Browsing by Subject "corona"

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  • Palmerio, E.; Kilpua, E. K. J.; Möstl, C.; Bothmer, V.; James, A. W.; Green, L. M.; Isavnin, A.; Davies, J. A.; Harrison, R. A. (2018)
    Predicting the magnetic field within an Earth-directed coronal mass ejection (CME) well before its arrival at Earth is one of the most important issues in space weather research. In this article, we compare the intrinsic flux rope type, that is, the CME orientation and handedness during eruption, with the in situ flux rope type for 20 CME events that have been uniquely linked from Sun to Earth through heliospheric imaging. Our study shows that the intrinsic flux rope type can be estimated for CMEs originating from different source regions using a combination of indirect proxies. We find that only 20% of the events studied match strictly between the intrinsic and in situ flux rope types. The percentage rises to 55% when intermediate cases (where the orientation at the Sun and/or in situ is close to 45 degrees) are considered as a match. We also determine the change in the flux rope tilt angle between the Sun and Earth. For the majority of the cases, the rotation is several tens of degrees, while 35% of the events change by more than 90 degrees. While occasionally the intrinsic flux rope type is a good proxy for the magnetic structure impacting Earth, our study highlights the importance of capturing the CME evolution for space weather forecasting purposes. Moreover, we emphasize that determination of the intrinsic flux rope type is a crucial input for CME forecasting models. Plain Language Summary Coronal mass ejections (CMEs) are huge eruptions from the Sun that can cause myriad of space weather effects at Earth. The ability of a CME to drive a geomagnetic storm is given largely by how its magnetic field is configured. Predicting the magnetic structure well before CME arrival at Earth is one of the major goals in space weather forecasting. Palmerio et al. (2018) study 20 CMEs observed both at the Sun and at Earth. They use observations of the solar disc to determine the magnetic structure at the Sun and then compare it with the magnetic structure estimated via magnetic field measurements near Earth. They report that the magnetic structures match closely only in 20% of the events studied. They also estimate the orientations of the CME axes at the Sun and at Earth. They find that 65% of the events change their orientations by less than 90 degrees. They conclude that knowledge of the CME magnetic structure at the Sun is an important factor in space weather forecasting, but the CME evolution after eruption has to be taken into account in order to improve current predictions.
  • Kilpua, Emilia K. J.; Pomoell, Jens; Price, Daniel; Sarkar, Ranadeep; Asvestari, Eleanna (2021)
    We investigate here the magnetic properties of a large-scale magnetic flux rope related to a coronal mass ejection (CME) that erupted from the Sun on September 12, 2014 and produced a well-defined flux rope in interplanetary space on September 14-15, 2014. We apply a fully data-driven and time-dependent magnetofrictional method (TMFM) using Solar Dynamics Observatory (SDO) magnetograms as the lower boundary condition. The simulation self-consistently produces a coherent flux rope and its ejection from the simulation domain. This paper describes the identification of the flux rope from the simulation data and defining its key parameters (e.g., twist and magnetic flux). We define the axial magnetic flux of the flux rope and the magnetic field time series from at the apex and at different distances from the apex of the flux rope. Our analysis shows that TMFM yields axial magnetic flux values that are in agreement with several observational proxies. The extracted magnetic field time series do not match well with in-situ components in direct comparison presumably due to interplanetary evolution and northward propagation of the CME. The study emphasizes also that magnetic field time-series are strongly dependent on how the flux rope is intercepted which presents a challenge for space weather forecasting.
