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Gary, G. A.

doi:10.1023/a:1012722021820

Cited by 466 publications

(330 citation statements)

References 30 publications

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“…When ¼ 0:5, the value of increases from 0.0016 at z ¼ 1 to 0.011 at z ¼ 4. Because of the bipolar structure of the active region magnetic field, the value of varies slowly between the poles and increases away from the poles, to values of order unity, consistent with the values found by Gary (2001). The initial velocity pulse (13) leads to the formation of the fast magnetosonic wave in the computational domain.…”

Section: Numerical Resultssupporting

confidence: 76%

Interaction of EIT Waves with Coronal Active Regions

Ofman

Thompson

2002

ApJ

179

168

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Large-scale coronal waves associated with flares were first observed by the Solar and Heliospheric Observatory (SOHO) Extreme ultraviolet Imaging Telescope (EIT). We present the first three-dimensional MHD modeling of the interaction of the EIT waves with active regions and the possibility of destabilization of an active region by these waves. The active region is modeled by an initially force-free, bipolar magnetic configuration with gravitationally stratified density. We include finite thermal pressure and resistive dissipation in our model. The EIT wave is launched at the boundary of the region, as a short time velocity pulse that travels with the local fast magnetosonic speed toward the active region. We find that the EIT wave undergoes strong reflection and refraction, in agreement with observations, and induces transient currents in the active region. The resulting Lorentz force leads to the dynamic distortion of the magnetic field and to the generation of secondary waves. The resulting magnetic compression of the plasma induces flows, which are particularly strong in the current-carrying active region. We investigate the effect of the magnetic field configuration and find that the current-carrying active region is destabilized by the impact of the wave. Analysis of the threedimensional interaction between EIT waves and active regions can serve as a diagnostic of the active region coronal magnetic structure and stability.

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Section: Numerical Resultssupporting

confidence: 76%

Interaction of EIT Waves with Coronal Active Regions

Ofman

Thompson

2002

ApJ

179

168

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“…9b in Appendix). Highly structured patterns observed in the EUV wavelength range indicate that the coronal plasma is controlled by the magnetic field, i.e., β 1 (for a discussion see Gary 2001). Since the relationship M A (BDW) only weakly depends on the value of β when it is smaller than ≈0.2 (see Fig.…”

Section: The Methods and Assumptionsmentioning

confidence: 99%

Band-splitting of coronal and interplanetary type II bursts

Vršnak

Magdalenić

Auraß

et al. 2002

A&A

176

147

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Abstract. Type II radio bursts recorded in the metric wavelength range are excited by MHD shocks traveling through the solar corona. They often expose the fundamental and harmonic emission band, both frequently being split in two parallel lanes that show a similar frequency drift and intensity behaviour. Our previous paper showed that band-splitting of such characteristics is a consequence of the plasma emission from the upstream and downstream shock regions. Consequently, the split can be used to evaluate the density jump at the shock front and to estimate the shock Mach number, which in combination with the shock speed inferred from the frequency drift provides an estimate of the Alfvén velocity and the magnetic field in the ambient plasma. In this paper such a procedure is applied to 18 metric type II bursts with the fundamental band starting frequencies up to 270 MHz. The obtained values show a minimum of the Alfvén velocity at the heliocentric distance R ≈ 2 amounting to v A ≈ 400-500 km s −1 . It then increases achieving a local maximum of v A ≈ 450-700 km s −1 at R ≈ 2.5. The implications regarding the process of formation and decay of MHD shocks in the corona are discussed. The coronal magnetic field in the range 1.3 < R < 3 decreases as R −3 to R −4 , or H −1.5 to H −2 if expressed as a function of the height. The results are compared with other estimates of the coronal magnetic field in the range 1 < R < 10. Combined data show that below H < 0.3 the magnetic field is dominated by active region fields, whereas above H = 1 it becomes radial, behaving roughly as B = 2 × R −2 with a plausible value of B ≈ 5 nT at 1 a.u.

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“…The plasma−β parameter varies greatly with height across the layers of the solar atmosphere (see Gary 2001 for well-constrained values). However, magnetic pressure generally dominates thermal pressure in the solar corona, and thus it is usual to assume plasma−β ≪ 1 when modelling a coronal environment.…”

Section: Mhd Wavesmentioning

confidence: 99%

Review Article: MHD Wave Propagation Near Coronal Null Points of Magnetic Fields

McLaughlin¹,

Hood²,

Moortel³

2010

Space Sci Rev

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We present a comprehensive review of MHD wave behaviour in the neighbourhood of coronal null points: locations where the magnetic field, and hence the local Alfvén speed, is zero. The behaviour of all three MHD wave modes, i.e. the Alfvén wave and the fast and slow magnetoacoustic waves, has been investigated in the neighbourhood of 2D, 2.5D and (to a certain extent) 3D magnetic null points, for a variety of assumptions, configurations and geometries. In general, it is found that the fast magnetoacoustic wave behaviour is dictated by the Alfvén-speed profile. In a β = 0 plasma, the fast wave is focused towards the null point by a refraction effect and all the wave energy, and thus current density, accumulates close to the null point. Thus, null points will be locations for preferential heating by fast waves. Independently, the Alfvén wave is found to propagate along magnetic fieldlines and is confined to the fieldlines it is generated on. As the wave approaches the null point, it spreads out due to the diverging fieldlines. Eventually, the Alfvén wave accumulates along the separatrices (in 2D) or along the spine or fan-plane (in 3D). Hence, Alfvén wave energy will be preferentially dissipated at these locations. It is clear that the magnetic field plays a fundamental role in the propagation and properties of MHD waves in the neighbourhood of coronal null points. This topic is a fundamental plasma process and results so far have also lead to critical insights into reconnection, mode-coupling, quasi-periodic pulsations and phase-mixing.

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Untitled

Cited by 466 publications

References 30 publications

Interaction of EIT Waves with Coronal Active Regions

Interaction of EIT Waves with Coronal Active Regions

Band-splitting of coronal and interplanetary type II bursts

Review Article: MHD Wave Propagation Near Coronal Null Points of Magnetic Fields

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