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1
Mishra, Wageesh, Kunjal Dave, Nandita Srivastava, and Luca Teriaca. "Multipoint remote and in situ observations of interplanetary coronal mass ejection structures during 2011 and associated geomagnetic storms." Monthly Notices of the Royal Astronomical Society 506, no. 1 (July 13, 2021): 1186–97. http://dx.doi.org/10.1093/mnras/stab1721.
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ABSTRACT We present multipoint remote and in situ observations of interplanetary coronal mass ejection (ICME) structures during the year 2011. The selected ICMEs arrived at Earth on 2011 March 11 and 2011 August 6, and led to geomagnetic storms. Around the launch of these CMEs from the Sun, the coronagraphs onboard STEREO-Aand-B and SOHO enabled the CMEs to be imaged from three longitudinally separated viewpoints. We attempt to identify the in situ plasma and magnetic parameters of the ICME structures at multiple locations, for example at both STEREO spacecraft and also at the ACE/Wind spacecraft near the first Sun–Earth Lagrangian point (L1), to investigate the global configuration, interplanetary propagation, arrival times and geomagnetic response of the ICMEs. The near-Earth identified ICMEs of March 11 and August 6 formed as a result of the interaction of two successive CMEs observed in the inner corona on March 7 (for the March 11 ICME) and on August 3–4 (for the August 6 ICME). Our study suggests that the structures associated with interacting CMEs, possibly as a result of deflection or large sizes, may reach to even larger longitudinally separated locations in the heliosphere. Our multipoint in situ analysis shows that the characteristics of the same shock, propagating in a pre-conditioned medium, may be different at different longitudinal locations in the heliosphere. Similarly, multiple cuts through the same ejecta/complex ejecta, formed as a result of CME–CME interaction, are found to have inhomogeneous properties. The study highlights the difficulties in connecting the local observations of an ICME from a single in situ spacecraft to its global structures.
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Morosan, D. E., E. Palmerio, B. J. Lynch, and E. K. J. Kilpua. "Extended radio emission associated with a breakout eruption from the back side of the Sun." Astronomy & Astrophysics 633 (January 2020): A141. http://dx.doi.org/10.1051/0004-6361/201936878.
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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 Nançay Radioheliograph, spectroscopic data from the Nançay 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.
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Lavraud, Benoit, and Alexis Rouillard. "Properties and processes that influence CME geo-effectiveness." Proceedings of the International Astronomical Union 8, S300 (June 2013): 273–84. http://dx.doi.org/10.1017/s1743921313011095.
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AbstractThe geo-effectiveness of coronal mass ejections (CME) is determined by a complex chain of processes. This paper highlights this fact by first discussing the importance of CMEs intrinsic properties set at the Sun (e.g., trajectory, eruption process, orientation, etc.). We then review other key processes that may occur during propagation (e.g., shocks, compressions, magnetic flux erosion) and in the specific interaction with Earth's magnetosphere (e.g., magnetic properties, preconditioning mechanisms). These processes sequentially have a significant influence on the final geo-effectiveness of CMEs. Their relative importance is discussed. While the CME's trajectory, magnetic field orientation, velocity and their duration as set at the Sun certainly are key ingredients to geo-effectiveness, other processes and properties, that at first appear secondary, often may be as important.
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Kahler, Stephen W. "Evidence for solar shock production of heliospheric near-relativistic and relativistic electron events." Proceedings of the International Astronomical Union 2, no. 14 (August 2006): 86. http://dx.doi.org/10.1017/s1743921307009891.
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AbstractProperties of near-relativistic (E ≳ 30 keV, NR) and relativistic (E ≳ 0.3 MeV) electron events produced near the Sun and observed within 1 AU are reviewed. Observations suggest the CME-driven shocks are the sources of many events, but flares are often sources for NR events.
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Jackson, B. V., P. P. Hick, A. Buffington, M. M. Bisi, and J. M. Clover. "SMEI direct, 3-D-reconstruction sky maps, and volumetric analyses, and their comparison with SOHO and STEREO observations." Annales Geophysicae 27, no. 11 (November 2, 2009): 4097–104. http://dx.doi.org/10.5194/angeo-27-4097-2009.
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Abstract. In this paper we present the results of the analysis of the late January 2007 Coronal Mass Ejection (CME) events recorded by the Solar Mass Ejection Imager (SMEI), the Solar TErrestrial RElations Observatory (STEREO), and the SOlar and Heliospheric Observatory (SOHO) spacecraft. This period occurs when the two STEREO spacecraft views are from close to Earth, and thus the views from both SMEI and the STEREO outer Heliospheric Imagers (HI-2s) coincide. Three-dimensional (3-D) analyses derived from SMEI data show many CMEs that have also been studied by others using short-term image subtractions (image-differencing techniques). During this interval we map several CME structures that are observed in both SMEI and the STEREO-A HI instruments. SMEI brightness analyses provided by short-term image subtractions ("difference images") and, alternatively, subtractions of a mean-brightness fit over a long-time duration, both show the extents of the CMEs travelling outward above the East limb that erupted from the Sun on 24 and 25 January 2007. The SMEI 3-D-reconstructions not only enhance distinct features within the CME events, but also reconcile difference-imaging results with those where a long-term base has been removed. In the January 2007 example the structure as mapped by CME difference images traces the sharp intensity gradients at the front of the CMEs; generally brighter ejected material follows behind the location of the CME front, but shows poorly in these because of its larger angular extent. Using the long-duration background removal enables SMEI's 3-D analysis to determine a mass for this CME sequence North of the ecliptic.
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Hewish, A. "Low Density Drivers of Strong Interplanetary Shocks." International Astronomical Union Colloquium 154 (1996): 5–13. http://dx.doi.org/10.1017/s0252921100029894.
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AbstractThe theory that most, if not all, interplanetary shocks are caused by coronal mass ejections (CMEs) faces serious problems in accounting for the strongest shocks. The difficulties include (i) a remarkable absence of very strong shocks during solar maximum 1980 when CMEs were prolific, (ii) unrealistic initial speeds near the Sun for impulsive models, (iii) the absence of rarefaction zones behind the shocks and (iv) sustained high speed flows following shocks which are not easily explained as consequences of CME eruptions. Observations of the proton temperature near 1 AU indicate that strong shock drivers have properties similar to high speed streams emitted by coronal holes. Eruptions of fast solar wind from coronal holes influenced by solar activity can explain the occurrence of the strongest interplanetary shocks.
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Lugaz, Noé, Charles J. Farrugia, and Nada Al-Haddad. "Complex Evolution of Coronal Mass Ejections in the Inner Heliosphere as Revealed by Numerical Simulations and STEREO Observations: A Review." Proceedings of the International Astronomical Union 8, S300 (June 2013): 255–64. http://dx.doi.org/10.1017/s174392131301106x.
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AbstractThe transit of coronal mass ejections (CMEs) from the Sun to 1 AU lasts on average one to five days. As they propagate, CMEs interact with the solar wind and preceding eruptions, which modify their properties. In the past ten years, the evolution of CMEs in the inner heliosphere has been investigated with the help of numerical simulations, through the analysis of remote-sensing heliospheric observations, especially with the SECCHI suite onboard STEREO, and through the analysis of multi-spacecraft in situ measurements. Most studies have focused on understanding the characteristics of the magnetic flux rope thought to form the core of the CME. Here, we first review recent work related to CME propagation in the heliosphere, which point towards the need to develop more complex models to analyze CME observations. In the second part of this article, we review some recent studies of CME-CME interaction, which also illustrate the complexity of phenomena occurring in the inner heliosphere.
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Corona-Romero, P., and J. A. Gonzalez-Esparza. "Dynamic evolution of interplanetary shock waves driven by CMEs." Proceedings of the International Astronomical Union 7, S286 (October 2011): 159–63. http://dx.doi.org/10.1017/s1743921312004784.
