  
Mass Fluxes ◽  
Solar Wind Structure ◽  
Cycle 24

AbstractInterplanetary conditions during the Cycle 23-24 minimum have attracted attention because they are noticeably different than those during other minima of the space age, exhibiting more solar wind stream interaction structures in addition to reduced mass fluxes and low magnetic field strengths. In this study we consider the differences in the solar wind source regions by applying Potential Field Source Surface models of the coronal magnetic field. In particular, we consider the large scale coronal field geometry that organizes the open field region locations and sizes, and the appearance of the helmet streamer structure that is another determiner of solar wind properties. The recent cycle minimum had an extraordinarily long entry phase (the decline of Cycle 23) that made it difficult to identify when the actual miminum arrived. In particular, the late 23rd cycle was characterized by diminishing photospheric fields and complex coronal structures that took several extra years to simplify to its traditional dipolar solar minimum state. The nearly dipolar phase, when it arrived, had a duration somewhat shorter than those of the previous cycles. The fact that the corona maintained an appearance more like a solar maximum corona through most of the quiet transitional phase between Cycles 23 and 24 gave the impression of a much more complicated solar minimum solar wind structure in spite of the weaknesses of the mass flux and interplanetary field. The extent to which the Cycle 23-24 transition will affect Cycle 24, and/or represents what happens during weak cycles in general, remains to be seen.

Empirical inner boundary conditions and rotation rates for solar wind models

2021 ◽  
Author(s):  
Huw Morgan
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Boundary Conditions ◽  
Coronal Magnetic Field ◽  
Height Range ◽  
Rotation Rates ◽  
Wind Structure ◽  
Solar Wind Structure ◽  
Coronal Electron ◽  
Made In

<p>To date, the inner boundary conditions for solar wind models are either directly or indirectly based on magnetic field extrapolation models of the photosphere. Furthermore, between the photosphere and Earth, there are no other direct empirical constraints on models. New breakthroughs in coronal rotation tomography, applied to coronagraph observations, allow maps of the coronal electron density to be made in the heliocentric height range 4-12 solar radii (Rs). We show that these maps (i) give a new empirical boundary condition for solar wind structure at a height where the coronal magnetic field has become radial, thus avoiding the need to model the complex inner coronal magnetic field, and (ii) give accurate rotation rates for the corona, of crucial importance to the accuracy of solar wind models and forecasts.</p>

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 solar-wind structure near the Sun detected by Doppler scintillation

Nature ◽  
1993 ◽  
Vol 366 (6455) ◽  
pp. 543-545 ◽  
Author(s):  
Richard Woo ◽  
Paul Gazis
Keyword(s):  
Solar Wind ◽  
Large Scale ◽  
The Sun ◽  
Wind Structure ◽  
Solar Wind Structure

scholarly journals DIVISION E COMMISSION 49: INTERPLANETARY PLASMA AND HELIOSPHERE

2015 ◽  
Vol 11 (T29A) ◽  
pp. 300-315
Author(s):  
Ingrid Mann ◽  
P. K. Manoharan ◽  
Natchimuthuk Gopalswamy ◽  
Carine Briand ◽  
Igor V. Chashei ◽  
...  
Keyword(s):  
Solar Wind ◽  
Historical Context ◽  
Work Related ◽  
Wind Structure ◽  
Solar Wind Structure ◽  
Long Time ◽  
Interplanetary Plasma ◽  
Similar Area ◽  
Cycle 24