  • Morosan, D. E.; Palmerio, E.; Lynch, B. J.; Kilpua, E. K. J. (2020)
    Context. Coronal mass ejections (CMEs) on the Sun are the largest explosions in the Solar System that can drive powerful plasma shocks. The eruptions, shocks, and other processes associated to CMEs are efficient particle accelerators and the accelerated electrons in particular can produce radio bursts through the plasma emission mechanism. Aims. Coronal mass ejections and associated radio bursts have been well studied in cases where the CME originates close to the solar limb or within the frontside disc. Here, we study the radio emission associated with a CME eruption on the back side of the Sun on 22 July 2012. Methods. Using radio imaging from the Nancay Radioheliograph, spectroscopic data from the Nancay Decametric Array, and extreme-ultraviolet observations from the Solar Dynamics Observatory and Solar Terrestrial Relations Observatory spacecraft, we determine the nature of the observed radio emission as well as the location and propagation of the CME. Results. We show that the observed low-intensity radio emission corresponds to a type II radio burst or a short-duration type IV radio burst associated with a CME eruption due to breakout reconnection on the back side of the Sun, as suggested by the pre-eruptive magnetic field configuration. The radio emission consists of a large, extended structure, initially located ahead of the CME, that corresponds to various electron acceleration locations. Conclusions. The observations presented here are consistent with the breakout model of CME eruptions. The extended radio emission coincides with the location of the current sheet and quasi-separatrix boundary of the CME flux and the overlying helmet streamer and also with that of a large shock expected to form ahead of the CME in this configuration.
  • Westerlund, Vanessa (Helsingin yliopisto, 2022)
    Under våren 2020 införde förlossningssjukhusen på grund av coronapandemin restriktioner som begränsade förlossningspartners rätt att närvara på sjukhuset till endast gälla förlossningssalen. Justitieombudsmannen (dnr 2463/ 2020) har senare konstaterat att HUS inte haft lagliga grunder för att begränsa stödpersonens deltagande på det sätt som de gjorde under början av pandemin. I min avhandling har jag med hjälp av narrativ metod samlat in och analyserat fyra mäns berättelser om tillträde i faderskap under tiden för begränsningarna. I min avhandling förstår jag faderskap och maskulinitet som socialt konstruerat. Med hjälp av Morgans (1996; 2011) och Finch (2007) koncept om föräldraskap som något som görs och uppvisas analyserar jag hurdana faderskapspraktiker som förekommer i mäns narrativ om sitt tillträde i faderskap. Jag analyserar också om faderskapspraktikerna har publiker inför vilka det är viktigt att praktikerna framstår som lyckade föreställningar om involverat faderskap (Dermott & Miller 2015) Jag förstår genuskodning som en dimension av familjepraktiker, och analyserar hur görandet av maskulinitet framkommer i narrativen som en dimension av familjepraktiker. Förlossningen som händelse visade sig vara en arena för familjepraktiker där det emotionella arbetet är ett tydligt inslag. Respondenternas narrativ präglades av uttryck för aktiv passivitet, familjepraktiken av att både hantera sina egna, starka känslor och dessutom den födande partnerns känslor för att kunna förkroppsliga idealet om den involverade fadern. Etiska och moraliska dimensioner är centrala inom görandet och uppvisandet av familjepraktiker. De känslor som respondenterna gav uttryck för förknippades starkt med moraliska frågor och framställdes i narrativen i överensstämmelse med narrativet om den involverade fadern. Görandet av faderskap och maskulinitet framstod som relationellt, och relationen till partnern betonades. Förlossningen visade sig för respondenterna handla mera om att göra partnerskap än faderskap. I narrativen fanns tydliga inslag av gemensamt aktörskap (Kuurne & Leppo 2022), där förlossningen uppfattades som delad och som att den hör till båda föräldrarna. Till skillnad från tidigare forskning (ex. Dolan & Coe 2011) som beskriver hur män i sina berättelser om förlossningen tenderat att försöka återskapa en bild av traditionell hegemonisk maskulinitet, tyder resultaten på att det emotionella arbete som respondenterna gav uttryck för ligger i linje med konceptet om vårdande maskuliniteter (Elliot 2016). Resultaten visar att enligt konceptet om hegemonisk maskulinitet (Connell & Messerschmidt 2005) utgör narrativet om involverat faderskap (Dermott & Miller 2015) samt konceptet vårdande maskuliniteter (Elliot 2016) den narrativa utgångspunkt som respondenterna i sina berättelser gett uttryck för.
