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Plasma evolution within an erupting coronal cavity  

David Long   Submitted: 2018-02-08 04:35

Coronal cavities have previously been observed associated with long-lived quiescent filaments and are thought to correspond to the associated magnetic flux rope. Although the standard flare model predicts a coronal cavity corresponding to the erupting flux rope, these have only been observed using broadband imaging data, restricting analysis to the plane-of-sky. We present a unique set of spectroscopic observations of an active region filament seen erupting at the solar limb in the extreme ultraviolet (EUV). The cavity erupted and expanded rapidly, with the change in rise phase contemporaneous with an increase in non-thermal electron energy flux of the associated flare. Hot and cool filamentary material was observed to rise with the erupting flux rope, disappearing suddenly as the cavity appeared. Although strongly blue-shifted plasma continued to be observed flowing from the apex of the erupting flux rope, this outflow soon ceased. These results indicate that the sudden injection of energy from the flare beneath forced the rapid eruption and expansion of the flux rope, driving strong plasma flows which resulted in the eruption of an under-dense filamentary flux rope.

Authors: David M. Long, Louise K. Harra, Sarah A. Matthews, Harry P. Warren, Kyoung-Sun Lee, George Doschek, Hirohisa Hara, Jack M. Jenkins
Projects: Hinode/EIS,SDO-AIA

Publication Status: Accepted in ApJ
Last Modified: 2018-02-08 16:19
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A Statistical Analysis of the Solar Phenomena Associated with Global EUV Waves  

David Long   Submitted: 2017-11-17 08:38

Solar eruptions are the most spectacular events in our solar system and are associated with many different signatures of energy release including solar flares, coronal mass ejections, global waves, radio emission and accelerated particles. Here, we apply the Coronal Pulse Identification and Tracking Algorithm (CorPITA) to the high cadence synoptic data provided by the Solar Dynamic Observatory (SDO) to identify and track global waves observed by SDO. 164 of the 362 solar flare events studied (45%) are found to have associated global waves with no waves found for the remaining 198 (55%). A clear linear relationship was found between the median initial velocity and the acceleration of the waves, with faster waves exhibiting a stronger deceleration (consistent with previous results). No clear relationship was found between global waves and type II radio bursts, electrons or protons detected in-situ near Earth. While no relationship was found between the wave properties and the associated flare size (with waves produced by flares from B to X-class), more than a quarter of the active regions studied were found to produce more than one wave event. These results suggest that the presence of a global wave in a solar eruption is most likely determined by the structure and connectivity of the erupting active region and the surrounding quiet solar corona rather than by the amount of free energy available within the active region.

Authors: David M. Long, Pearse Murphy, Georgina Graham, Eoin P. Carley, David Pérez-Suárez
Projects: GOES X-rays,SDO-AIA,SoHO-LASCO,Wind

Publication Status: Accepted for publication in Solar Physics
Last Modified: 2017-11-17 14:24
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Measuring the magnetic field of a trans-equatorial loop system using coronal seismology  

David Long   Submitted: 2017-04-04 01:00

"EIT waves" are freely-propagating global pulses in the low corona which are strongly associated with the initial evolution of coronal mass ejections (CMEs). They are thought to be large-amplitude, fast-mode magnetohydrodynamic waves initially driven by the rapid expansion of a CME in the low corona. An "EIT wave" was observed on 6 July 2012 to impact an adjacent trans-equatorial loop system which then exhibited a decaying oscillation as it returned to rest. Observations of the loop oscillations were used to estimate the magnetic field strength of the loop system by studying the decaying oscillation of the loop, measuring the propagation of ubiquitous transverse waves in the loop and extrapolating the magnetic field from observed magnetograms. Observations from the Atmospheric Imaging Assembly onboard the Solar Dynamics Observatory (SDO/AIA) and the Coronal Multi-channel Polarimeter (CoMP) were used to study the event. An Empirical Mode Decomposition analysis was used to characterise the oscillation of the loop system in CoMP Doppler velocity and line width and in AIA intensity. The loop system was shown to oscillate in the 2nd harmonic mode rather than at the fundamental frequency, with the seismological analysis returning an estimated magnetic field strength of ~5.5±1.5 G. This compares to the magnetic field strength estimates of ~1-9 G and ~3-9 G found using the measurements of transverse wave propagation and magnetic field extrapolation respectively.

