Unusually low density regions in the compressed slow wind: Solar wind transients of small coronal hole origin

We report on two small solar wind transients embedded in the corotating interaction region, characterized by surprisingly lower proton density compared with their surrounding regions. In addition to lower density, these two small solar wind transients showed other interesting features like higher proton temperature, higher alpha-proton ratios, and lower charge states (C+6/C+5 and O+7/O+6). A synthesized picture for event One combining the observations by STEREO B, ACE, and Wind showed that this small solar transient has an independent magnetic field. Back-mapping links the origin of the small solar transient to a small coronal hole on the surface of the Sun. Considering these special features and the back-mapping, we conclude that such small solar wind transients may have originated from a small coronal hole at low latitudes.

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Relation Between Coronal Hole Areas on the Sun and the Solar Wind Parameters at 1 AU

Solar Physics ◽

10.1007/s11207-012-0101-y ◽

2012 ◽

Vol 281 (2) ◽

pp. 793-813 ◽

Cited By ~ 44

Author(s):

T. Rotter ◽

A. M. Veronig ◽

M. Temmer ◽

B. Vršnak

Keyword(s):

Solar Wind ◽

Coronal Hole ◽

The Sun ◽

Solar Wind Parameters

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Low Density Drivers of Strong Interplanetary Shocks

International Astronomical Union Colloquium ◽

10.1017/s0252921100029894 ◽

1996 ◽

Vol 154 ◽

pp. 5-13

Author(s):

A. Hewish

Keyword(s):

High Speed ◽

Solar Maximum ◽

Coronal Holes ◽

Strong Shock ◽

Low Density ◽

The Sun ◽

Interplanetary Shocks ◽

Fast Solar Wind ◽

Proton Temperature ◽

High Speed Flows

AbstractThe theory that most, if not all, interplanetary shocks are caused by coronal mass ejections (CMEs) faces serious problems in accounting for the strongest shocks. The difficulties include (i) a remarkable absence of very strong shocks during solar maximum 1980 when CMEs were prolific, (ii) unrealistic initial speeds near the Sun for impulsive models, (iii) the absence of rarefaction zones behind the shocks and (iv) sustained high speed flows following shocks which are not easily explained as consequences of CME eruptions. Observations of the proton temperature near 1 AU indicate that strong shock drivers have properties similar to high speed streams emitted by coronal holes. Eruptions of fast solar wind from coronal holes influenced by solar activity can explain the occurrence of the strongest interplanetary shocks.

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EISCAT measurements of the solar wind

Annales Geophysicae ◽

10.1007/s00585-996-1235-8 ◽

1996 ◽

Vol 14 (12) ◽

pp. 1235-1245 ◽

Cited By ~ 20

Author(s):

A. R. Breen ◽

W. A. Coles ◽

R. R. Grall ◽

M. T. Klinglesmith ◽

J. Markkanen ◽

...

Keyword(s):

Solar Wind ◽

Slow Solar Wind ◽

The Sun ◽

Interplanetary Scintillation ◽

Final Velocity ◽

Flow Vector ◽

Fast Wind ◽

Interaction Regions ◽

Slow Wind ◽

Eiscat Measurements

Abstract. EISCAT observations of interplanetary scintillation have been used to measure the velocity of the solar wind at distances between 15 and 130 R⊙ (solar radii) from the Sun. The results show that the solar wind consists of two distinct components, a fast stream with a velocity of ~800 km s–1 and a slow stream at ~400 km s–1. The fast stream appears to reach its final velocity much closer to the Sun than expected. The results presented here suggest that this is also true for the slow solar wind. Away from interaction regions the flow vector of the solar wind is purely radial to the Sun. Observations have been made of fast wind/slow wind interactions which show enhanced levels of scintillation in compression regions.