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AbstractWe present a study about the propagation of interplanetary shock waves driven by super magnetosonic coronal mass ejections (CMEs). The discussion focuses on a model which describes the dynamic relationship between the CME and its driven shock and the way to approximate the trajectory of shocks based on those relationships, from near the Sun to 1 AU. We apply the model to the analysis of a case study in which our calculations show quantitative and qualitative agreements with different kinds of data. We discuss the importance of solar wind and CME initial conditions on the shock wave evolution.
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Lago, A. Dal, L. E. Antunes Vieira, E. Echer, L. A. Balmaceda, M. Rockenbach, and W. D. Gonzalez. "Extreme solar-terrestrial events." Proceedings of the International Astronomical Union 12, S328 (October 2016): 233–36. http://dx.doi.org/10.1017/s1743921317004185.
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AbstractExtreme solar-terrestrial events are those in which very energetic solar ejections hit the earth?s magnetosphere, causing intense energization of the earth?s ring current. Statistically, their occurrence is approximately once per Gleissberg solar cycle (70-100yrs). The solar transient occurred on July, 23rd (2012) was potentially one of such extreme events. The associated coronal mass ejection (CME), however, was not ejected towards the earth. Instead, it hit the STEREO A spacecraft, located 120 degrees away from the Sun-Earth line. Estimates of the geoeffectiveness of such a CME point to a scenario of extreme Space Weather conditions. In terms of the ring current energization, as measured by the Disturbance Storm-Time index (Dst), had this CME hit the Earth, it would have caused the strongest geomagnetic storm in space era.
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McKenna-Lawlor, S. M. P., M. Dryer, Z. Smith, K. Kecskemety, C. D. Fry, W. Sun, C. S. Deehr, D. Berdichevsky, K. Kudela, and G. Zastenker. "Arrival times of Flare/Halo CME associated shocks at the Earth: comparison of the predictions of three numerical models with these observations." Annales Geophysicae 20, no. 7 (July 31, 2002): 917–35. http://dx.doi.org/10.5194/angeo-20-917-2002.
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Abstract. The arrival times at L1 of eleven travelling shocks associated both with X-ray flaring and with halo CMEs recorded aboard SOHO/LASCO have been considered. Close to the Sun the velocities of these events were estimated using either Type II radio records or CME speeds. Close to the Earth the shocks were detected in the data of various solar wind plasma, interplanetary magnetic field (IMF) and energetic particle experiments aboard SOHO, ACE, WIND, INTERBALL-1 and IMP-8. The real-time shock arrival predictions of three numerical models, namely the Shock Time of Arrival Model (STOA), the Interplanetary Shock Propagation Model (ISPM) and the Hakamada-Akasofu-Fry Solar Wind Model (HAFv.2) were tested against these observations. This is the first time that energetic protons (tens of keV to a few MeV) have been used to complement plasma and IMF data in validating shock propagation models. The models were all generally successful in predicting shock arrivals. STOA provided the smallest values of the "predicted minus measured" arrival times and displayed a typical predictive precision better than about 8 h. The ratio of the calculated standard deviation of the transit times to Earth to the standard deviation of the measurements was estimated for each model (treating interacting events as composite shocks) and these ratios turned out to be 0.60, 1.15 and 1.02 for STOA, ISPM and HAFv.2, respectively. If an event in the sample for which the shock velocity was not well known is omitted from consideration, these ratios become 0.36, 0.76 and 0.81, respectively. Larger statistical samples should now be tested. The ratio of the in situ shock velocity and the "Sun to L1" transit velocity (Vsh /Vtr) was in the range of 0.7–0.9 for individual, non-interacting, shock events. HAFv.2 uniquely provided information on those changes in the COBpoint (the moving Connection point on the shock along the IMF to the OBserver) which directly influenced energetic particle rise times. This model also illustrated the non-uniform upstream conditions through which the various shocks propagated; furthermore it simulated shock deformation on a scale of fractions of an AU. On the spatial scale (300 RE ), where near-Earth spacecraft are located, the passing shocks, in conformity with the models, were found to be locally planar. The shocks also showed tilting relative to the Sun-Earth line, probably reflecting the inherent directionality associated with their solar origin. Key words. Interplanetary physics (energetic particles; interplanetary shocks; solar wind plasma)
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Gopalswamy, N., S. Yashiro, S. Akiyama, P. Mäkelä, H. Xie, M. L. Kaiser, R. A. Howard, and J. L. Bougeret. "Coronal mass ejections, type II radio bursts, and solar energetic particle events in the SOHO era." Annales Geophysicae 26, no. 10 (October 15, 2008): 3033–47. http://dx.doi.org/10.5194/angeo-26-3033-2008.
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Abstract. Using the extensive and uniform data on coronal mass ejections (CMEs), solar energetic particle (SEP) events, and type II radio bursts during the SOHO era, we discuss how the CME properties such as speed, width and solar-source longitude decide whether CMEs are associated with type II radio bursts and SEP events. We discuss why some radio-quiet CMEs are associated with small SEP events while some radio-loud CMEs are not associated with SEP events. We conclude that either some fast and wide CMEs do not drive shocks or they drive weak shocks that do not produce significant levels of particle acceleration. We also infer that the Alfvén speed in the corona and near-Sun interplanetary medium ranges from <200 km/s to ~1600 km/s. Radio-quiet fast and wide CMEs are also poor SEP producers and the association rate of type II bursts and SEP events steadily increases with CME speed and width (i.e. energy). If we consider western hemispheric CMEs, the SEP association rate increases linearly from ~30% for 800 km/s CMEs to 100% for ≥1800 km/s. Essentially all type II bursts in the decametre-hectometric (DH) wavelength range are associated with SEP events once the source location on the Sun is taken into account. This is a significant result for space weather applications, because if a CME originating from the western hemisphere is accompanied by a DH type II burst, there is a high probability that it will produce an SEP event.
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Thejappa, G., and R. J. MacDowall. "Localization of type II and type III radio burst sources using multi-spacecraft observations." Proceedings of the International Astronomical Union 4, S257 (September 2008): 329–34. http://dx.doi.org/10.1017/s1743921309029500.
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AbstractA method for the localization of the radio burst sources associated with the flare accelerated electron beams and coronal mass ejection (CME) shocks is presented. This method involves the computations of the ray trajectories, time delays, and optical depths in the refracting solar atmosphere. The coordinates of the radiating source can be obtained by comparing the time delays and intensity ratios of the bursts observed by widely separated spacecraft with the computed group delays and intensity ratios at exit points of the rays from the solar atmosphere. This method is applied to a type III radio burst observed by the STEREO spacecraft.
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Díaz-Castillo, S. M., J. C. Martínez Oliveros, and B. Calvo-Mozo. "Evidence of in-situ Type II radio bursts in interplanetary shocks." Proceedings of the International Astronomical Union 12, S327 (October 2016): 134–39. http://dx.doi.org/10.1017/s1743921317004008.
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AbstractWe present a database of 11 interplanetary shocks associated to coronal mass ejections (CMEs) observed by STEREO and Wind missions between 2006 and 2011 that show evidence of Type II radio burst. For all events, we calculated the principal characteristics of the shock driver, the intensity and geometrical configuration of the in-situ shock and checked for the existence of in-situ type II radio burst. We made a comparative analysis of two CME events (on 18 August 2010 and 4 June 2011), which are apparently associated to two or more magnetic structures which interact in space (i.e. CMEs, SIRs, CIRs). These events show varied shock configurations and intensities. We found evidence of in-situ type II radio bursts in one of the events studied, suggesting that the geometry of the shock (quasi-perpendicularity) is also critical for the generation and/or detection of radio emission in-situ.
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Wimmer-Schweingruber, Robert F. "Interplanetary Disturbances Affecting Space Weather." Proceedings of the International Astronomical Union 8, S300 (June 2013): 297–306. http://dx.doi.org/10.1017/s1743921313011125.