Authors: David M. Long, Gherardo Valori, David Pérez-Suárez, Richard J. Morton, Alberto Marcos Vásquez
Projects: MLSO/CoMP,SDO-AIA

Publication Status: Accepted for publication in A&A
Last Modified: 2017-04-04 08:09
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Understanding the Physical Nature of Coronal "EIT Waves"  

David Long   Submitted: 2016-11-21 03:14

For almost 20 years the physical nature of globally propagating waves in the solar corona (commonly called "EIT waves") has been controversial and subject to debate. Additional theories have been proposed over the years to explain observations that did not fit with the originally proposed fast-mode wave interpretation. However, the incompatibility of observations made using the Extreme-ultraviolet Imaging Telescope (EIT) onboard the Solar and Heliospheric Observatory with the fast-mode wave interpretation was challenged by differing viewpoints from the twin Solar Terrestrial Relations Observatory spacecraft and higher spatial/temporal resolution data from the Solar Dynamics Observatory. In this article, we reexamine the theories proposed to explain "EIT waves" to identify measurable properties and behaviours that can be compared to current and future observations. Most of us conclude that "EIT waves" are best described as fast-mode large-amplitude waves/shocks that are initially driven by the impulsive expansion of an erupting coronal mass ejection in the low corona.

Authors: David M. Long, D. Shaun Bloomfield, Peng-Fei Chen, Cooper Downs, Peter T. Gallagher, Ryun Young Kwon, Kamalam Vanninathan, Astrid M. Veronig, Angelos Vourlidas, Bojan Vrsnak, Alexander Warmuth, Tomislav Zic
Projects: SDO-AIA,SoHO-EIT,STEREO

Publication Status: Accepted for publication in Solar Physics
Last Modified: 2016-11-21 12:28
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The energetics of a global shock wave in the low solar corona  

David Long   Submitted: 2015-01-08 04:10

As the most energetic eruptions in the solar system, coronal mass ejections (CMEs) can produce shock waves at both their front and flanks as they erupt from the Sun into the heliosphere. However, the amount of energy produced in these eruptions, and the proportion of their energy required to produce the waves, is not well characterised. Here we use observations of a solar eruption from 2014 February 25 to estimate the energy budget of an erupting CME and the globally-propagating "EIT wave" produced by the rapid expansion of the CME flanks in the low solar corona. The "EIT wave" is shown using a combination of radio spectra and extreme ultraviolet images to be a shock front with a Mach number greater than one. Its initial energy is then calculated using the Sedov-Taylor blast-wave approximation, which provides an approximation for a shock front propagating through a region of variable density. This approach provides an initial energy estimate of ≈2.8x1031 ergs to produce the "EIT wave", which is approximately 10% the kinetic energy of the associated CME (shown to be ≈2.5x1032 ergs). These results indicate that the energy of the "EIT wave" may be significant and must be considered when estimating the total energy budget of solar eruptions.

Authors: David M. Long, Deborah Baker, David R. Williams, Eoin P. Carley, Peter T. Gallagher, Pietro Zucca
Projects: Hinode/EIS,SDO-AIA

Publication Status: Accepted for publication in ApJ
Last Modified: 2015-01-09 12:50
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CorPITA: An Automated Algorithm for the Identification and Analysis of Coronal "EIT Waves"  

David Long   Submitted: 2014-03-27 05:55

The continuous stream of data available from the Atmospheric Imaging Assembly (AIA) telescopes onboard the Solar Dynamics Observatory (SDO) spacecraft has allowed a deeper understanding of the Sun. However, the sheer volume of data has necessitated the development of automated techniques to identify and analyse various phenomena. In this article, we describe the Coronal Pulse Identification and Tracking Algorithm (CorPITA) for the identification and analysis of coronal "EIT waves". CorPITA uses an intensity-profile technique to identify the propagating pulse, tracking it throughout its evolution before returning estimates of its kinematics. The algorithm is applied here to a data-set from February 2011, allowing its capabilities to be examined and critiqued. This algorithm forms part of the SDO Feature Finding Team initiative and will be implemented as part of the Heliophysics Event Knowledgebase (HEK). This is the first fully automated algorithm to identify and track the propagating "EIT wave" rather than any associated phenomena and will allow a deeper understanding of this controversial phenomenon.