  • Hofmeister, Stefan J.; Asvestari, Eleanna; Guo, Jingnan; Heidrich-Meisner, Verena; Heinemann, Stephan G.; Magdalenic, Jasmina; Poedts, Stefaan; Samara, Evangelia; Temmer, Manuela; Vennerstrom, Susanne; Veronig, Astrid; Vrsnak, Bojan; Wimmer-Schweingruber, Robert (2022)
    Since the 1970s it has been empirically known that the area of solar coronal holes affects the properties of high-speed solar wind streams (HSSs) at Earth. We derive a simple analytical model for the propagation of HSSs from the Sun to Earth and thereby show how the area of coronal holes and the size of their boundary regions affect the HSS velocity, temperature, and density near Earth. We assume that velocity, temperature, and density profiles form across the HSS cross section close to the Sun and that these spatial profiles translate into corresponding temporal profiles in a given radial direction due to the solar rotation. These temporal distributions drive the stream interface to the preceding slow solar wind plasma and disperse with distance from the Sun. The HSS properties at 1 AU are then given by all HSS plasma parcels launched from the Sun that did not run into the stream interface at Earth distance. We show that the velocity plateau region of HSSs as seen at 1 AU, if apparent, originates from the center region of the HSS close to the Sun, whereas the velocity tail at 1 AU originates from the trailing boundary region. Small HSSs can be described to entirely consist of boundary region plasma, which intrinsically results in smaller peak velocities. The peak velocity of HSSs at Earth further depends on the longitudinal width of the HSS close to the Sun. The shorter the longitudinal width of an HSS close to the Sun, the more of its "fastest" HSS plasma parcels from the HSS core and trailing boundary region have impinged upon the stream interface with the preceding slow solar wind, and the smaller is the peak velocity of the HSS at Earth. As the longitudinal width is statistically correlated to the area of coronal holes, this also explains the well-known empirical relationship between coronal hole areas and HSS peak velocities. Further, the temperature and density of HSS plasma parcels at Earth depend on their radial expansion from the Sun to Earth. The radial expansion is determined by the velocity gradient across the HSS boundary region close to the Sun and gives the velocity-temperature and density-temperature relationships at Earth their specific shape. When considering a large number of HSSs, the assumed correlation between the HSS velocities and temperatures close to the Sun degrades only slightly up to 1 AU, but the correlation between the velocities and densities is strongly disrupted up to 1 AU due to the radial expansion. Finally, we show how the number of particles of the piled-up slow solar wind in the stream interaction region depends on the velocities and densities of the HSS and preceding slow solar wind plasma.
  • Lindström, Olivia (Helsingin yliopisto, 2022)
    Previous studies have shown that the workload has increased for teachers due to Covid-19, which can have affected their job satisfaction. At the same time, other challenges have been reported in the teaching profession that creates a concern regarding the number of teachers who want to change jobs. Research also shows that it has been challenging for principals to balance the various tasks of leadership during Covid-19, which raises questions regarding what kind of leadership needs to be prioritized by principals during a longer period of crisis. The purpose of this study was thus to find out what kind of support primary school teachers need to maintain job satisfaction during Covid-19, how primary school teachers describe principals' leadership and what kind of leadership primary school teachers consider important during Covid-19. Previous studies in the research area that concern primary school teachers' job satisfaction and principals' leadership were used as a background for the study. Seven certified primary school teachers with at least one year of work experience during Covid-19 participated in the study. The study used qualitative research methods and semi-structured interviews as data collection method. The transcribed interviews were analyzed using inductive content analysis. The study was based on a phenomenological perspective. In line with previous research, the results of the study showed that the informants thought that the collegial support had been the most important support for maintaining job satisfaction during Covid-19. The informants also thought that they needed more peace of mind than they had during Covid-19, because it took a lot of time to get acquainted with new rules and restrictions. The results showed that the informants thought that principals had a greater focus on administrative leadership than the pedagogical leadership during Covid-19. At the same time, the informants believed that principals did not have the opportunity to lead during Covid-19, but instead acted as mediators of information. In line with previous research, clear communication was highlighted as an important part of principals' leadership during Covid-19. It was also clear that according to primary school teachers, it is important that the principal is physically present in the school and visible to the teachers during Covid-19.
