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We report a detailed observational study of two quasi-periodic fast-propagating (QFP) magnetosonic wave events occurred on 2011 March 09 and 10, respectively. Interestingly, both the two events have two wave trains (WTs): one main and strong (WT-1) whereas the second appears small and weak (WT-2). Peculiar and common characteristics of the two events are observed, namely: 1) the two QFP waves are accompanied with brightenings during the whole stage of the eruptions; 2) both the two main wave trains are nearly propagating along the same direction; 3) EUV waves are found to be associated with the two events. Investigating various aspects of the target events, we argue that: 1) the second event is accompanied with a flux rope eruption during the whole stage; 2) the second event eruption produces a new filament-like (FL) dark feature; 3) the ripples of the two WT-2 QFP waves seem to result from different triggering mechanisms. Based on the obtained observational results, we propose that the funnel-like coronal loop system is indeed playing an important role in the two WT-1 QFP waves. The development of the second WT-2 QFP wave can be explained as due to the dispersion of the main EUV front. The co-existence of the two events offer thereby a significant opportunity to reveal what driving mechanisms and structures are tightly related to the waves., 9 figures,ApJ,accepted, December 19,2019

Solar energetic particles (SEPs) are an important product of solar activity. They are connected to solar active regions and flares, coronal mass ejections (CMEs), EUV waves, shocks, Type II and III radio emissions, and X-ray bursts. These phenomena are major probes of the partition of energy in solar eruptions, as well as for the organization, dynamics, and relaxation of coronal and interplanetary magnetic fields. Many of these phenomena cause terrestrial space weather, posing multiple hazards for humans and their technology from space to the ground. Since particular flares, shocks, CMEs, and EUV waves produce SEP events but others do not, since propagation effects from the low corona to 1 AU appear important for some events but not others, and since Type II and III radio emissions and X-ray bursts are sometimes produced by energetic particles leaving these acceleration sites, it is necessary to study the whole system with a multi-frequency and multi-instrument perspective that combines both in-situ and remote observations with detailed modelling of phenomena. This article demonstrates this comprehensive approach, and shows its necessity, by analysing a trio of unusual and striking solar eruptions, radio and X-ray bursts, and SEP events that occurred on 4 November 2015. These events show both strong similarities and differences from standard events and each other, despite having very similar interplanetary conditions and only two are sites and CME genesis regions. They are therefore major targets for further in-depth observational studies, and for testing both existing and new theories and models. Based on the very limited modelling available we identify the aspects that are and are not understood, and we discuss ideas that may lead to improved understanding of the SEP, radio, and space-weather events., 56 pages, 25 figures; Accepted for publication in Solar Physics

Problematika stvaranja i razvoja globalnih koroninih valova uzrokovanih koroninim erupcijama je problematika koja se zadnjih godina vrlo intenzivno istražuje. Ovaj rad predstavlja doprinos istraživanju u tom području. Simuliran je nastanak magnetosonicnih valova potaknutih širenjem cilindričnog klipa. Za kvantitativnu analizu općenitih svojstava stvaranja vala, koja ne ovise o specifičnim svojstvima okruženja upotrijebljene su osnovne početne konfiguracije. Uočeno je da već i te najjednostavnije početne konfiguracije prouzrokuju klipno-valnu morfologiju i kinematiku koji zadovoljavajuće predstavljaju promatrana svojstva koroninih valova. U početnoj fazi val i ekspandirajući izvor ne mogu se jasno razgraničiti, tj., potrebno je izvjesno vrijeme prije nego što se val odvoji od “klipa”. Nakon toga, val nastavlja gibanje kao tzv. “jednostavni val”. U početnom stadiju, koja odgovara fazi ubrzanja klipa, amplituda vala raste, valna fronta se ustrmljuje, a fazna brzina vala raste. U određenom trenutku ustrmljivanje vala rezultira pojavom diskontinuiteta u valnoj fronti, tj., valna fronta postaje udarni val. Vrijeme/udaljenost nastanka udarnog vala je kraće u slučaju impulzivnijih širenja područja izvora. Nakon zaustavljanja klipa, započinje smanjivanje amplitude i