The upstream‐propagating Alfvénic fluctuations with power law spectra in the upstream region of the Earth's bow shock

Wang, Xin; Tu, Chuanyi; Wang, Linghua; He, Jiansen; Marsch, E.

doi:10.1002/2015gl063893

Cited by 14 publications

(17 citation statements)

References 33 publications

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“…However, at the solar minimum we can only observe SAFPs in the slow solar wind. It is consistent with the result in Wang et al () that SAFPs of 1995 mostly occur in the slow solar wind. Second, more SAFPs occurred at solar maximum.…”

Section: Discussionsupporting

confidence: 93%

“…It is often considered as a signature of a cascade according to the critical balance theory (Goldreich & Sridhar, 1995;Schekochihin et al, 2009;Tessein et al, 2009) and may also be explained by the influence of intermittent structures on the solar wind turbulence (Luo et al, 2011;Pei et al, 2016;Wang et al, 2014Wang et al, , 2016. However, for the SAFPs found by Wang et al (2015) the power and spectral index anisotropy were not investigated. Moreover, in their work only the cases with B X > 0.7B 0 were considered.…”

Section: 1002/2017ja024422mentioning

confidence: 99%

“…They are mostly observed in the upstream region of the Earth bow shock. Wang et al () found for the first time upstream‐propagating Alfvénic fluctuations with a power law spectrum (SAFP) in the frequency range from 0.004 to 0.04 Hz. In their work, 47 cases of such SAFPs were found in the year 1995, and most of them occurred in the slow solar wind.…”

Section: Introductionmentioning

confidence: 99%

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A Study on Sunward Propagating Alfvénic Fluctuations With a Power Law Spectrum Observed by the Wind Spacecraft

Wang

et al. 2017

JGR Space Physics

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Sunward propagating Alfvénic fluctuations with a power law spectrum (SAFP) have been recently observed in the upstream region of the Earth's bow shock. However, some physical properties of these fluctuations such as anisotropy remain unclear. Here we develop a new method for identifying SAFPs, and present for the first time the anisotropy of SAFPs power and spectral index. In this method, the propagation direction determination of SAFPs does not rely on a radial magnetic geometry but the pitch angle distribution of strahl electron outflow. Therefore, the SAFPs with any value of θRB (angle between the global mean magnetic field and the Sun‐to‐Earth radial direction) can be identified, so that enables the study of the spectral anisotropy. We find 508 SAFPs using the Wind spacecraft measurements from 1995 to 2014. We show that the SAFP has an averaged spectral index of −1.77 ± 0.28 and the index changes continuously from −2.18 ± 0.21 when θRB=0°–10° to −1.71 ± 0.03 when θRB=80°–90°. These SAFPs are observed more frequently in the slow solar wind especially at solar minimum. We also select antisunward propagating Alfvénic fluctuations with a power law spectrum using the same method for comparison. The results indicate that the power spectrum of SAFP is steeper, and the spectral intensity as well as the power anisotropy of SAFP is weaker. These new findings may provide information on the generation of turbulence in the upstream region.

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Section: Discussionsupporting

confidence: 93%

Section: 1002/2017ja024422mentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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A Study on Sunward Propagating Alfvénic Fluctuations With a Power Law Spectrum Observed by the Wind Spacecraft

Wang

et al. 2017

JGR Space Physics

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“…These instabilities can generate waves in the upstream region (e.g. Blanco-Cano et al 2011;Wang et al 2015;Strumik et al 2015), so that an increased level A&A 592, A118 (2016) of fluctuations is expected before and after the shocks associated with ICMEs.…”

Section: Introductionmentioning

confidence: 99%

Superposed epoch study of ICME sub-structures near Earth and their effects on Galactic cosmic rays

Masías-Meza

Dasso

Démoulin

et al. 2016

A&A

113

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Context. Interplanetary coronal mass ejections (ICMEs) are the interplanetary manifestations of solar eruptions. The overtaken solar wind forms a sheath of compressed plasma at the front of ICMEs. Magnetic clouds (MCs) are a subset of ICMEs with specific properties (e.g. the presence of a flux rope). When ICMEs pass near Earth, ground observations indicate that the flux of Galactic cosmic rays (GCRs) decreases. Aims. The main aims of this paper are to find common plasma and magnetic properties of different ICME sub-structures and which ICME properties affect the flux of GCRs near Earth. Methods. We used a superposed epoch method applied to a large set of ICMEs observed in situ by the spacecraft ACE, between 1998 and 2006. We also applied a superposed epoch analysis on GCRs time series observed with the McMurdo neutron monitors. Results. We find that slow MCs at 1 AU have on average more massive sheaths. We conclude that this is because they are more effectively slowed down by drag during their travel from the Sun. Slow MCs also have a more symmetric magnetic field and sheaths expanding similarly as their following MC, while in contrast, fast MCs have an asymmetric magnetic profile and a sheath in compression. In all types of MCs, we find that the proton density and the temperature and the magnetic fluctuations can diffuse within the front of the MC due to 3D reconnection. Finally, we derive a quantitative model that describes the decrease in cosmic rays as a function of the amount of magnetic fluctuations and field strength. Conclusions. The obtained typical profiles of sheath, MC and GCR properties corresponding to slow, middle, and fast ICMEs, can be used for forecasting or modelling these events, and to better understand the transport of energetic particles in ICMEs. They are also useful for improving future operative space weather activities.

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“…Local bending of the interplanetary magnetic field line can make determination of the sunward direction difficult (see He et al 2011). Wang et al (2015) defined the intervals with waves propagating in a direction opposite to that of the observed strahl electron outflow to be sunward propagating.…”

Section: Introductionmentioning

confidence: 99%

Sunward-Propagating Alfvénic Fluctuations Observed in the Heliosphere

Wang

Belcher

et al. 2016

ApJL

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The mixture/interaction of anti-sunward propagating Alfvénic fluctuations (AFs) and sunward-propagating Alfvénic fluctuations (SAFs) is believed to result in the decrease of Alfvénicity of solar wind fluctuations with increasing heliocentric distance. However, SAFs are rarely observed at 1 AU and solar wind AFs are found to be generally outward.Using the measurements from Voyager 2 and Wind, we perform a statistical survey of SAFs in the heliosphere inside 6 AU. We first report two SAF events observed by Voyager 2. One is in the anti-sunward magnetic sector with a strong positive correlation between the fluctuations of magnetic field and solar wind velocity. The other one is in the sunward magnetic sector with a strong negative magnetic fieldvelocity correlation. Statistically, the percentage of SAFs increases gradually with heliocentric distance, from about 2.7% at 1.0 AU to about 8.7% at 5.5 AU. These results provide new clues to help understand the generation mechanism of SAFs.2 LI ET AL.

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The upstream‐propagating Alfvénic fluctuations with power law spectra in the upstream region of the Earth's bow shock

Cited by 14 publications

References 33 publications

A Study on Sunward Propagating Alfvénic Fluctuations With a Power Law Spectrum Observed by the Wind Spacecraft

A Study on Sunward Propagating Alfvénic Fluctuations With a Power Law Spectrum Observed by the Wind Spacecraft

Superposed epoch study of ICME sub-structures near Earth and their effects on Galactic cosmic rays

Sunward-Propagating Alfvénic Fluctuations Observed in the Heliosphere

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