E-Print Archive

There are 3882 abstracts currently viewable.


Search:

Advanced Search
Options
Main Page Add New E-Print Submitter
Information
Feedback
News Help/FAQ About Preferences
Manage Key Phrase
Notification
A global view of velocity fluctuations in the corona below 1.3 R_odot with CoMP  

Richard Morton   Submitted: 2016-09-06 03:48

The Coronal Multi-channel Polarimeter (CoMP) has previously demonstrated the presence of Doppler velocity fluctuations in the solar corona. The observed fluctuations are thought to be transverse waves, i.e. highly incompressible motions whose restoring force is dominated by the magnetic tension, some of which demonstrate clear periodicity. We aim to exploit CoMP's ability to provide high cadence observations of the off-limb corona to investigate the properties of velocity fluctuations in a range of coronal features, providing insight into how(if) the properties of the waves are influenced by the varying magnetic topology in active regions, quiet Sun and open fields regions. An analysis of Doppler velocity time-series of the solar corona from the 10,747 Å Iron XIII line is performed, determining the velocity power spectra and using it as a tool to probe wave behaviour. Further, the average phase speed and density for each region are estimated and used to compute the spectra for energy density and energy flux. In addition, we assess the noise levels associated with the CoMP data, deriving analytic formulae for the uncertainty on Doppler velocity measurements and providing a comparison by estimating the noise from the data. It is found that the entire corona is replete with transverse wave behaviour. The corresponding power spectra indicates that the observed velocity fluctuations are predominately generated by stochastic processes, with the spectral slope of the power varying between the different magnetic regions. Most strikingly, all power spectra reveal the presence of enhanced power occurring at ~3~mHz, potentially implying that the excitation of coronal transverse waves by p-modes is a global phenomenon.

Authors: Morton, R. J.; Tomczyk, S.; Pinto, R. F.
Projects: None

Publication Status: In Press
Last Modified: 2016-09-07 12:12
Go to main E-Print page  Edit Entry  Download Preprint  Delete Entry 

Investigating Alfvénic wave propagation in coronal open-field regions  

Richard Morton   Submitted: 2015-08-03 01:55

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.

Authors: R. J. Morton, S. Tomczyk & R. Pinto
Projects:

Publication Status: Published Nature Communications
Last Modified: 2015-08-11 16:05
Go to main E-Print page  Edit Entry  Download Preprint  Delete Entry 

High-resolution observations of active region moss and its dynamics  

Richard Morton   Submitted: 2014-05-23 01:52

The High resolution Coronal Imager (Hi-C) has provided the sharpest view of the EUV corona to date. In this paper we exploit its impressive resolving power to provide the first analysis of the fine-scale structure of moss in an active region. The data reveal that the moss is made up of a collection of fine threads, that have widths with a mean and standard deviation of 440±190 km (Full Width Half Maximum). The brightest moss emission is located at the visible head of the fine-scale structure and the fine structure appears to extend into the lower solar atmosphere. The emission decreases along the features implying the lower sections are most likely dominated by cooler transition region plasma. These threads appear to be the cool, lower legs of the hot loops. In addition, the increased resolution allows for the first direct observation of physical displacements of the moss fine-structure in a direction transverse to its central axis. Some of these transverse displacements demonstrate periodic behaviour, which we interpret as a signature of kink (Alfvénic) waves. Measurements of the properties of the transverse motions are made and the wave motions have means and standard deviations of 55±37 km for the transverse displacement amplitude, 77±33 s for the period and 4.7±2.5 km s-1 for the velocity amplitude. The presence of waves in the transition region of hot loops could have important implications for the heating of active regions.

