Conditions needed for generation of type II radio emission in the interplanetary space

<p>Eruptive events such as Coronal mass ejections (CMEs) and flares cangenerate shock waves. Tracking shock waves and predicting their arrival at Earth is a subject of numerous space weather studies. Ground-based radio observations allow us to locate shock waves in the low corona while space-based radio observations provide us opportunity to track shock waves in the inner heliosphere. We present a case study of CME/flare event, associated shock wave and its radio signature, i.e. type II radio burst.</p><p>In order to analyze the shock wave parameters, we employed a robust paradigm. We reconstructed the shock wave in 3D using multi-viewpoint observations and modelled the evolution of its parameters using a 3D MHD background coronal model produced by the MAS (Magnetohydrodynamics Around a Sphere).</p><p>To map regions on the shock wave surface, possibly associated with the electron acceleration, we combined 3D shock modelling results with the 3D source positions of the type II burst obtained using the radio triangulation technique. We localize the region of interest on the shock surface and examine the shock wave parameters to understand the relationship between the shock wave and the radio event. We analyzed the evolution of the upstream plasma characteristics and shock wave parameters during the full duration of the type II radio emission. First results indicate that shock wave geometry and its relationship with shock strength play an important role in the acceleration of electrons responsible for the generation of type II radio bursts.</p>

Well-defined EUV wave associated with a CME-driven shock

Aims. We report on a well-defined EUV wave observed by the Extreme Ultraviolet Imager (EUVI) on board the Solar Terrestrial Relations Observatory (STEREO) and the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory (SDO). The event was accompanied by a shock wave driven by a halo CME observed by the Large Angle and Spectrometric Coronagraph (LASCO-C2/C3) on board the Solar and Heliospheric Observatory (SOHO), as evidenced by the occurrence of type II bursts in the metric and dekameter-hectometric wavelength ranges. We investigated the kinematics of the EUV wave front and the radio source with the purpose of verifying the association between the EUV wave and the shock wave. Methods. The EUV wave fronts were determined from the SDO/AIA images by means of two appropriate directions (slices). The heights (radial propagation) of the EUV wave observed by STEREO/EUVI and of the radio source associated with the shock wave were compared considering the whole bandwidth of the harmonic lane of the radio emission, whereas the speed of the shock was estimated using the lowest frequencies of the harmonic lane associated with the undisturbed corona, using an appropriate multiple of the Newkirk (1961, ApJ, 133, 983) density model and taking into account the H/F frequency ratio fH∕fF = 2. The speed of the radio source associated with the interplanetary shock was determined using the Mann et al. (1999, A&A, 348, 614) density model. Results. The EUV wave fronts determined from the SDO/AIA images revealed the coexistence of two types of EUV waves, a fast one with a speed of ~560 km s−1, and a slower one with a speed of ~250 km s−1, which corresponds approximately to one-third of the average speed of the radio source (~680 km s−1). The radio signature of the interplanetary shock revealed an almost constant speed of ~930 km s−1, consistent with the linear speed of the halo CME (950 km s−1) and with the values found for the accelerating coronal shock (~535–823 km s−1), taking into account the gap between the radio emissions.

Radiolab - three different approaches

The three papers in this ‘suite’ have a special background and context. At the 2010 conference SoundActs in Aarhus the three panellists were each given the task to provide a paper with an analysis of the same sound object, thus exhibiting and contrasting different scholarly approaches to sound studies. The object was selected by Torben Sangild, who was familiar with the chosen context: the signature of the US radio programme and podcast Radiolab. The two other participants did not know the context and chose to analyse the sound object without further contextual investigation. This object was chosen for several reasons. First of all, it is brief (less than 17 seconds), which meant that it was possible to make a detailed analysis; at the same time, though, it is relatively complex, which means that it can accommodate three different analyses. It is a sound object with a global audience, taken from one of the most popular podcasts worldwide, accessible on the internet. Finally, it is a piece of functional sound design, rather than a work of art, which raises the question of context more clearly. The result is three rather different approaches: 1) a process analysis, observing analytical listening strategies towards the constructed object, 2) a vocal analysis, regarding the sound object as a polyphony of voices, and 3) a contextual analysis, framing the sound object as a radio signature. Ola Stockfelt analyses the sound object as something that is constructed via his own repeated listening process – as a scholarly-analytical analysis of the subjective act of creating meaning. He draws on presumptions and prejudices, demonstrating the impossibility of a purely structural listening. The analysis relates these hermeneutical reflections to formal musicological observations of harmony, timbre, space and rhythm in some detail. Ansa Lønstrup’s paper analyses the sound object as a polyphony of voices. Her analysis is inspired by two phenomenologists: Don Ihde, whose notion of ‘voice’ is understood in a more general sense as the voices of all things, and Lawrence Ferrara, who methodologically operates within tree levels of investigation: 1) the syntax, 2) the semantic and 3) the ontology level. Accordingly, this analysis is conducted, as if the sound object was performed by a vocal ensemble oscillating ‘between a musical and a speech act’. Torben Sangild’s paper focuses on the concrete function of the sound object as a radio signature. This prompts a generic analysis and a semantic model of radio signatures in general, eclectically employing formal, indexical, gestural, discursive and contextual levels of meaning. The analysis of the Radiolab signature focuses on the overall gesture of tension and release as well as the semantic elements in a constellation with the content and style of the radio programme. After the three individual contributions, a brief summary and conclusion will follow, answering any questions that may arise in the process.