Evolving Solar Wind Flow Properties of Magnetic Inversions Observed by Helios

Abstract In its first encounter at solar distances as close as r = 0.16AU, Parker Solar Probe (PSP) observed numerous local reversals, or inversions, in the heliospheric magnetic field (HMF), which were accompanied by large spikes in solar wind speed. Both solar and in situ mechanisms have been suggested to explain the existence of HMF inversions in general. Previous work using Helios 1, covering 0.3–1AU, observed inverted HMF to become more common with increasing r, suggesting that some heliospheric driving process creates or amplifies inversions. This study expands upon these findings, by analysing inversion-associated changes in plasma properties for the same large data set, facilitated by observations of ‘strahl’ electrons to identify the unperturbed magnetic polarity. We find that many inversions exhibit anti-correlated field and velocity perturbations, and are thus characteristically Alfvénic, but many also depart strongly from this relationship over an apparent continuum of properties. Inversions depart further from the ‘ideal’ Alfvénic case with increasing r, as more energy is partitioned in the field, rather than the plasma, component of the perturbation. This departure is greatest for inversions with larger density and magnetic field strength changes, and characteristic slow solar wind properties. We find no evidence that inversions which stray further from ‘ideal’ Alfvénicity have different generation processes from those which are more Alfvénic. Instead, different inversion properties could be imprinted based on transport or formation within different solar wind streams.

Download Full-text

MHD effects of the solar wind flow around planets

Nonlinear Processes in Geophysics ◽

10.5194/npg-7-201-2000 ◽

2000 ◽

Vol 7 (3/4) ◽

pp. 201-210 ◽

Cited By ~ 2

Author(s):

H. K. Biernat ◽

N. V. Erkaev ◽

C. J. Farrugia ◽

D. F. Vogl ◽

W. Schaffenberger

Keyword(s):

Magnetic Field ◽

Solar Wind ◽

Mach Number ◽

Boundary Conditions ◽

Wind Flow ◽

Magnetic Shear ◽

Thermal Anisotropy ◽

Terrestrial Magnetosphere ◽

Solar Wind Flow

Abstract. The study of the interaction of the solar wind with magnetized and unmagnetized planets forms a central topic of space research. Focussing on planetary magnetosheaths, we review some major developments in this field. Magnetosheath structures depend crucially on the orientation of the interplanetary magnetic field, the solar wind Alfvén Mach number, the shape of the obstacle (axisymmetric/non-axisymmetric, etc.), the boundary conditions at the magnetopause (low/high magnetic shear), and the degree of thermal anisotropy of the plasma. We illustrate the cases of Earth, Jupiter and Venus. The terrestrial magnetosphere is axisymmetric and has been probed in-situ by many spacecraft. Jupiter's magnetosphere is highly non-axisymmetric. Furthermore, we study magnetohydrodynamic effects in the Venus magnetosheath.

Download Full-text

Understanding Solar Wind Formation by Identifying the Origins of In Situ Observations

10.5194/egusphere-egu21-6200 ◽

2021 ◽

Author(s):

Samantha Wallace ◽

Nicholeen M. Viall ◽

Charles N. Arge

Keyword(s):