  • Ryan, A. M.; Gallagher, P. T.; Carley, E. P.; Brentjens, M. A.; Murphy, P. C.; Vocks, C.; Morosan, D. E.; Reid, H.; Magdalenic, J.; (AIP), Leibniz Institut fur Astrophysik; Zucca, P.; Fallows, R.; Mann, G.; Kerdraon, A.; Halfwerk, R. (2021)
    The solar corona is a highly-structured plasma which can reach temperatures of more than similar to 2 MK. At low frequencies (decimetric and metric wavelengths), scattering and refraction of electromagnetic waves are thought to considerably increase the imaged radio source sizes (up to a few arcminutes). However, exactly how source size relates to scattering due to turbulence is still subject to investigation. The theoretical predictions relating source broadening to propagation effects have not been fully confirmed by observations due to the rarity of high spatial resolution observations of the solar corona at low frequencies. Here, the LOw Frequency ARray (LOFAR) was used to observe the solar corona at 120-180 MHz using baselines of up to similar to 3.5 km (corresponding to a resolution of similar to 1-2 ') during the partial solar eclipse of 2015 March 20. A lunar de-occultation technique was used to achieve higher spatial resolution (similar to 0.6 ') than that attainable via standard interferometric imaging (similar to 2.4 '). This provides a means of studying the contribution of scattering to apparent source size broadening. It was found that the de-occultation technique reveals a more structured quiet corona that is not resolved from standard imaging, implying scattering may be overestimated in this region when using standard imaging techniques. However, an active region source was measured to be similar to 4 ' using both de-occultation and standard imaging. This may be explained by the increased scattering of radio waves by turbulent density fluctuations in active regions, which is more severe than in the quiet Sun.
  • Malik, Adnan; Lehtola, Laura; Isosomppi, Sanna; Smura, Teemu; Saarenheimo, Jaana; Anttila, Veli-Jukka; Särelä, Eeva (2022)
    We describe an outbreak of delta variant SARS-CoV-2 on a psychogeriatric ward of elderly patients. Retrospectively collected data was analysed using Fisher's exact test to assess the association between patients' vaccination status and infection rates, severity of disease and mortality. Vaccination with two doses was shown to reduce severity of disease (5% vs. 75%, p < 0.001) and mortality (5% vs. 50%, p < 0.018) amongst an elderly inpatient population during an outbreak of delta variant SARS-CoV-2. Vaccination should be encouraged in elderly care institutions. Furthermore, adequate vaccination in elderly care institutions is an important consideration in current booster (third/fourth) dose schedules.
  • Wiklund, Mari; Honko, Mari; Kanto, Laura; Råman, Joonas (2021)
  • Lumme, E.; Kazachenko, M. D.; Fisher, G. H.; Welsch, B. T.; Pomoell, J.; Kilpua, E.K.J. (2019)
    We study how the input-data cadence affects the photospheric energy and helicity injection estimates in eruptive NOAA Active Region 11158. We sample the novel 2.25-minute vector magnetogram and Dopplergram data from the Helioseismic and Magnetic Imager (HMI) instrument onboard the Solar Dynamics Observatory (SDO) spacecraft to create input datasets of variable cadences ranging from 2.25 minutes to 24 hours. We employ state-of-the-art data processing, velocity, and electric-field inversion methods for deriving estimates of the energy and helicity injections from these datasets. We find that the electric-field inversion methods that reproduce the observed magnetic-field evolution through the use of Faraday's law are more stable against variable cadence: the PDFI (PTD-Doppler-FLCT-Ideal, where PTD refers to Poloidal-Toroidal Decomposition, and FLCT to Fourier Local Correlation Tracking) electric-field inversion method produces consistent injection estimates for cadences from 2.25 minutes up to two hours, implying that the photospheric processes acting on time scales below two hours contribute little to the injections, or that they are below the sensitivity of the input data and the PDFI method. On other hand, the electric-field estimate derived from the output of DAVE4VM (Differential Affine Velocity Estimator for Vector Magnetograms), which does not fulfill Faraday's law exactly, produces significant variations in the energy and helicity injection estimates in the 2.25 minutes - two hours cadence range. We also present a third, novel DAVE4VM-based electric-field estimate, which corrects the poor inductivity of the raw DAVE4VM estimate. This method is less sensitive to the changes of cadence, but it still faces significant issues for the lowest of considered cadences (two hours). We find several potential problems in both PDFI- and DAVE4VM-based injection estimates and conclude that the quality of both should be surveyed further in controlled environments.
