Transients and Mass Ejections Observed in Radio Occultation Measurements of the Solar Corona (original) (raw)
Related papers
Radio Observations of Coronal Mass Ejection Initiation and Development in the Low Solar Corona
Frontiers in Astronomy and Space Sciences, 2020
Coronal mass ejections (CMEs) are large eruptions of plasma and magnetic field from the low solar corona into the heliosphere. These eruptions are often associated with energetic electrons that produce various kinds of radio emission. However, there is ongoing investigation into exactly where, when, and how the electron acceleration occurs during flaring and eruption, and how the associated radio emission can be exploited as a diagnostic of both particle acceleration and CME eruptive physics. Here, we review past and present developments in radio observations of flaring and eruption, from the destabilization of flux ropes to the development of a CME and the eventual driving of shocks in the corona. We concentrate primarily on the progress made in CME radio physics in the past two decades and show how radio imaging spectroscopy provides the ability to diagnose the locations and kinds of electron acceleration during eruption, which provides insight into CME eruptive models in the early stages of their evolution (< 10 R ⊙). We finally discuss how new instrumentation in the radio domain will pave the way for a deeper understanding of CME physics in the near future.
The Astrophysical Journal, 2013
Low-frequency (80 MHz) imaging and spectral (≈85-20 MHz) observations of moving type IV radio bursts associated with coronal mass ejections (CMEs) from the Sun on three different days are reported. The estimated drift speed of the bursts is in the range ≈150-500 km s −1. We find that all three bursts are most likely due to second harmonic plasma emission from the enhanced electron density in the associated white-light CMEs. The derived maximum magnetic field strength of the latter is B ≈ 4 G at a radial distance of r ≈ 1.6 R .
Propagation of Solar Energetic Particles During Multiple Coronal Mass Ejection Events
Solar Physics, 2016
We study solar energetic particle (SEP) events during multiple solar eruptions. The analysed sequences, on 24-26 November 2000, 9-13 April 2001, and 22-25 August 2005, consisted of halo-type coronal mass ejections (CMEs) that originated from the same active region and were associated with intense flares, EUV waves, and interplanetary (IP) radio type II and type III bursts. The first two solar events in each of these sequences showed SEP enhancements near Earth, but the third in the row did not. We observed that in these latter events the type III radio bursts were stopped at much higher frequencies than in the earlier events, indicating that the bursts did not reach the typical plasma density levels near Earth. To explain the missing third SEP event in each sequence, we suggest that the earlier-launched CMEs and the CME-driven shocks either reduced the seed particle population and thus led to inefficient particle acceleration, or that the earlier-launched CMEs and shocks changed the propagation paths or prevented the propagation of both the electron beams and SEPs, so that they did not get detected near Earth even when the shock arrivals were recorded.
Comparative analysis of solar radio bursts before and during CME propagation
Astronomy & Astrophysics
Context. As is well known, coronal mass ejection (CME) propagation often results in the fragmentation of the solar atmosphere on smaller regions of density (magnetic field) enhancement (depletion). It is expected that this type of fragmentation may have radio signatures. Aims. The general aim of the present paper is to perform a comparative analysis of type III solar and narrow-band type-III-like radio burst properties before and during CME events, respectively. The main goal is to analyze radio observational signatures of the dynamical processes in solar corona. In particular, we aim to perform a comparison of local plasma parameters without and with CME propagation, based on the analysis of decameter radio emission data. Methods. In order to examine this intuitive expectation, we performed a comparison of usual type III bursts before the CME with narrow-band type-III-like bursts, which are observationally detectable on top of the background type IV radio bursts associated with CME...
Solar Physics, 2011
On 17 January 2005 two fast coronal mass ejections were recorded in close succession during a 3B/X3.8 flare. Both were accompanied by metreto-kilometre type-III groups tracing energetic electrons escaping into the interplanetary space and by decametre-to-hectometre type-II bursts attributed to CME-driven shock waves. A peculiar type-III burst observed near the intersection, on the dynamic spectrum, of the two CME fronts (at heliocentric distance 38 R ⊙ ), was associated with the interaction of the CMEs. Near-relativistic electrons observed by the EPAM experiment onboard ACE near 1 AU revealed successive particle releases that can be associated with the two flare/CME events and the low-frequency type-III burst at the time of CME interaction. Although the decametre-to-hectometre spectral signatures of the two type-III groups appeared similar, the metric radio emission reveals distinctive differences that suggest evolving acceleration regions in the corona. The role of shock acceleration is clearly established at low energies, by the type II radio emission. We compare the pros and cons of shock acceleration and acceleration in the course of magnetic reconnection for the escaping electron beams revealed by the type III bursts and the in situ measurements.
