A Brief Overview
We all know that our star, the sun, radiates light and heat which affects us daily by driving weather patterns on Earth. However, more people are becoming aware of the sun's invisible force - a continuous stream of electromagnetic radiation and charged particles (aka plasmas) called the solar wind, which influences all the planets, asteroids, comets, and even space dust in our solar system. Much like there are seasons, winds, clouds, and storms in terrestrial weather, there are analogs in the solar cycle, solar wind, plasma clouds, and solar and geomagnetic storms, which make up space weather. Unlike Earth storms, the sun can erupt suddenly, unleashing a cloud of energetic particles that can disrupt radio and GPS signals, zap satellites, and even damage pipelines and power stations on the ground! Thankfully, with new satellites such as ELFIN and the Parker Solar Probe, we are learning more about the sun's outbursts and profiling the highly dynamic system of electrical currents that connect the Earth and sun, and permeate our entire solar system. Understanding and predicting space weather is critical as we venture outside of our planet's protective magnetic shield, colonizing the moon and eventually sending astronauts to other planets (see the research significance page).
The sun is made up of ionized (charged) hydrogen and helium, and due to its 30 day rotation period, these moving charged particles create the largest magnetic field in the solar system. Since the material at the sun's equator moves faster than the material near the poles, this forces the subsurface magnetic field to form twists and knots, which can become so powerful that they can block heat from rising. These regions of relatively cooler solar surface thus appear darker and are called sunspots. Large sunspots can harbor complex magnetic fields, and when these fields realign themselves they can cause violent solar eruptions known as solar flares and "coronal mass ejections." Luckily, Earth is surrounded by its own magnetic field, the magnetosphere, which protects us from the brunt of these solar storms. A geomagnetic storm, which usually accompanies CMEs, is a major disturbance of Earth's magnetosphere that occurs when there is a very efficient exchange of energy from the solar wind into the space environment surrounding Earth. These storms result from variations in the solar wind that produces major changes in the currents, plasmas, and fields in Earth’s magnetosphere. The solar wind conditions that are effective for creating geomagnetic storms are sustained (for several to many hours) periods of high-speed solar wind, and most importantly, a southward directed solar wind magnetic field (opposite the direction of Earth’s field) at the dayside of the magnetosphere. This condition is effective for transferring energy from the solar wind into Earth’s magnetosphere and can ultimately cause a lot of damage to electrical systems.
Predicting space weather requires special satellites to observe the changing environmental conditions in near-Earth space, from the Sun's atmosphere all the way to the Earth's magnetosphere and upper atmosphere. It is distinct from the concept of weather within the Earth's planetary atmosphere (troposphere and stratosphere). Space weather is the description of changes in the ambient plasma, magnetic fields, radiation and other matter in space. Much of space weather is driven by energy carried through interplanetary space by the solar wind from regions near the surface of the Sun and the Sun's atmosphere.