Authors: R J Morton & J A McLaughlin
Projects: None

Publication Status: Accepted ApJ
Last Modified: 2014-05-26 13:02
Go to main E-Print page  Edit Entry  Download Preprint  Delete Entry 

Magneto-seismological insights into the penumbral chromosphere and evidence for wave damping in spicules  

Richard Morton   Submitted: 2014-05-14 01:50

The observation of propagating magneto-hydrodynamic kink waves in magnetic structures and measurement of their properties (amplitude, phase speed) can be used to diagnose the plasma conditions in the neighbourhood of the magnetic structure via magneto-seismology (MS). We aim to reveal properties of the chromosphere/Transition Region above the sunspot penumbra using this technique. Hinode observed a sunspot as it was crossing the limb, providing a unique side on view of the sunspot atmosphere. The presence of large spicule-like jets is evident in \ion{Ca}{II} H images. The jets are found to support transverse wave motions that displace the central axis, which can be interpreted as a kink wave. The properties of a wave event are measured and used to determine the magnetic and density stratification along the structure. We also measure the width of the spicule and the intensity profile along the structure. The measured wave properties reveal an initial rapid increase in amplitude with height above the solar surface, followed by a decrease in amplitude. The MS inversion suggests this initial increase corresponds to large changes in density and magnetic field strength. In addition, we provide the first measurements of spicule width with height, which confirm that the spicule under goes rapid expansion. The measured expansion shows good agreement with the results from the MS. The observed variations in plasma parameters are suggested to be partly due to the presence of a gravitational stratified, ambient atmosphere. Combining width measurements with phase speed measurements implies the observed decrease in wave amplitude at greater heights can be explained by wave damping. Hence, we provide the first direct evidence of wave damping in chromospheric spicules and the quality factor of the damping is found to be significantly smaller than estimated coronal values.

Authors: R J Morton
Projects: Hinode/SOT

Publication Status: Accepted A&A
Last Modified: 2014-05-14 13:09
Go to main E-Print page  Edit Entry  Download Preprint  Delete Entry 

The generation and damping of propagating MHD kink waves in the solar atmosphere  

Richard Morton   Submitted: 2014-01-29 03:04

The source of the non-thermal energy required for the heating of the upper solar atmosphere to temperatures in excess of a million degrees and the acceleration of the solar wind to hundreds of kilometres per second is still unclear. One such mechanism for providing the required energy flux is incompressible torsional Alfvén and kink magnetohydrodynamic (MHD) waves, which are magnetically dominated waves supported by the Sun's pervasive and complex magnetic field. In particular, propagating MHD kink waves have recently been observed to be ubiquitous throughout the solar atmosphere, but, until now, critical details of the transport of the kink wave energy throughout the Sun's atmosphere were unclear. Here, the ubiquity of the waves is exploited for statistical studies in the highly dynamic solar chromosphere. This large-scale investigation allows for the determination of the chromospheric kink wave velocity power spectra, a missing link necessary for determining the energy transport between the photosphere and corona. Crucially, the power spectra contains evidence for horizontal photospheric motions being the main mechanism for kink wave generation in the quiescent Sun. In addition, a comparison to measured coronal power spectra is provided, revealing frequency-dependent transmission profiles suggesting there is enhanced damping of kink waves in the lower corona.

Authors: R. J. Morton, G. Verth, A. Hillier, R. Erdélyi
Projects: None

Publication Status: In press - March 2014
Last Modified: 2014-01-29 12:20
Go to main E-Print page  Edit Entry  Download Preprint  Delete Entry 

The dynamical behaviour of a jet in an on-disk coronal hole observed with AIA/SDO  