Geophysical Research Letters, 2005
1] A halo coronal mass ejection (CME) was detected on January 20, 2004. We use solar remote sensing data (SOHO, Culgoora) and near-Earth in situ data (Cluster) to identify the CME source event and show that it was a long duration flare in which a magnetic flux rope was ejected, carrying overlying coronal arcade material along with it. We demonstrate that signatures of both the arcade material and the flux rope material are clearly identifiable in the Cluster and ACE data, indicating that the magnetic field orientations changed little as the material traveled to the Earth, and that the methods we used to infer coronal magnetic field configurations are effective. Citation: Fazakerley, A. N., (2005), Relating near-Earth observations of an interplanetary coronal mass ejection to the conditions at its site of origin in the solar corona, Geophys. Res. Lett., 32, L13105,
The Astrophysical Journal, 2012
It has been suggested that type II radio bursts are due to energetic electrons accelerated at coronal shocks. Radio observations, however, have poor or no spatial resolutions to pinpoint the exact acceleration locations of these electrons. In this paper, we discuss a promising approach to infer the electron acceleration location by combining radio and white light observations. The key assumption is to relate specific morphological features (e.g., spectral bumps) of the dynamic spectra of type II radio bursts to imaging features (e.g., coronal mass ejection (CME) going into a streamer) along the CME (and its driven shock) propagation. In this study, we examine the CME-streamer interaction for the solar eruption dated on 2003 November 1. The presence of spectral bump in the relevant type II radio burst is identified, which is interpreted as a natural result of the shock-radio-emitting region entering the dense streamer structure. The study is useful for further determinations of the location of type II radio burst and the associated electron acceleration by CME-driven shock.
2015
Intensive flare (>M5.0 X-ray class) associated Coronal Mass Ejections (CMEs), during 2008- 2013 in solar cycle 24, are separated into two groups based on CME speed. Group-I contains 31 CME events with speed below 900 km/s and Group-II contains 27 CME events with speed above 900 km/s. (i) The mean CME speeds of Groups I and II are found to be 558 km/s and 1629 km/s, and the mean CME width of the Group-II is slightly higher than the Group-I. The CMEs of Group-II are highly decelerated than the CMEs of Group-I. (ii) The rise time and duration of intensive flares of Group-II is slightly greater than those of Group-I. (iii) While 60% of Group-I events are located on the southern hemisphere, 85% of Group-II events are located on the northern hemisphere. (iv) The number of Halos, DH type IIs, SEP events associated with Group-II are respectively 2, 3 and 6 times that of Group-I. (v) Utilizing the density models of suitably connecting the corona and interplanetary medium, the shock...
Geophysical Research Letters, 1998
We present for the first time an almost complete frequency coverage of a Shock Associated (SA) radio event and related phenomena observed on May 6, 1996 at 9:27 UT. It is observed from the base of the solar corona up to almost 1 Astronomical Unit (AU) from the Sun by the following radio astronomical instruments: the Ondřejov spectrometer operating between 4.5 GHz and 1 GHz (radiation produced near the chromosphere); the Thermopyles Artemis-IV spectrograph operating between 600 MHz and 110 MHz (distance range about 1.1-1.4 R from sun center); the Nançay Decameter Array operating between 75 and 25 MHz (distance range about 1.4-2 R ); and the RAD2 and RAD1 radio receivers on the WIND spacecraft covering the range from 14 MHz to about 20 kHz (distance range between 3 R and about 1 AU). Observations at the Nançay Decameter Array clearly show that the SA event starts from a coronal type II radio burst which traces the progression of a shock wave through the corona above 1.8 R -2 R from the sun center. This SA event has no associated radio emission in the decimetric-metric range, thus there is no evidence for electron injection in the low/middle corona.