CME liftoff with high-frequency fragmented type II burst emission

Aims: Solar radio type II bursts are rarely seen at frequencies higher than a few hundred MHz. Since metric type II bursts are thought to be signatures of propagating shock waves, it is of interest to know how these shocks, and the type II bursts, are formed. In particular, how are high-frequency, fragmented type II bursts created? Are there differences in shock acceleration or in the surrounding medium that could explain the differences to the "typical" metric type IIs? Methods: We analyse one unusual metric type II event in detail, with comparison to white-light, EUV, and X-ray observations. As the radio event was associated with a flare and a coronal mass ejection (CME), we investigate their connection. We then utilize numerical MHD simulations to study the shock structure induced by an erupting CME in a model corona including dense loops. Results: Our simulations show that the fragmented part of the type II burst can be formed when a coronal shock driven by a mass ejection passes through a system of dense loops overlying the active region.To produce fragmented emission, the conditions for plasma emission have to be more favourable inside the loop than in the interloop area. The obvious hypothesis, consistent with our simulation model, is that the shock strength decreases significantly in the space between the denser loops. The later, more typical type II burst appears when the shock exits the dense loop system and finally, outside the active region, the type II burst dies out when the changing geometry no longer favours the electron shock-acceleration.Comment: 7 pages, 9 figures, A&A accepte

Usability and user experience evaluation model for investigating coordinated assistive technologies with blind and visually impaired

Abstract. The objective of this thesis is to examine how should usability and user experience of a cooperative assistive technology for blind and visually impaired be evaluated in a field setting. The target system in this study was developed by a doctoral student, who was also responsible for conducting an experiment in Pakistan. It is important to evaluate assistive technology for visually impaired because of poor adoption rates, while the number of visually impaired people needing them is going to increase. The research includes literature review on development of assistive technologies, and existing usability and user experience methods. Theory is supported with qualitative and quantitative methods. Discussions with three experts in Finland were held and analysed. An experiment for eleven blind and visually impaired people was conducted in Pakistan. This included interviews, analysed observations, and a validation of a user experience questionnaire, meCUE 2.0. Discussions with the research team and consultations from usability and user experience experts were used to assess the results of the research and to develop an evaluation model suitable for the prototype system in specified setting. The first main finding of this thesis is the developed model called UUXCAT for VIP. It can be used to evaluate cooperative assistive technology in a field setting. Development of the model was an iterative process and is based on synthesis of existing methods and available research. The second main finding is the extended contexts questionnaire. New contexts add dimensions that were missing from other methods. These contexts are trust and confidence, social, physical, and culture, and are relevant to visually impaired and the cooperative aspect of the system. The study is limited by Covid-19 as the planned experiment in Finland was not carried out that could further validate the model

Strategic Planning for Web-based Learning and Teaching at Tampere University of Technology

In: A.J. Kallenberg and M.J.J.M. van de Ven (Eds), 2002, The New Educational Benefits of ICT in Higher Education: Proceedings. Rotterdam: Erasmus Plus BV, OECR ISBN 90-9016127-9The purpose of this paper is to discuss the action to support the development of web-based learning and teaching in higher education. A central question is how web-based learning and teaching should be incorporated into the strategic planning of the University

Microflaring of a solar Bright point

A solar X-ray Bright point (BP) was observed with the SUMER-spectrograph of the SOHO-observatory. The data consist of four far-UV spectral lines formed between 2 10^4 - 6 10^5 K, with 2 arcsec spatial, 2.8 min temporal and 4 km/s spectral resolution. A striking feature is the strong microflaring and appearance of several short lived transients. Using simultaneous magnetic field measurements the region observed seemed to lie above a cancelling flux region. With respect to the filling factor and emission measure this particular BP was similar to the average surface of a moderately active solar type star.Comment: 7 pages, 6 figures, in press Astronomy and Astrophysics; for Fig.3 it is recommended to download separately the colour version h3653f3.pd

Shock-related radio emission during coronal mass ejection lift-off?

