We present study of the complex event consisting of several solar wind transients detected by Advanced Composition Explorer (ACE) on 4 -7 August 2011, that caused a geomagnetic storm with Dst= −110 nT. The supposed coronal sources -three flares and coronal mass ejections (CMEs) occurred on 2 -4 August 2011 in the active region (AR) 11261. To investigate the solar origin and formation of these transients we studied kinematic and thermodynamic properties of the expanding coronal structures using the Solar Dynamics Observatory/Atmospheric Imaging Assembly (SDO/AIA) EUV images and the differential emission measure (DEM) diagnostics. The Helioseismic and Magnetic Imager (HMI) magnetic field maps were used as the input data for the 3D magnetohydrodynamic (MHD) model to describe the flux rope ejection (Pagano, Mackay, and Poedts, 2013b). We characterize the early phase of the flux rope ejection in the corona, where the usual three-component CME structure formed. The flux rope ejected with a speed of about 200 km s −1 to the height of 0.25 R ⊙ . The kinematics of the modeled CME front agrees well with the Solar Terrestrial Relations Observatory (STEREO) EUV measurements. Using the results of the plasma diagnostics and MHD modeling, we calculated the ion charge ratios of carbon and oxygen as well as the mean charge state of iron ions of the 2 August 2011 CME, taking into account the processes of heating, cooling, expansion, ionization, and recombination of the moving plasma in the corona up to the frozen-in region. We estimated a probable heating rate of the CME plasma in the low corona by matching the calculated ion composition parameters of the CME with those measured in situ for the solar wind transients. We also consider the similarities and discrepancies between the results of the MHD simulation and the observations.

No abstract

-We investigate the case of disagreement between predicted and observed in-situ parameters of the recurrent high-speed solar wind streams (HSSs) existing for Carrington rotation (CR) 2118 (December 2011) in comparison with CRs 2117 and 2119. The HSSs originated at the Sun from a recurrent polar coronal hole (CH) expanding to mid-latitudes, and its area in the central part of the solar disk increased with the rotation number. This part of the CH was responsible for the equatorial flank of the HSS directed to the Earth. The time and speed of arrival for this part of the HSS to the Earth were predicted by the hierarchical empirical model based on EUV-imaging and the Wang-Sheeley-Arge ENLIL semi-empirical model. The predicted parameters were compared with those measured in-situ. It was found, that for CR 2117 and CR 2119, the predicted HSS speed values agreed with the measured ones within the typical accuracy of ±100 km s À1 . During CR 2118, the measured speed was on 217 km s À1 less than the value predicted in accordance with the increased area of the CH. We suppose that at CR 2118, the HSS overtook and interacted with complex ejecta formed from three merged coronal mass ejections (CMEs) with a mean speed about 400 km s À1 . According to simulations of the Drag-based model, this complex ejecta might be created by several CMEs starting from the Sun in the period between 25 and 27 December 2011 and arriving to the Earth simultaneously with the HSS. Due to its higher density and magnetic field strength, the complex ejecta became an obstacle

On 2017 September 6 and 10, the strongest X9.3 and X8.2 flares of the decade occurred in the active region NOAA Active Region 12673. During these flares, the Sun Watcher with Active Pixels and Image Processing (SWAP) telescope on board the Project for Onboard Autonomy 2 (PROBA2) satellite registered the unusual alternate brightening and darkening of the western corona at the heliocentric distances ≈1.2–1.7 R ☉. The X9.3 flare on 2017 September 6 was accompanied by coronal brightening up to 30%–45% at distances ≈1.35–1.7 R ☉. Numerical simulations showed that this brightening might be produced by resonant scattering of the flare radiation by the Fe ix–Fe xi ions in the coronal plasma at the temperature T ∼ 0.8–1 MK, and the densities seriously reduced in comparison with the typical values for the quiet background corona probably moving outward with velocities of 30–40 km s−1. At the maximum of the flare and one hour later, two coronal mass ejections (CMEs) originated, which dimmed the coronal emission in the SWAP 174 Å passband above the western limb by 20%–30%. The X8.2 flare on September 10 was accompanied by a CME, which rose up and progressively dimmed the western part of the corona up to 60%. An hour later the darkening, produced by a global rearrangement of the magnetic field structure and an evacuation of a significant part of the coronal plasma, extended over the complete western limb. A differential emission measure (DEM) analysis showed a decrease in the electron density of the background plasma with T ∼ 1–2 MK at distances 1.24–1.33 R ☉ by 2–3.5 times after the CME. At the same time, an additional DEM peak at T ≈ 0.8 MK appeared, which may be associated with an additional emission in the SWAP passband produced by the flare radiation resonantly scattered by the coronal plasma.

We analyzed statistics, solar sources and properties of interplanetary coronal mass ejections (ICMEs) in the solar wind. In comparison with the first eight years of Cycle 23, during the same period of Cycle 24 the yearly numbers of ICMEs were less correlated with the flare numbers (0.68 vs 0.78) and sunspot numbers (0.66 vs 0.81), whereas the ICME correlation with coronal mass ejections (CMEs) was higher (0.77 vs 0.70). For the period Space Research Institute (IKI RAS) 84/32, Profsoyznaya str., Moscow, 117810, Russia SOLA: ICME_and_their_Solar_Origins_rev-2.tex; 19 February 2018; 2:58; p. 1 D.Rodkin et al.of the Earth-directed CMEs supplemented by modeling of their propagation in the heliosphere using the kinematic models (the ballistic and drag-based model) and the Wang-Sheeley-Arge Enlil Cone MHD-based model. A detailed analysis of the ICME solar sources in the period under study showed that in 11 cases out of 23 (48 %) the observed ICME might be associated with two or more sources. In cases of multiple-source events, the resulting solar wind disturbances may be described as complex (merged) structures occurred due to the stream interactions with properties depending on the type of participating streams. As a reliable marker for identification of interacting streams and their sources, we used the plasma ion composition, as it becomes frozen in the low corona and remains unchanged in the heliosphere. According to the ion composition signatures, we classified these cases into three types: complex ejecta originating from weak and strong CME-CME interactions, as well as merged interaction regions (MIRs) originating from the CME-high-speed stream (HSS) interactions. We described temporal profiles of the ion composition for the single-source and multi-source solar wind structures and compared them with the ICME signatures determined from the kinematic and magnetic field parameters of the solar wind. In singlesource events, the ion charge state, as a rule, has one-peak enhancement with average duration of ∼ 1 day, which is similar to the mean ICME duration of 1.12 days derived from the Richardson and Cane list. In the multi-source events, the total profile of the ion charge state consists of a sequence of enhancements associated with interaction between the participating streams. On average, the total duration of complex structures appearing due to the CME-CME and CME-HSS interactions as determined from their ion composition is 2.4 days, which is more than 2 times longer than that of the single-source events.