Richard Morton   Submitted: 2013-10-30 03:15

{EUV jets situated in coronal holes are thought to play an important role in supplying heated material to the corona and solar wind. The multi-wavelength capabilities and high signal-to-noise of detectors on-board SDO allows for detailed study of these jet's evolution. We aim to exploit SDO's capabilities to reveal information on the jet dynamics and obtain estimates for plasma properties associated with the jet.} {We study the dynamics an EUV jet with AIA/SDO at a coronal hole boundary. The details of the jet evolution are discussed and measurements of the jet's parameters, e.g. length, width, life time, outward speed, are obtained. Further, automated emission measure analysis is exploited to determine estimates for the temperature and density of the jet. A propagating transverse wave supported by the jet spire is also observed. Measurement of the wave properties are exploited for magneto-seismology and are used in conjunction with the emission measure results to estimate the magnetic field strength of the jet.} {We present a detailed description of the jet's evolution, with new evidence for plasma flows, prior to the jet's initiation, along the loops at the base of the jet and also find further evidence that flows along the jet spire consist of multiple, quasi-periodic small-scale plasma ejection events. In addition, DEM analysis suggests that the jet has temperatures of log{5.89pm0.08} K and electron densities of log{8.75pm0.05}~cm-3. Measured properties of the transverse wave suggest the wave is heavily damped as it propagates along the jet spire with speeds of sim110 km s-1. The magneto-seismological inversion of the wave parameters provides values of B=1.21pm0.2~G along the jet spire, which is in line with previous estimates for open fields in coronal holes. }

Authors: K. Chandrashekhar, R. J. Morton, D. Banerjee and G. R. Gupta
Projects: SDO-AIA

Publication Status: Accepted A&A
Last Modified: 2013-10-30 17:01
Go to main E-Print page  Edit Entry  Download Preprint  Delete Entry 

Observations of ubiquitous compressive waves in the Sun's chromosphere  

Richard Morton   Submitted: 2013-06-19 06:29

The details of the mechanism(s) responsible for the observed heating and dynamics of the solar atmosphere still remain a mystery. Magnetohydrodynamic (MHD) waves are thought to play a vital role in this process. Although it has been shown that incompressible waves are ubiquitous in off-limb solar atmospheric observations their energy cannot be readily dissipated. We provide here, for the first time, on-disk observation and identification of concurrent MHD wave modes, both compressible and incompressible, in the solar chromosphere. The observed ubiquity and estimated energy flux associated with the detected MHD waves suggest the chromosphere is a vast reservoir of wave energy with the potential to meet chromospheric and coronal heating requirements. We are also able to propose an upper bound on the flux of the observed wave energy that is able to reach the corona based on observational constraints, which has important implications for the suggested mechanism(s) for quiescent coronal heating.

Authors: R. J. Morton, G. Verth, D. B. Jess, D. Kuridze, M. S. Ruderman, M. Mathioudakis, R. Erdelyi
Projects: None

Publication Status: Published Nature Communications, 3, 1315 (2012)
Last Modified: 2013-06-19 11:44
Go to main E-Print page  Edit Entry  Download Preprint  Delete Entry 

Hi-C & AIA observations of transverse MHD waves in active regions  

Richard Morton   Submitted: 2013-05-02 07:08

The recent launch of the High resolution Coronal imager (Hi-C) provided a unique opportunity to study the EUV corona with unprecedented spatial resolution. We utilize these observations to investigate the properties of low frequency (50-200 s) active region transverse waves, whose omnipresence had been suggested previously. The five-fold improvement in spatial resolution over SDO/AIA reveals coronal loops with widths 150-310 km and that these loops support transverse waves with displacement amplitudes <50 km. However, the results suggest that wave activity in the coronal loops is of low energy, with typical velocity amplitudes <3 km s-1. An extended time-series of SDO data suggest low-energy wave behaviour is typical of the coronal structures both before and after the Hi-C observations.

Authors: R J Morton & J A McLaughlin
Projects: None

Publication Status: Accepted A&A Letters
Last Modified: 2013-05-02 09:04
Go to main E-Print page  Edit Entry  Download Preprint  Delete Entry 

