scholarly journals Plasma depletion layer: the role of the slow mode waves

2004 ◽  
Vol 22 (12) ◽  
pp. 4259-4272 ◽  
Author(s):  
Y. L. Wang ◽  
J. Raeder ◽  
C. T. Russell
Keyword(s):  
Solar Wind ◽  
Depletion Layer ◽  
Slow Mode ◽  
Local Flow ◽  
Flux Tubes ◽  
Mode Group ◽  
A New Technique ◽  
Plasma Depletion

Abstract. The plasma depletion layer (PDL) is a layer on the sunward side of the magnetopause with lower plasma density and higher magnetic field compared to their corresponding values in the upstream magnetosheath. The depletion layer usually occurs during northward (IMF) conditions with low magnetic shear across the magnetopause. We have previously validated the Raeder global model by comparing the computed formation of a magnetosheath density depletion with in-situ observations. We also have performed a detailed force analysis and found the varying roles that different MHD forces play along the path of a plasma parcel flowing around the magnetopause. That study resulted in a new description of the behavior of magnetosheath magnetic flux tubes which better explains the plasma depletion along a flux tube. The slow mode waves have been observed in the magnetosheath and have been used to explain the formation of the PDL in some of the important PDL models. In this study, we extend our former work by investigating the possible role of the slow mode waves for the formation of the PDL, using global MHD model simulations. We propose a new technique to test where a possible slow mode front may occur in the magnetosheath by comparing the slow mode group velocity with the local flow velocity. We find that the slow mode fronts can exist in certain regions in the magnetosheath under certain solar wind conditions. The existence and location of such fronts clearly depend on the IMF. We do not see from our global simulation results either the sharpening of the slow mode front into a slow mode shock or noticeable changes of the flow and field in the magnetosheath across the slow mode front, which implies that the slow mode front is not likely responsible for the formation of the PDL, at least for the stable solar wind conditions used in these simulations. Also, we do not see the two-layered slow mode structures shown in some observations and proposed in certain PDL models. Instead, we see only a one-layered spatial PDL structure under the stable solar wind conditions used in this study.

scholarly journals Plasma depletion layer: its dependence on solar wind conditions and the Earth dipole tilt

2004 ◽  
Vol 22 (12) ◽  
pp. 4273-4290 ◽  
Author(s):  
Y. L. Wang ◽  
J. Raeder ◽  
C. T. Russell
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Outer Boundary ◽  
Strong Dependence ◽  
Depletion Layer ◽  
Slow Mode ◽  
The Earth ◽  
Plasma Depletion ◽  
Dipole Tilt ◽  
The Imf

Abstract. The plasma depletion layer (PDL) is a layer on the sunward side of the magnetopause with lower plasma density and higher magnetic field compared to their corresponding upstream magnetosheath values. It is believed that the PDL is controlled jointly by conditions in the solar wind plasma and the (IMF). In this study, we extend our former model PDL studies by systematically investigating the dependence of the PDL and the slow mode front on solar wind conditions using global MHD simulations. We first point out the difficulties for the depletion factor method and the plasma β method for defining the outer boundary of the plasma depletion layer. We propose to use the N/B ratio to define the PDL outer boundary, which can give the best description of flux tube depletion. We find a strong dependence of the magnetosheath environment on the solar wind magnetosonic Mach number. A difference between the stagnation point and the magnetopause derived from the open-closed magnetic field boundary is found. We also find a strong and complex dependence of the PDL and the slow mode front on the IMF Bz. A density structure right inside the subsolar magnetopause for higher IMF Bz;might be responsible for some of this dependence. Both the IMF tilt and clock angles are found to have little influence on the magnetosheath and the PDL structures. However, the IMF geometry has a much stronger influence on the slow mode fronts in the magnetosheath. Finally, the Earth dipole tilt is found to play a minor role for the magnetosheath geometry and the PDL along the Sun-Earth line. A complex slow mode front geometry is found for cases with different Earth dipole tilts. Comparisons between our results with those from some former studies are conducted, and consistencies and inconsistencies are found. Key words. Magnetospheric physics (magnetosheath, solar wind-magnetosphere interactions) – Space plasma physics (numerical simulation studies)

scholarly journals Plasma depletion layer: Magnetosheath flow structure and forces