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AbstractThe Sun somehow accelerates the solar wind, an incessant stream of plasma originating in coronal holes and some, as yet unidentified, regions. Occasionally, coronal, and possibly sub-photospheric structures, conspire to energize a spectacular eruption from the Sun which we call a coronal mass ejection (CME). These can leave the Sun at very high speeds and travel through the interplanetary medium, resulting in a large-scale disturbance of the ambient background plasma. These interplanetary CMEs (ICMEs) can drive shocks which in turn accelerate particles, but also have a distinct intrinsic magnetic structure which is capable of disturbing the Earth's magnetic field and causing significant geomagnetic effects. They also affect other planets, so they can and do contribute to space weather throughout the heliosphere. This paper presents a historical review of early space weather studies, a modern-day example, and discusses space weather throughout the heliosphere.
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Li, Xiaolei, Yuming Wang, Jingnan Guo, Rui Liu, and Bin Zhuang. "Radial velocity map of solar wind transients in the field of view of STEREO/HI1 on 3 and 4 April 2010." Astronomy & Astrophysics 649 (May 2021): A58. http://dx.doi.org/10.1051/0004-6361/202039766.
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Context. The solar wind transients propagating out in the inner heliosphere can be observed in white-light images from Heliospheric Imager-1 (HI1), an instrument of the Sun Earth Connection Coronal and Heliospheric Investigation on board the Solar Terrestrial Relations Observatory (STEREO), from two perspectives. The spatial velocity distribution inside solar wind transients is key to understanding their dynamic evolution processes. Aims. We generated a velocity map of transients in 3D space based on 2D white-light images and used it to estimate the expansion rate as well as some kinematic properties of solar wind transients. Methods. Based on the recently developed correlation-aided reconstruction method in our previous work, which can recognize and locate 3D solar wind transients from STEREO/HI1 image data, we further developped a new technique for deriving the spatial distribution of the radial velocities of the most pronounced features inside solar wind transients. Results. The technique was applied to events including a coronal mass ejection (CME) and three small-scale transients, so-called blobs, observed by HI1 on 3–4 April 2010 to reconstruct their radial velocity maps. The results match the forward-modeling results, simulations, and in situ observations at 1 AU fairly well. According to the obtained spatial distributions of height and radial velocity of the CME, we analyzed the self-similarity of the radial expansion of the CME ejecta. The dimensionless radial expansion rate of the northern and middle parts of the CME ejecta varies in the range of 0.7−1.0 at heliocentric distance between 25 R⊙ and 55 R⊙ and the rate of the southern part in the range of 0.3−0.5, suggesting that the CME structure was distorted and shaped by the ambient solar wind. The technique we developed is expected to be applied to more events.
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Asvestari, E., J. Pomoell, E. Kilpua, S. Good, T. Chatzistergos, M. Temmer, E. Palmerio, S. Poedts, and J. Magdalenic. "Modelling a multi-spacecraft coronal mass ejection encounter with EUHFORIA." Astronomy & Astrophysics 652 (August 2021): A27. http://dx.doi.org/10.1051/0004-6361/202140315.
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Context. Coronal mass ejections (CMEs) are a manifestation of the Sun’s eruptive nature. They can have a great impact on Earth, but also on human activity in space and on the ground. Therefore, modelling their evolution as they propagate through interplanetary space is essential. Aims. EUropean Heliospheric FORecasting Information Asset (EUHFORIA) is a data-driven, physics-based model, tracing the evolution of CMEs through background solar wind conditions. It employs a spheromak flux rope, which provides it with the advantage of reconstructing the internal magnetic field configuration of CMEs. This is something that is not included in the simpler cone CME model used so far for space weather forecasting. This work aims at assessing the spheromak CME model included in EUHFORIA. Methods. We employed the spheromak CME model to reconstruct a well observed CME and compare model output to in situ observations. We focus on an eruption from 6 January 2013 that was encountered by two radially aligned spacecraft, Venus Express and STEREO-A. We first analysed the observed properties of the source of this CME eruption and we extracted the CME properties as it lifted off from the Sun. Using this information, we set up EUHFORIA runs to model the event. Results. The model predicts arrival times from half to a full day ahead of the in situ observed ones, but within errors established from similar studies. In the modelling domain, the CME appears to be propagating primarily southward, which is in accordance with white-light images of the CME eruption close to the Sun. Conclusions. In order to get the observed magnetic field topology, we aimed at selecting a spheromak rotation angle for which the axis of symmetry of the spheromak is perpendicular to the direction of the polarity inversion line (PIL). The modelled magnetic field profiles, their amplitude, arrival times, and sheath region length are all affected by the choice of radius of the modelled spheromak.
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Czechowski, Andrzej, and Jens Kleimann. "Nanodust dynamics during a coronal mass ejection." Annales Geophysicae 35, no. 5 (September 4, 2017): 1033–49. http://dx.doi.org/10.5194/angeo-35-1033-2017.
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Abstract. The dynamics of nanometer-sized grains (nanodust) is strongly affected by electromagnetic forces. High-velocity nanodust was proposed as an explanation for the voltage bursts observed by STEREO. A study of nanodust dynamics based on a simple time-stationary model has shown that in the vicinity of the Sun the nanodust is trapped or, outside the trapped region, accelerated to high velocities. We investigate the nanodust dynamics for a time-dependent solar wind and magnetic field configuration in order to find out what happens to nanodust during a coronal mass ejection (CME). The plasma flow and the magnetic field during a CME are obtained by numerical simulations using a 3-D magnetohydrodynamic (MHD) code. The equations of motion for the nanodust particles are solved numerically, assuming that the particles are produced from larger bodies moving in near-circular Keplerian orbits within the circumsolar dust cloud. The charge-to-mass ratios for the nanodust particles are taken to be constant in time. The simulation is restricted to the region within 0.14 AU from the Sun. We find that about 35 % of nanodust particles escape from the computational domain during the CME, reaching very high speeds (up to 1000 km s−1). After the end of the CME the escape continues, but the particle velocities do not exceed 300 km s−1. About 30 % of all particles are trapped in bound non-Keplerian orbits with time-dependent perihelium and aphelium distances. Trapped particles are affected by plasma ion drag, which causes contraction of their orbits.
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Bhatt, Miral, Nandita Srivastava, and Ravindra Jadhav. "Study of Stealth CMEs and associated ICMEs." Proceedings of the International Astronomical Union 13, S340 (February 2018): 89–90. http://dx.doi.org/10.1017/s1743921318002053.
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AbstractGenerally Coronal Mass Ejections (CMEs) are large eruptions of plasma and magnetic field from the Sun into interplanetary space. CMEs are most frequently associated with a variety of phenomena occurring in the lower corona before, during and after onset of eruption and generally are visible in coronagraph observation. Stealth CMEs do not obviously exhibit any of the low-coronal signatures (LCS) like solar flares, flows, jets, coronal dimmings or brightenings, filament eruptions or the formation of flare loop arcades. In this study, five stealth CMEs are selected using LASCO/SOHO CME catalogue and associated ICMEs (Interplanetaty CMEs) are identified using data from STEREO, ACE and WIND.
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Pluta, Adam, Niclas Mrotzek, Angelos Vourlidas, Volker Bothmer, and Neel Savani. "Combined geometrical modelling and white-light mass determination of coronal mass ejections." Astronomy & Astrophysics 623 (March 2019): A139. http://dx.doi.org/10.1051/0004-6361/201833829.