Evidence for the photospheric excitation of incompressible chromspheric waves  

Richard Morton   Submitted: 2013-03-12 03:02

Observing the excitation mechanisms of incompressible transverse waves is vital for determining how energy propagates through the lower solar atmosphere. We aim to show the connection between convectively driven photospheric flows and incompressible chromospheric waves. The observations presented here show the propagation of incompressible motion through the quiet lower solar atmosphere, from the photosphere to the chromosphere. We determine flow vectors to search for signatures of vortex motion and compare results to photospheric flows present in convective simulations. Further, we search for the chromospheric response to vortex motions. Evidence is presented that suggests incompressible waves can be excited by the vortex motions of a strong magnetic flux concentration in the photosphere. A chromospheric counterpart to the photospheric vortex motion is also observed, presenting itself as a quasi-periodic torsional motion. Fine-scale, fibril structures that emanate from the chromospheric counterpart support transverse waves that are driven by the observed torsional motion. A new technique for obtaining details of transverse waves from time-distance diagrams is presented and the properties of transverse waves (e.g., amplitudes and periods) excited by the chromospheric torsional motion are measured.

Authors: R. J. Morton, G. Verth, V. Fedun, S. Shelyag, R. Erd'elyi
Projects: Other

Publication Status: Accepted ApJ - Expected May
Last Modified: 2013-03-18 03:05
Go to main E-Print page  Edit Entry  Download Preprint  Delete Entry 

Chromospheric jets around the edges of sunspots  

Richard Morton   Submitted: 2012-05-11 02:32

Evidence is beginning to be put forward that demonstrates the role of the chromosphere in supplying energy and mass to the corona. We aim to asses the role of chromospheric jets in active region dynamics}{Using a combination of the {Hinode/SOT} Ca II H and TRACE 1550 {AA} and 1600 {AA} filters we examine chromospheric jets situated at the edge of a sunspot.}{Analysis reveals a near continuous series of jets, that raise chromospheric material into the low corona above a sunspot. The jets have average rise speeds of 30 km,s-1 and a range of 10-100km,s-1. Enhanced emission observed at the jets leading edge suggests the formation of a shock front. Increased emission in TRACE bandpasses above the sunspot and the disappearance of the jets from the Ca II filter suggests that some of the chromospheric jet material is at least heated to sim0.1MK. The evidence suggests that the jets could be a mechanism which provides a steady, low-level heating for active region features.

Authors: R. J. Morton
Projects: Hinode/SOT

Publication Status: In Press A&A
Last Modified: 2012-05-11 11:52
Go to main E-Print page  Edit Entry  Download Preprint  Delete Entry 

Observations of quasi-periodic phenomena associated with a large blowout solar jet  

Richard Morton   Submitted: 2012-04-24 02:13

A variety of periodic phenomena have been observed in conjunction with large solar jets. We aim to find further evidence for {(quasi-)}periodic behaviour in solar jets and determine what the periodic behaviour can tell us about the excitation mechanism and formation process of the large solar jet. Using the 304 {AA} (He-II), 171 {AA} (Fe IX), 193 {AA} (Fe XII/XXIV) and 131 {AA} (Fe VIII/XXI) filters on-board the Solar Dynamic Observatory (SDO) Atmospheric Imaging Assembly (AIA), we investigate the intensity oscillations associated with a solar jet. Evidence is provided for multiple magnetic reconnection events occurring between a pre-twisted, closed field and open field lines. Components of the jet are seen in multiple SDO/AIA filters covering a wide range of temperatures, suggesting the jet can be classified as a blowout jet. Two bright, elongated features are observed to be co-spatial with the large jet, appearing at the jet's footpoints. Investigation of these features reveal they are defined by multiple plasma ejections. The ejecta display (quasi-)periodic behaviour on timescales of 50 s and have rise velocities of 40-150 km,s-1 along the open field lines. Due to the suggestion that the large jet is reconnection-driven and the observed properties of the ejecta, we further propose that these ejecta events are similar to type-II spicules. The bright features also display (quasi)-periodic intensity perturbations on the timescale of 300 s. Possible explanations for the existence of the (quasi-)periodic perturbations in terms of jet dynamics and the response of the transition region are discussed.