Authors: David M. Long, D. Shaun Bloomfield, Peter T. Gallagher, David Pérez-Suárez
Projects: SDO-AIA

Publication Status: Accepted for publication in Solar Physics
Last Modified: 2014-03-31 07:26
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Measuring the Magnetic Field Strength of the Quiet Solar Corona Using ''EIT Waves''  

David Long   Submitted: 2013-05-23 02:00

Variations in the propagation of globally-propagating disturbances (commonly called ''EIT waves'') through the low solar corona offer a unique opportunity to probe the plasma parameters of the solar atmosphere. Here, high-cadence observations of two ''EIT wave'' events taken using the Atmospheric Imaging Assembly (AIA) instrument onboard the Solar Dynamics Observatory (SDO) are combined with spectroscopic measurements from the Extreme ultraviolet Imaging Spectrometer (EIS) onboard the Hinode spacecraft and used to examine the variability of the quiet coronal magnetic-field strength. The combination of pulse kinematics from SDO/AIA and plasma density from Hinode/EIS is used to show that the magnetic-field strength is in the range ~2-6 G in the quiet corona. The magnetic-field estimates are then used to determine the height of the pulse, allowing a direct comparison with theoretical values obtained from magnetic-field measurements from the Helioseismic and Magnetic Imager (HMI) onboard SDO using PFSS and local-domain extrapolations. While local-scale extrapolations predict heights inconsistent with prior measurements, the agreement between observations and the PFSS model indicates that ''EIT waves'' are a global phenomenon influenced by global-scale magnetic field.

Authors: David M. Long, David R. Williams, St?phane Régnier, Louise K. Harra
Projects: Hinode/EIS,Hinode/SOT,SDO-AIA,SDO-HMI

Publication Status: Solar Physics (in press)
Last Modified: 2013-05-23 16:17
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The Wave Properties of Coronal Bright Fronts Observed Using SDO/AIA  

David Long   Submitted: 2011-09-27 04:06

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: Long, David M., DeLuca, Edward E., Gallagher, Peter T.
Projects: SDO-AIA,STEREO

Publication Status: ApJL (in press)
Last Modified: 2011-09-27 10:19
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Deceleration and Dispersion of Large-scale Coronal Bright Fronts  

David Long   Submitted: 2011-04-21 12:57

One of the most dramatic manifestations of solar activity are large-scale coronal bright fronts (CBFs) observed in extreme ultraviolet (EUV) images of the solar atmosphere. To date, the energetics and kinematics of CBFs remain poorly understood, due to the low image cadence and sensitivity of previous EUV imagers and the limited methods used to extract the features. In this paper, the trajectory and morphology of CBFs was determined in order to investigate the varying properties of a sample of CBFs, including their kinematics and pulse shape, dispersion, and dissipation. We have developed a semi-automatic intensity profiling technique to extract the morphology and accurate positions of CBFs in 2.5-10 min cadence images from STEREO/EUVI. The technique was applied to sequences of 171A and 195A images from STEREO/EUVI in order to measure the wave properties of four separate CBF events. Following launch at velocities of ~240-450kms-1 each of the four events studied showed significant negative acceleration ranging from ~ -290 to -60ms-2. The CBF spatial and temporal widths were found to increase from ~50 Mm to ~200 Mm and ~100 s to ~1500 s respectively, suggesting that they are dispersive in nature. The variation in position-angle averaged pulse-integrated intensity with propagation shows no clear trend across the four events studied. These results are most consistent with CBFs being dispersive magnetoacoustic waves.