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Context. We use forward modelling on multi-viewpoint coronagraph observations to estimate the 3-dimensional morphology, initial speed and deprojected masses of Coronal Mass Ejections (CMEs). The CME structure is described via the Graduated Cylindrical Shell (GCS) model, which enables the measurement of CME parameters in a consistent and comparable manner. Aims. This is the first large-scale use of the GCS model to estimate CME masses, so we discuss inherent peculiarities and implications for the mass determination with a special focus on CME events emerging from close to the observer’s central meridian. Further, we analyse the CME characteristics best suited to estimate the CME mass in a timely manner to make it available to CME arrival predictions. Methods. We apply the method to a set of 122 bright events observed simultaneously from two vantage points with the COR2 coronagraphs onboard of the twin NASA STEREO spacecraft. The events occurred between January 2007 and December 2013 and are compiled in an online catalogue within the EU FP7 project HELCATS. We statistically analyse the derived CME parameters, their mutual connection and their relation to the solar cycle. Results. We show that the derived morphology of intense disk events is still systematically overestimated by up to a factor of 2 with stereoscopic modelling, which is the same order of magnitude as for observations from only one vantage point. The overestimation is very likely a combination of projection effects as well as the increased complexity of separating CME shocks and streamers from CME fronts for such events. We further show that CME mass determination of disk events can lead to overestimation of the mass by about a factor of 10 or more, in case of overlapping bright structures. Conclusions. We conclude that for stereoscopic measurements of disk events, the measurement of the initial CME speed is the most reliable one. We further suggest that our presented CME speed-mass correlation is most suited to estimate the CME mass early from coronagraph observations.
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Cremades, H., C. H. Mandrini, M. C. López Fuentes, L. Merenda, I. Cabello, F. M. López, and M. Poisson. "A long-duration active region: Evolution and quadrature observations of ejective events." Proceedings of the International Astronomical Union 12, S327 (October 2016): 60–66. http://dx.doi.org/10.1017/s174392131700028x.
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AbstractUnknown aspects of the initiation, evolution, and associated phenomena of coronal mass ejections (CMEs), together with their capability of perturbing the fragile technological equilibrium on which nowadays society depends, turn them a compelling subject of study. While space weather forecasts are thus far not able to predict when and where in the Sun will the next CME take place, various CME triggering mechanisms have been proposed, without reaching consensus on which is the predominant one. To improve our knowledge in these respects, we investigate a long-duration active region throughout its life, from birth until decay along five solar rotations, in connection with its production of ejective events. We benefit from the wealth of solar remote-sensing data with improved temporal, spatial, and spectral resolution provided by the ground-breaking space missions STEREO, SDO, and SOHO. During the investigated time interval, which covers the months July – November 2010, the STEREO spacecraft were nearly 180 degrees apart, allowing for the uninterrupted tracking of the active region and its ensuing CMEs. The ejective aspect is examined from multi-viewpoint coronagraphic images, while the dynamics of the active region photospheric magnetic field are inspected by means of SDO/HMI data for specific subintervals of interest. The ultimate goal of this work in progress is to identify common patterns in the ejective aspect that can be connected with the active region characteristics.
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Yu, J., L. Berger, C. Drews, R. Wimmer-Schweingruber, and A. Taut. "Spectral variation of suprathermal protons associated with stream interaction regions: STEREO A/PLASTIC observations." Astronomy & Astrophysics 615 (July 2018): A126. http://dx.doi.org/10.1051/0004-6361/201732444.
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Context. The observation of power-law spectra of suprathermal particles is typically associated with the occurrence of stream interaction regions (SIRs), indicating that these particles are accelerated close to the observer. However, recent observations have identified the existence of sunwards streaming particles at low suprathermal energies following SIRs. In addition, the observational evidence for turnover spectra in the low suprathermal energies has also been presented, suggesting that these particles might be accelerated at remote shocks and travel back to the Sun along the interplanetary magnetic field lines. Aims. We investigate the spectral evolution and variation of suprathermal protons from SIR to SIR as the observer moves from inside the compression regions of SIRs to the outside undisturbed solar wind regions away from the reverse shocks. Methods. The spectral analysis in the range from solar wind to suprathermal energies was based on proton data, which are obtained by the Plasma and Suprathermal Ion Composition instrument (PLASTIC) on the Solar Terrestrial Relations Observatory mission (STEREO). Results. All spectra in the compressed fast wind regions (F′ regions) of twelve SIRs exhibit power-law suprathermal tails. Six of them show clear turnover spectra at velocities below 2500 km s−1 in the undisturbed fast solar wind regions (F regions) following the compression regions, while the remaining six events exhibit continuous power-law spectra. Overall, the spectra at velocities higher than 2500 km s−1 harden in the F regions, consistent with previous observations.
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Jebaraj, I. C., J. Magdalenić, T. Podladchikova, C. Scolini, J. Pomoell, A. M. Veronig, K. Dissauer, V. Krupar, E. K. J. Kilpua, and S. Poedts. "Using radio triangulation to understand the origin of two subsequent type II radio bursts." Astronomy & Astrophysics 639 (July 2020): A56. http://dx.doi.org/10.1051/0004-6361/201937273.
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Context. Eruptive events such as coronal mass ejections (CMEs) and flares accelerate particles and generate shock waves which can arrive at Earth and can disturb the magnetosphere. Understanding the association between CMEs and CME-driven shocks is therefore highly important for space weather studies. Aims. We present a study of the CME/flare event associated with two type II bursts observed on September 27, 2012. The aim of the study is to understand the relationship between the observed CME and the two distinct shock wave signatures. Methods. The multiwavelength study of the eruptive event (CME/flare) was complemented with radio triangulation of the associated radio emission and modelling of the CME and the shock wave employing MHD simulations. Results. We found that, although temporal association between the type II bursts and the CME is good, the low-frequency type II (LF-type II) burst occurs significantly higher in the corona than the CME and its relationship to the CME is not straightforward. The analysis of the EIT wave (coronal bright front) shows the fastest wave component to be in the southeast quadrant of the Sun. This is also the quadrant in which the source positions of the LF-type II were found to be located, probably resulting from the interaction between the shock wave and a streamer. Conclusions. The relationship between the CME/flare event and the shock wave signatures is discussed using the temporal association, as well as the spatial information of the radio emission. Further, we discuss the importance and possible effects of the frequently non-radial propagation of the shock wave.
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Zucca, P., D. E. Morosan, A. P. Rouillard, R. Fallows, P. T. Gallagher, J. Magdalenic, K. L. Klein, et al. "Shock location and CME 3D reconstruction of a solar type II radio burst with LOFAR." Astronomy & Astrophysics 615 (July 2018): A89. http://dx.doi.org/10.1051/0004-6361/201732308.
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Context. Type II radio bursts are evidence of shocks in the solar atmosphere and inner heliosphere that emit radio waves ranging from sub-meter to kilometer lengths. These shocks may be associated with coronal mass ejections (CMEs) and reach speeds higher than the local magnetosonic speed. Radio imaging of decameter wavelengths (20–90 MHz) is now possible with the Low Frequency Array (LOFAR), opening a new radio window in which to study coronal shocks that leave the inner solar corona and enter the interplanetary medium and to understand their association with CMEs. Aims. To this end, we study a coronal shock associated with a CME and type II radio burst to determine the locations at which the radio emission is generated, and we investigate the origin of the band-splitting phenomenon. Methods. Thetype II shock source-positions and spectra were obtained using 91 simultaneous tied-array beams of LOFAR, and the CME was observed by the Large Angle and Spectrometric Coronagraph (LASCO) on board the Solar and Heliospheric Observatory (SOHO) and by the COR2A coronagraph of the SECCHI instruments on board the Solar Terrestrial Relation Observatory(STEREO). The 3D structure was inferred using triangulation of the coronographic observations. Coronal magnetic fields were obtained from a 3D magnetohydrodynamics (MHD) polytropic model using the photospheric fields measured by the Heliospheric Imager (HMI) on board the Solar Dynamic Observatory (SDO) as lower boundary. Results. The type II radio source of the coronal shock observed between 50 and 70 MHz was found to be located at the expanding flank of the CME, where the shock geometry is quasi-perpendicular with θBn ~ 70°. The type II radio burst showed first and second harmonic emission; the second harmonic source was cospatial with the first harmonic source to within the observational uncertainty. This suggests that radio wave propagation does not alter the apparent location of the harmonic source. The sources of the two split bands were also found to be cospatial within the observational uncertainty, in agreement with the interpretation that split bands are simultaneous radio emission from upstream and downstream of the shock front. The fast magnetosonic Mach number derived from this interpretation was found to lie in the range 1.3–1.5. The fast magnetosonic Mach numbers derived from modelling the CME and the coronal magnetic field around the type II source were found to lie in the range 1.4–1.6.