Authors: R. J. Morton, A. K. Srivastava, R. Erd'elyi
Projects: SDO-AIA

Publication Status: In print
Last Modified: 2012-04-25 12:19
Go to main E-Print page  Edit Entry  Download Preprint  Delete Entry 

Torsional Alfvén waves: Magneto-seismology in static anddynamic coronal plasmas  

Richard Morton   Submitted: 2011-08-17 08:32

This abstract was corrupted following database problems and is being recovered. It will be restored as quickly as possible. Any questions, please send them to Alisdair. Sorry for any incovenience.


Authors: R. Morton, M. Ruderman, R. Erdelyi,
Projects: None

Publication Status: accepted A&A
Last Modified: 2011-08-17 12:02
Go to main E-Print page  Edit Entry  Download Preprint  Delete Entry 

Non-axisymmetric oscillations of stratified coronal magnetic loops with elliptical cross-sections  

Richard Morton   Submitted: 2010-11-11 02:39

We study non-axisymmetric oscillations of a straight magnetic tube with an elliptic cross-section and density varying along the tube. The governing equations for kink and fluting modes in the thin tube approximation are derived. We found that there are two kink modes, polarised along the large and small axes of the elliptic cross-section. We have shown that the ratio of frequencies of the first overtone and fundamental harmonic is the same for both kink modes and independent of the ratio of the ellipse axes. On the basis of this result we concluded that the estimates of the atmospheric scale height obtained using simultaneous observations of the fundamental harmonic and first overtone of the coronal loop kink oscillations are independent of the ellipticity of the loop cross-section.

Authors: R. J. Morton, M. S. Ruderman
Projects: None

Publication Status: Submitted A&A
Last Modified: 2010-11-11 10:59
Go to main E-Print page  Edit Entry  Download Preprint  Delete Entry 

Observations of sausage modes in magnetic pores  

Richard Morton   Submitted: 2010-11-11 02:37

We present here evidence for the observation of the magneto-hydrodynamic (MHD) sausage modes in magnetic pores in the solar photosphere. Further evidence for the omnipresent nature of acoustic global modes is also found. The empirical decomposition method of wave analysis is used to identify the oscillations detected through a 4170 {AA} 'blue continuum' filter observed with the Rapid Oscillations in the Solar Atmosphere (ROSA) instrument. Out of phase, periodic behavior in pore size and intensity is used as an indicator of the presence of magneto-acoustic sausage oscillations. Multiple signatures of the magneto-acoustic sausage mode are found in a number of pores. The periods range from as short as 30 s up to 450 s. A number of the magneto-acoustic sausage mode oscillations found have periods of 3 and 5 minutes, similar to the acoustic global modes of the solar interior. It is proposed that these global oscillations could be the driver of the sausage type magneto-acoustic MHD wave modes in pores.

Authors: R.J. Morton, R. Erdélyi, D.B. Jess, M. Mathioudakis
Projects: None

Publication Status: Submitted ApJL
Last Modified: 2010-11-11 10:59
Go to main E-Print page  Edit Entry  Download Preprint  Delete Entry 

DAMPING OF KINK OSCILLATIONS BY COOLING OF CORONAL LOOP PLASMA  

Richard Morton   Submitted: 2009-05-12 04:20

We present here a comparative study between the observed damping of fast kink oscillations and the theoretical model of damping due to the cooling of the coronal loops. A recent time dependent model of a cooling coronal loop predicts that transverse oscillations of the loop could be significantly damped due to the cooling process. The theory is applied to examples of TRACE observations of damped kink oscillations. We find that, for cooling timescales that are typical of EUV loops (500 - 2000 s), the observed damping of the kink oscillations can be accounted for almost entirely by the cooling process in half of the examples. In the other examples the cooling process could still have significant influence on the damping, however, another mechanism(s) of damping, e.g. resonant absorption, may be additionally required to account for the remaining decay of oscillations.