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Formation of current sheets and plasmoids within corotating/stream interaction regions

10.5194/egusphere-egu2020-2102 ◽

2020 ◽

Author(s):

Timofey Sagitov ◽

Roman Kislov

Keyword(s):

Magnetic Field ◽

Solar Wind ◽

Coronal Hole ◽

High Speed ◽

Solar Rotation ◽

Coronal Holes ◽

Rotation Period ◽

The Sun ◽

Current Sheets ◽

Interaction Regions

<p>High speed streams originating from coronal holes are long-lived plasma structures that form corotating interaction regions (CIRs) or stream interface regions (SIRs) in the solar wind. The term CIR is used for streams existing for at least one solar rotation period, and the SIR stands for streams with a shorter lifetime. Since the plasma flows from coronal holes quasi-continuously, CIRs/SIRs simultaneously expand and rotate around the Sun, approximately following the Parker spiral shape up to the Earth&#8217;s orbit.</p><p>Coronal hole streams rotate not only around the Sun but also around their own axis of simmetry, resembling a screw. This effect may occur because of the following mechanisms: (1) the existence of a difference between the solar wind speed at different sides of the stream, (2) twisting of the magnetic field frozen into the plasma, and&#160; (3) a vortex-like motion of the edge of the mothering coronal hole at the Sun. The screw type of the rotation of a CIR/SIR can lead to centrifugal instability if CIR/SIR inner layers have a larger angular velocity than the outer. Furthermore, the rotational plasma movement and the stream distortion can twist magnetic field lines. The latter contributes to the pinch effect in accordance with a well-known criterion of Suydam instability (Newcomb, 1960, doi: 10.1016/0003-4916(60)90023-3). Owing to the presence of a cylindrical current sheet at the boundary of a coronal hole, conditions for tearing instability can also appear at the CIR/SIR boundary. Regardless of their geometry, large scale current sheets are subject to various instabilities generating plasmoids. Altogether, these effects can lead to the formation of a turbulent region within CIRs/SIRs, making them filled with current sheets and plasmoids.&#160;</p><p>We study a substructure of CIRs/SIRs, characteristics of their rotation in the solar wind, and give qualitative estimations of possible mechanisms which lead to splitting of the leading edge a coronal hole flow and consequent formation of current sheets within CIRs/SIRs.</p>

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Evidence for Plasma Heating at Thin Current Sheets in the Solar Wind

The Astrophysical Journal ◽

10.3847/2041-8213/ac4701 ◽

2022 ◽

Vol 924 (2) ◽

pp. L22

Author(s):

Zilu Zhou ◽

Xiaojun Xu ◽

Pingbing Zuo ◽

Yi Wang ◽

Qi Xu ◽

...

Keyword(s):

Magnetic Field ◽

Solar Wind ◽

Plasma Heating ◽

Magnetic Field Direction ◽

Current Sheets ◽

Proton Temperature ◽

Fast Wind ◽

Wind Spacecraft ◽

Slow Wind ◽

The Magnetic Field

Abstract Plasma heating at thin current sheets in the solar wind is examined using magnetic field and plasma data obtained by the WIND spacecraft in the past 17 years from 2004 to 2019. In this study, a thin current sheet is defined by an abrupt rotation (larger than 45°) of the magnetic field direction in 3 s. A total of 57,814 current sheets have been identified, among which 25,018 current sheets are located in the slow wind and 19,842 current sheets are located in the fast wind. Significant plasma heating is found at current sheets in both slow and fast wind. Proton temperature increases more significantly at current sheets in the fast wind than in the slow wind, while the enhancement in electron temperature is less remarkable at current sheets in the fast wind. The results reveal that plasma heating commonly exists at thin current sheets in the solar wind regardless of the wind speed, but the underlying heating mechanisms might be different.

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Radial Evolution of the Solar Wind and Associating Turbulence Based on the Synergetic Measurement from Parker Solar Probe and 1 au Observations

10.5194/egusphere-egu21-15718 ◽

2021 ◽

Author(s):

Die Duan ◽

Jiansen He ◽

Xingyu Zhu ◽

Daniel Verscharen ◽

Trevor Bowen ◽

...