2004 ◽  
Vol 22 (3) ◽  
pp. 1001-1017 ◽  
Author(s):  
Y. L. Wang ◽  
J. Raeder ◽  
C. T. Russell
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Pressure Gradient ◽  
Flux Tube ◽  
Equatorial Plane ◽  
Depletion Layer ◽  
Gradient Force ◽  
Pressure Gradient Force ◽  
Slow Mode ◽  
Plasma Depletion

Abstract. The plasma depletion layer (PDL) is a layer on the sunward side of the magnetopause with lower plasma density and higher magnetic field compared to the corresponding upstream magnetosheath values. In a previous study, we have validated the UCLA global (MHD) model in studying the formation of the PDL by comparing model results, using spacecraft solar wind observations as the driver, with in situ PDL observations. In this study, we extend our previous work and examine the detailed MHD forces responsible for the PDL formation. We argue that MHD models, instead of gasdynamic models, should be used to study the PDL, because gasdynamic models cannot produce the PDL on the sunward side of the magnetopause. For northward (IMF), flux tube depletion occurs in almost all the subsolar magnetosheath. However, the streamlines closest to the magnetopause and the stagnation line show the greatest depletion. The relative strength of the various MHD forces changes along these streamlines. Forces along a flux tube at different stages of its depletion in the magnetosheath are analyzed. We find that a strong plasma pressure gradient force along the magnetic field at the bow shock and a pressure gradient force along the flux tube within the magnetosheath usually exist pushing plasma away from the equatorial plane to deplete the flux tube. More complex force structures along the flux tube are found close to the magnetopause. This new, more detailed description of flux tube depletion is compared with the results of Zwan and Wolf (1976) and differences are found. Near the magnetopause, the pressure gradient force along the flux tube either drives plasma away from the equatorial plane or pushes plasma toward the equatorial plane. As a result, a slow mode structure is seen along the flux tube which might be responsible for the observed two-layered slow mode structures. Key words. Magnetospheric physics (magnetosheath; solar wind-magnetosphere interactions). Space plasma physics (numerical simulations studies)

Source-dependent properties of the background slow solar wind encountered by Parker Solar Probe

2021 ◽  
Author(s):  
Léa Griton ◽  
Sarah Watson ◽  
Nicolas Poirier ◽  
Alexis Rouillard ◽  
Karine Issautier ◽  
...  
Keyword(s):  
Solar Wind ◽  
Extreme Ultraviolet ◽  
Plasma Heating ◽  
Coronal Holes ◽  
Slow Solar Wind ◽  
Source Surface ◽  
Field Source ◽  
Flux Tubes ◽  
Field Lines

<p>Different states of the slow solar wind are identified from in-situ measurements by Parker Solar Probe (PSP) inside 50 solar radii from the Sun (Encounters 1, 2, 4, 5 and 6). At such distances the wind measured at PSP has not yet undergone significant transformation related to the expansion and propagation of the wind. We focus in this study on the properties of the quiet solar wind with no magnetic switchbacks. The Slow Solar Wind (SSW) states differ by their density, flux, plasma beta and magnetic pressure. PSP's magnetic connectivity established with Potential Field Source Surface (PFSS) reconstructions, tested against extreme ultraviolet (EUV) and white-light imaging, reveals the different states under study generally correspond to transitions from streamers to equatorial coronal holes. Solar wind simulations run along these differing flux tubes reproduce the slower and denser wind measured in the streamer and the more tenuous wind measured in the coronal hole. Plasma heating is more intense at the base of the streamer field lines rooted near the boundary of the equatorial hole than those rooted closer to the center of the hole. This results in a higher wind flux driven inside the streamer than deeper inside the equatorial hole. </p>

In Situ Heating of the Nightside Martian Upper Atmosphere and Ionosphere: The Role of Solar Wind Electron Precipitation

