"Version: 20191201"--Title page verso.Includes bibliographical references.1. Introduction -- 2. What can be learned from modern data? -- 2.1. Strength of solar flares -- 2.2. Solar particle events -- 2.3. Major geomagnetic storms3. State-of-the-art theory and modeling -- 3.1. Solar and stellar dynamos -- 3.2. Particle acceleration at the sun4. Cosmogenic isotopes as proxies for solar energetic …