Authors: Long, D. M., Gallagher, P. T., McAteer, R. T. J., Bloomfield, D.S.
Projects: STEREO

Publication Status: A&A (in press)
Last Modified: 2011-04-22 14:08
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David Long   Submitted: 2008-04-30 03:47

The kinematics of a globally propagating disturbance (also known as an "EIT wave") is discussed using Extreme UltraViolet Imager (EUVI) data from Solar Terrestrial Relations Observatory (STEREO ). We show for the first time that an impulsively generated propagating disturbance has similar kinematics in all four EUVI passbands (304, 171, 195, and 284 ?). In the 304 Å passband the disturbance shows a velocity peak of 238?20 km s-1 within ∼28 minutes of its launch, varying in acceleration from 76 m s-2 to -102 m s-2. This passband contains a strong contribution from a Si XI line (303.32 ?) with a peak formation temperature of ∼1.6 MK. The 304 Å emission may therefore be coronal rather than chromospheric in origin. Comparable velocities and accelerations are found in the coronal 195 Å passband, while lower values are found in the lower cadence 284 ? passband. In the higher cadence 171 Å passband the velocity varies significantly, peaking at 475?47 km s-1 within ∼20 minutes of launch, with a variation in acceleration from 816 m s-2 to -413 m s-2. The high image cadence of the 171 Å passband (2.5 minutes compared to 10 minutes for the similar temperature response 195 Å passband) is found to have a major effect on the measured velocity and acceleration of the pulse, which increase by factors of ∼2 and ∼10, respectively. This implies that previously measured values (e.g., using EIT) may have been underestimated. We also note that the disturbance shows strong reflection from a coronal hole in both the 171 and 195 Å passbands. The observations are consistent with an impulsively generated fast-mode magnetoacoustic wave.

Authors: Long, D. M., Gallagher, P. T., McAteer, R. T. J., Bloomfield, D. S
Projects: STEREO

Publication Status: ApJ (accepted)
Last Modified: 2008-04-30 08:51
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David Long   Submitted: 2008-04-30 03:47

The kinematics of a globally propagating disturbance (also known as an 'EIT wave') is discussed using Extreme UltraViolet Imager (EUVI) data from Solar Terrestrial Relations Observatory (STEREO ). We show for the first time that an impulsively generated propagating disturbance has similar kinematics in all four EUVI passbands (304, 171, 195, and 284 A). In the 304 Å passband the disturbance shows a velocity peak of 238±20 km s-1 within ∼28 minutes of its launch, varying in acceleration from 76 m s-2 to -102 m s-2. This passband contains a strong contribution from a Si XI line (303.32 A) with a peak formation temperature of ∼1.6 MK. The 304 Å emission may therefore be coronal rather than chromospheric in origin. Comparable velocities and accelerations are found in the coronal 195 A passband, while lower values are found in the lower cadence 284 A passband. In the higher cadence 171 Å passband the velocity varies significantly, peaking at 475±47 km s-1 within ∼20 minutes of launch, with a variation in acceleration from 816 m s-2 to -413 m s-2. The high image cadence of the 171 Å passband (2.5 minutes compared to 10 minutes for the similar temperature response 195 A passband) is found to have a major effect on the measured velocity and acceleration of the pulse, which increase by factors of ∼2 and ∼10, respectively. This implies that previously measured values (e.g., using EIT) may have been underestimated. We also note that the disturbance shows strong reflection from a coronal hole in both the 171 and 195 A passbands. The observations are consistent with an impulsively generated fast-mode magnetoacoustic wave.

Authors: Long, D. M., Gallagher, P. T., McAteer, R. T. J., Bloomfield, D. S
Projects: STEREO

Publication Status: ApJ (accepted)
Last Modified: 2008-04-30 10:01
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Subject will be restored when possible  

