Shock location and CME 3D reconstruction of a solar type II radio burst with LOFAR

Context. Type II radio bursts are evidence of shocks in the solar atmosphere and inner heliosphere that emit radio waves ranging from sub-meter to kilometer lengths. These shocks may be associated with coronal mass ejections (CMEs) and reach speeds higher than the local magnetosonic speed. Radio imaging of decameter wavelengths (20–90 MHz) is now possible with the Low Frequency Array (LOFAR), opening a new radio window in which to study coronal shocks that leave the inner solar corona and enter the interplanetary medium and to understand their association with CMEs. Aims. To this end, we study a coronal shock associated with a CME and type II radio burst to determine the locations at which the radio emission is generated, and we investigate the origin of the band-splitting phenomenon. Methods. Thetype II shock source-positions and spectra were obtained using 91 simultaneous tied-array beams of LOFAR, and the CME was observed by the Large Angle and Spectrometric Coronagraph (LASCO) on board the Solar and Heliospheric Observatory (SOHO) and by the COR2A coronagraph of the SECCHI instruments on board the Solar Terrestrial Relation Observatory(STEREO). The 3D structure was inferred using triangulation of the coronographic observations. Coronal magnetic fields were obtained from a 3D magnetohydrodynamics (MHD) polytropic model using the photospheric fields measured by the Heliospheric Imager (HMI) on board the Solar Dynamic Observatory (SDO) as lower boundary. Results. The type II radio source of the coronal shock observed between 50 and 70 MHz was found to be located at the expanding flank of the CME, where the shock geometry is quasi-perpendicular with θBn ~ 70°. The type II radio burst showed first and second harmonic emission; the second harmonic source was cospatial with the first harmonic source to within the observational uncertainty. This suggests that radio wave propagation does not alter the apparent location of the harmonic source. The sources of the two split bands were also found to be cospatial within the observational uncertainty, in agreement with the interpretation that split bands are simultaneous radio emission from upstream and downstream of the shock front. The fast magnetosonic Mach number derived from this interpretation was found to lie in the range 1.3–1.5. The fast magnetosonic Mach numbers derived from modelling the CME and the coronal magnetic field around the type II source were found to lie in the range 1.4–1.6.

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Evolution of the Alfvén Mach number associated with a coronal mass ejection shock

Astronomy and Astrophysics ◽

10.1051/0004-6361/201936449 ◽

2020 ◽

Vol 633 ◽

pp. A56 ◽

Cited By ~ 3

Author(s):

Ciara A. Maguire ◽

Eoin P. Carley ◽

Joseph McCauley ◽

Peter T. Gallagher

Keyword(s):

Mach Number ◽

Radio Emission ◽

Radio Burst ◽

Large Scale ◽

Extreme Ultraviolet ◽

Splitting Method ◽

Large Angle ◽

Electron Acceleration ◽

Phase Evolution ◽

Type Ii

The Sun regularly produces large-scale eruptive events, such as coronal mass ejections (CMEs) that can drive shock waves through the solar corona. Such shocks can result in electron acceleration and subsequent radio emission in the form of a type II radio burst. However, the early-phase evolution of shock properties and its relationship to type II burst evolution is still subject to investigation. Here we study the evolution of a CME-driven shock by comparing three commonly used methods of calculating the Alfvén Mach number (MA), namely: shock geometry, a comparison of CME speed to a model of the coronal Alfvén speed, and the type II band-splitting method. We applied the three methods to the 2017 September 2 event, focusing on the shock wave observed in extreme ultraviolet by the Solar Ultraviolet Imager on board GOES-16, in white-light by the Large Angle and Spectrometric Coronagraph on board SOHO, and the type II radio burst observed by the Irish Low Frequency Array. We show that the three different methods of estimating shock MA yield consistent results and provide a means of relating shock property evolution to the type II emission duration. The type II radio emission emerged from near the nose of the CME when MA was in the range 1.4–2.4 at a heliocentric distance of ∼1.6 R⊙. The emission ceased when the CME nose reached ∼2.4 R⊙, despite an increasing Alfvén Mach number (up to 4). We suggest the radio emission cessation is due to the lack of quasi-perpendicular geometry at this altitude, which inhibits efficient electron acceleration and subsequent radio emission.

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Evolution of the Alfvén Mach number associated with a coronal mass ejection shock

10.5194/egusphere-egu2020-11425 ◽

2020 ◽

Author(s):

Ciara Maguire ◽

Eoin Carley ◽

Joseph McCauley ◽

Peter Gallagher

Keyword(s):

Mach Number ◽

Radio Emission ◽

Radio Burst ◽

Large Scale ◽

Extreme Ultraviolet ◽

Splitting Method ◽

Large Angle ◽

Electron Acceleration ◽

Phase Evolution ◽

Type Ii

The Sun regularly produces large-scale eruptive events, such as coronal mass ejections (CMEs) that can drive shock waves through the solar corona. Such shocks can result in electron acceleration and subsequent radio emission in the form of a type II radio burst. However, the early-phase evolution of shock properties and its relationship to type II burst evolution is still subject to investigation. Here we study the evolution of a CME-driven shock by comparing three commonly used methods of calculating the Alfv&#233;n Mach number (MA), namely: shock geometry, a comparison of CME speed to a model of the coronal Alfv&#233;n speed, and the type II band-splitting method. We applied the three methods to the 2017 September 2 event, focusing on the shock wave observed in extreme ultraviolet (EUV) by the Solar Ultraviolet Imager (SUVI) on board GOES-16, in white-light by the Large Angle and Spectrometric Coronagraph (LASCO) on board SOHO, and the type II radio burst observed by the Irish Low Frequency Array (I-LOFAR). We show that the three different methods of estimating shock MA yield consistent results and provide a means of relating shock property evolution to the type II emission duration. The type II radio emission emerged from near the nose of the CME when MA&#160;was in the range 1.4-2.4 at a heliocentric distance of&#160;&#8764;1.6&#160;R&#8857;. The emission ceased when the CME nose reached&#160;&#8764;2.4&#160;R&#8857;, despite an increasing Alfv&#233;n Mach number (up to 4). We suggest the radio emission cessation is due to the lack of quasi-perpendicular geometry at this altitude, which inhibits efficient electron acceleration and subsequent radio emission.