Authors: Morton, R.J., Erdelyi, R.
Projects: TRACE

Publication Status: ApJ (submitted)
Last Modified: 2009-05-12 07:28
Go to main E-Print page  Edit Entry  Download Preprint  Delete Entry 

MHD waves in a compressible magnetic flux tube with elliptical cross-section  

Richard Morton   Submitted: 2008-10-30 07:21

The propagation of magnetohydrodynamic (MHD) waves in a finite, compressible magnetic flux tube with an elliptical cross-section embedded in a magnetic environment is investigated. Presented is the derivation of the general dispersion relation of linear magneto-acoustic wave propagation for a compressible magnetic flux tube with elliptical cross-section in a plasma with finite beta. The wave modes of propagation for the n=0 (symmetric) sausage and n=1 (anti-symmetric) kink oscillations are then examined in the limit of the thin flux tube approximation. It is shown that a compressible magnetic tube with elliptical cross-section supports slow and fast magneto-acoustic waves. In the thin tube approximation the slow sausage mode and the slow and fast kink modes are found in analogue to a circular cross-section. However, the kink modes propagate with different phase speeds depending on whether the axial displacement takes place along the major or minor axis of the ellipse. This feature is present in both the slow and the fast bands, providing two infinite sets of slow kink modes and two infinite sets of fast kink modes, i.e. each corresponding cylindrical mode splits into two sets of modes due to the ellipticity. The difference between the phase speeds along the different axis is dependent on the ratio of the lengths of the two axis. Analytical expressions for the phase speeds are found. It is shown that the sausage modes do not split due to the introduced ellipticity, only the phase speed is modified when compared to the appropriate cylindrical counterpart. The percentage difference between the periods of the circular and elliptical cross-sections is also calculated, which reaches up to 21% for oscillations along the major axis approximately twice the length of the minor axis. The level of difference in period could be very important in magneto-seismological applications, when observed periods are inverted into diagnostic properties (e.g. magnetic field strength, gravitational scale height, tube expansion parameter, ect.). Also shown is the perturbation of focal points of the elliptical cross-section for different modes. It is found that the focal points are unperturbed for the sausage mode, but are perturbed for all higher modes.

Authors: R. Erdelyi, R.J. Morton
Projects:

Publication Status: A&A, Accepted
Last Modified: 2008-11-05 06:41
Go to main E-Print page  Edit Entry  Download Preprint  Delete Entry 


Key
Go to main E-Print pageGo to main E-Print page.
Download PreprintDownload Preprint.
Submitter's HomepageSubmitters Homepage.
Edit EntryEdit Entry.
Delete AbstractDelete abstract.

Abstracts by Author
A global view of velocity fluctuations in the corona below 1.3 $R_odot$ with CoMP
Investigating Alfv?nic wave propagation in coronal open-field regions
High-resolution observations of active region moss and its dynamics
Magneto-seismological insights into the penumbral chromosphere and evidence for wave damping in spicules
The generation and damping of propagating MHD kink waves in the solar atmosphere
The dynamical behaviour of a jet in an on-disk coronal hole observed with AIA/SDO
Observations of ubiquitous compressive waves in the Sun's chromosphere
Hi-C & AIA observations of transverse MHD waves in active regions
Evidence for the photospheric excitation of incompressible chromspheric waves
Chromospheric jets around the edges of sunspots
Observations of quasi-periodic phenomena associated with a large blowout solar jet
Torsional Alfvén waves: Magneto-seismology in static and dynamic coronal plasmas
Non-axisymmetric oscillations of stratified coronal magnetic loops with elliptical cross-sections
Observations of sausage modes in magnetic pores
DAMPING OF KINK OSCILLATIONS BY COOLING OF CORONAL LOOP PLASMA
MHD waves in a compressible magnetic flux tube with elliptical cross-section

Related Pages
MSU Solar Physics.
Max Millennium Science Mail Archive.
Max Millennium Message of the Day Mail Archive.
Max Millennium Flare Catalog

Archive Maintainer
Alisdair Davey



© 2003 Solar Physics Group - Montana State University