David Long   Submitted: 2008-04-30 03:47

The kinematics of a globally propagating disturbance (also known as an 'EIT wave') is discussed using Extreme UltraViolet Imager (EUVI) data from Solar Terrestrial Relations Observatory (STEREO ). We show for the first time that an impulsively generated propagating disturbance has similar kinematics in all four EUVI passbands (304, 171, 195, and 284 A). In the 304 Å passband the disturbance shows a velocity peak of 238±20 km s-1 within ∼28 minutes of its launch, varying in acceleration from 76 m s-2 to -102 m s-2. This passband contains a strong contribution from a Si XI line (303.32 A) with a peak formation temperature of ∼1.6 MK. The 304 Å emission may therefore be coronal rather than chromospheric in origin. Comparable velocities and accelerations are found in the coronal 195 A passband, while lower values are found in the lower cadence 284 A passband. In the higher cadence 171 Å passband the velocity varies significantly, peaking at 475±47 km s-1 within ∼20 minutes of launch, with a variation in acceleration from 816 m s-2 to -413 m s-2. The high image cadence of the 171 Å passband (2.5 minutes compared to 10 minutes for the similar temperature response 195 A passband) is found to have a major effect on the measured velocity and acceleration of the pulse, which increase by factors of ∼2 and ∼10, respectively. This implies that previously measured values (e.g., using EIT) may have been underestimated. We also note that the disturbance shows strong reflection from a coronal hole in both the 171 and 195 A passbands. The observations are consistent with an impulsively generated fast-mode magnetoacoustic wave.

Authors: Long, D. M., Gallagher, P. T., McAteer, R. T. J., Bloomfield, D. S
Projects: STEREO

Publication Status: ApJ (accepted)
Last Modified: 2008-04-30 10:01
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Subject will be restored when possible  

David Long   Submitted: 2008-04-30 03:47

The kinematics of a globally propagating disturbance (also known as an 'EIT wave') is discussed using Extreme UltraViolet Imager (EUVI) data from Solar Terrestrial Relations Observatory (STEREO ). We show for the first time that an impulsively generated propagating disturbance has similar kinematics in all four EUVI passbands (304, 171, 195, and 284 A). In the 304 Å passband the disturbance shows a velocity peak of 238±20 km s-1 within ∼28 minutes of its launch, varying in acceleration from 76 m s-2 to -102 m s-2. This passband contains a strong contribution from a Si XI line (303.32 A) with a peak formation temperature of ∼1.6 MK. The 304 Å emission may therefore be coronal rather than chromospheric in origin. Comparable velocities and accelerations are found in the coronal 195 A passband, while lower values are found in the lower cadence 284 A passband. In the higher cadence 171 Å passband the velocity varies significantly, peaking at 475±47 km s-1 within ∼20 minutes of launch, with a variation in acceleration from 816 m s-2 to -413 m s-2. The high image cadence of the 171 Å passband (2.5 minutes compared to 10 minutes for the similar temperature response 195 A passband) is found to have a major effect on the measured velocity and acceleration of the pulse, which increase by factors of ∼2 and ∼10, respectively. This implies that previously measured values (e.g., using EIT) may have been underestimated. We also note that the disturbance shows strong reflection from a coronal hole in both the 171 and 195 A passbands. The observations are consistent with an impulsively generated fast-mode magnetoacoustic wave.

Authors: Long, D. M., Gallagher, P. T., McAteer, R. T. J., Bloomfield, D. S
Projects: STEREO

Publication Status: ApJ (accepted)
Last Modified: 2008-09-23 21:03
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Subject will be restored when possible  

David Long   Submitted: 2008-04-30 03:47

The kinematics of a globally propagating disturbance (also known as an 'EIT wave') is discussed using Extreme UltraViolet Imager (EUVI) data from Solar Terrestrial Relations Observatory (STEREO ). We show for the first time that an impulsively generated propagating disturbance has similar kinematics in all four EUVI passbands (304, 171, 195, and 284 A). In the 304 Å passband the disturbance shows a velocity peak of 238±20 km s-1 within ∼28 minutes of its launch, varying in acceleration from 76 m s-2 to -102 m s-2. This passband contains a strong contribution from a Si XI line (303.32 A) with a peak formation temperature of ∼1.6 MK. The 304 Å emission may therefore be coronal rather than chromospheric in origin. Comparable velocities and accelerations are found in the coronal 195 A passband, while lower values are found in the lower cadence 284 A passband. In the higher cadence 171 Å passband the velocity varies significantly, peaking at 475±47 km s-1 within ∼20 minutes of launch, with a variation in acceleration from 816 m s-2 to -413 m s-2. The high image cadence of the 171 Å passband (2.5 minutes compared to 10 minutes for the similar temperature response 195 A passband) is found to have a major effect on the measured velocity and acceleration of the pulse, which increase by factors of ∼2 and ∼10, respectively. This implies that previously measured values (e.g., using EIT) may have been underestimated. We also note that the disturbance shows strong reflection from a coronal hole in both the 171 and 195 A passbands. The observations are consistent with an impulsively generated fast-mode magnetoacoustic wave.

