Untitled

Moortel, I. De; Ireland, J.; Walsh, R. W.; Hood, A. W.

doi:10.1023/a:1020956421063

Cited by 190 publications

(193 citation statements)

References 0 publications

Supporting

Mentioning

174

Contrasting

Order By: Relevance

“…We assume the background density and gas pressure are uniform and labelled as ρ 0 and p 0 respectively. However, we note that a spatial variation in ρ 0 can cause phase mixing (Heyvaerts & Priest 1983;De Moortel et al 1999;Hood et al 2002).…”

Section: Basic Equilibriummentioning

confidence: 95%

“…MHD wave motions have recently been observed in the Sun's atmosphere with the SOHO and TRACE satellites, see for example the detection of slow magnetoacoustic waves by Berghmans & Clette (1999) and De Moortel et al (2000) and of fast magnetoacoustic waves by Nakariakov et al (1999). It is clear that the local coronal magnetic field plays a key role in determining their propagation properties.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

MHD mode coupling in the neighbourhood of a 2D null point

McLaughlin¹,

Hood²

2006

A&A

View full text Add to dashboard Cite

Context. At this time there does not exist a robust set of rules connecting low and high β waves across the β ≈ 1 layer. The work here contributes specifically to what happens when a low β fast wave crosses the β ≈ 1 layer and transforms into high β fast and slow waves. Aims. The nature of fast and slow magnetoacoustic waves is investigated in a finite β plasma in the neighbourhood of a twodimensional null point. Methods. The linearised equations are solved in both polar and cartesian forms with a two-step Lax-Wendroff numerical scheme. Analytical work (e.g. small β expansion and WKB approximation) also complement the work. Results. It is found that when a finite gas pressure is included in magnetic equilibrium containing an X-type null point, a fast wave is attracted towards the null by a refraction effect and that a slow wave is generated as the wave crosses the β ≈ 1 layer. Current accumulation occurs close to the null and along nearby separatrices. The fast wave can now pass through the origin due to the non-zero sound speed, an effect not previously seen in related papers but clear seen for larger values of β. Some of the energy can now leave the region of the null point and there is again generation of a slow wave component (we find that the fraction of the incident wave converted to a slow wave is proportional to β). We conclude that there are two competing phenomena; the refraction effect (due to the variable Alfvén speed) and the contribution from the non-zero sound speed. Conclusions. These experiments illustrate the importance of the magnetic topology and of the location of the β ≈ 1 layer in the system.

show abstract

Section: Basic Equilibriummentioning

confidence: 95%

Section: Introductionmentioning

confidence: 99%

MHD mode coupling in the neighbourhood of a 2D null point

McLaughlin¹,

Hood²

2006

A&A

View full text Add to dashboard Cite

show abstract

“…Under the β = 0 assumption, the plasma pressure plays no part in the dynamics of the system, and so the linearised equation of mass continuity has no influence on the momentum equation and so in effect the plasma is arbitrarily compressible (Craig & Watson 1992) and we assume the background gas density is uniform (ρ 0 ). A spatial variation in ρ 0 can cause phase mixing (Heyvaerts & Priest 1983;De Moortel et al 1999;Hood et al 2002).…”

Section: Why Is This Area Of Study Interesting or Important?mentioning

confidence: 99%

“…Several different types of MHD wave motions have now been observed by various solar instruments: slow magnetoacoustic waves have been seen in SOHO data (e.g. Ofman et al 1997;DeForest & Gurman 1998;Berghmans & Clette 1999;Kliem et al 2002;Wang et al 2002) and TRACE data (De Moortel et al 2000). Fast magnetoacoustic waves have been seen with TRACE (Aschwanden et al 1999(Aschwanden et al , 2002Nakariakov et al 1999;Wang & Solanki 2004) and Hinode (Ofman & Wang 2008).…”

Section: Introductionmentioning

confidence: 99%

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

McLaughlin¹,

Hood²,

Moortel³

2010

Space Sci Rev

Self Cite

View full text Add to dashboard Cite

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.

show abstract

“…Such bright signal might be the result of the AR loop oscillation. Previously, propagating disturbances in AR loops were reported by many researchers (e.g., De Moortel et al 2000;Wang et al 2009a;McIntosh & De Pontieu 2009;Tian et al 2011). Such propagating disturbances were similar to our observed disturbance except that they were periodic.…”

Section: Conclusion and Discussionmentioning

confidence: 98%

SDO/AIA and Hinode/EIS observations of interaction between an EUV wave and active region loops

Liu¹,

Zhang²,

Li³

et al. 2012

Proc. IAU

View full text Add to dashboard Cite

We present detailed analysis of an extreme ultraviolet (EUV) wave and its interaction with active region (AR) loops observed by the Solar Dynamics Observatory/Atmospheric Imaging Assembly and the Hinode EUV Imaging Spectrometer (EIS). This wave was initiated from AR 11261 on 2011 August 4 and propagated at velocities of 430-910 km s −1 . It was observed to traverse another AR and cross over a filament channel on its path. The EUV wave perturbed neighboring AR loops and excited a disturbance that propagated toward the footpoints of these loops. EIS observations of AR loops revealed that at the time of the wave transit, the original redshift increased by about 3 km s −1 , while the original blueshift decreased slightly. After the wave transit, these changes were reversed. When the EUV wave arrived at the boundary of a polar coronal hole, two reflected waves were successively produced and part of them propagated above the solar limb. The first reflected wave above the solar limb encountered a large-scale loop system on its path, and a secondary wave rapidly emerged 144 Mm ahead of it at a higher speed. These findings can be explained in the framework of a fast-mode magnetosonic wave interpretation for EUV waves, in which observed EUV waves are generated by expanding coronal mass ejections.

show abstract

Untitled

Cited by 190 publications

References 0 publications

MHD mode coupling in the neighbourhood of a 2D null point

MHD mode coupling in the neighbourhood of a 2D null point

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

SDO/AIA and Hinode/EIS observations of interaction between an EUV wave and active region loops

Contact Info

Product

Resources

About