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LOFAR observations of a jet-driven piston shock in the low solar corona

10.5194/egusphere-egu21-7602 ◽

2021 ◽

Author(s):

Ciara Maguire ◽

Eoin Carley ◽

Pietro Zucca ◽

Nicole Vilmer ◽

Peter Gallagher

Keyword(s):

Radio Burst ◽

Extreme Ultraviolet ◽

Large Angle ◽

Low Frequency ◽

Density Fluctuations ◽

Plasma Emission ◽

Type Ii ◽

Radio Waves ◽

Type Ii Radio Bursts ◽

Electron Density Fluctuations

The Sun produces highly dynamic and eruptive events that can drive shocks through the corona. These shocks can accelerate electrons, which result in plasma emission in the form of a type II radio burst. Despite a large number of type II radio bursts observations, the precise origin of coronal shocks is still subject to investigation. Here we present a well-observed solar eruptive event that occurred on 16 October 2015, focusing on a jet observed in the extreme ultraviolet by the SDO Atmospheric Imaging Assembly, a streamer observed in white-light by the Large Angle and&#160; Spectrometric Coronagraph, and a metric type II radio burst observed by the LOw-Frequency Array (LOFAR) radio telescope. For the first time, LOFAR has interferometrically imaged the fundamental and harmonic sources of a type II radio burst and revealed that the sources did not appear to be co-spatial, as would be expected from the plasma emission mechanism. We correct for the separation between the fundamental and harmonic using a model which accounts for the scattering of radio waves by electron density fluctuations in a turbulent plasma. This allows us to show the type II radio sources were located &#8764;0.5 Rsun above the jet and propagated at a speed of &#8764;1000 km s&#8722;1, which was significantly faster than the jet speed of &#8764;200 km s&#8722;1. This suggests that the type II burst was generated by a piston shock driven by the jet in the low corona.

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A BROKEN SOLAR TYPE II RADIO BURST INDUCED BY A CORONAL SHOCK PROPAGATING ACROSS THE STREAMER BOUNDARY

The Astrophysical Journal ◽

10.1088/0004-637x/750/2/158 ◽

2012 ◽

Vol 750 (2) ◽

pp. 158 ◽

Cited By ~ 31

Author(s):

X. L. Kong ◽

Y. Chen ◽

G. Li ◽

S. W. Feng ◽

H. Q. Song ◽

...

Keyword(s):

Radio Burst ◽

Type Ii ◽

Coronal Shock ◽

Solar Type

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The Broken Lane of a Type II Radio Burst Caused by Collision of a Coronal Shock with a Flare Current Sheet

Solar Physics ◽

10.1007/s11207-016-1007-x ◽

2016 ◽

Vol 291 (11) ◽

pp. 3369-3384 ◽

Cited By ~ 5

Author(s):

Guannan Gao ◽

Min Wang ◽

Ning Wu ◽

Jun Lin ◽

E. Ebenezer ◽

...

Keyword(s):

Current Sheet ◽

Radio Burst ◽

Type Ii ◽

Coronal Shock

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Real-time forecasting of ICME shock arrivals at L1 during the "April Fool’s Day" epoch: 28 March – 21 April 2001

Annales Geophysicae ◽

10.5194/angeo-20-937-2002 ◽

2002 ◽

Vol 20 (7) ◽

pp. 937-945 ◽

Cited By ~ 26

Author(s):

W. Sun ◽

M. Dryer ◽

C. D. Fry ◽

C. S. Deehr ◽

Z. Smith ◽

...

Keyword(s):

Real Time ◽

Radio Burst ◽

Type Ii ◽

Interplanetary Shocks ◽

Arrival Times ◽

Interplanetary Coronal Mass Ejection ◽

Coronal Shock ◽

Ex Post ◽

Interplanetary Physics ◽

Ex Post Facto

Abstract. The Sun was extremely active during the "April Fool’s Day" epoch of 2001. We chose this period between a solar flare on 28 March 2001 to a final shock arrival at Earth on 21 April 2001. The activity consisted of two presumed helmet-streamer blowouts, seven M-class flares, and nine X-class flares, the last of which was behind the west limb. We have been experimenting since February 1997 with real-time, end-to-end forecasting of interplanetary coronal mass ejection (ICME) shock arrival times. Since August 1998, these forecasts have been distributed in real-time by e-mail to a list of interested scientists and operational USAF and NOAA forecasters. They are made using three different solar wind models. We describe here the solar events observed during the April Fool’s 2001 epoch, along with the predicted and actual shock arrival times, and the ex post facto correction to the real-time coronal shock speed observations. It appears that the initial estimates of coronal shock speeds from Type II radio burst observations and coronal mass ejections were too high by as much as 30%. We conclude that a 3-dimensional coronal density model should be developed for application to observations of solar flares and their Type II radio burst observations.Key words. Interplanetary physics (flare and stream dynamics; interplanetary shocks) – Magnetosheric physics (storms and substorms)

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