Authors: Long, D. M., Gallagher, P. T., McAteer, R. T. J., Bloomfield, D. S
Projects: STEREO

Publication Status: ApJ (accepted)
Last Modified: 2008-05-09 04:54
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Subject will be restored when possible  

David Long   Submitted: 2008-04-30 03:47

The kinematics of a globally propagating disturbance (also known as an 'EIT wave') is discussed using Extreme UltraViolet Imager (EUVI) data from Solar Terrestrial Relations Observatory (STEREO ). We show for the first time that an impulsively generated propagating disturbance has similar kinematics in all four EUVI passbands (304, 171, 195, and 284 A). In the 304 Å passband the disturbance shows a velocity peak of 238±20 km s-1 within ∼28 minutes of its launch, varying in acceleration from 76 m s-2 to -102 m s-2. This passband contains a strong contribution from a Si XI line (303.32 A) with a peak formation temperature of ∼1.6 MK. The 304 Å emission may therefore be coronal rather than chromospheric in origin. Comparable velocities and accelerations are found in the coronal 195 A passband, while lower values are found in the lower cadence 284 A passband. In the higher cadence 171 Å passband the velocity varies significantly, peaking at 475±47 km s-1 within ∼20 minutes of launch, with a variation in acceleration from 816 m s-2 to -413 m s-2. The high image cadence of the 171 Å passband (2.5 minutes compared to 10 minutes for the similar temperature response 195 A passband) is found to have a major effect on the measured velocity and acceleration of the pulse, which increase by factors of ∼2 and ∼10, respectively. This implies that previously measured values (e.g., using EIT) may have been underestimated. We also note that the disturbance shows strong reflection from a coronal hole in both the 171 and 195 A passbands. The observations are consistent with an impulsively generated fast-mode magnetoacoustic wave.

Authors: Long, D. M., Gallagher, P. T., McAteer, R. T. J., Bloomfield, D. S
Projects: STEREO

Publication Status: ApJ (accepted)
Last Modified: 2008-09-23 21:03
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Subject will be restored when possible  

David Long   Submitted: 2008-04-30 03:47

The kinematics of a globally propagating disturbance (also known as an 'EIT wave') is discussed using Extreme UltraViolet Imager (EUVI) data from Solar Terrestrial Relations Observatory (STEREO ). We show for the first time that an impulsively generated propagating disturbance has similar kinematics in all four EUVI passbands (304, 171, 195, and 284 A). In the 304 Å passband the disturbance shows a velocity peak of 238±20 km s-1 within ∼28 minutes of its launch, varying in acceleration from 76 m s-2 to -102 m s-2. This passband contains a strong contribution from a Si XI line (303.32 A) with a peak formation temperature of ∼1.6 MK. The 304 Å emission may therefore be coronal rather than chromospheric in origin. Comparable velocities and accelerations are found in the coronal 195 A passband, while lower values are found in the lower cadence 284 A passband. In the higher cadence 171 Å passband the velocity varies significantly, peaking at 475±47 km s-1 within ∼20 minutes of launch, with a variation in acceleration from 816 m s-2 to -413 m s-2. The high image cadence of the 171 Å passband (2.5 minutes compared to 10 minutes for the similar temperature response 195 A passband) is found to have a major effect on the measured velocity and acceleration of the pulse, which increase by factors of ∼2 and ∼10, respectively. This implies that previously measured values (e.g., using EIT) may have been underestimated. We also note that the disturbance shows strong reflection from a coronal hole in both the 171 and 195 A passbands. The observations are consistent with an impulsively generated fast-mode magnetoacoustic wave.