2021 ◽  
Vol 909 (2) ◽  
pp. 108
Author(s):  
D.-D. Niu ◽  
J. Cui ◽  
H. Gu ◽  
X. -S. Wu ◽  
Y. -T. Cao ◽  
...  
Keyword(s):  
Solar Wind ◽  
Upper Atmosphere ◽  
Electron Precipitation ◽  
In Situ Heating ◽  
Solar Wind Electron

The forming slow solar wind imaged along streamer rays by the wide-angle imager on Parker Solar Probe

2020 ◽  
Author(s):  
Nicolas Poirier ◽  
Athanasios Kouloumvakos ◽  
Alexis P. Rouillard ◽  
Rui Pinto ◽  
Angelos Vourlidas ◽  
...  
Keyword(s):  
Solar Wind ◽  
Heliospheric Current Sheet ◽  
Slow Solar Wind ◽  
Wide Field ◽  
Flux Tubes ◽  
Solar Origin ◽  
High Resolution Images ◽  
The Individual ◽  
Coronal Structures

<p>The Wide-field Imager for Solar PRobe (WISPR) obtained the first high-resolution images of coronal rays at heights below 15 R<sub>sun</sub> when Parker Solar Probe (PSP) was located inside 0.25 AU during the first encounter. We exploit these remarkable images to reveal the structure of coronal rays at scales that are not easily discernible in images taken from near 1 AU. To analyze and interpret WISPR observations which evolve rapidly both radially and longitudinally, we construct a latitude versus time map using full WISPR dataset from the first encounter. From the exploitation of this map and also from sequential WISPR images we show the presence of multiple sub-structures inside streamers and pseudo-streamers. WISPR unveils the fine-scale structure of the densest part of streamer rays that we identify as the solar origin of the heliospheric plasma sheet typically measured in situ in the solar wind. We exploit 3-D magneto-hydrodynamic (MHD) models and we construct synthetic white-light images to study the origin of the coronal structures observed by WISPR. Overall, including the effect of the spacecraft relative motion towards the individual coronal structures we can interpret several observed features by WISPR. Moreover, we relate some coronal rays to folds in the heliospheric current sheet that are unresolved from 1 AU. Other rays appear to form as a result of the inherently inhomogeneous distribution of open magnetic flux tubes. This work was funded by the European Research Council through the project SLOW_SOURCE - DLV-819189.</p>

scholarly journals Magnetic helicity content in solar wind flux ropes

2008 ◽  
Vol 4 (S257) ◽  
pp. 379-389 ◽  
Author(s):  
Sergio Dasso
Keyword(s):  
Solar Wind ◽  
Interplanetary Medium ◽  
Dynamical Evolution ◽  
Magnetic Clouds ◽  
Magnetic Helicity ◽  
Flux Tubes ◽  
Global Configuration ◽  
Flux Ropes ◽  
Field Lines

AbstractMagnetic helicity (H) is an ideal magnetohydrodynamical (MHD) invariant that quantifies the twist and linkage of magnetic field lines. In magnetofluids with low resistivity, H decays much less than the energy, and it is almost conserved during times shorter than the global diffusion timescale. The extended solar corona (i.e., the heliosphere) is one of the physical scenarios where H is expected to be conserved. The amount of H injected through the photospheric level can be reorganized in the corona, and finally ejected in flux ropes to the interplanetary medium. Thus, coronal mass ejections can appear as magnetic clouds (MCs), which are huge twisted flux tubes that transport large amounts of H through the solar wind. The content of H depends on the global configuration of the structure, then, one of the main difficulties to estimate it from single spacecraft in situ observations (one point - multiple times) is that a single spacecraft can only observe a linear (one dimensional) cut of the MC global structure. Another serious difficulty is the intrinsic mixing between its spatial shape and its time evolution that occurs during the observation period. However, using some simple assumptions supported by observations, the global shape of some MCs can be unveiled, and the associated H and magnetic fluxes (F) can be estimated. Different methods to quantify H and F from the analysis of in situ observations in MCs are presented in this review. Some of these methods consider a MC in expansion and going through possible magnetic reconnections with its environment. We conclude that H seems to be a ‘robust’ MHD quantity in MCs, in the sense that variations of H for a given MC deduced using different methods, are typically lower than changes of H when a different cloud is considered. Quantification of H and F lets us constrain models of coronal formation and ejection of flux ropes to the interplanetary medium, as well as of the dynamical evolution of MCs in the solar wind.