Solar Wind ◽

Solar Wind Speed ◽

Source Region ◽

Heliospheric Current Sheet ◽

Slow Solar Wind ◽

The Sun ◽

Flux Transport ◽

Model Driven ◽

In Situ Observations

Solar wind formation can be separated into three physical steps &#8211; source, release, and acceleration &#8211; that each leave distinct observational signatures on plasma parcels.&#160; The Wang-Sheeley-Arge (WSA) model driven by Air Force Data Assimilative Photospheric Flux Transport (ADAPT) time-dependent photospheric field maps now has the ability to connect in situ observations more rigorously to their precise source at the Sun, allowing us to investigate the physical processes involved in solar wind formation. &#160;&#160;In this talk, I will highlight my PhD dissertation research in which we use the ADAPT-WSA model to either characterize the solar wind emerging from specific sources, or investigate the formation process of various solar wind populations. &#160;In the first study, we test the well-known inverse relationship between expansion factor (fs) and observed solar wind speed (vobs) for solar wind that emerges from a large sampling of pseudostreamers, to investigate if field line expansion plays a physical role in accelerating the solar wind from this source region.&#160; We find that there is no correlation between fs and vobs at pseudostreamer cusps. In the second study, we determine the source locations of the first identified quasiperiodic density structures (PDSs) inside 0.6 au. Our modeling provides confirmation of these events forming via magnetic reconnection both near to and far from the heliospheric current sheet (HCS) &#8211; a direct test of the Separatrix-web (S-web) theory of slow solar wind formation.&#160; In the final study, we use our methodology to identify the source regions of the first observations from the Parker Solar Probe (PSP) mission.&#160; Our modeling enabled us to characterize the closest to the Sun observed coronal mass ejection (CME) to date as a streamer blowout.&#160; We close with future ways that ADAPT-WSA can be used to test outstanding questions of solar wind formation.

Download Full-text

Quantifying the latitudinal representivity of in situ solar wind observations

Journal of Space Weather and Space Climate ◽

10.1051/swsc/2020009 ◽

2020 ◽

Vol 10 ◽

pp. 8 ◽

Cited By ~ 1

Author(s):

Mathew J. Owens ◽

Matthew Lang ◽

Pete Riley ◽

Mike Lockwood ◽

Amos S. Lawless

Keyword(s):

Magnetic Field ◽

Solar Wind ◽

Wind Speed ◽

Solar Minimum ◽

Numerical Models ◽

Solar Wind Speed ◽

Cycle Phase ◽

Model State ◽

Fast Wind

Advanced space-weather forecasting relies on the ability to accurately predict near-Earth solar wind conditions. For this purpose, physics-based, global numerical models of the solar wind are initialized with photospheric magnetic field and coronagraph observations, but no further observation constraints are imposed between the upper corona and Earth orbit. Data assimilation (DA) of the available in situ solar wind observations into the models could potentially provide additional constraints, improving solar wind reconstructions, and forecasts. However, in order to effectively combine the model and observations, it is necessary to quantify the error introduced by assuming point measurements are representative of the model state. In particular, the range of heliographic latitudes over which in situ solar wind speed measurements are representative is of primary importance, but particularly difficult to assess from observations alone. In this study we use 40+ years of observation-driven solar wind model results to assess two related properties: the latitudinal representivity error introduced by assuming the solar wind speed measured at a given latitude is the same as that at the heliographic equator, and the range of latitudes over which a solar wind measurement should influence the model state, referred to as the observational localisation. These values are quantified for future use in solar wind DA schemes as a function of solar cycle phase, measurement latitude, and error tolerance. In general, we find that in situ solar wind speed measurements near the ecliptic plane at solar minimum are extremely localised, being similar over only 1° or 2° of latitude. In the uniform polar fast wind above approximately 40° latitude at solar minimum, the latitudinal representivity error drops. At solar maximum, the increased variability of the solar wind speed at high latitudes means that the latitudinal representivity error increases at the poles, though becomes greater in the ecliptic, as long as moderate speed errors can be tolerated. The heliospheric magnetic field and solar wind density and temperature show very similar behaviour.

Download Full-text

Analysis of the Internal structure of the Streamer Blow Out Observed by the Parker Solar Probe during the First Solar Encounter

10.5194/egusphere-egu2020-22182 ◽

2020 ◽

Author(s):

Teresa Nieves-Chinchilla ◽

Adam Szabo ◽

Kelly E. Korreck ◽

Nathalia Alzate ◽

Laura A. Balmaceda ◽

...

Keyword(s):

