How often does a storm (or an eruption) happen on the Sun? A solar storm can happen as often as several times a day, but it all depends on what year you are talking about.

Just like there are many different types of volcanic eruptions on Earth, the Sun offers its own spectacular shows of various explosions. Whereas small volcanic eruptions producing 0.001 to .01 cubic kilometers of materials occur once every few months, the Sun constantly releases energy into space. Every so often an eruption will occur on the Sun, sending out massive energy in sizes more than you would imagine! The most commonly described solar eruptions include solar flares, prominences, and coronal mass ejections:

1. Solar Flares

These are brief but enormous outbursts of energy from an active region (near sunspots) on the surface of the Sun. Lasting from minutes to hours, it may take us a day or two to feel the effects on Earth. Each explosion generates billions of tons of electrically charged particles and radiation (from radio wave to high energy gamma rays) enough to power the United States for 10,000 years. It also raises the temperature of the flare region to tens of millions of degrees. When headed our way, solar flares can cause radio blackouts.

2. Prominences

Prominences are bright cloud-like features in the solar atmosphere when seen over the edge of the Sun (solar limb). They appear dark when seen against the bright solar disk. Then we call them filaments. Visible as loops of magnetic fields that trap hot ionized gas (plasma) inside, they are larger than the size of Earth. As the trapped gas becomes unstable, prominences can erupt violently into space. They are not storms but they can erupt into storms sometimes.

3. Coronal Mass Ejections (CMEs)

CMEs are huge magnetic bubbles of plasma that erupts from the Sun's corona and travels through space at millions of miles an hour. They are often associated with solar flares and prominence eruptions but they can also occur in the absence of either of these processes. Many times larger than solar flares, they are as powerful as billions of nuclear explosions. When they are directed at Earth, they can cause geomagnetic disturbances and produce beautiful auroras. They can also affect radio communications, electrical power systems and satellites orbiting Earth. Although CMEs are quite frequent (several a day during solar maximum), only a fraction of them hits the Earth's magnetosphere and causes geomagnetic storms. Severe storms occur with a frequency of about 100 times over the 11-year cycle of solar activity.

Summary

During a solar minimum, a week or more will pass without any solar eruptions. Nearing the apex of the cycle (for Cycle 23 it was 2000-2001), there are multiple eruptions every day. NASA scientists, together with other government agencies, are working hard to provide accurate forecast several days in advance of the largest and most violent explosions on the Sun's outer atmosphere.

References

SOHO Education and Public Outreach Page
http://sohowww.nascom.nasa.gov/explore/

RHESSI Mission and Solar Flares
http://hesperia.gsfc.nasa.gov/hessi/

Space Weather Forecasts
http://www.spaceweather.com/

The Sun in Action
http://science.nasa.gov/ssl/PAD/SOLAR/default.htm

Carolyn Ng is a member of the Sun-Earth Connection Education Forum (SECEF) at NASA Goddard Space Flight Center. SECEF is a partnership between Goddard and UC Berkeley's Space Sciences Laboratory. We work with many missions' education specialists and scientists to educate K-12 and beyond about the active Sun and its effects on life and society. See http://sunearth.gsfc.nasa.gov/ for resources and programs.