Keyword(s):

Solar Wind ◽

Slow Waves ◽

Proton Density ◽

The Sun ◽

Wind Model ◽

Great Opportunity ◽

Extra Energy ◽

Earth Environment ◽

Radial Evolution ◽

Inner Heliosphere

<div> <div>The 4th encounter (~30 Rs away from the sun) of the Parker Solar Probe (PSP) is a great opportunity to observe the radial evolution of the solar wind from the inner heliosphere to the near-earth environment when the sun, PSP, and the earth are quasi-radial aligned. Similar features of the solar wind are observed from both PSP and Wind (at 1 au) measurements. The accelerating-solar-wind model could be more suitable than the constant speed model for the observation, which means the solar wind is still accelerating from 30 Rs to 1 au. Both PSP and Wind measure the co-existence of the Alfvenic and compressive fluctuations in the solar wind. The correlated radial velocity (dVR), proton density (dn) and temperature (dT) fluctuations indicate the nature of the compressive fluctuations are outward-propagating slow waves. However, dn and dB is not correlated from PSP, but correlated from Wind, which indicates the propagating direction of the slow waves is changed. Comparing the radial evolution of the energies of both Alfvenic and compressive fluctuations with the WKB model, we find the observed energy decays slower than the theoretical prediction, which indicates an extra energy injection during the solar wind propagation.</div> </div><p></p>

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Numerical Simulation on the Propagation and Deflection of Fast Coronal Mass Ejections (CMEs) Interacting with a Corotating Interaction Region in Interplanetary Space

10.5194/egusphere-egu2020-1815 ◽

2020 ◽

Author(s):

Fang Shen ◽

Yousheng Liu ◽

Yi Yang

Keyword(s):

Solar Wind ◽

Coronal Mass Ejections ◽

Interplanetary Space ◽

Three Dimensional ◽

Flux Rope ◽

Interaction Region ◽

The Sun ◽

Corotating Interaction Region ◽

The Common ◽

Wind Flows

<p>Previous research has shown that the deflection of coronal mass ejections (CMEs) in interplanetary space, especially fast CMEs, is a common phenomenon. The deflection caused by the interaction with background solar wind is an important factor to determine whether CMEs could hit Earth or not. As the Sun rotates, there will be interactions between solar wind flows with different speeds. When faster solar wind runs into slower solar wind<br>ahead, it will form a compressive area corotating with the Sun, which is called a corotating interaction region (CIR). These compression regions always have a higher density than the common background solar wind. When interacting with CME, will this make a difference in the deflection process of CME? In this research, first, a three-dimensional (3D) flux-rope CME initialization model is established based on the graduated cylindrical shell (GCS)<br>model. Then this CME model is introduced into the background solar wind, which is obtained using a 3D IN (INterplanetary) -TVD-MHD model. The Carrington Rotation (CR) 2154 is selected as an example to simulate the propagation and deflection of fast CME when it interacts with background solar wind, especially with the CIR structure.</p><p>The simulation results show that: (1) the fast CME will deflect eastward when it propagates into the background solar wind without the CIR; (2) when the fast CME hits the CIR on its west side, it will also deflect eastward, and the deflection angle will increase compared with the situation without CIR.</p>

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Solar-Wind Structure

Oxford Research Encyclopedia of Physics ◽

10.1093/acrefore/9780190871994.013.19 ◽

2020 ◽

Author(s):

Mathew J. Owens

Keyword(s):

Magnetic Field ◽

Solar Wind ◽

Interstellar Medium ◽

Solar Atmosphere ◽

Solar Surface ◽

Spatial Scales ◽

The Sun ◽

Archimedean Spiral ◽

Fast Wind ◽

Slow Wind

The hot solar atmosphere continually expands out into space to form the solar wind, which drags with it the Sun’s magnetic field. This creates a cavity in the interstellar medium, extending far past the outer planets, within which the solar magnetic-field dominates. While the physical mechanisms by which the solar atmosphere is heated are still debated, the resulting solar wind can be readily understood in terms of the pressure difference between the hot, dense solar atmosphere and the cold, tenuous interstellar medium. This results in an accelerating solar-wind profile which becomes supersonic long before it reaches Earth orbit. The large-scale structure of the magnetic field carried by the solar wind is that of an Archimedean spiral, owing to the radial solar-wind flow away from the Sun and the rotation of the magnetic footpoints with the solar surface. Within this relatively simple picture, however, is a range of substructure, on all observable time and spatial scales. Solar-wind flows are largely bimodal in character. “Fast” wind comes from open magnetic-field regions, which have a single connection to the solar surface. “Slow” wind, on the other hand, appears to come from the vicinity of closed magnetic field regions, which have both ends connected to the Sun. Interaction of fast and slow wind leads to patterns of solar-wind compression and expansion which sweep past Earth. Within this relatively stable structure of flows, huge episodic eruptions of solar material further perturb conditions. At the smaller scales, turbulent eddies create unpredictable variations in solar-wind conditions. These solar-wind structures are of great interest as they give rise to space weather that can adversely affect space- and ground-based technologies, as well as pose a threat to humans in space.

