Solar wind stream interaction regions throughout the heliosphere

Richardson, I. G.

doi:10.1007/s41116-017-0011-z

Cited by 271 publications

(255 citation statements)

References 272 publications

(472 reference statements)

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“…The spatial distribution of anisotropic wind, with slower speeds always occurring in the rarefaction edges of high speed streams (figure 6) shows that rarefaction during transit is responsible for the relatively low speed of some anisotropic wind (Pizzo 1991). The reason slower speeds are not observable at the leading edge of high speed streams is because by 0.3 AU they have already been accelerated by the faster wind to form a co-rotating interaction region (Burlaga 1974;Pizzo 1991;McGregor et al 2011;Richardson 2018). Note that we have chosen to distinguish between the edges and the core of coronal holes; at the edge of coronal holes the magnetic field lines typically undergo large separations as a function of height in the corona, which has the effect of reducing both the wind speed (Levine et al 1977;Wang & Sheeley 1991;Cranmer et al 2007;Pinto et al 2016) and charge state ratios (Wang et al 2009).…”

Section: Known Properties Of Coronal Hole Windmentioning

confidence: 99%

Diagnosing solar wind origins usingin situmeasurements in the inner heliosphere

Stansby

Horbury

Matteini

2018

Monthly Notices of the Royal Astronomical Society

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Robustly identifying the solar sources of individual packets of solar wind measured in interplanetary space remains an open problem. We set out to see if this problem is easier to tackle using solar wind measurements closer to the Sun than 1 AU, where the mixing and dynamical interaction of different solar wind streams is reduced. Using measurements from the Helios mission, we examined how the proton core temperature anisotropy and cross helicity varied with distance. At 0.3 AU there are two clearly separated anisotropic and isotropic populations of solar wind, that are not distinguishable at 1 AU. The anisotropic population is always Alfvénic and spans a wide range of speeds. In contrast the isotropic population has slow speeds, and contains a mix of Alfvénic wind with constant mass fluxes, and non-Alfvénic wind with large and highly varying mass fluxes. We split the in-situ measurements into three categories according these observations, and suggest that these categories correspond to wind that originated in the core of coronal holes, in or near active regions or the edges of coronal holes, and as small transients form streamers or pseudostreamers. Although our method by itself is simplistic, it provides a new tool that can be used in combination with other methods for identifying the sources of solar wind measured by Parker Solar Probe and Solar Orbiter.

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Section: Known Properties Of Coronal Hole Windmentioning

confidence: 99%

Diagnosing solar wind origins usingin situmeasurements in the inner heliosphere

Stansby

Horbury

Matteini

2018

Monthly Notices of the Royal Astronomical Society

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“…Stream interaction regions (SIRs) are important drivers of magnetospheric activity (Gosling & Pizzo, 1999;Kilpua et al, 2017;Tsurutani et al, 2006) and in particular can be important for energizing Earth's radiation belts (Bortnik et al, 2006;Borovsky & Denton, 2006;Miyoshi & Kataoka, 2005;Paulikas & Blake, 1979;Yuan & Zong, 2012). SIRs, formed when a faster solar wind overtakes a slower wind, can sometimes form forward shocks by 1 AU (Jian et al, 2006;Richardson, 2018), potentially leading to shock-induced ULF wave activity in the magnetosphere. The compression region between the two solar wind streams is also a source of broadband magnetospheric ULF wave power derived from intrinsic solar wind dynamic pressure fluctuations (Kilpua et al, 2013).…”

Section: Introductionmentioning

confidence: 99%

The Source, Significance, and Magnetospheric Impact of Periodic Density Structures Within Stream Interaction Regions

Kepko

Viall

2019

JGR Space Physics

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We present several examples of magnetospheric ultralow frequency pulsations associated with stream interaction regions and demonstrate that the observed magnetospheric pulsations were also present in the solar wind number density. The distance of the solar wind monitor ranged from just upstream of Earth's bow shock to 261 RE, with a propagation time delay of up to 90 min. The number density oscillations far upstream of Earth are offset from similar oscillations observed within the magnetosphere by the advection timescale, suggesting that the periodic dynamic pressure enhancements were time stationary structures, passively advecting with the ambient solar wind. The density structures are larger than Earth's magnetosphere and slowly altered the dynamic pressure enveloping Earth, leading to a quasi‐static and globally coherent “forced‐breathing” of Earth's dayside magnetospheric cavity. The impact of these periodic solar wind density structures was observed in both magnetospheric magnetic field and energetic particle data. We further show that the structures were initially smaller‐amplitude, spatially larger, structures in the upstream slow solar wind and that the higher‐speed wind compressed and amplified these preexisting structures leading to a series of quasiperiodic density structures with periods typically near 20 min. Similar periodic density structures have been observed previously at L1 and in remote images, but never in the context of solar wind shocks and discontinuities. The existence of periodic density structures within stream interaction regions may play an important role in magnetospheric particle acceleration, loss, and transport, particularly for outer zone electrons that are highly responsive to ultralow frequency wave activity.

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“…While a uniform slow-wind flow at Earth would have a density of about 10 cm −3 , in a compression region this value can double. These phenomena are the already mentioned CIRs (see, e.g., Gosling & Pizzo 1999;Richardson 2018), that are particularly prominent at the minimum phase of the Solar activity cycle. In addition to the spatial variations of fast streams, slow streams, and CIRs, there are CMEs (for a review see Chen 2011).…”

Section: Solar Wind Structurementioning

confidence: 66%

On the usefulness of existing solar wind models for pulsar timing corrections

Tiburzi

Verbiest

Shaifullah

et al. 2019

Monthly Notices of the Royal Astronomical Society

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Dispersive delays due to the Solar wind introduce excess noise in high-precision pulsar timing experiments, and must be removed in order to achieve the accuracy needed to detect, e.g., low-frequency gravitational waves. In current pulsar timing experiments, this delay is usually removed by approximating the electron density distribution in the Solar wind either as spherically symmetric, or with a two-phase model that describes the contributions from both high-and low-speed phases of the Solar wind. However, no dataset has previously been available to test the performance and limitations of these models over extended timescales and with sufficient sensitivity. Here we present the results of such a test with an optimal dataset of observations of pulsar J0034−0534, taken with the German stations of LOFAR. We conclude that the spherical approximation performs systematically better than the two-phase model at almost all angular distances, with a residual root-mean-square (rms) given by the two-phase model being up to 28% larger than the result obtained with the spherical approximation. Nevertheless, the spherical approximation remains insufficiently accurate in modelling the Solar-wind delay (especially within 20 degrees of angular distance from the Sun), as it leaves timing residuals with rms values that reach the equivalent of 0.3 µs at 1400 MHz. This is because a spherical model ignores the large daily variations in electron density observed in the Solar wind. In the short term, broadband observations or simultaneous observations at low frequencies are the most promising way forward to correct for Solar-wind induced delay variations.

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Solar wind stream interaction regions throughout the heliosphere

Cited by 271 publications

References 272 publications

Diagnosing solar wind origins usingin situmeasurements in the inner heliosphere

Diagnosing solar wind origins usingin situmeasurements in the inner heliosphere

The Source, Significance, and Magnetospheric Impact of Periodic Density Structures Within Stream Interaction Regions

On the usefulness of existing solar wind models for pulsar timing corrections

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