Magnetic Field ◽

Solar Wind ◽

Internal Structure ◽

Flux Rope ◽

Internal Force ◽

Slow Solar Wind ◽

Angle Distribution ◽

The Hours ◽

The Magnetic Field

We present an analysis of the internal structure of a coronal mass ejection (CME)&#160;detected by in situ&#160;instruments onboard the Parker Solar Probe (PSP) spacecraft during its first solar&#160;encounter. On 2018 November 11 at 23:53 UT, the FIELDS magnetometer measured an increase&#160;in strength of the magnetic field as well as a coherent change in the field direction. The SWEAP&#160;instrument simultaneously detected the low proton temperature and signatures of bi-directionality in&#160;the electron pitch angle distribution (PAD). These signatures are indicative of a CME embedded in the&#160;slow solar wind. In conjunction with PSP was the STEREO A spacecraft, which enabled the remote&#160;observation of a streamer blow-out by the SECCHI suite of instruments. The source at the Sun of&#160;the slow and well-structured&#160;flux-rope was identified in an overlying streamer.Our detailed inspection of the internal transient structure magnetic properties suggests high complexity&#160;in deviations from an ideal&#160;flux rope 3D topology. Reconstructions of the magnetic field&#160;conguration reveal a highly distorted structure consistent with the highly elongated `bubble' observed&#160;remotely. A double-ring substructure observed in the SECCHI-COR2 eld of view (FOV) is&#160;suggestive of a double internal&#160;flux rope. Furthermore, we describe a scenario in which mixed topology&#160;of a closed&#160;flux rope is combined with the magnetically open structure, which helps explain the&#160;flux&#160;dropout observed in the measurements of the electron PAD. Our justication for this is the plethora&#160;of structures observed by the EUV imager (SECCHI-EUVI) in the hours preceding the streamer blowout&#160;evacuation. Finally, taking advantage of the unique observations from PSP, we explore the first&#160;stages of the effects of coupling with the solar wind and the evolutionary processes in the magnetic&#160;structure. We found evidence of bifurcated current sheets in the structure boundaries suggestive of&#160;magnetic reconnection. Our analysis of the internal force imbalance indicates that internal Lorentz&#160;forces continue to dominate the evolution of the structure in the COR2 FOV and serves as the main&#160;driver of the internal&#160;flux rope distortion as detected in situ at PSP solar distance.

Download Full-text

Automatic parameterization for magnetometer zero offset determination

Geoscientific Instrumentation Methods and Data Systems ◽

10.5194/gi-1-103-2012 ◽

2012 ◽

Vol 1 (2) ◽

pp. 103-109 ◽

Cited By ~ 3

Author(s):

M. A. Pudney ◽

C. M. Carr ◽

S. J. Schwartz ◽

S. I. Howarth

Keyword(s):

Magnetic Field ◽

Solar Wind ◽

Field Measurements ◽

Slow Solar Wind ◽

Fixed Parameter ◽

Zero Offset ◽

Parameter Approach ◽

The Magnetic Field ◽

Key Parameter

Abstract. In-situ magnetic field measurements are of critical importance in understanding how the Sun creates and controls the heliosphere. To ensure the measurements are accurate, it is necessary to track the combined slowly varying spacecraft magnetic field and magnetometer zero offset – the systematic error in the sensor measurements. For a 3-axis stabilised spacecraft, in-flight correction of zero offsets primarily relies on the use of Alfvénic rotations in the magnetic field. We present a method to automatically determine a key parameter related to the ambient compressional variance of the signal (which determines the selection criteria for identifying clear Alfvénic rotations). We apply our method to different solar wind conditions, performing a statistical analysis of the data periods required to achieve a 70% chance of calculating an offset using Helios datasets. We find that 70% of 40 min data periods in regions of fast solar wind possess sufficient rotational content to calculate an offset. To achieve the same 70% calculation probability in regions of slow solar wind requires data periods of 2 h duration. We also find that 40 min data periods at perihelion compared to 1 h and 40 min data periods at aphelion are required to achieve the same 70% calculation probability. We compare our method with previous work that uses a fixed parameter approach and demonstrate an improvement in the calculation probability of up to 10% at aphelion and 5% at perihelion.

Download Full-text

Number density structures in the inner heliosphere

Astronomy and Astrophysics ◽

10.1051/0004-6361/201732567 ◽

2018 ◽

Vol 613 ◽

pp. A62 ◽

Cited By ~ 7

Author(s):

D. Stansby ◽

T. S. Horbury

Keyword(s):