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ICMEs and low plasma density in the solar wind observed at L1

10.5194/egusphere-egu21-1799 ◽

2021 ◽

Author(s):

Brigitte Schmieder ◽

Christine Verbeke ◽

Emmanuel Chané ◽

Pascal Démoulin ◽

Stefaan Poedts ◽

...

Keyword(s):

Solar Wind ◽

Plasma Density ◽

Flux Rope ◽

Low Density ◽

The Sun ◽

Left Behind ◽

Fast Speed ◽

First Case ◽

Low Density Plasma ◽

Density Plasma

<p>Different regimes of the solar wind have been observed at L1 during and after the passage of ICMEs, particularly anomalies with very low plasma density. From the observations at L1 (ACE) we identified different possible cases. A first case was explained by the evacuation of the plasma due over expansion of the ICME (May 2002). The second case on July 2002 is intriguing.In July 2002, three halo fast speed ICMEs, with their origin in the central part of the Sun, have surprisingly a poor impact on the magnetosphere (Dst > -28 nT).&#160;&#160; Analyzing the characteristics of the first ICME at L1, we conclude that the spacecraft crosses the ICME with a large impact (Bx component in GSE coordinates is dominant). The plasma density is low, just behind this first ICME. Next, we explore the generic conditions of low density formation in the EUHFORIA simulations.The very low density plasma after the sheath could be explained by the spacecraft crossing, on the side of the flux rope, while behind the front shock. We investigate two possible interpretations. The shock was able to compress and accelerate so much the plasma that a lower density is left behind. This can also be due to an effect of the sheath magnetic field which extends the flux rope &#160;effect on the sides of it, &#160;&#160;&#160;so a decrease of plasma density could occur like behind a moving object (here the sheath field). The following ICME, with also a low density, could be an intrinsic case with the formation in the corona of a cavity. Finally, we present some runs of EUHFORIA which fit approximately these data and argue in favor of the possible interpretations detailed above.</p>

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Alfvénic turbulence in solar wind originating near coronal hole boundaries: heavy-ion effects?

Annales Geophysicae ◽

10.5194/angeo-24-785-2006 ◽

2006 ◽

Vol 24 (2) ◽

pp. 785-789 ◽

Cited By ~ 1

Author(s):

B. Bavassano ◽

N. A. Schwadron ◽

E. Pietropaolo ◽

R. Bruno

Keyword(s):

Magnetic Field ◽

Solar Wind ◽

Coronal Hole ◽

Field Measurements ◽

Heavy Ion ◽

Parker Spiral ◽

Fast Wind ◽

Ion Effects ◽

Field Lines ◽

Slow Wind

Abstract. The mid-latitude phases of the Ulysses mission offer an excellent opportunity to investigate the solar wind originating near the coronal hole boundaries. Here we report on Alfvénic turbulence features, revealing a relevant presence of in-situ generated fluctuations, observed during the wind rarefaction phase that charaterizes the transition from fast to slow wind. Heavy-ion composition and magnetic field measurements indicate a strict time correspondence of the locally generated fluctuations with 1) the crossing of the interface between fast and slow wind and 2) the presence of strongly underwound magnetic field lines (with respect to the Parker spiral). Recent studies suggest that such underwound magnetic configurations correspond to fast wind magnetic lines that, due to footpoint motions at the Sun, have their inner leg transferred to slow wind and are stretched out by the velocity gradient. If this is a valid scenario, the existence of a magnetic connection across the fast-slow wind interface is a condition that, given the different state of the two kinds of wind, may favour the development of processes acting as local sources of turbulence. We suggest that heavy-ion effects could be responsible of the observed turbulence features.

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