Investigating the conditions of the formation of a type II radio burst on 2014 January 8

Journal Article · Thu Oct 20 04:00:00 EDT 2016 · Astrophysical Journal

DOI:https://doi.org/10.3847/0004-637X/830/2/70· OSTI ID:22868592

Su, W.; Cheng, X.; Ding, M. D.; Chen, P. F. ^[1]; Ning, Z. J.

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1. School of Astronomy and Space Science, Nanjing University, Nanjing 210023 (China)

It is believed that type II radio bursts are generated by shock waves. In order to understand the generation conditions of type II radio bursts, we analyze the physical parameters of a shock front. The type II radio burst we selected was observed by the Siberian Solar Radio Telescope (SSRT) and Learmonth radio station and was associated with a limb coronal mass ejection (CME) occurring on 2014 January 8 observed by the Atmospheric Imaging Assembly on board the Solar Dynamics Observatory. The evolution of the CME in the inner corona presents a double-layered structure that propagates outward. We fit the outer layer (OL) of the structure with a partial circle and divide it into seven directions from −45° to 45° with an angular separation of 15°. We measure the OL speed along the seven directions and find that the speed in the direction of −15° with respect to the central direction is the fastest. We use the differential emission measure method to calculate the physical parameters at the OL at the moment when the type II radio burst was initiated, including the temperature (T), emission measure (EM), temperature ratio (T{sub d}/T{sub u}), compression ratio (X), and Alfvén Mach number (M {sub A}). We compare the quantities X and M {sub A} to those obtained from band-splitting in the radio spectrum, and find that this type II radio burst is generated at a small region of the OL that is located at the sector in the 45° direction. The results suggest that the generation of type II radio bursts (shocks) requires larger values of X and M {sub A} rather than simply a higher speed of the disturbance.

• OSTI ID: 22868592
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 2 Vol. 830; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
COMPARATIVE EVALUATIONS
COMPRESSION RATIO
DISTURBANCES
EMISSION
LAYERS
LIMBS
MACH NUMBER
MASS
RADIO TELESCOPES
SHOCK WAVES
SOLAR CORONA
SPECTRA
SUN