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Investigating Alfvénic wave propagation in coronal open-field regions.

Morton RJ, Tomczyk S, Pinto R - Nat Commun (2015)

Bottom Line: The existence of Alfvén waves far from the Sun has been known since the 1970s, and recently the presence of ubiquitous Alfvénic waves throughout the solar atmosphere has been confirmed.However, the presence of atmospheric Alfvénic waves does not, alone, provide sufficient support for wave-based models; the existence of counter-propagating Alfvénic waves is crucial for the development of turbulence.The results enhance our knowledge of Alfvénic wave propagation in the solar atmosphere, providing support and constraints for some of the recent Alfvén wave turbulence models.

View Article: PubMed Central - PubMed

Affiliation: 1] Department of Mathematics and Information Sciences, Northumbria University, Newcastle Upon Tyne NE1 8ST, UK. [2] High Altitude Observatory, National Center for Atmospheric Research, Boulder, Colorado 80307-3000, USA.

ABSTRACT
The physical mechanisms behind accelerating solar and stellar winds are a long-standing astrophysical mystery, although recent breakthroughs have come from models invoking the turbulent dissipation of Alfvén waves. The existence of Alfvén waves far from the Sun has been known since the 1970s, and recently the presence of ubiquitous Alfvénic waves throughout the solar atmosphere has been confirmed. However, the presence of atmospheric Alfvénic waves does not, alone, provide sufficient support for wave-based models; the existence of counter-propagating Alfvénic waves is crucial for the development of turbulence. Here, we demonstrate that counter-propagating Alfvénic waves exist in open coronal magnetic fields and reveal key observational insights into the details of their generation, reflection in the upper atmosphere and outward propagation into the solar wind. The results enhance our knowledge of Alfvénic wave propagation in the solar atmosphere, providing support and constraints for some of the recent Alfvén wave turbulence models.

No MeSH data available.


Related in: MedlinePlus

Average frequency power spectra and ratios of counter-propagating waves.The predominance of power in outward propagating waves (box method—black solid and track method—green dash-dot) is clear in the wavenumber-integrated power spectra (a). The spectra also provide insight into the power of the inward propagating waves (box method—blue dash and track method—red dash-triple dot). The total power spectrum is also shown for reference (dots). The horizontal dotted line is the estimate for the data noise associated with the total power spectra, while the solid horizontal line is the data noise split between inward and outward components. (b) The ratio of inward to outward power is displayed as a function of frequency and reveals a frequency-dependent trend suggestive of partial reflection of the waves in the corona. The vertical dashed line highlights the frequency after which noise begins to dominate the inward power spectra. The error bars in both plots show the s.e.m.
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f3: Average frequency power spectra and ratios of counter-propagating waves.The predominance of power in outward propagating waves (box method—black solid and track method—green dash-dot) is clear in the wavenumber-integrated power spectra (a). The spectra also provide insight into the power of the inward propagating waves (box method—blue dash and track method—red dash-triple dot). The total power spectrum is also shown for reference (dots). The horizontal dotted line is the estimate for the data noise associated with the total power spectra, while the solid horizontal line is the data noise split between inward and outward components. (b) The ratio of inward to outward power is displayed as a function of frequency and reveals a frequency-dependent trend suggestive of partial reflection of the waves in the corona. The vertical dashed line highlights the frequency after which noise begins to dominate the inward power spectra. The error bars in both plots show the s.e.m.

Mentions: The power spectrum for the Doppler velocity time–distance diagrams is determined for a range of frequencies (f) and wavenumbers (k) in the vertical direction, and the outward and inward propagating signals are decomposed. To analyse the waves, both an f–k diagram (Fig. 2) and wavenumber-integrated power spectra are calculated (Fig. 3). A prominent ridge in the left half of the f–k diagram corresponding to negative frequencies confirms the dominance of outward propagating waves. No clear ridge exists for the inward propagating waves although there is significant power in the low frequency part of the spectrum. Such ridges have also been found in f–k diagrams for large quiescent coronal loops40.