brzine vala. Za vrijeme širenja, najveći dio područja izvora postaje izuzetno razrijeđen, što prouzrokuje zatamnjenje korone koje nastaje nakon erupcije. Nasuprot tome, gustoća se na rubu područja izvora povećava, te uvećana ostaje čak i kada širenje prestane, što je mogući uzrok stacionarnih lokaliziranih povećanja sjaja ponekad uočenih na rubovima eruptiranih koroninih struktura. Nadalje, u pozadini vala dolazi do smanjenja gustoće, što je ponekad moguće uočiti kao prolazno putujuće koronino zatamnjenje. Uočena je veoma dobra povezanost između impulzivnosti širenja područja izvora i amplitude vala kao i fazne brzine vala. Rezultati dobiveni za cilindrični klip su također uspoređeni sa onima dobivenim u slučaju jednodimenzionalnog klipa i njemu pridruženog ravninskog vala, radi dobivanja boljeg uvida u utjecaj različitih geometrija na evoluciju vala. Detaljno su analizirane numeričke simulacije radi dobivanja uvida u prirodu različitih pojava koji se događaju u Sunčevoj atmosferi kao posljedica erupcija nestabilnih koroninih struktura. Iako simulacije uzimaju u obzir samo osnovna svojstva erupcija magnetskog užeta, analiza simulacija otkriva važne informacije o različitim pojavama povezanih s erupcijom. Dobiven je kvanitativni odnos između dinamike erupcije i evolucije koroninog iii magnetohidrodinamičkog vala velike amplitude te povezanih kromosferskih poremećaja koje se šire u niže slojeve atmosfere. Pokazano je da širenje kromosferskog Moretonovog valnog poremećaja može biti aproksimirano tzv. “switch-on” udarnim valom konstantne amplitude koji se giba duž magnetskog polja, prema dubljim slojevima kromosfere. Prikazana analiza otkriva prirodu sekundarnih pojava koji se opažaju kao uzlazna gibanja u koroni, sekundarni udarni valovi, valne kompozicije, sekundarni spori poremećaji velike amplitude itd. Također je pokazano da erupcije mogu uzrokovati opaziv Moretonov val i sekundarni spori koronin val samo ako su dovoljno impulzivne i karakterizirane jakim bočnim širenjem. U slabijim erupcijama mogu se opaziti samo primarni valovi u koroni. U jakim erupcijama primarni val se giba s Alfvén-Machovim brojem znatno većim od 1 i ustrmljuje se u udarni val zbog nelinearnog širenja valne fronte. Nakon faze vođene erupcijom, smetnja evoluira u slobodno šireći jednostavni val karakteriziran značajnim usporavanjem, smanjenjem amplitude i širenjem valnog profila. U slabijim događajima koronin val ne prelazi u udarni val i širi se brzinom bliskoj magnetosoničnoj brzini okolne plazme. Magnetosonic wave formation driven by an expanding cylindrical piston is numerically simulated to obtain better physical insight into the initiation and evolution of largescale coronal waves caused by coronal eruptions. Several very basic initial configurations are employed to analyze intrinsic characteristics of MHD wave formation that do not depend on specific properties of the environment. It turns out that these simple initial configurations result in piston/wave morphologies and kinematics that reproduce common characteristics of coronal waves. In the initial stage, the wave and the expanding source region cannot be clearly resolved; i.e. a certain time is needed before the wave detaches from the piston. Thereafter, it continues to travel as what is called a “simple wave.” During the acceleration stage of the source region inflation, the wave is driven by the piston expansion, so its amplitude and phase-speed increase, whereas the wavefront profile steepens. At a given point, a discontinuity forms in the wavefront profile; i.e. the leading edge of the wave becomes shocked. The time/distance required for the shock formation is shorter for a more impulsive source-region expansion. After the piston stops, the wave amplitude and phase speed start to decrease. During the expansion, most of the source region becomes strongly rarefied, which reproduces the coronal dimming left behind the eruption. However, the density increases at the source-region boundary, and stays enhanced even after the expansion stops, which might explain stationary brightenings that are sometimes observed at the edges of the erupted coronal structure. Also, in the rear of the wave a weak density depletion develops, trailing the wave, which is sometimes observed as weak transient coronal dimming. Finally, we find a well-defined relationship between the impulsiveness of the source-region expansion and the wave amplitude and phase speed. The results for the cylindrical piston are also compared with the outcome for a planar wave that is formed by a one-dimensional piston, to find out how different geometries affect the