Solar Wind ◽

Distribution Functions ◽

Slow Solar Wind ◽

Number Density ◽

Ion Distribution ◽

Pressure Balance ◽

Data Set ◽

Wide Range ◽

Inner Heliosphere

Aims. The origins and generation mechanisms of the slow solar wind are still unclear. Part of the slow solar wind is populated by number density structures, discrete patches of increased number density that are frozen in to and move with the bulk solar wind. In this paper we aimed to provide the first in-situ statistical study of number density structures in the inner heliosphere. Methods. We reprocessed in-situ ion distribution functions measured by Helios in the inner heliosphere to provide a new reliable set of proton plasma moments for the entire mission. From this new data set we looked for number density structures measured within 0.5 AU of the Sun and studied their properties. Results. We identified 140 discrete areas of enhanced number density. The structures occurred exclusively in the slow solar wind and spanned a wide range of length scales from 50 Mm to 2000 Mm, which includes smaller scales than have been previously observed. They were also consistently denser and hotter that the surrounding plasma, but had lower magnetic field strengths, and therefore remained in pressure balance. Conclusions. Our observations show that these structures are present in the slow solar wind at a wide range of scales, some of which are too small to be detected by remote sensing instruments. These structures are rare, accounting for only 1% of the slow solar wind measured by Helios, and are not a significant contribution to the mass flux of the solar wind.

Download Full-text

Automatic parameterization for magnetometer zero offset determination

Geoscientific Instrumentation Methods and Data Systems Discussions ◽

10.5194/gid-2-245-2012 ◽

2012 ◽

Vol 2 (1) ◽

pp. 245-266

Author(s):

M. A. Pudney ◽

C. M. Carr ◽

S. J. Schwartz ◽

S. I. Howarth

Keyword(s):

Magnetic Field ◽

Solar Wind ◽

Field Measurements ◽

Slow Solar Wind ◽

Fixed Parameter ◽

Zero Offset ◽

Parameter Approach ◽

The Magnetic Field ◽

Key Parameter

Abstract. In-situ magnetic field measurements are of critical importance in understanding how the Sun creates and controls the heliosphere. To ensure the measurements are accurate, it is necessary to track the combined slowly-varying spacecraft magnetic field and magnetometer zero offset – the systematic error in the sensor measurements. For a 3-axis stabilised spacecraft, in-flight correction of zero offsets primarily relies on the use of Alfvénic rotations in the magnetic field. We present a method to automatically determine a key parameter related to the ambient compressional variance of the signal (which determines the selection criteria for identifying clear Alfvénic rotations). We apply our method to different solar wind conditions, performing a statistical analysis of the data periods required to achieve a 70% chance of calculating an offset using Helios datasets. We find that 70% of 40 min data periods in regions of fast solar wind possess sufficient rotational content to calculate an offset. To achieve the same 70% calculation probability in regions of slow solar wind requires data periods of 2 h duration. We also find that 40 min data periods at perihelion compared to 1 h and 40 min data periods at aphelion are required to achieve the same 70% calculation probability. We compare our method with previous work that uses a fixed parameter approach and demonstrate an improvement in the calculation probability of up to 10% at aphelion and 5% at perihelion.

Download Full-text

Cluster observations of sudden impulses in the magnetotail caused by interplanetary shocks and pressure increases

Annales Geophysicae ◽

10.5194/angeo-23-609-2005 ◽

2005 ◽

Vol 23 (2) ◽

pp. 609-624 ◽

Cited By ~ 26

Author(s):

K. E. J. Huttunen ◽

J. Slavin ◽

M. Collier ◽

H. E. J. Koskinen ◽

A. Szabo ◽

...

Keyword(s):

