The response of our space environment to the constantly changing Sun is known as space weather. When the space environment is disturbed by the variable outputs of the Sun, technologies that we depend on, both in orbit and on the ground can be affected. Some of the most dramatic space weather effects occur in association with eruptions of material from the solar atmosphere into interplanetary space. The increasing deployment of radiation-, current-, and field-sensitive technological systems over the last few decades together with the increasing presence of complex systems in space make society more vulnerable to solar-terrestrial disturbances.

Space weather disturbances are generally caused by solar storms. There are two different types of events on the Sun that trigger disturbances in the Earth's environment. One type is called a solar flare because the brightening of a small area on the Sun heralds its occurrence. The other type of storm is called a coronal mass ejection (CME).

Near solar activity maximum, the sun produces about 3 CMEs every day, whereas near solar minimum it produces only about 1 CME every 5 days.

CME ejection over a 6 hr. period

The faster CMEs have outward speeds of up to 2000 kilometers per second, considerably greater than the normal solar wind speeds of about 400 kilometers per second. These produce large shock waves in the solar wind. Some of the solar wind ions are accelerated by the shock, which then becomes a source of intense and long-lasting energetic particle enhancements in interplanetary space .. the heliosphere.

A spectacular view of two sungrazing comets following similar orbits as they enter the outer solar atmosphere. Shortly afterwards a large CME was observed.

Even the dense coronal mass ejections qualify as a pretty good vacuum, with something like 100 billion particles (10^{11}) per cubic centimeter. For example, on Earth at 1 atmosphere, you have something like 3x10^{19} air molecules per cubic centimeter around you; so a Coronal Mass Ejection  can be 1/100,000,000th as dense as our environment.

The Heliosphere
The expanding solar wind forms a bubble in the interstellar material thought to extend at least 100 AU from
the Sun. (For comparison, the outermost planet, Pluto, orbits the Sun at about 40 AU distance.) Space weather occurs everywhere within this bubble known as the `heliosphere'. Every object in the solar system experiences the equivalent of Earth's space weather, although its detailed characteristics differ from place to place.

Many things can happen in the magnetosphere during a magnetic storm because a lot of energy is being dumped into the system. When impacted by plasma from space or even from the far reaches of the magnetosphere, the electrons, protons, and oxygen ions of Earth?s Van Allen radiation belts become denser, hotter, and faster. Due to their motion, these particles produce as much as a million amperes of electrical current, a jolt of power that can decrease the strength of Earth's magnetic field. Some of the  current flows along Earth's magnetic field lines and into the upper atmosphere. The passage of electric current through the upper atmosphere and the loss of electrons  and protons from the magnetosphere can cause the atmosphere to warm and expand, increasing the density at high altitudes.


A simulation of a CME impact on the Earth's magnetosphere based on real data .. the color of the solar wind reflects density with darker and redder indicating higher density. The blue circle shows the aurora.