evolution of the wave. An in-depth analysis of numerical simulations is performed to obtain a better insight into the nature of various phenomena occurring in the solar atmosphere as a consequence of the eruption of unstable coronal structures. Although the simulations take into account only the most basic characteristics of a flux-rope eruption, the simulation analysis reveals important information on various eruption-related effects. It quantifies the relation v between the eruption dynamics and the evolution of the large-amplitude coronal magnetohydrodynamic wave and the associated chromospheric downward-propagating perturbation. We show that the downward propagation of the chromospheric Moreton-wave disturbance can be approximated by a constant-amplitude switch-on shock that moves through a medium of rapidly decreasing Alfvén velocity. The presented analysis reveals the nature of secondary effects that are observed as coronal upflows, secondary shocks, various forms of wave-trains, delayed large-amplitude slow disturbances, transient coronal depletions, etc. We also show that the eruption can cause an observable Moreton wave and a secondary coronal front only if it is powerful enough and is preferably characterized by significant lateral expansion. In weaker eruptions, only the coronal and transition region signatures of primary waves are expected to be observed. In powerful events, the primary wave moves at an Alfvén Mach number significantly larger than 1 and steepens into a shock due to the nonlinear evolution of the wavefront. After the eruption-driven phase, the perturbation evolves as a freely propagating simple wave, characterized by a significant deceleration, amplitude decrease, and wave-profile broadening. In weak events the coronal wave does not develop into a shock and propagates at a speed close to the ambient magnetosonic speed.

Freely propagating global waves in the solar atmosphere are commonly observed using extreme ultraviolet passbands (EUV or "EIT waves"), and less regularly in H-alpha (Moreton–Ramsey waves). Despite decades of research, joint observations of EUV and Moreton–Ramsey waves remain rare, complicating efforts to quantify the connection between these phenomena. We present observations of four homologous global waves originating from the same active region between 2014 March 28 and 30 and observed using both EUV and H-alpha data. Each global EUV wave was observed by the Solar Dynamics Observatory, with the associated Moreton–Ramsey waves identified using the Global Oscillations Network Group network. All of the global waves exhibit high initial velocity (e.g., 842–1388 km s−1 in the 193 A passband) and strong deceleration (e.g., −1437 to −782 m s−2 in the 193 A passband) in each of the EUV passbands studied, with the EUV wave kinematics exceeding those of the Moreton–Ramsey wave. The density compression ratio of each global wave was estimated using both differential emission measure and intensity variation techniques, with both indicating that the observed waves were weakly shocked with a fast magnetosonic Mach number slightly greater than one. This suggests that, according to current models, the global coronal waves were not strong enough to produce Moreton–Ramsey waves, indicating an alternative explanation for these observations. Instead, we conclude that the evolution of the global waves was restricted by the surrounding coronal magnetic field, in each case producing a downward-angled wavefront propagating toward the north solar pole, which perturbed the chromosphere and was observed as a Moreton–Ramsey wave.

Flares, dimmings, and extreme ultraviolet (EUV) waves are three types of eruptive phenomena on the Sun, which are main drivers of space weather. Fast and reliable detection of these phenomena helps augment space weather predictions. In the current paper, we introduce Solar Demon, the first software that detects all three phenomena, using a modular design to exploit synergies. While Solar Demon runs in near real-time on SDO/AIA synoptic quick-look images to provide fast detections of flares, dimmings, and EUV waves for space weather purposes, it also processes new Atmospheric Imaging Assembly (AIA) synoptic science images on a regular basis to build dedicated science quality catalogs. An overview of Solar Demon is given, with a focus on the algorithms for EUV wave detection and characterization. Several first results, such as flare and dimming butterfly diagrams for the rising part of Solar Cycle 24, are presented. The main advantages, challenges, and future prospects for Solar Demon are outlined in the Section 5.