Cut-off features in interplanetary solar radio type IV emission

Solar radio type IV bursts can sometimes show directivity, so that no burst is observed when the source region in located far from the solar disk center. This has recently been verified also from space observations, at decameter wavelengths, using a 3D-view to the Sun with STEREO and Wind satellites. It is unclear whether the directivity is caused by the emission mechanism, by reduced radio wave formation toward certain directions, or by absorption/blocking of radio waves along the line of sight. We present here observations of three type IV burst events that occurred on 23, 25, and 29 July 2004, and originated from the same active region. The source location of the first event was near the solar disk center and in the third event near the west limb. Our analysis shows that in the last two events the type IV bursts experienced partial cut-offs in their emission, that coincided with the appearance of shock-related type II bursts. The type II bursts were formed at the flanks and leading fronts of propagating coronal mass ejections (CMEs). These events support the suggestion of absorption toward directions where the type II shock regions are located.</div

Formation of Isolated Radio Type II Bursts at Low Frequencies

The first appearance of radio type II burst emission at decameter-hectometer (DH) waves typically occurs in connection, and often simultaneously, with other types of radio emissions. As type II bursts are signatures of propagating shock waves that are associated with flares and coronal mass ejections (CMEs), a rich variety of radio emissions can be expected. However, sometimes DH type II bursts appear in the dynamic spectra without other or earlier radio signatures. One explanation for them could be that the flare-CME launch happens on the far side of the Sun, and the emission is observed only when the source gets high enough in the solar atmosphere. In this study we have analysed 26 radio type II bursts that started at DH waves and were well-separated ('isolated') from other radio emission features. These bursts were identified from all DH type II bursts observed in 1998 - 2016, and for 12 events we had observations from at least two different viewing angles with the instruments on board Wind and the Solar Terrestrial Relations Observatory (STEREO) satellites. We found that only 30% of the type II bursts had their source origin on the far side of the Sun, but also that no bursts originated from the central region of the Sun (longitudes E30 - W40). Almost all of the isolated DH type II bursts could be associated with a shock near the CME leading front, and only few were determined to be shocks near the CME flank regions. In this respect our result differs from earlier findings. Our analysis, which included inspection of various CME and radio emission characteristics, suggests that the isolated DH type II bursts could be a special subgroup within DH type II bursts, where the radio emission requires particular coronal conditions to form and to die out

Formation of Radio Type II Bursts During a Multiple Coronal Mass Ejection Event

We study the solar event on 27 September 2001 that consisted of three consecutive coronal mass ejections (CMEs) originating from the same active region, which were associated with several periods of radio type II burst emission at decameter-hectometer (DH) wavelengths. Our analysis shows that the first radio burst originated from a low-density environment, formed in the wake of the first, slow CME. The frequency-drift of the burst suggests a low-speed burst driver, or that the shock was not propagating along the large density gradient. There is also evidence of band-splitting within this emission lane. The origin of the first shock remains unclear, as several alternative scenarios exist. The second shock showed separate periods of enhanced radio emission. This shock could have originated from a CME bow shock, caused by the fast and accelerating second or third CME. However, a shock at CME flanks is also possible, as the density depletion caused by the three CMEs would have affected the emission frequencies and hence the radio source heights could have been lower than usual. The last type II burst period showed enhanced emission in a wider bandwidth, which was most probably due to the CME-CME interaction. Only one shock that could reliably be associated with the investigated CMEs was observed to arrive near Earth. </p

Investigating the origins of two extreme solar particle events: proton source profile and associated electromagnetic emissions

We analyze the high-energy particle emission from the Sun in two extreme solar particle events, in which protons are accelerated to relativistic energies and can cause a significant signal even in the ground-based particle detectors. Analysis of a relativistic proton event is based on modeling of the particle transport and interaction, from a near-Sun source through the solar wind and the Earth’s magnetosphere and atmosphere to a detector on the ground. This allows us to deduce the time profile of the proton source at the Sun and compare it with observed electromagnetic emissions. The 2 May 1998 event is associated with flare and coronal mass ejection (CME) well observed by the Nan¸cay Radioheliograph, so that the images of radio sources are available. For the 2 November 2003 event, there are available the low-corona images of the CME liftoff obtained at the Mauna Loa Solar Observatory. Those complementary data sets are analyzed jointly with the broadband dynamic radio spectra, EUV images and other data available for both events. We find a common scenario for both eruptions, including the flare’s dual impulsive phase, the CME-launch-associated decimetric-continuum burst, and the late, low-frequency type III radio bursts at the time of the relativistic proton injection into the interplanetary medium. The analysis supports the idea that the two considered events start with emission of relativistic protons previously accelerated during the flare and CME launch, then trapped in large-scale magnetic loops and later released by the expanding CME

Investigating the Origins of Two Extreme Solar Particle Events: Proton Source Profile and Associated Electromagnetic Emissions

We analyze the high-energy particle emission from the Sun in two extreme solar particle events. in which protons are accelerated to relativistic energies and can cause a significant signal even in the ground-based particle detectors. Analysis of a relativistic proton event is based on modeling of the particle transport and interaction, from a near-Sun source through the solar wind and the Earth's magnetosphere and atmosphere to a detector on the ground. This allows us to deduce the time profile of the proton source at the Sun and compare it with observed electromagnetic emissions. The 1998 May 2 event is associated with a. flare and a coronal mass ejection (CME), which were well observed by the Nancay Radioheliograph, thus. the images of the. radio sources are available. For the 2003 November 2 event, the low corona images of the CME liftoff obtained at the Mauna Loa Solar Observatory. are available. Those complementary data sets are analyzed jointly with the broadband dynamic radio spectra, EUV images, and other data available for both events. We find a common scenario for both eruptions, including the flare's dual impulsive phase, the CME-launch-associated decimetric-continuum burst, and the late, low-frequency type III radio bursts at the time of the relativistic proton injection into the interplanetary medium. The analysis supports the idea that the two considered events start with emission of relativistic protons previously accelerated during the flare and CME launch, then trapped in large-scale magnetic loops and later released by the expanding CME

Type II radio precursor and X-ray flare emission

International audienc

Type II radio precursor and X-ray flare emission

International audienc

Type II radio precursor and X-ray flare emission

International audienc