The Dynamic Ionosphere-Thermosphere System: Variability from Minutes to Decades

The ionosphere-thermosphere (IT) system is an externally driven system. The external forcing consists of solar radiation in the X-ray ultraviolet (XUV, 1–30 nm), extreme ultraviolet (EUV, 30–120 nm), and far ultraviolet (FUV, 120–200 nm); auroral energetic particle precipitation and electromagnetic energy resulting from solar wind–magnetosphere interactions; and waves from the lower atmosphere. Driven by these external forcing, various internal processes take place, including photoionization, photodissociation, heat conduction, radiative cooling, and ion-neutral coupling, which manifest through chemical, energetic, dynamic, and electrodynamic processes. The interplay between external forcing and internal processes leads to complex IT system variability, spanning space weather and space climate timescales. Space weather variability includes rapid changes driven by solar flares and day-to-day variability driven by the high-speed solar winds, coronal mass ejections, and lower atmosphere waves. Space climate variability encompasses diurnal, solar rotational, seasonal, solar cycle, and multidecadal variations. In this presentation, we examine IT variability across timescales, from minute-scale fluctuations caused by solar flares to long-term multidecadal trends, using both model simulations and observational data.