Understanding Solar Flares and Energetic Events: Open questions, observational requirements, and instrumental needs over the coming decade

TL;DR

The paper addresses fundamental open questions about solar flares, including what triggers magnetic reconnection, where and how particles are accelerated, how energy propagates through the solar atmosphere, and how flare physics scales across sizes and relates to stellar activity. It proposes a multi-wavelength, high-cadence observational strategy coupled with advanced numerical modelling to define precise instrumental requirements for the coming decade, and frames the UK's role in international collaborations to meet these goals. Key contributions include explicit observational thresholds across hard X-ray, gamma-ray, soft X-ray, and UV/EUV domains, and advocacy for flare-optimised instrumentation such as SPARK, Solar-C/EUVST, and OSIRIS, supported by modelling and atomic data. The anticipated impact is improved understanding of magnetic reconnection and particle acceleration, enhanced space-weather forecasting, and sustained UK leadership in heliophysics and space infrastructure protection.

Abstract

Solar flares are the largest energy-release events in the Solar System, allowing us to study fundamental physical phenomena under extreme conditions. Those include magnetic reconnection, particle acceleration, radiation transport, and various plasma physics processes, all of which occur throughout the heliosphere and rest of the Universe. Flares and eruptive events are also components of geo-effective space weather. Their impacts from a space weather perspective are numerous, such as harm to satellites, disruption to GPS, communications and power systems, and impacts on passenger air travel. A comprehensive understanding of solar flares is therefore not just a compelling science problem, but also important for national security and infrastructure. This white paper (WP) addresses critical open science questions related to solar flares. Key observations and capabilities required to make significant advancements over the coming decade are identified. The UK has a robust and vibrant solar flare community. We are key partners in international collaborations, and also provide instrumentation for existing and upcoming ESA/NASA/JAXA space missions. Continuing this effort over the coming decade is vital to maintain UK leadership in this field, achieve Solar System Advisory Panel roadmap goals, and to work under the UK Space Agency's National Space Strategy Pillars. Several complementary WPs have been submitted that discuss instruments or concepts that would directly address the observational requirements we describe (including: SPARK, solar optimised IFUs, Solar-C/EUVST, and OSIRIS), as well as required numerical modelling efforts and infrastructure.