  • Pitkänen, Kati; Hannonen, Olga; Toso, Stefania; Gallent, Nick; Hamiduddin, Iqbal; Halseth, Greg; Hall, Michael C.; Müller, Dieter K.; Treivish, Andrey; Nefedova, Tatiana (Matkailututkimus, 2020)
    Matkailututkimus 16, 2 (2020)
  • Morosan, D. E.; Palmerio, E.; Pomoell, J.; Vainio, R.; Palmroth, M.; Kilpua, E. K. J. (2020)
    Context. Some of the most prominent sources for particle acceleration in our Solar System are large eruptions of magnetised plasma from the Sun called coronal mass ejections (CMEs). These accelerated particles can generate radio emission through various mechanisms. Aims. CMEs are often accompanied by a variety of solar radio bursts with different shapes and characteristics in dynamic spectra. Radio bursts directly associated with CMEs often show movement in the direction of CME expansion. Here, we aim to determine the emission mechanism of multiple moving radio bursts that accompanied a flare and CME that took place on 14 June 2012. Methods. We used radio imaging from the Nancay Radioheliograph, combined with observations from the Solar Dynamics Observatory and Solar Terrestrial Relations Observatory spacecraft, to analyse these moving radio bursts in order to determine their emission mechanism and three-dimensional (3D) location with respect to the expanding CME. Results. In using a 3D representation of the particle acceleration locations in relation to the overlying coronal magnetic field and the CME propagation, for the first time, we provide evidence that these moving radio bursts originate near the CME flanks and that some are possible signatures of shock-accelerated electrons following the fast CME expansion in the low corona. Conclusions. The moving radio bursts, as well as other stationary bursts observed during the eruption, occur simultaneously with a type IV continuum in dynamic spectra, which is not usually associated with emission at the CME flanks. Our results show that moving radio bursts that could traditionally be classified as moving type IVs can represent shock signatures associated with CME flanks or plasma emission inside the CME behind its flanks, which are closely related to the lateral expansion of the CME in the low corona. In addition, the acceleration of electrons generating this radio emission appears to be favoured at the CME flanks, where the CME encounters coronal streamers and open field regions.
  • Wagner, Andreas; Asvestari, Eleanna; Temmer, Manuela; Heinemann, S. G.; Pomoell, Jens (2022)
    Context. In this paper, we present a validation scheme to investigate the quality of coronal magnetic field models, which is based on comparisons with observational data from multiple sources. Aims. Many of these coronal models may use a range of initial parameters that produce a large number of physically reasonable field configurations. However, that does not mean that these results are reliable and comply with the observations. With an appropriate validation scheme, which is the aim of this work, the quality of a coronal model can be assessed. Methods. The validation scheme was developed with the example of the EUropean Heliospheric FORecasting Information Asset (EUHFORIA) coronal model. For observational comparison, we used extreme ultraviolet and white-light data to detect coronal features on the surface (open magnetic field areas) and off-limb (streamer and loop) structures from multiple perspectives (Earth view and the Solar Terrestrial Relations Observatory - STEREO). The validation scheme can be applied to any coronal model that produces magnetic field line topology. Results. We show its applicability by using the validation scheme on a large set of model configurations, which can be efficiently reduced to an ideal set of parameters that matches best with observational data. Conclusions. We conclude that by using a combined empirical visual classification with a mathematical scheme of topology metrics, a very efficient and objective quality assessment for coronal models can be performed.