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Klimchuk, James A., Lidia van Driel-Gesztelyi, Carolus J. Schrijver, Donald B. Melrose, Lyndsay Fletcher, Natchimuthuk Gopalswamy, Richard A. Harrison, et al. "COMMISSION 10: SOLAR ACTIVITY." Proceedings of the International Astronomical Union 4, T27A (December 2008): 79–103. http://dx.doi.org/10.1017/s1743921308025350.
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Commission 10 deals with solar activity in all of its forms, ranging from the smallest nanoflares to the largest coronal mass ejections. This report reviews scientific progress over the roughly two-year period ending in the middle of 2008. This has been an exciting time in solar physics, highlighted by the launches of the Hinode and STEREO missions late in 2006. The report is reasonably comprehensive, though it is far from exhaustive. Limited space prevents the inclusion of many significant results. The report is divided into the following sections: Photosphere and chromosphere; Transition region; Corona and coronal heating; Coronal jets; flares; Coronal mass ejection initiation; Global coronal waves and shocks; Coronal dimming; The link between low coronal CME signatures and magnetic clouds; Coronal mass ejections in the heliosphere; and Coronal mass ejections and space weather. Primary authorship is indicated at the beginning of each section.
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Morosan, D. E., E. Palmerio, J. E. Räsänen, E. K. J. Kilpua, J. Magdalenić, B. J. Lynch, A. Kumari, J. Pomoell, and M. Palmroth. "Electron acceleration and radio emission following the early interaction of two coronal mass ejections." Astronomy & Astrophysics 642 (October 2020): A151. http://dx.doi.org/10.1051/0004-6361/202038801.
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Context. Coronal mass ejections (CMEs) are large eruptions of magnetised plasma from the Sun that are often accompanied by solar radio bursts produced by accelerated electrons. Aims. A powerful source for accelerating electron beams are CME-driven shocks, however, there are other mechanisms capable of accelerating electrons during a CME eruption. So far, studies have relied on the traditional classification of solar radio bursts into five groups (Type I–V) based mainly on their shapes and characteristics in dynamic spectra. Here, we aim to determine the origin of moving radio bursts associated with a CME that do not fit into the present classification of the solar radio emission. Methods. By using radio imaging from the Nançay Radioheliograph, combined with observations from the Solar Dynamics Observatory, Solar and Heliospheric Observatory, and Solar Terrestrial Relations Observatory spacecraft, we investigate the moving radio bursts accompanying two subsequent CMEs on 22 May 2013. We use three-dimensional reconstructions of the two associated CME eruptions to show the possible origin of the observed radio emission. Results. We identified three moving radio bursts at unusually high altitudes in the corona that are located at the northern CME flank and move outwards synchronously with the CME. The radio bursts correspond to fine-structured emission in dynamic spectra with durations of ∼1 s, and they may show forward or reverse frequency drifts. Since the CME expands closely following an earlier CME, a low coronal CME–CME interaction is likely responsible for the observed radio emission. Conclusions. For the first time, we report the existence of new types of short duration bursts, which are signatures of electron beams accelerated at the CME flank. Two subsequent CMEs originating from the same region and propagating in similar directions provide a complex configuration of the ambient magnetic field and favourable conditions for the creation of collapsing magnetic traps. These traps are formed if a CME-driven wave, such as a shock wave, is likely to intersect surrounding magnetic field lines twice. Electrons will thus be further accelerated at the mirror points created at these intersections and eventually escape to produce bursts of plasma emission with forward and reverse drifts.
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Файнштейн, Виктор, Victor Fainshtein, Ярослав Егоров, and Yaroslav Egorov. "Radial distributions of magnetic field strength in the solar corona as derived from data on fast halo CMEs." Solar-Terrestrial Physics 4, no. 1 (March 31, 2018): 3–11. http://dx.doi.org/10.12737/stp-41201801.
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In recent years, information about the distance between the body of rapid coronal mass ejection (CME) and the associated shock wave has been used to measure the magnetic field in the solar corona. In all cases, this tech-nique allows us to find coronal magnetic field radial profiles B(R) applied to the directions almost perpendicular to the line of sight. We have determined radial distributions of magnetic field strength along the directions close to the Sun–Earth axis. For this purpose, using the “ice-cream cone” model and SOHO/LASCO data, we found 3D characteristics for fast halo coronal mass ejections (HCMEs) and for HCME-related shocks. With these data we managed to obtain the B(R) distributions as far as ≈43 solar radii from the Sun’s center, which is approximately twice as far as those in other studies based on LASCO data. We have concluded that to improve the accuracy of this method for finding the coronal magnetic field we should develop a technique for detecting CME sites moving in the slow and fast solar wind. We propose a technique for selecting CMEs whose central (paraxial) part actually moves in the slow wind.
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Файнштейн, Виктор, Victor Fainshtein, Ярослав Егоров, and Yaroslav Egorov. "Radial distributions of magnetic field strength in the solar corona as derived from data on fast halo CMEs." Solnechno-Zemnaya Fizika 4, no. 1 (March 29, 2018): 3–13. http://dx.doi.org/10.12737/szf-41201801.
Full textAbstract:
In recent years, information about the distance between the body of rapid coronal mass ejection (CME) and the associated shock wave has been used to measure the magnetic field in the solar corona. In all cases, this tech-nique allows us to find coronal magnetic field radial profiles B(R) applied to the directions almost perpendicular to the line of sight. We have determined radial distributions of magnetic field strength along the directions close to the Sun–Earth axis. For this purpose, using the “ice-cream cone” model and SOHO/LASCO data, we found 3D characteristics for fast halo coronal mass ejections (HCMEs) and for HCME-related shocks. With these data we managed to obtain the B(R) distributions as far as ≈43 solar radii from the Sun’s center, which is approximately twice as far as those in other studies based on LASCO data. We have concluded that to improve the accuracy of this method for finding the coronal magnetic field we should develop a technique for detecting CME sites moving in the slow and fast solar wind. We propose a technique for selecting CMEs whose central (paraxial) part actually moves in the slow wind.
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Williams, A. O., J. A. Davies, S. E. Milan, A. P. Rouillard, C. J. Davis, C. H. Perry, and R. A. Harrison. "Deriving solar transient characteristics from single spacecraft STEREO/HI elongation variations: a theoretical assessment of the technique." Annales Geophysicae 27, no. 12 (December 1, 2009): 4359–68. http://dx.doi.org/10.5194/angeo-27-4359-2009.
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Abstract. Recently, a technique has been developed whereby the radial velocity, Vr, and longitude direction, β, of propagation of an outward-moving solar transient, such as a Coronal Mass Ejection (CME), can be estimated from its track in a time-elongation map produced using Heliospheric Imager (HI) observations from a single STEREO spacecraft. The method employed, which takes advantage of an artefact of projective geometry, is based on the evaluation of the best fit of the time-elongation profile of the transient, extracted from a time-elongation map, to a set of theoretical functions corresponding to known combinations of radial velocity and direction; here we present an initial theoretical assessment of the efficacy of this technique. As the method relies on the manual selection of points along the time-elongation profile, an assessment of the accuracy with which this is feasible, is initially made. The work then presented assesses theoretically this method of recovering the velocity and propagation direction of solar transients from their time-elongation profiles using a Monte-Carlo simulation approach. In particular, we assess the range of elongations over which it is necessary to make observations in order to accurately recover these parameters. Results of the Monte-Carlo simulations suggest that it is sufficient to track a solar transient out to around 40° elongation to provide accurate estimates of its associated radial velocity and direction; the accuracy to which these parameters can be estimated for a transient tracked over a particular elongation extent is, however, sensitive to its velocity and direction relative to the Sun-Spacecraft line. These initial results suggest that this technique based on single spacecraft STEREO/HI observations could prove extremely useful in terms of providing an early warning of a CME impact on the near-Earth environment.