AbstractAfter a little more than forty years of work related to the interplanetary plasma and the heliosphere the IAU's Commission 49 was formally discontinued in 2015. The commission started its work when the first spacecraft were launched to measure the solar wind in–situ away from Earth orbit, both inward and outward from 1 AU. It now hands over its activities to a new commission during an era of space research when Voyager 1 measures in–situ the parameters of the local interstellar medium at the edge of the heliosphere. The commission will be succeeded by C.E3 with a similar area of responsibility but with more focused specific tasks that the community intends to address during the coming several years. This report includes a short description of the motivation for this commission and of the historical context. It then describes work from 2012 to 2015 during the present solar cycle 24 that has been the weakest in the space era so far. It gave rise to a large number of studies on solar energetic particles and cosmic rays. Other studies addressed e.g. the variation of the solar wind structure and energetic particle fluxes on long time scales, the detection of dust in the solar wind and the Voyager measurements at the edge of the heliosphere. The research is based on measurements from spacecraft that are at present operational and motivated by the upcoming Solar Probe + and Solar Orbiter missions to explore the vicinity of the Sun. We also report here the progress on new and planned radio instruments and their importance for heliospheric studies. Contributors to this report are Carine Briand, Yoichiro Hanaoka, Eduard Kontar, David Lario, Ingrid Mann, John D. Richardson.

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>

Large scale solar wind structure: Non-dipolar features and consequences

2013 ◽  
Author(s):  
J. G. Luhmann ◽  
M. Ellenburg ◽  
P. Riley ◽  
D. Odstrcil ◽  
G. Petrie ◽  
...  
Keyword(s):  
Solar Wind ◽  
Large Scale ◽  
Wind Structure ◽  
Solar Wind Structure

scholarly journals On the relationship between magnetic cloud field polarity and geoeffectiveness

2012 ◽  
Vol 30 (7) ◽  
pp. 1037-1050 ◽  
Author(s):  
E. K. J. Kilpua ◽  
Y. Li ◽  
J. G. Luhmann ◽  
L. K. Jian ◽  
C. T. Russell
Keyword(s):  
Solar Wind ◽  
Opposite Polarity ◽  
Magnetic Clouds ◽  
Solar Cycles ◽  
Field Polarity ◽  
Wind Structure ◽  
Intense Storm ◽  
Solar Wind Structure ◽  
Speed Solar Wind ◽  
Cycle 24

Abstract. In this paper, we have investigated geoeffectivity of near-Earth magnetic clouds during two periods concentrated around the last two solar minima. The studied magnetic clouds were categorised according to the behaviour of the Z-component of the interplanetary magnetic field (BZ) into bipolar (BZ changes sign) and unipolar (BZ maintains its sign) clouds. The magnetic structure of bipolar clouds followed the solar cycle rule deduced from observations over three previous solar cycles, except during the early rising phase of cycle 24 when both BZ polarities were identified almost with the same frequency. We found a clear difference in the number of unipolar clouds whose axial field points south (S-type) between our two study periods. In particular, it seems that the lack of S-type unipolar clouds contributed to relatively low geomagnetic activity in the early rising phase of cycle 24. We estimated the level of magnetospheric activity using a Dst prediction formula with the measured BZ and by reversing the sign of BZ. We found that bipolar clouds with fields rotating south-to-north (SN) and north-to-south (NS) were equally geoeffective, but their geoeffectiveness was clearly modified by the ambient solar wind structure. Geoeffectivity of NS-polarity clouds was enhanced when they were followed by a higher-speed solar wind, while the majority of geoeffective SN-polarity clouds lacked the trailing faster wind. A leading shock increased the geoeffectiveness of both NS- and SN-polarity clouds, in particular, in the case of an intense storm. We found that in 1995–1998, SN-polarity clouds were more geoeffective, while in 2006–2011 NS-polarity clouds produced more storms. A considerably larger fraction of events were trailed by a higher-speed solar wind during our latter study period, which presumably increased geoeffectivity of NS-polarity. Thus, our study demonstrates that during low and moderate solar activity, geoeffectivity of opposite polarity bipolar clouds may depend significantly on the surrounding solar wind structure. In addition, different polarities also give different temporal storm evolutions: a storm from an SN-polarity cloud is expected to occur, on average, half-a-day earlier than a storm from an NS-polarity cloud.

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