Coronagraphic images from SOHO revealed a partial halo coronal mass ejection (CME with a width greater than 120 degrees) leaving the Sun on 5 April. Closer examination by the SIDC space weather forecaster revealed this eruption had a far side origin, with no obvious signatures of the eruption on the Sun's earth-facing side. The SDO imagery underneath shows the Sun at temperatures of 700.000 degrees (AIA 171). Around 04:00UTC on 5 April, it shows a violent eruption in the solar outer atmosphere (the "corona") near its east limb, followed about an hour later by an apparently much slower eruption with -as seen from Earth- a horizontal, wide slab of plasma gradually moving northward starting from around 45 degrees north (see annotated image). The post-eruption coronal loops appear about an hour later, from a location about halfway between the first eruption and the lift-off of the second eruption.
That there are at least 2 CMEs at work seems also evident from the SOHO/LASCO coronagraphic imagery. The main CME is directed to the east and related to the first, rather violent eruption. It's becoming first visible at 04:12UTC in LASCO C2 imagery and has a plane-of-the-sky speed near 400 km/s. The second CME has a fuzzier outline and becomes visible around 08:00UTC. Related to the much slower eruption, it has a plane-of-the-sky speed near 250 km/s and is directed to the north-north-east. In the imagery underneath, the wide-field EUV image obtained by PROBA2/SWAP has been overlaid on the coronagraphic images by SOHO/LASCO. SWAP's off-disk corona has been enhanced (annotated image).
One of the possible scenarios is that the first, more violent eruption destabilized the magnetic environment of a filament, that subsequently got ejected into space. STEREO-A is preceding the Earth by 32 degrees, while Solar Orbiter was located - as seen from Earth- 12 degrees beyond the west limb (map), so there's basically a blanc area of 78 degrees in longitude that is not covered by any of the satellites capable of EUV-imaging, precisely the area of our current interest. Nonetheless, the first image available from Solar Orbiter for 5 April shows a plasma feature over the northwest limb -as seen from SolO- around 06:00UTC (upper image SolO/FSI 304, lower image SolO/FSI 174; both off-disk enhanced). This is very likely corresponding to the wide slab of plasma as observed by e.g. SDO and PROBA2 around that time. The first eruption took indeed place almost on the opposite side of the Sun as seen from SolO, and so most of the features seen around 06:00UTC are likely related to the second eruption. Note the different shapes of the feature are due to line-of-sight effects. As further SolO/EUI images become available in the coming days, it may become clearer what happened on the Sun's far side early on 5 April.
