Solar wind turbulence during the solar cycle deduced from Galileo coronal radio-sounding experiments

Ефимов, А. И.; Samoznaev, L. N.; Bird, M. K.; Чашей, И. В.; Plettemeier, Dirk

doi:10.1016/j.asr.2008.03.025

Cited by 33 publications

(16 citation statements)

References 13 publications

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“…Distinct anisotropy in density inhomogeneity length scales was inherent to the model at low SO, but by about 7R most of the component spatial lengths were below flux tube width L LOS , allowing a rough approximation to isotropic behavior. Interestingly, at and above 7R the 3-D isotropic quasi-static turbulence model (Efimov et al 2008) reproduced solar wind outflow speeds expected from the literature and mass flux considerations, at least to 12R .…”

Section: Discussionsupporting

confidence: 72%

“…(Hollweg & Harrington 1968;Jokipii 1973;Woo 1978). Armand et al (1987), Efimov et al (2008) and presented an isotropic turbulence model to evaluate coronal FF. The model assumes a quasi-static isotropic 3-D spatial electron density inhomogeneity spectrum.…”

Section: Isotropic Quasi-static Turbulence Modelmentioning

confidence: 99%

“…Section 4 develops a two-component model of the frequency measure fluctuations, then provides the parameters used to implement the model and gives results. In Section 5, a comparison is made between the solar wind speeds based on mass conservation in the flux tubes, and speed predictions from an established isotropic turbulence bulk flow model (Armand et al 1987;Efimov et al 2008), highlighting di↵erences in the lower coronal region for which quasi-static isotropic turbulence models may be inapplicable. Our conclusions are summarized in Section 6.…”

Section: Introductionmentioning

confidence: 99%

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Spacecraft Radio Frequency Fluctuations in the Solar Corona: A MESSENGER–HELIOS Composite Study

Wexler

Hollweg

Ефимов

et al. 2019

ApJ

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Fluctuations in plasma electron density may play a role in solar coronal energy transport and dissipation of wave energy. Transcoronal spacecraft radio sounding observations reveal frequency fluctuations (FF) that encode the electron number density disturbances, allowing exploration of coronal compressive wave and advected inhomogeneity models. Primary FF observations from MESSENGER 2009 and published FF residuals from HELIOS 1975-1976 superior conjunctions were combined to produce a composite view of equatorial region FF near solar minimum over solar o↵set range 1.4-25R. Methods to estimate the electron number density fluctuation variance from the observed FF were developed. We created a simple stacked flux tube model that incorporated both propagating slow density waves and advected spatial density variations to explain the observed FF. Slow density waves accounted for most of the FF at low solar o↵set, while spatial density inhomogeneities advected at solar wind speed dominated above the sonic point at 6R. Corresponding spatial scales ranged 1-38 Mm, with scales above 10 Mm contributing most to FF variance. Flux-tube structuring of the model introduced radial elongation anistropy at lower solar o↵sets, but geometric conditions for isotropy were achieved as the the flux tube widths increased further out in the corona. The model produced agreement with the FF observations up to 12R. FF analysis provides information on electron density fluctuations in the solar corona, and should take into account the background compressive slow waves and solar wind-related advection of quasi-static spatial density variations.

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Section: Discussionsupporting

confidence: 72%

Section: Isotropic Quasi-static Turbulence Modelmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Spacecraft Radio Frequency Fluctuations in the Solar Corona: A MESSENGER–HELIOS Composite Study

Wexler

Hollweg

Ефимов

et al. 2019

ApJ

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“…Increases in C N 2 (R) and decreases in l i (R) would lead to more scattering. Work on both n e (R) and dn(R)/n e (R) may be useful [e.g., Efimov et al, 2008;Cairns et al, 2009]. It is quite possible that scattering observations and theory will provide useful constraints on these five quantities and therefore on the processes heating the solar corona and accelerating the solar wind.…”

Section: Discussion and Summarymentioning

confidence: 99%

“…While it is fairly well established that the turbulence spectrum largely follows the Kolmogorov scaling (with a = 11/3) at scales larger than about 100 km, there is some evidence that it flattens, with a decreasing to values as low as 3, at scales between a few kilometers and a few hundred kilometers [Bastian, 1994]. There is also some evidence for variation of the turbulence power law spectrum with heliocentric distance [e.g., Efimov et al, 2008]. Furthermore, there is evidence for significant variation in the index between the slow and fast solar wind [Manoharan et al, 1994].…”

Section: Density Turbulencementioning

confidence: 99%

Constraints on coronal turbulence models from source sizes of noise storms at 327 MHz

Subramanian

Cairns

2011

J. Geophys. Res.

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[1] We seek to reconcile observations of small source sizes in the solar corona at 327 MHz with predictions of scattering models that incorporate refractive index effects, inner scale effects, and a spherically diverging wavefront. We use an empirical prescription for the turbulence amplitude C N 2 (R) based on very long baseline interferometry observations by Spangler et al. of compact radio sources against the solar wind for heliocentric distances R ≈ 10-50 R . We use the Coles and Harmon model for the inner scale l i (R), which is presumed to arise from cyclotron damping. In view of the prevalent uncertainty in the power law index that characterizes solar wind turbulence at various heliocentric distances, we retain this index as a free parameter. We find that the inclusion of spherical divergence effects suppresses the predicted source size substantially. We also find that inner scale effects significantly reduce the predicted source size. An important general finding for solar sources is that the calculations substantially underpredict the observed source size. Three possible, nonexclusive, interpretations of this general result are proposed. First and simplest, future observations with better angular resolution will detect much smaller sources. Consistent with this, previous observations of small sources in the corona at metric wavelengths are limited by the instrument resolution. Second, the spatially varying level of turbulence C N 2 (R) is much larger in the inner corona than predicted by straightforward extrapolation sunward of the empirical prescription, which was based on observations between 10 and 50 R . Either the functional form or the constant of proportionality could be different. Third, perhaps the inner scale is smaller than the model, leading to increased scattering. These results and interpretations are discussed and compared with earlier work.

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Analysis of an Interplanetary Coronal Mass Ejection by a Spacecraft Radio Signal: A Case Study

et al. 2017

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Tracking radio communication signals from planetary spacecraft with ground‐based telescopes offers the possibility to study the electron density and the interplanetary scintillation of the solar wind. Observations of the telemetry link of planetary spacecraft have been conducted regularly with ground antennae from the European Very Long Baseline Interferometry Network, aiming to study the propagation of radio signals in the solar wind at different solar elongations and distances from the Sun. We have analyzed the Mars Express spacecraft radio signal phase fluctuations while, based on a 3‐D heliosphere plasma simulation, an interplanetary coronal mass ejection (ICME) crossed the radio path during one of our observations on 6 April 2015. Our measurements showed that the phase scintillation indices increased by a factor of 4 during the passage of the ICME. The method presented here confirms that the phase scintillation technique based on spacecraft signals provides information of the properties and propagation of the ICMEs in the heliosphere.

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Solar wind turbulence during the solar cycle deduced from Galileo coronal radio-sounding experiments

Cited by 33 publications

References 13 publications

Spacecraft Radio Frequency Fluctuations in the Solar Corona: A MESSENGER–HELIOS Composite Study

Spacecraft Radio Frequency Fluctuations in the Solar Corona: A MESSENGER–HELIOS Composite Study

Constraints on coronal turbulence models from source sizes of noise storms at 327 MHz

Analysis of an Interplanetary Coronal Mass Ejection by a Spacecraft Radio Signal: A Case Study

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