scholarly journals Evolution of interplanetary coronal mass ejections and magnetic clouds in the heliosphere

2013 ◽  
Vol 8 (S300) ◽  
pp. 245-254
Author(s):  
Pascal Démoulin
Keyword(s):  
Solar Wind ◽  
Physical Properties ◽  
Coronal Mass Ejections ◽  
Magnetic Measurements ◽  
Flux Rope ◽  
Magnetic Clouds ◽  
The Sun ◽  
Interplanetary Coronal Mass Ejections

AbstractInterplanetary Coronal Mass Ejections (ICMEs), and more specifically Magnetic Clouds (MCs), are detected with in situ plasma and magnetic measurements. They are the continuation of the CMEs observed with imagers closer to the Sun. A review of their properties is presented with a focus on their magnetic configuration and its evolution. Many recent observations, both in situ and with imagers, point to a key role of flux ropes, a conclusion which is also supported by present coronal eruptive models. Then, is a flux rope generically present in an ICME? How to quantify its 3D physical properties when it is detected locally as a MC? Is it a simple flux rope? How does it evolve in the solar wind? This paper reviews our present answers and limited understanding to these questions.

scholarly journals MHD model of magnetosheath flow: comparison with AMPTE/IRM observations on 24 October, 1985

1998 ◽  
Vol 16 (5) ◽  
pp. 518-527 ◽  
Author(s):  
C. J. Farrugia ◽  
H. K. Biernat ◽  
N. V. Erkaev ◽  
L. M. Kistler ◽  
G. Le ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Steady State ◽  
Depletion Layer ◽  
Local Magnetic Field ◽  
Tangential Discontinuity ◽  
Stagnation Line ◽  
Line Flow ◽  
Mhd Model ◽  
Plasma Depletion

Abstract. We compare numerical results obtained from a steady-state MHD model of solar wind flow past the terrestrial magnetosphere with documented observations made by the AMPTE/IRM spacecraft on 24 October, 1985, during an inbound crossing of the magnetosheath. Observations indicate that steady conditions prevailed during this about 4 hour-long crossing. The magnetic shear at spacecraft entry into the magnetosphere was 15°. A steady density decrease and a concomitant magnetic field pile-up were observed during the 40 min interval just preceding the magnetopause crossing. In this plasma depletion layer (1) the plasma beta dropped to values below unity; (2) the flow speed tangential to the magnetopause was enhanced; and (3) the local magnetic field and velocity vectors became increasingly more orthogonal to each other as the magnetopause was approached (Phan et al., 1994). We model parameter variations along a spacecraft orbit approximating that of AMPTE/IRM, which was at slightly southern GSE latitudes and about 1.5 h post-noon Local Time. We model the magnetopause as a tangential discontinuity, as suggested by the observations, and take as input solar wind parameters those measured by AMPTE/IRM just prior to its bow shock crossing. We find that computed field and plasma profiles across the magnetosheath and plasma depletion layer match all observations closely. Theoretical predictions on stagnation line flow near this low-shear magnetopause are confirmed by the experimental findings. Our theory does not give, and the data on this pass do not show, any localized density enhancements in the inner magnetosheath region just outside the plasma depletion layer.Key words. Steady-state magnetosheath · Plasma depletion layer · Stagnation line flow

scholarly journals The structure and origin of magnetic clouds in the solar wind

1998 ◽  
Vol 16 (1) ◽  
pp. 1-24 ◽  
Author(s):  
V. Bothmer ◽  
R. Schwenn
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Magnetic Flux ◽  
Flux Tube ◽  
White Light ◽  
Large Scale ◽  
Magnetic Clouds ◽  
Flux Tubes ◽  
Magnetic Flux Tubes