Aims: We identify the source of fast-drifting decimetric-metric radio emission that is sometimes observed prior to the so-called flare continuum emission. Fast-drift structures and continuum bursts are also observed in association with coronal mass ejections (CMEs), not only flares. Methods: We analyse radio spectral features and images acquired at radio, H-alpha, EUV, and soft X-ray wavelengths, during an event close to the solar limb on 2 June 2003. Results: The fast-drifting decimetric-metric radio burst corresponds to a moving, wide emission front in the radio images, which is normally interpreted as a signature of a propagating shock wave. A decimetric-metric type II burst where only the second harmonic lane is visible could explain the observations. After long-lasting activity in the active region, the hot and dense loops could be absorbing or suppressing emission at the fundamental plasma frequency. The observed burst speed suggests a super-Alfvenic velocity for the burst driver. The expanding and opening loops, associated with the flare and the early phase of CME lift-off, could be driving the shock. Alternatively, an instantaneous but fast loop expansion could initiate a freely propagating shock wave. The later, complex-looking decametre-hectometre wave type III bursts indicate the existence of a propagating shock, although no interplanetary type II burst was observed during the event. The data does not support CME bow shock or a shock at the flanks of the CME as the origin of the fast-drift decimetric-metric radio source. Therefore super-Alfvenic loop expansion is the best candidate for the initiation of the shock wave, and this result challenges the current view of metric/coronal shocks originating either in the flanks of CMEs or from flare blast waves.Comment: 4 pages, 3 figures, accepted by A&A (Research Note

The energy sources of CME acceleration

We investigate the possibility that during the fast acceleration phase of a coronal mass ejection (CME), a freely propagating shock wave could be launched. We test this hypothesis by calculating the speeds of blast waves by using the Taylor-Sedov equation in changing density solar atmosphere, and compare these speeds with the radio type II burst speeds during the CME event on 17 February 2000. The matching speeds and the realistic value of the blast wave energy, 10²⁴ J, lead us to suggest that the CME acceleration phase may involve shocks separating from the initial CME driver

Visibility and Origin of Compact Interplanetary Radio Type IV Bursts

We have analyzed radio typeIV bursts in the interplanetary (IP) space at decameter-hectometer (DH) wavelengths to determine their source origin and a reason for the observed directivity. We used radiodynamic spectra from the instruments on three different spacecraft, STEREO-A, Wind, and STEREO-B, which were located approximately 90 degrees apart from each other in 2011-2012, and thus gave a 360 degree view of the Sun. The radio data were compared to white-light and extreme ultraviolet (EUV) observations of flares, EUV waves, and coronal mass ejections (CMEs) in five solar events. We find that the reason that compact and intense DH typeIV burst emission is observed from only one spacecraft at a time is the absorption of emission in one direction and that the emission is blocked by the solar disk and dense corona in the other direction. The geometry also makes it possible to observe metric typeIV bursts in the low corona from a direction where the higher-located DH typeIV emission is not detectable. In the absorbed direction we found streamers, and they were estimated to be the locations of typeII bursts, caused by shocks at the CME flanks. The high-density plasma was therefore most probably formed by shock-streamer interaction. In some cases, the typeII-emitting region was also capable of stopping later-accelerated electron beams, which were visible as typeIII bursts that ended near the typeII burst lanes

Origin of wide-band IP type II bursts

Context. Different types of interplanetary (IP) type II bursts have been observed, where the more usual ones show narrow-band and patchy emissions, sometimes with harmonics, and which at intervals may disappear completely from the dynamic spectrum. The more unusual bursts are wide-band and diffuse, show no patches or breaks or harmonic emission, and often have long durations. Type II bursts are thought to be plasma emission, caused by propagating shock waves, but a synchrotron-emitting source has also been proposed as the origin for the wide-band type IIs.Aims. Our aim is to find out where the wide-band IP type II bursts originate and what is their connection to particle acceleration.Methods. We analyzed in detail 25 solar events that produced well-separated, wide-band IP type II bursts in 2001–2011. Their associations to flares, coronal mass ejections (CMEs), and solar energetic particle events (SEPs) were investigated. Results. Of the 25 bursts, 18 were estimated to have heights corresponding to the CME leading fronts, suggesting that they were created by bow shocks ahead of the CMEs. However, seven events were found in which the burst heights were significantly lower and which showed a different type of height-time evolution. Almost all the analyzed wide-band type II bursts were associated with very high-speed CMEs, originating from different parts of the solar hemisphere. In terms of SEP associations, many of the SEP events were weak, had poor connectivity due to the eastern limb source location, or were masked by previous events. Some of the events had precursors in specific energy ranges. These properties and conditions affected the intensity-time profiles and made the injection-timebased associations with the type II bursts difficult to interpret. In several cases where the SEP injection times could be determined, the radio dynamic spectra showed other features (in addition to the wide-band type II bursts) that could be signatures of shock fronts.Conclusions. We conclude that in most cases (in 18 out of 25 events) the wide-band IP type II bursts can be plasma emission, formed at or just above the CME leading edge. The results for the remaining seven events might suggest the possibility of a synchrotron source. These events, however, occurred during periods of high solar activity, and coronal conditions affecting the results of the burst height calculations cannot be ruled out. The observed wide and diffuse emission bands may also indicate specific CME leading edge structures and special shock conditions