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Maguire, Ciara A., Eoin P. Carley, Joseph McCauley, and Peter T. Gallagher. "Evolution of the Alfvén Mach number associated with a coronal mass ejection shock." Astronomy & Astrophysics 633 (January 2020): A56. http://dx.doi.org/10.1051/0004-6361/201936449.
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The Sun regularly produces large-scale eruptive events, such as coronal mass ejections (CMEs) that can drive shock waves through the solar corona. Such shocks can result in electron acceleration and subsequent radio emission in the form of a type II radio burst. However, the early-phase evolution of shock properties and its relationship to type II burst evolution is still subject to investigation. Here we study the evolution of a CME-driven shock by comparing three commonly used methods of calculating the Alfvén Mach number (MA), namely: shock geometry, a comparison of CME speed to a model of the coronal Alfvén speed, and the type II band-splitting method. We applied the three methods to the 2017 September 2 event, focusing on the shock wave observed in extreme ultraviolet by the Solar Ultraviolet Imager on board GOES-16, in white-light by the Large Angle and Spectrometric Coronagraph on board SOHO, and the type II radio burst observed by the Irish Low Frequency Array. We show that the three different methods of estimating shock MA yield consistent results and provide a means of relating shock property evolution to the type II emission duration. The type II radio emission emerged from near the nose of the CME when MA was in the range 1.4–2.4 at a heliocentric distance of ∼1.6 R⊙. The emission ceased when the CME nose reached ∼2.4 R⊙, despite an increasing Alfvén Mach number (up to 4). We suggest the radio emission cessation is due to the lack of quasi-perpendicular geometry at this altitude, which inhibits efficient electron acceleration and subsequent radio emission.
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Lugaz, Noé, Ilia I. Roussev, and Igor V. Sokolov. "The August 24, 2002 coronal mass ejection: when a western limb event connects to earth." Proceedings of the International Astronomical Union 4, S257 (September 2008): 391–98. http://dx.doi.org/10.1017/s1743921309029615.
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AbstractWe discuss how some coronal mass ejections (CMEs) originating from the western limb of the Sun are associated with space weather effects such as solar energetic particles (SEPs), shocks or geo-effective ejecta at Earth. We focus on the August 24, 2002 coronal mass ejection, a fast (~2000 km s−1) eruption originating from W81. Using a three-dimensional magneto-hydrodynamic simulation of this ejection with the Space Weather Modeling Framework (SWMF), we show how a realistic initiation mechanism enables us to study the deflection of the CME in the corona and the heliosphere. Reconnection of the erupting magnetic field with that of neighboring streamers and active regions modify the solar connectivity of the field lines connecting to Earth and can also partly explain the deflection of the eruption during the first tens of minutes. Comparing the results at 1 AU of our simulation with observations by the ACE spacecraft, we find that the simulated shock does not reach Earth, but has a maximum angular span of about 120°, and reaches 35° West of Earth in 58 hours. We find no significant deflection of the CME and its associated shock wave in the heliosphere, and we discuss the consequences for the shock angular span.
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Berdichevsky, D. B., C. J. Farrugia, B. J. Thompson, R. P. Lepping, D. V. Reames, M. L. Kaiser, J. T. Steinberg, S. P. Plunkett, and D. J. Michels. "Halo-coronal mass ejections near the 23rd solar minimum: lift-off, inner heliosphere, and in situ (1 AU) signatures." Annales Geophysicae 20, no. 7 (July 31, 2002): 891–916. http://dx.doi.org/10.5194/angeo-20-891-2002.
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Abstract. The extreme ultraviolet (EUV) signatures of a solar lift-off, decametric and kilometric radio burst emissions and energetic particle (EP) inner heliospheric signatures of an interplanetary shock, and in situ identification of its driver through solar wind observations are discussed for 12 isolated halo coronal mass ejections (H-CMEs) occurring between December 1996 and 1997. For the aforementioned twelve and the one event added in the discussion, it is found that ten passed several necessary conditions for being a "Sun-Earth connection". It is found that low corona EUV and Ha chromospheric signatures indicate filament eruption as the cause of H-CME. These signatures indicate that the 12 events can be divided into two major subsets, 7 related to active regions (ARs) and 5 unrelated or related to decayed AR. In the case of events related to AR, there is indication of a faster lift-off, while a more gradual lift-off appears to characterize the second set. Inner heliospheric signatures – the presence of long lasting enhanced energetic particle flux and/or kilometric type II radio bursts – of a driven shock were identified in half of the 12 events. The in situ (1 AU) analyses using five different solar wind ejecta signatures and comparisons with the bidirectional flow of suprathermal particles and Forbush decreases result in indications of a strong solar wind ejecta signatures for 11 out of 12 cases. From the discussion of these results, combined with work by other authors for overlapping events, we conclude that good Sun-Earth connection candidates originate most likely from solar filament eruptions with at least one of its extremities located closer to the central meridian than ~ 30° E or ~ 35° W with a larger extension in latitudinal location possible. In seven of the twelve cases it appears that the encountered ejecta was driving a shock at 1 AU. Support for this interpretation is found on the approximately equal velocity of the shock and the ejecta leading-edge. These shocks were weak to moderate in strength, and a comparison of their transit time with their local speed indicated a deceleration. In contradistinction with this result on shocks, the transit time versus the local speed of the ejecta appeared either to indicate that the ejecta as a whole traveled at constant speed or underwent a small amount of acceleration. This is a result that stands for cases with and without fast stream observations at their rear end. Seven out of twelve ejecta candidate intervals were themselves interplanetary magnetic cloud (IMC) or contained a previously identified IMC. As a by-product of this study, we noticed two good ejecta candidates at 1 AU for which observation of a H-CME or CME appears to be missing.Key words. Radio science (remote sensing); Solar physics, astrophysics and astronomy (flares and mass ejections); Space plasma physics (nonlinear phenomena)
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Grison, Benjamin, Jan Souček, Vratislav Krupar, David Píša, Ondrej Santolík, Ulrich Taubenschuss, and František Nĕmec. "Shock deceleration in interplanetary coronal mass ejections (ICMEs) beyond Mercury’s orbit until one AU." Journal of Space Weather and Space Climate 8 (2018): A54. http://dx.doi.org/10.1051/swsc/2018043.
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The CDPP propagation tool is used to propagate interplanetary coronal mass ejections (ICMEs) observed at Mercury by MESSENGER to various targets in the inner solar system (VEX, ACE, STEREO-A and B). The deceleration of ICME shock fronts between the orbit of Mercury and 1 AU is studied on the basis of a large dataset. We focus on the interplanetary medium far from the solor corona, to avoid the region where ICME propagation modifications in velocity and direction are the most drastic. Starting with a catalog of 61 ICMEs recorded by MESSENGER, the propagation tool predicts 36 ICME impacts with targets. ICME in situ signatures are investigated close to predicted encounter times based on velocities estimated at MESSENGER and on the default propagation tool velocity (500 km s−1). ICMEs are observed at the targets in 26 cases and interplanetary shocks (not followed by magnetic ejecta) in two cases. Comparing transit velocities between the Sun and MESSENGER ($ {\bar{v}}_{\mathrm{SunMess}}$) and between MESSENGER and the targets ($ {\bar{v}}_{\mathrm{MessTar}}$), we find an average deceleration of 170 km s−1 (28 cases). Comparing $ {\bar{v}}_{\mathrm{MessTar}}$ to the velocities at the targets (v Tar), average ICME deceleration is about 160 km s−1 (13 cases). Our results show that the ICME shock deceleration is significant beyond Mercury’s orbit. ICME shock arrival times are predicted with an average accuracy of about six hours with a standard deviation of eleven hours. Focusing on two ICMEs detected first at MESSENGER and later on by two targets illustrates our results and the variability in ICME propagations. The shock velocity of an ICME observed at MESSENGER, then at VEX and finally at STEREO-B decreases all the way. Predicting arrivals of potentially effective ICMEs is an important space weather issue. The CDPP propagation tool, in association with in situ measurements between the Sun and the Earth, can permit to update alert status of such arrivals.