Investigating Alfvénic wave propagation in coronal open-field regions.

Morton RJ, Tomczyk S, Pinto R - Nat Commun (2015)

Average frequency power spectra and ratios of counter-propagating waves.The predominance of power in outward propagating waves (box method—black solid and track method—green dash-dot) is clear in the wavenumber-integrated power spectra (a). The spectra also provide insight into the power of the inward propagating waves (box method—blue dash and track method—red dash-triple dot). The total power spectrum is also shown for reference (dots). The horizontal dotted line is the estimate for the data noise associated with the total power spectra, while the solid horizontal line is the data noise split between inward and outward components. (b) The ratio of inward to outward power is displayed as a function of frequency and reveals a frequency-dependent trend suggestive of partial reflection of the waves in the corona. The vertical dashed line highlights the frequency after which noise begins to dominate the inward power spectra. The error bars in both plots show the s.e.m.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4525157&req=5

f3: Average frequency power spectra and ratios of counter-propagating waves.The predominance of power in outward propagating waves (box method—black solid and track method—green dash-dot) is clear in the wavenumber-integrated power spectra (a). The spectra also provide insight into the power of the inward propagating waves (box method—blue dash and track method—red dash-triple dot). The total power spectrum is also shown for reference (dots). The horizontal dotted line is the estimate for the data noise associated with the total power spectra, while the solid horizontal line is the data noise split between inward and outward components. (b) The ratio of inward to outward power is displayed as a function of frequency and reveals a frequency-dependent trend suggestive of partial reflection of the waves in the corona. The vertical dashed line highlights the frequency after which noise begins to dominate the inward power spectra. The error bars in both plots show the s.e.m.
Mentions: The power spectrum for the Doppler velocity time–distance diagrams is determined for a range of frequencies (f) and wavenumbers (k) in the vertical direction, and the outward and inward propagating signals are decomposed. To analyse the waves, both an f–k diagram (Fig. 2) and wavenumber-integrated power spectra are calculated (Fig. 3). A prominent ridge in the left half of the f–k diagram corresponding to negative frequencies confirms the dominance of outward propagating waves. No clear ridge exists for the inward propagating waves although there is significant power in the low frequency part of the spectrum. Such ridges have also been found in f–k diagrams for large quiescent coronal loops40.

Bottom Line: The existence of Alfvén waves far from the Sun has been known since the 1970s, and recently the presence of ubiquitous Alfvénic waves throughout the solar atmosphere has been confirmed.However, the presence of atmospheric Alfvénic waves does not, alone, provide sufficient support for wave-based models; the existence of counter-propagating Alfvénic waves is crucial for the development of turbulence.The results enhance our knowledge of Alfvénic wave propagation in the solar atmosphere, providing support and constraints for some of the recent Alfvén wave turbulence models.

View Article: PubMed Central - PubMed

Affiliation: 1] Department of Mathematics and Information Sciences, Northumbria University, Newcastle Upon Tyne NE1 8ST, UK. [2] High Altitude Observatory, National Center for Atmospheric Research, Boulder, Colorado 80307-3000, USA.

ABSTRACT
The physical mechanisms behind accelerating solar and stellar winds are a long-standing astrophysical mystery, although recent breakthroughs have come from models invoking the turbulent dissipation of Alfvén waves. The existence of Alfvén waves far from the Sun has been known since the 1970s, and recently the presence of ubiquitous Alfvénic waves throughout the solar atmosphere has been confirmed. However, the presence of atmospheric Alfvénic waves does not, alone, provide sufficient support for wave-based models; the existence of counter-propagating Alfvénic waves is crucial for the development of turbulence. Here, we demonstrate that counter-propagating Alfvénic waves exist in open coronal magnetic fields and reveal key observational insights into the details of their generation, reflection in the upper atmosphere and outward propagation into the solar wind. The results enhance our knowledge of Alfvénic wave propagation in the solar atmosphere, providing support and constraints for some of the recent Alfvén wave turbulence models.

No MeSH data available.


Related in: MedlinePlus