8217 20261110112237.0 CTALK-2026-0155 Berghmans, D. CROSS-SCALE OBSERVATIONS OF SOLAR FLARES BY EUI AND STIX ON SOLAR ORBITER 2026 2026-11-03 Major solar flares are at the origin of many space weather phenomena. Besides the flash across the entire spectrum, flares are associated with shock waves, particle acceleration, radio bursts, prominence eruptions and CMEs. Since 2024, Solar Orbiter has embarked on a series of campaigns to observe Major Solar Flares. In this presentation we discuss the results so far of a series of unique data sets collected mainly by the STIX instrument and the HRIEUV telescope of the EUI instrument. As an X-ray imaging spectrometer, STIX has continuously observed on the order of 10^5 flares from solar minimum in 2020 till now. For the high resolution HRIEUV imager it is much harder to catch a flare, because it can operate only occasionally and with subfield as small as 1/30th of the solar disk at perihelion. Thanks to the so-called short exposures at 2s cadence, HRIEUV can however for the first time observe flare dynamics at small length & time-scales that have remained veiled for earlier EUV imagers due to pixel saturation & blooming. These Solar Orbiter Major Flare observations indicate that flares are not always the monolithic, catastrophic collapse of an entire magnetic structure but rather a build-up or an avalanche of magnetic threads reconnecting. The footpoint kernels in the flare ribbons have time and length-scales that are barely resolved with the 2s cadence /100 km pixel size characteristics of HRIEUV datasets. Also the width of some post-flare loops are at the 2-pixel scale suggesting the actual width is smaller than 200km. These small scales pose new questions on the required energy and plasma densities. Whereas the impact of solar flares can be felt at heliospheric scales, the data from Solar Orbiter are thus telling us that the physics driving major flares, operates at remarkably small spatial and temporal scales. Using this insight for timely flare reporting suggests that modest resolution requirements for monitoring instruments might be suboptimal. STCE EUI solar flares corona Chitta, L.P. Collier, H. Dominique, M. Hayes, L. Kasporova, J. Kraaikamp , E. Lorincik, J. Rodriguez, L. Verbeeck, C. European Space Weather Week 2026, Florence, Italy david.berghmans@ksb-orb.be https://esww.aeronomie.be/conference/program 4899760 http://publi2-as.oma.be/record/8217/files/20261103-CrossScaleObservationsOfSolarFlares-DavidBerghmans.pdf 10738 http://publi2-as.oma.be/record/8217/files/20261103-CrossScaleObservationsOfSolarFlares-DavidBerghmans.jpg?subformat=icon-180 icon-180 14615 http://publi2-as.oma.be/record/8217/files/20261103-CrossScaleObservationsOfSolarFlares-DavidBerghmans.gif?subformat=icon icon Invited CTALKINVI