The radial evolution of solar wind speeds

McGregor, S. L.; Hughes, W. J.; Arge, C. N.; Odstrčil, D.; Schwadron, N. A.

doi:10.1029/2010ja016006

Cited by 37 publications

(53 citation statements)

References 20 publications

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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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“…Meanwhile, some unexpected features of the solar wind speed radial evolution has been experimentally found (McGregor et al 2011). A simple comparison of theoretical and empirical models shows that even the most easily predictable parameter, the solar wind speed at 1 AU, is forecasted better by empirical models rather than by models using Parker's solution .…”

Section: Introductionmentioning

confidence: 99%

Puzzles of the Interplanetary Magnetic Field in the Inner Heliosphere

Khabarova

Обридко

2012

ApJ

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Deviations of the interplanetary magnetic field (IMF) from Parker's model are frequently observed in the heliosphere at different distances r from the Sun. Usually, it is supposed that the IMF behavior corresponds to Parker's model overall, but there is some turbulent component that impacts and disrupts the full picture of the IMF spatial and temporal distribution. However, the analysis of multi-spacecraft in-ecliptic IMF measurements from 0.29 AU to 5 AU shows that the IMF radial evolution is rather far from expected. The radial IMF component decreases with the adiabatic power index (|B r | ∝ r −5/3 ), the tangential component |B r | ∝ r −1 , and the IMF strength B ∝ r −1.4 . This means that the IMF is not completely frozen in the solar wind. It is possible that turbulent processes in the inner heliosphere significantly influence the IMF expansion. This is confirmed by the analysis of the B r distribution's radial evolution. B r has a well-known bimodal histogram only at 0.7-2.0 AU. The bimodality effect gradually disappears from 1 AU to 4 AU, and B r becomes quasi-normally distributed at 3-4 AU (which is a sign of rapid vanishing of the stable sector structure with heliocentric distance). We consider a quasi-continuous magnetic reconnection, occurring both at the heliospheric current sheet and at local current sheets inside the IMF sectors, to be a key process responsible for the solar wind turbulization with heliocentric distance as well as for the breakdown of the "frozen-in IMF" law.

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“…In particular, it is pretty clear that the WSA model is sensitive to magnetogram resolution (Jian et al 2011;McGregor et al 2011;Riley et al 2012), since the resolution determines the magnetic field mapping, and the structure of the different flux-tubes. In the simulations presented here, we use high-resolution solar MDI magnetogram with a set of spherical harmonic coefficients of the order of n=90, while the WSO maps and the artificially refined maps are of the order of n=73.…”

Section: Mhd Modelmentioning

confidence: 99%

The Effect of Limited Spatial Resolution of Stellar Surface Magnetic Field Maps on Magnetohydrodynamic Wind and Coronal X-Ray Emission Models

Garraffo

Cohen

Drake

et al. 2013

ApJ

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We study the influence of the spatial resolution on scales of 5 deg and smaller of solar surface magnetic field maps on global magnetohydrodynamic solar wind models, and on a model of coronal heating and X-ray emission. We compare the solutions driven by a low-resolution Wilcox Solar Observatory magnetic map, the same map with spatial resolution artificially increased by a refinement algorithm, and a high-resolution Solar and Heliospheric Observatory Michelson Doppler Imager map. We find that both the wind structure and the X-ray morphology are affected by the fine-scale surface magnetic structure. Moreover, the X-ray morphology is dominated by the closed loop structure between mixed polarities on smaller scales and shows significant changes between high and low resolution maps. We conclude that three-dimensional modeling of coronal X-ray emission has greater surface magnetic field spatial resolution requirements than wind modeling, and can be unreliable unless the dominant mixed polarity magnetic flux is properly resolved.

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The radial evolution of solar wind speeds

Cited by 37 publications

References 20 publications

Diagnosing solar wind origins usingin situmeasurements in the inner heliosphere

Diagnosing solar wind origins usingin situmeasurements in the inner heliosphere

Puzzles of the Interplanetary Magnetic Field in the Inner Heliosphere

The Effect of Limited Spatial Resolution of Stellar Surface Magnetic Field Maps on Magnetohydrodynamic Wind and Coronal X-Ray Emission Models

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