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KIRÁLY, PÉTER. "SOLAR ENERGETIC PARTICLES." International Journal of Modern Physics A 20, no. 29 (November 20, 2005): 6634–41. http://dx.doi.org/10.1142/s0217751x05029678.
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Energetic particles recorded in the Earth environment and in interplanetary space have a multitude of origins, i.e. acceleration and propagation histories. At early days practically all sufficiently energetic particles were considered to have come either from solar flares or from interstellar space. Later on, co-rotating interplanetary shocks, the termination shock of the supersonic solar wind, planetary bow shocks and magnetospheres, and also coronal mass ejections (CME) were recognized as energetic particle sources. It was also recognized that less energetic (suprathermal) particles of solar origin and pick-up ions have also a vital role in giving rise to energetic particles in interplanetary disturbances. The meaning of the term "solar energetic particles" (SEP) is now somewhat vague, but essentially it refers to particles produced in disturbances fairly directly related to solar processes. Variation of intensity fluctuations with energy and with the phase of the solar cycle will be discussed. Particular attention will be given to extremes of time variation, i.e. to very quiet periods and to large events. While quiet-time fluxes are expected to shed light on some basic coronal processes, large events dominate the fluctuation characteristics of cumulated fluence, and the change of that fluctuation with energy and with the phase of the solar cycle may also provide important clues. Mainly ISEE-3 and long-term IMP-8 data will be invoked. Energetic and suprathermal particles that may never escape into interplanetary space may play an important part in heating the corona of the sun.
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Schwenn, R., A. Dal Lago, E. Huttunen, and W. D. Gonzalez. "The association of coronal mass ejections with their effects near the Earth." Annales Geophysicae 23, no. 3 (March 30, 2005): 1033–59. http://dx.doi.org/10.5194/angeo-23-1033-2005.
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Abstract. To this day, the prediction of space weather effects near the Earth suffers from a fundamental problem: The radial propagation speed of "halo" CMEs (i.e. CMEs pointed along the Sun-Earth-line that are known to be the main drivers of space weather disturbances) towards the Earth cannot be measured directly because of the unfavorable geometry. From inspecting many limb CMEs observed by the LASCO coronagraphs on SOHO we found that there is usually a good correlation between the radial speed and the lateral expansion speed Vexp of CME clouds. This latter quantity can also be determined for earthward-pointed halo CMEs. Thus, Vexp may serve as a proxy for the otherwise inaccessible radial speed of halo CMEs. We studied this connection using data from both ends: solar data and interplanetary data obtained near the Earth, for a period from January 1997 to 15 April 2001. The data were primarily provided by the LASCO coronagraphs, plus additional information from the EIT instrument on SOHO. Solar wind data from the plasma instruments on the SOHO, ACE and Wind spacecraft were used to identify the arrivals of ICME signatures. Here, we use "ICME" as a generic term for all CME effects in interplanetary space, thus comprising not only ejecta themselves but also shocks as well. Among 181 front side or limb full or partial halo CMEs recorded by LASCO, on the one hand, and 187 ICME events registered near the Earth, on the other hand, we found 91 cases where CMEs were uniquely associated with ICME signatures in front of the Earth. Eighty ICMEs were associated with a shock, and for 75 of them both the halo expansion speed Vexp and the travel time Ttr of the shock could be determined. The function Ttr=203-20.77*ln (Vexp) fits the data best. This empirical formula can be used for predicting further ICME arrivals, with a 95% error margin of about one day. Note, though, that in 15% of comparable cases, a full or partial halo CME does not cause any ICME signature at Earth at all; every fourth partial halo CME and every sixth limb halo CME does not hit the Earth (false alarms). Furthermore, every fifth transient shock or ICME or isolated geomagnetic storm is not caused by an identifiable partial or full halo CME on the front side (missing alarms).
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Hanuise, C., J. C. Cerisier, F. Auchère, K. Bocchialini, S. Bruinsma, N. Cornilleau-Wehrlin, N. Jakowski, et al. "From the Sun to the Earth: impact of the 27-28 May 2003 solar events on the magnetosphere, ionosphere and thermosphere." Annales Geophysicae 24, no. 1 (March 7, 2006): 129–51. http://dx.doi.org/10.5194/angeo-24-129-2006.
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Abstract. During the last week of May 2003, the solar active region AR 10365 produced a large number of flares, several of which were accompanied by Coronal Mass Ejections (CME). Specifically on 27 and 28 May three halo CMEs were observed which had a significant impact on geospace. On 29 May, upon their arrival at the L1 point, in front of the Earth's magnetosphere, two interplanetary shocks and two additional solar wind pressure pulses were recorded by the ACE spacecraft. The interplanetary magnetic field data showed the clear signature of a magnetic cloud passing ACE. In the wake of the successive increases in solar wind pressure, the magnetosphere became strongly compressed and the sub-solar magnetopause moved inside five Earth radii. At low altitudes the increased energy input to the magnetosphere was responsible for a substantial enhancement of Region-1 field-aligned currents. The ionospheric Hall currents also intensified and the entire high-latitude current system moved equatorward by about 10°. Several substorms occurred during this period, some of them - but not all - apparently triggered by the solar wind pressure pulses. The storm's most notable consequences on geospace, including space weather effects, were (1) the expansion of the auroral oval, and aurorae seen at mid latitudes, (2) the significant modification of the total electron content in the sunlight high-latitude ionosphere, (3) the perturbation of radio-wave propagation manifested by HF blackouts and increased GPS signal scintillation, and (4) the heating of the thermosphere, causing increased satellite drag. We discuss the reasons why the May 2003 storm is less intense than the October-November 2003 storms, although several indicators reach similar intensities.
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Aran, A., B. Sanahuja, and D. Lario. "Fluxes and fluences of SEP events derived from SOLPENCO." Annales Geophysicae 23, no. 9 (November 22, 2005): 3047–53. http://dx.doi.org/10.5194/angeo-23-3047-2005.
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Abstract. We have developed aran04 a tool for rapid predictions of proton flux and fluence profiles observed during gradual solar energetic particle (SEP) events and upstream of the associated traveling interplanetary shocks. This code, named SOLPENCO (for SOLar Particle ENgineering COde), contains a data base with a large set of interplanetary scenarios under which SEP events develop. These scenarios are basically defined by the solar longitude of the parent solar activity, ranging from E75 to W90, and by the position of the observer, located at 0.4 AU or at 1.0 AU, from the Sun. We are now analyzing the performance and reliability of SOLPENCO. We address here two features of SEP events especially relevant to space weather purposes: the peak flux and the fluence. We analyze how the peak flux and the fluence of the synthetic profiles generated by SOLPENCO vary as a function of the strength of the CME-driven shock, the heliolongitude of the solar parent activity and the particle energy considered. In particular, we comment on the dependence of the fluence on the radial distance of the observer (which does not follow an inverse square law), and we draw conclusions about the influence of the shock as a particle accelerator in terms of its evolving strength and the heliolongitude of the solar site where the SEP event originated.