Properties of High-Energy Solar Particle Events Associated with Solar Radio Emissions

We have analysed 58 high-energy proton events and 36 temporally related near-relativistic electron events from the years 1997 - 2015 for which the velocity dispersion analysis of the first-arriving particles gave the apparent path lengths between 1 and 3 AU. We investigated the dependence of the characteristics of the proton events on the associations of type II, III, and IV radio bursts. We also examined the properties of the soft X-ray flares and coronal mass ejections associated with these events. All proton events were associated with decametric type III radio bursts, while type IV emission was observed only in the meter wavelengths in some of the events (32/58). Almost all proton events (56/58) were associated with radio type II bursts: 11 with metric (m) type II only, 11 with decametric-hectometric (DH) only, and 34 with type II radio bursts at both wavelength ranges. By examining several characteristics of the proton events, we discovered that the proton events can be divided into two categories. The characteristics of events belonging to the same category were similar, while they significantly differed between events in different categories. The distinctive factors between the categories were the wavelength range of the associated type II radio emission and the temporal relation of the proton release with respect to the type II onset. In Category 1 are the events which were associated with only metric type II emission or both m and DH type II and the release time of protons was before the DH type II onset (18/56 events). Category 2 consists of the events which were associated with only DH type II emission or both m and DH type II and the protons were released at or after the DH type II onset (31/56 events). For seven of the 56 events we were not able to determine a definite category due to timing uncertainties. The events in Category 1 had significantly higher intensity rise rates, shorter rise times, lower release heights, and harder energy spectra than Category 2 events. Category 1 events also originated from magnetically well-connected regions and had only small time differences between the proton release times and the type III onsets. The soft X-ray flares for these events had significantly shorter rise times and durations than for Category 2 events. We found 36 electron events temporally related to the proton events, which fulfilled the same path length criterion as the proton events. We compared the release times of protons and electrons at the Sun, and discovered that in 19 of the 36 events protons were released almost simultaneously (within +/- 7 minutes) with the electrons, in 16 events protons were released later than the electrons, and in one event electrons were released after the protons. The simultaneous proton and electron events and the delayed proton events did not unambiguously fall in the two categories of proton events, although most of the events in which the protons were released after the electrons belonged to Category 2. We conclude that acceleration of protons in Category 1 events occurred low in the corona, either by CME-driven shocks or below the CMEs in solar flares or in CME initiation related processes. It seems plausible that protons in Category 2 events were accelerated by CME-driven shocks high in the solar corona. Large delays of protons with respect to type III onsets in the events where protons were released after the electrons suggest late acceleration or release of protons close to the Sun, but the exact mechanism causing the delay remained unclear

Radio Bursts Associated with Flare and Ejecta in the 13 July 2004 Event

We investigate coronal transients associated with a GOES M6.7 class flare and a coronal mass ejection (CME) on 13 July 2004. During the rising phase of the flare, a filament eruption, loop expansion, a Moreton wave, and an ejecta were observed. An EIT wave was detected later on. The main features in the radio dynamic spectrum were a frequency-drifting continuum and two type II bursts. Our analysis shows that if the first type II burst was formed in the low corona, the burst heights and speed are close to the projected distances and speed of the Moreton wave (a chromospheric shock wave signature). The frequency-drifting radio continuum, starting above 1 GHz, was formed almost two minutes prior to any shock features becoming visible, and a fast-expanding piston (visible as the continuum) could have launched another shock wave. A possible scenario is that a flare blast overtook the earlier transient, and ignited the first type II burst. The second type II burst may have been formed by the same shock, but only if the shock was propagating at a constant speed. This interpretation also requires that the shock-producing regions were located at different parts of the propagating structure, or that the shock was passing through regions with highly different atmospheric densities. This complex event, with a multitude of radio features and transients at other wavelengths, presents evidence for both blast-wave-related and CME-related radio emissions.Comment: 14 pages, 6 figures; Solar Physics Topical Issue, in pres