Anticipating the next decade of Sun‐Earth system variations

Abstract

Approximately every decade, the Sun enters a new phase when its magnetic activity increases from quiescent conditions to peak values about 3–5 years later. This intensified solar activity gradually reduces over the next 6–7 years, returning the system to “quiet” conditions. The near‐periodic 11‐year solar cycle is manifested by the regular presence of large sunspots during high solar activity (solar maximum) and few, if any, sunspots during quiet periods (solar minimum).This cycle, in turn, creates significant observable effects on Earth and its surrounding environment. During times of peak solar activity, Earth's atmosphere warms globally. In the past decade, the Sun's increased brightness at solar maximum warmed the Earth's atmosphere by about 0.1 degree Kelvin (0.1 K) in the 10 kilometers nearest to the surface (the troposphere), 1 K near 50 kilometers in altitude (at the top of the stratosphere), and 400 K at an altitude of 500 kilometers in the thermosphere. During this time, total ozone concentration increased by a few percent, offsetting for a while the overall decline associated with chlorofluorocarbon (CFC) pollution. Electron densities in the ionosphere and neutral densities in the thermosphere increased by 1–2 orders of magnitude, altering the propagation of radio waves that enable communication and increasing the drag on spacecraft in low‐Earth orbits.