Abstract. Plasma and magnetic field data from the Helios 1/2 spacecraft have been used to investigate the structure of magnetic clouds (MCs) in the inner heliosphere. 46 MCs were identified in the Helios data for the period 1974–1981 between 0.3 and 1 AU. 85% of the MCs were associated with fast-forward interplanetary shock waves, supporting the close association between MCs and SMEs (solar mass ejections). Seven MCs were identified as direct consequences of Helios-directed SMEs, and the passage of MCs agreed with that of interplanetary plasma clouds (IPCs) identified as white-light brightness enhancements in the Helios photometer data. The total (plasma and magnetic field) pressure in MCs was higher and the plasma-β lower than in the surrounding solar wind. Minimum variance analysis (MVA) showed that MCs can best be described as large-scale quasi-cylindrical magnetic flux tubes. The axes of the flux tubes usually had a small inclination to the ecliptic plane, with their azimuthal direction close to the east-west direction. The large-scale flux tube model for MCs was validated by the analysis of multi-spacecraft observations. MCs were observed over a range of up to ~60° in solar longitude in the ecliptic having the same magnetic configuration. The Helios observations further showed that over-expansion is a common feature of MCs. From a combined study of Helios, Voyager and IMP data we found that the radial diameter of MCs increases between 0.3 and 4.2 AU proportional to the distance, R, from the Sun as R0.8 (R in AU). The density decrease inside MCs was found to be proportional to R–2.4, thus being stronger compared to the average solar wind. Four different magnetic configurations, as expected from the flux-tube concept, for MCs have been observed in situ by the Helios probes. MCs with left- and right-handed magnetic helicity occurred with about equal frequencies during 1974–1981, but surprisingly, the majority (74%) of the MCs had a south to north (SN) rotation of the magnetic field vector relative to the ecliptic. In contrast, an investigation of solar wind data obtained near Earth's orbit during 1984–1991 showed a preference for NS-clouds. A direct correlation was found between MCs and large quiescent filament disappearances (disparition brusques, DBs). The magnetic configurations of the filaments, as inferred from the orientation of the prominence axis, the polarity of the overlying field lines and the hemispheric helicity pattern observed for filaments, agreed well with the in situ observed magnetic structure of the associated MCs. The results support the model of MCs as large-scale expanding quasi-cylindrical magnetic flux tubes in the solar wind, most likely caused by SMEs associated with eruptions of large quiescent filaments. We suggest that the hemispheric dependence of the magnetic helicity structure observed for solar filaments can explain the preferred orientation of MCs in interplanetary space as well as their solar cycle behavior. However, the white-light features of SMEs and the measured volumes of their interplanetary counterparts suggest that MCs may not simply be just Hα-prominences, but that SMEs likely convect large-scale coronal loops overlying the prominence axis out of the solar atmosphere.

scholarly journals The multi-scale nature of the solar wind

2019 ◽  
Vol 16 (1) ◽  
Author(s):  
Daniel Verscharen ◽  
Kristopher G. Klein ◽  
Bennett A. Maruca
Keyword(s):  
Solar Wind ◽  
Distribution Functions ◽  
Magnetized Plasma ◽  
Global Dynamics ◽  
Spatial And Temporal Scales ◽  
Multi Scale ◽  
Expansion Time ◽  
Collective Plasma

AbstractThe solar wind is a magnetized plasma and as such exhibits collective plasma behavior associated with its characteristic spatial and temporal scales. The characteristic length scales include the size of the heliosphere, the collisional mean free paths of all species, their inertial lengths, their gyration radii, and their Debye lengths. The characteristic timescales include the expansion time, the collision times, and the periods associated with gyration, waves, and oscillations. We review the past and present research into the multi-scale nature of the solar wind based on in-situ spacecraft measurements and plasma theory. We emphasize that couplings of processes across scales are important for the global dynamics and thermodynamics of the solar wind. We describe methods to measure in-situ properties of particles and fields. We then discuss the role of expansion effects, non-equilibrium distribution functions, collisions, waves, turbulence, and kinetic microinstabilities for the multi-scale plasma evolution.

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