Solar Flares and Impact on Earth

Abstract

The Sun exhibits different kinds of activity and its appearance is permanently changing, as it is revealed by numerous ground and space observations. The most well-known phenomenon is the 11-year solar activity cycle with an increasing and decreasing number of sunspots on the Sun surface over this period. These sunspots can be tens of thousands of kilometers across. They usually exist as pairs with opposite magnetic polarity alternating every solar cycle. A number of sunspots tend to peak at the solar maximum and are generally manifested closer to the Sun’s equator. Sunspots are darker and cooler than their surroundings because these are regions of the reducing energy convective transport from the hot interiors, which is inhibited by strong magnetic fields. The polarity of the Sun’s magnetic dipole changes every 11 years. This means that the North Magnetic Pole becomes the South one and vice versa. Because solar activity changes from one 11-year cycle to another, the doubled cycles (22 years and longer) are also distinguishable from each other. Irregularity is specifically manifested by a minimum of sunspots and solar activity during several cycles, as significantly occurred in the seventeenth century and is now known as the Maunder Minimum. These cycles strongly impact the Earth’ climate. During the last 11-year cycle, an unusual solar minimum occurred in 2008 and lasted much longer with lower amounts of sunspots than normal. Therefore, solar activity recurrence is not stable. Moreover, theory claims that magnetic instabilities in the Sun core could cause fluctuations with periods that could last tens of thousands of years.

Solar flares, coronal mass ejection (CME), and solar proton events (SPEs) are the most characteristic phenomena of these changes in solar activity and their external manifestation. The activity rate as noted above is closely related with the 11-year solar cycle. These solar flare events are often accompanied by the huge ejected amounts of high-energy protons and electrons well exceeding the “normal” energy levels of solar-wind particles. Solar flares, coronal mass ejections (CMEs), solar proton events (SPEs), and normal ejections from the Sun known as “solar wind” have an effect throughout the solar system – especially its inner parts. These phenomena determine the state of geomagnetic fields of planets. Solar plasma and electromagnetic emissions thus have important interactions with the solar system bodies with particular significance for Earth. Solar weather processes impact the Earth’s upper, middle, and lower atmosphere and even can have negative impacts at the surface. Basically, solar activity events determine the space weather which influences planetary environment and, in particular, the life on Earth. This chapter addresses the known science that is associated with solar flares as well as how these solar flares play a key role in triggering other energetic and harmful solar phenomena. Finally it addresses how solar flares, CMEs, and SPEs in particular impact the Earth’s atmosphere and magnetosphere and especially how these phenomena can create significant negative impacts and major infrastructure risks to the world’s current economic and technological systems.