Authors: Long, D. M., Gallagher, P. T., McAteer, R. T. J., Bloomfield, D. S
Projects: STEREO

Publication Status: ApJ (accepted)
Last Modified: 2008-05-09 06:57
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Subject will be restored when possible  

David Long   Submitted: 2008-04-30 03:47

The kinematics of a globally propagating disturbance (also known as an 'EIT wave') is discussed using Extreme UltraViolet Imager (EUVI) data from Solar Terrestrial Relations Observatory (STEREO ). We show for the first time that an impulsively generated propagating disturbance has similar kinematics in all four EUVI passbands (304, 171, 195, and 284 A). In the 304 Å passband the disturbance shows a velocity peak of 238±20 km s-1 within ∼28 minutes of its launch, varying in acceleration from 76 m s-2 to -102 m s-2. This passband contains a strong contribution from a Si XI line (303.32 A) with a peak formation temperature of ∼1.6 MK. The 304 Å emission may therefore be coronal rather than chromospheric in origin. Comparable velocities and accelerations are found in the coronal 195 A passband, while lower values are found in the lower cadence 284 A passband. In the higher cadence 171 Å passband the velocity varies significantly, peaking at 475±47 km s-1 within ∼20 minutes of launch, with a variation in acceleration from 816 m s-2 to -413 m s-2. The high image cadence of the 171 Å passband (2.5 minutes compared to 10 minutes for the similar temperature response 195 A passband) is found to have a major effect on the measured velocity and acceleration of the pulse, which increase by factors of ∼2 and ∼10, respectively. This implies that previously measured values (e.g., using EIT) may have been underestimated. We also note that the disturbance shows strong reflection from a coronal hole in both the 171 and 195 A passbands. The observations are consistent with an impulsively generated fast-mode magnetoacoustic wave.

Authors: Long, D. M., Gallagher, P. T., McAteer, R. T. J., Bloomfield, D. S
Projects: STEREO

Publication Status: ApJ (accepted)
Last Modified: 2008-09-23 21:03
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Subject will be restored when possible  

David Long   Submitted: 2008-04-30 03:46

The kinematics of a globally propagating disturbance (also known as an "EIT wave") is discussed using Extreme UltraViolet Imager (EUVI) data from Solar Terrestrial Relations Observatory (STEREO ). We show for the first time that an impulsively generated propagating disturbance has similar kinematics in all four EUVI passbands (304, 171, 195, and 284 A). In the 304 Å passband the disturbance shows a velocity peak of 238?20 km s-1 within ∼28 minutes of its launch, varying in acceleration from 76 m s-2 to -102 m s-2. This passband contains a strong contribution from a Si XI line (303.32 A) with a peak formation temperature of ∼1.6 MK. The 304 Å emission may therefore be coronal rather than chromospheric in origin. Comparable velocities and accelerations are found in the coronal 195 A passband, while lower values are found in the lower cadence 284 A passband. In the higher cadence 171 Å passband the velocity varies significantly, peaking at 475?47 km s-1 within ∼20 minutes of launch, with a variation in acceleration from 816 m s-2 to -413 m s-2. The high image cadence of the 171 Å passband (2.5 minutes compared to 10 minutes for the similar temperature response 195 A passband) is found to have a major effect on the measured velocity and acceleration of the pulse, which increase by factors of ∼2 and ∼10, respectively. This implies that previously measured values (e.g., using EIT) may have been underestimated. We also note that the disturbance shows strong reflection from a coronal hole in both the 171 and 195 A passbands. The observations are consistent with an impulsively generated fast-mode magnetoacoustic wave.

Authors: Long, D. M., Gallagher, P. T., McAteer, R. T. J., Bloomfield, D. S
Projects: STEREO

Publication Status: ApJ (accepted)
Last Modified: 2008-09-23 21:03
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Abstracts by Author
Plasma evolution within an erupting coronal cavity
A Statistical Analysis of the Solar Phenomena Associated with Global EUV Waves
Measuring the magnetic field of a trans-equatorial loop system using coronal seismology
Understanding the Physical Nature of Coronal "EIT Waves"
The energetics of a global shock wave in the low solar corona
CorPITA: An Automated Algorithm for the Identification and Analysis of Coronal "EIT Waves"
Measuring the Magnetic Field Strength of the Quiet Solar Corona Using ''EIT Waves''
The Wave Properties of Coronal Bright Fronts Observed Using SDO/AIA
Deceleration and Dispersion of Large-scale Coronal Bright Fronts
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