Magnetic Field ◽

Solar Wind ◽

Dynamic Pressure ◽

Solar Wind Speed ◽

Interplanetary Shock ◽

Wind Pressure ◽

Shock Propagation ◽

Interplanetary Shocks ◽

Maximum Variance ◽

The Magnetic Field

Abstract. Sudden impulses (SI) in the tail lobe magnetic field associated with solar wind pressure enhancements are investigated using measurements from Cluster. The magnetic field components during the SIs change in a manner consistent with the assumption that an antisunward moving lateral pressure enhancement compresses the magnetotail axisymmetrically. We found that the maximum variance SI unit vectors were nearly aligned with the associated interplanetary shock normals. For two of the tail lobe SI events during which Cluster was located close to the tail boundary, Cluster observed the inward moving magnetopause. During both events, the spacecraft location changed from the lobe to the magnetospheric boundary layer. During the event on 6 November 2001 the magnetopause was compressed past Cluster. We applied the 2-D Cartesian model developed by collier98 in which a vacuum uniform tail lobe magnetic field is compressed by a step-like pressure increase. The model underestimates the compression of the magnetic field, but it fits the magnetic field maximum variance component well. For events for which we could determine the shock normal orientation, the differences between the observed and calculated shock propagation times from the location of WIND/Geotail to the location of Cluster were small. The propagation speeds of the SIs between the Cluster spacecraft were comparable to the solar wind speed. Our results suggest that the observed tail lobe SIs are due to lateral increases in solar wind dynamic pressure outside the magnetotail boundary.

Download Full-text

Magnetopause energy transfer dependence on the interplanetary magnetic field and the Earth's magnetic dipole axis orientation

Annales Geophysicae ◽

10.5194/angeo-30-515-2012 ◽

2012 ◽

Vol 30 (3) ◽

pp. 515-526 ◽

Cited By ~ 10

Author(s):

M. Palmroth ◽

R. C. Fear ◽

I. Honkonen

Keyword(s):

Magnetic Field ◽

Energy Transfer ◽

Interplanetary Magnetic Field ◽

Large Data ◽

Seasonal Effect ◽

Dipole Orientation ◽

Data Set ◽

Axis Orientation ◽

Simulation Results ◽

The Imf

Abstract. We examine the spatial variation of magnetospheric energy transfer using a global magnetohydrodynamic (MHD) simulation (GUMICS-4) and a large data set of flux transfer events (FTEs) observed by the Cluster spacecraft. Our main purpose is to investigate whether it is possible to validate previous results on the spatial energy transfer variation from the GUMICS-4 simulation using the statistical occurrence of FTEs, which are manifestations of magnetospheric energy transfer. Previous simulation results have suggested that the energy transfer pattern at the magnetopause rotates according to the interplanetary magnetic field (IMF) orientation, and here we investigate whether a similar rotation is seen in the locations at which FTE signatures are observed. We find that there is qualitative agreement between the simulation and observed statistics, as the peaks in both distributions rotate as a function of the IMF clock angle. However, it is necessary to take into account the modulation of the statistical distribution that is caused by a bias towards in situ FTE signatures being observed in the winter hemisphere (an effect that has previously been predicted and observed in this data set). Taking this seasonal effect into account, the FTE locations support the previous simulation results and confirm the earlier prediction that the energy transfers in the plane of the IMF. In addition, we investigate the effect of the dipole orientation (both the dipole tilt angle and its orientation in the plane perpendicular to the solar wind flow) on the energy transfer spatial distribution. We find that the energy transfer occurs mainly in the summer hemisphere, and that the dayside reconnection region is located asymmetrically about the subsolar position. Finally, we find that the energy transfer is 10% larger at equinox conditions than at solstice, contributing to the discussion concerning the semiannual variation of magnetospheric dynamics (known as "the Russell-McPherron effect").

Download Full-text

Global coronal and heliospheric magnetic field modelling for Solar Orbiter

10.5194/egusphere-egu21-11005 ◽

2021 ◽

Author(s):

Thomas Wiegelmann ◽

Thomas Neukirch ◽

Iulia Chifu ◽

Bernd Inhester

Keyword(s):

Magnetic Field ◽

Solar Rotation ◽

Coronal Magnetic Field ◽

Important Research ◽

Parker Spiral ◽

Important Research Topic ◽

Mhd Equilibria ◽

Solar Wind Flow ◽

Nonlinear Force

Computing the solar coronal magnetic field and plasma environment is an important research topic on it's own right and also important for space missions like Solar Orbiter to guide the analysis of remote sensing and in-situ instruments. In the inner solar corona plasma forces can be neglected and the field is modelled under the assumption of a vanishing Lorentz-force. Further outwards (above about two solar radii) plasma forces and the solar wind flow has to be considered. Finally in the heliosphere one has to consider that the Sun is rotating and the well known Parker-spiral forms. We have developed codes based on optimization principles to solve nonlinear force-free, magneto-hydro-static and stationary MHD-equilibria. In the present work we want to extend these methods by taking the solar rotation into account.

Download Full-text