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Hosteaux, S., E. Chané, and S. Poedts. "Effect of the solar wind density on the evolution of normal and inverse coronal mass ejections." Astronomy & Astrophysics 632 (December 2019): A89. http://dx.doi.org/10.1051/0004-6361/201935894.
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Context. The evolution of magnetised coronal mass ejections (CMEs) and their interaction with the background solar wind leading to deflection, deformation, and erosion is still largely unclear as there is very little observational data available. Even so, this evolution is very important for the geo-effectiveness of CMEs. Aims. We investigate the evolution of both normal and inverse CMEs ejected at different initial velocities, and observe the effect of the background wind density and their magnetic polarity on their evolution up to 1 AU. Methods. We performed 2.5D (axisymmetric) simulations by solving the magnetohydrodynamic equations on a radially stretched grid, employing a block-based adaptive mesh refinement scheme based on a density threshold to achieve high resolution following the evolution of the magnetic clouds and the leading bow shocks. All the simulations discussed in the present paper were performed using the same initial grid and numerical methods. Results. The polarity of the internal magnetic field of the CME has a substantial effect on its propagation velocity and on its deformation and erosion during its evolution towards Earth. We quantified the effects of the polarity of the internal magnetic field of the CMEs and of the density of the background solar wind on the arrival times of the shock front and the magnetic cloud. We determined the positions and propagation velocities of the magnetic clouds and thus also the stand-off distance of the leading shock fronts (i.e. the thickness of the magnetic sheath region) and the deformation and erosion of the magnetic clouds during their evolution from the Sun to the Earth. Inverse CMEs were found to be faster than normal CMEs ejected in the same initial conditions, but with smaller stand-off distances. They also have a higher magnetic cloud length, opening angle, and mass. Synthetic satellite time series showed that the shock magnitude is not affected by the polarity of the CME. However, the density peak of the magnetic cloud is dependent on the polarity and, in case of inverse CMEs, also on the background wind density. The magnitude of the z-component of the magnetic field was not influenced by either the polarity or the wind density.
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Pohjolainen, Silja, and Nasrin Talebpour Sheshvan. "Formation of Isolated Radio Type II Bursts at Low Frequencies." Solar Physics 296, no. 5 (May 2021). http://dx.doi.org/10.1007/s11207-021-01828-y.
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AbstractThe 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.
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Barnes, D., J. A. Davies, R. A. Harrison, J. P. Byrne, C. H. Perry, V. Bothmer, J. P. Eastwood, et al. "CMEs in the Heliosphere: III. A Statistical Analysis of the Kinematic Properties Derived from Stereoscopic Geometrical Modelling Techniques Applied to CMEs Detected in the Heliosphere from 2008 to 2014 by STEREO/HI-1." Solar Physics 295, no. 11 (November 2020). http://dx.doi.org/10.1007/s11207-020-01717-w.
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AbstractWe present an analysis of coronal mass ejections (CMEs) observed by the Heliospheric Imagers (HIs) onboard NASA’s Solar Terrestrial Relations Observatory (STEREO) spacecraft. Between August 2008 and April 2014 we identify 273 CMEs that are observed simultaneously, by the HIs on both spacecraft. For each CME, we track the observed leading edge, as a function of time, from both vantage points, and apply the Stereoscopic Self-Similar Expansion (SSSE) technique to infer their propagation throughout the inner heliosphere. The technique is unable to accurately locate CMEs when their observed leading edge passes between the spacecraft; however, we are able to successfully apply the technique to 151, most of which occur once the spacecraft-separation angle exceeds $180^{\circ }$ 180 ∘ , during solar maximum. We find that using a small half-width to fit the CME can result in inferred acceleration to unphysically high velocities and that using a larger half-width can fail to accurately locate the CMEs close to the Sun because the method does not account for CME over-expansion in this region. Observed velocities from SSSE are found to agree well with single-spacecraft (SSEF) analysis techniques applied to the same events. CME propagation directions derived from SSSE and SSEF analysis agree poorly because of known limitations present in the latter.
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Temmer, Manuela. "Space weather: the solar perspective." Living Reviews in Solar Physics 18, no. 1 (June 29, 2021). http://dx.doi.org/10.1007/s41116-021-00030-3.
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AbstractThe Sun, as an active star, is the driver of energetic phenomena that structure interplanetary space and affect planetary atmospheres. The effects of Space Weather on Earth and the solar system is of increasing importance as human spaceflight is preparing for lunar and Mars missions. This review is focusing on the solar perspective of the Space Weather relevant phenomena, coronal mass ejections (CMEs), flares, solar energetic particles (SEPs), and solar wind stream interaction regions (SIR). With the advent of the STEREO mission (launched in 2006), literally, new perspectives were provided that enabled for the first time to study coronal structures and the evolution of activity phenomena in three dimensions. New imaging capabilities, covering the entire Sun-Earth distance range, allowed to seamlessly connect CMEs and their interplanetary counterparts measured in-situ (so called ICMEs). This vastly increased our knowledge and understanding of the dynamics of interplanetary space due to solar activity and fostered the development of Space Weather forecasting models. Moreover, we are facing challenging times gathering new data from two extraordinary missions, NASA’s Parker Solar Probe (launched in 2018) and ESA’s Solar Orbiter (launched in 2020), that will in the near future provide more detailed insight into the solar wind evolution and image CMEs from view points never approached before. The current review builds upon the Living Reviews article by Schwenn from 2006, updating on the Space Weather relevant CME-flare-SEP phenomena from the solar perspective, as observed from multiple viewpoints and their concomitant solar surface signatures.
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Klein, Karl-Ludwig. "Radio Astronomical Tools for the Study of Solar Energetic Particles II.Time-Extended Acceleration at Subrelativistic and Relativistic Energies." Frontiers in Astronomy and Space Sciences 7 (March 11, 2021). http://dx.doi.org/10.3389/fspas.2020.580445.
Full textAbstract:
Solar energetic particle (SEP) events are commonly separated in two categories: numerous “impulsive” events of relatively short duration, and a few “gradual” events, where SEP-intensities may stay enhanced over several days at energies up to several tens of MeV. In some gradual events the SEP spectrum extends to relativistic energies (>1 GeV), over shorter durations. The two categories are strongly related to an idea developed in the 1960s based on radio observations: Type III bursts, which were addressed in a companion chapter, outline impulsive acceleration of electrons to subrelativistic energies, while the large and the relativistic SEP events were ascribed to a second acceleration process. At radio wavelengths, typical counterparts were bursts emitted by electrons accelerated at coronal shock waves (type II bursts) and by electron populations in large-scale closed coronal structures (type IV bursts). Both burst types are related to coronal mass ejections (CMEs). Type II bursts from metric to kilometric wavelengths tend to accompany large SEP events, which is widely considered as a confirmation that CME-driven shocks accelerate the SEPs. But type II bursts, especially those related to SEP events, are most often accompanied by type IV bursts, where the electrons are rather accelerated in the wake of the CME. Individual event studies suggest that although the CME shock is the most plausible accelerator of SEPs up to some yet unknown limiting energy, the relativistic SEP events show time structure that rather points to coronal acceleration related to type IV bursts. This chapter addresses the question what type II bursts tell us about coronal shock waves and how type II and type IV radio bursts are related with relativistic proton signatures as seen by particle detectors on the Earth and by their gamma-ray emission in the solar atmosphere, focusing on two relativistic SEP events, on 2005 Jan 20 and 2017 Sep 10. The importance of radio emissions as a complement to the upcoming SEP observations from close to the Sun is underlined.
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Ameri, Dheyaa, Eino Valtonen, and Silja Pohjolainen. "Properties of High-Energy Solar Particle Events Associated with Solar Radio Emissions." Solar Physics 294, no. 9 (September 2019). http://dx.doi.org/10.1007/s11207-019-1512-9.
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Abstract 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 ${\pm}\,7$ ± 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.