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Coronal mass ejections (CMEs) often show different features in different bandpasses. By combining data in white-light (WL) and ultraviolet (UV) bands, we have applied different techniques to derive plasma temperatures, electron density, internal radial speed, and so on, within a fast CME. They serve as extensive tests of the diagnostic capabilities developed for the observations provided by future multichannel coronagraphs (such as Solar Orbiter/Metis, Chinese Advanced Space-based Solar Observatory/Lyα Solar Telescope (LST), and PROBA-3/ASPIICS). The data involved include WL images acquired by Solar and Heliospheric Observatory (SOHO)/Large Angle Spectroscopic Coronagraph (LASCO) coronagraphs, and intensities measured by the SOHO/UV Coronagraph Spectrometer (UVCS) at 2.45 R⊙ in the UV (H i Lyα and O vi 1032 Å lines) and WL channels. Data from the UVCS WL channel have been employed for the first time to measure the CME position angle with the polarization-ratio technique. Plasma electron and effective temperatures of the CME core and void are estimated by combining UV and WL data. Due to the CME expansion and the possible existence of prominence segments, the transit of the CME core results in decreases in the electron temperature down to 105 K. The front is observed as a significant dimming in the Lyα intensity, associated with a line broadening due to plasma heating and flows along the line of sight. The 2D distribution of plasma speeds within the CME body is reconstructed from LASCO images and employed to constrain the Doppler dimming of the Lyα line and simulate future CME observations by Metis and LST. [ABSTRACT FROM AUTHOR]

Observations of the solar corona in the FeXIV 530.3 nm 'green line' have been very important in the past, and are planned for future coronagraphs on-board forthcoming space missions such as PROBA-3 and Aditya. For these instruments, a very important parameter to be optimized is the spectral width of the band-pass filter to be centred over the 'green line'. Focusing on solar eruptions, motions occurring along the line of sight will Doppler shift the line profiles producing an emission that will partially fall out of the narrower pass-band, while broader pass-band will provide observations with reduced spectral purity. To address these issues, we performed numerical (MHD) simulation of CME emission in the 'green line' and produced synthetic images assuming 4 different widths of the pass-band (Δλ = 20 Å, 10 Å, 5 Å, and 2 Å). It turns out that, as expected, during solar eruptions a significant fraction of 'green line' emission will be lost using narrower filters; on the other hand these images will have a higher spectral purity and will contain emission coming from parcels of plasma expanding only along the plane of the sky. This will provide a better definition of single filamentary features and will help isolating single slices of plasma through the eruption, thus reducing the problem of superposition of different features along the line of sight and helping physical interpretation of limb events. For these reasons, we suggest to use narrower band passes (Δλ ≤ 2 Å) for the observations of solar eruptions with future coronagraphs. [ABSTRACT FROM AUTHOR]

Abstract: We study the 3-D kinematics of a Coronal Mass Ejection (CME) using data acquired by the LASCO C2 and UVCS instruments on board SOHO, and the COR1 coronagraphs and EUVI telescopes on board STEREO. The event, which occurred on May 20, 2007, was a partial-halo CME associated with a prominence eruption. This is the first CME studied with UVCS data that occurred in the STEREO era. The longitudinal angle between the STEREO spacecrafts was ∼7.7° at that time, and this allowed us to reconstruct via triangulation technique the 3-D trajectory of the erupting prominence observed by STEREO/EUVI. Information on the 3-D expansion of the CME provided by STEREO/COR1 data have been combined with spectroscopic observations by SOHO/UVCS. First results presented here show that line-of-sight velocities derived from spectroscopic data are not fully in agreement with those previously derived via triangulation technique, thus pointing out possible limitations of this technique. [Copyright &y& Elsevier]

After the first observations of the extended solar corona in the UV carried out starting from late '70s with rocket experiments, and later on with the Spartan flights, the field was revolutionized thanks to the UVCS (UV Coronagraph Spectrometer) instrument on-board SOHO mission. UVCS observed the UV extended corona (tipically above 0.5 solar radii from the limb) at different latitudes over more than 15 years (1996-2012), and captured the transit of hundreds of small- and large-scale solar eruptions (CMEs, jets, prominences). These observations (combined with data acquired by other instruments) allowed to derive unique information on the early evolution of plasma embedded in solar eruptions, and on related topics (e.g. 3D structure, post-CME Current Sheets, CME-driven shocks). The same data led also to fundamental new discoveries on the Solar Wind, and allowed to characterize the backround corona being crossed by each solar eruption.At present UVCS is not taking data anymore since 2012, but lot of data in the archive still have to be analysed; for the next future, no similar instruments have been selected at present as a payload of forthcoming solar missions. Nevertheless, the next generation multi-channel coronagraphs (such as Metis on-board Solar Orbiter) will observe at the same time and same locations the Visible Light and the UV HI Lyman-alpha extended corona. These data will really provide a new view not only of solar eruptions, but also of the ambient solar wind. Future prospects will be summarized here. [ABSTRACT FROM AUTHOR]