Skip to main content
U.S. flag

An official website of the United States government

What Is Space Weather?

Purple, red, and blue striations show flux ropes on the Sun.
Courtesy of NASA

Rain, wind, and storms are everyday features of our weather on Earth. But beyond our atmosphere, scientists are monitoring phenomena in space that are a close cousin to terrestrial weather. The term “space weather” was adopted in the late 20th century to describe the changing conditions in space around our planet, and has become a keen area of study for many heliophysicists, meteorologists, and skywatchers.

Understanding space weather means looking beyond our experiences on the Earth’s surface. Rather than wind, rain, thunder, and seasonal changes, space weather is defined by the geospace and interplanetary conditions ( plasmas temperatures, particle densities and energies, solar wind speeds, magnetic field orientations, and magnetic reconnection). Space weather has different impacts to us (like aurora) than terrestrial weather.

Causes of Space Weather

It all starts at the Sun—our dynamic star that’s continuously changing, following its solar activity cycle

As the Sun changes, so does the space around it, called the heliosphere. As the solar cycle evolves, changes in the Sun's magnetic field store vast amounts of energy. Often this energy dissipates gradually, heating the Sun's atmosphere or is swept away by solar wind. Sometimes a fraction of it is released impulsively, triggering powerful events that can lead to severe space weather near Earth. 

During years of high activity, called solar maximum, events like solar flares and eruptions occur more often and release enormous amounts of extra energy over the course of just a few minutes—a typical eruption can release two hundred times more  energy than humans use in an entire year! When those eruptions or solar flares are directed toward Earth, they travel 93 million miles from the sun to our planet and cause “geomagnetic storms.” 

NOAA’s satellites, sensors, and imaging technology record those events for researchers at NOAA’s National Centers for Environmental Information and NOAA’s Space Weather Prediction Center (SWPC) to monitor and study the Sun and space weather. 

SWPC analyzes the real-time data 24 hours a day to predict changes in space weather, issuing alerts and warnings when necessary and classifying the events into NOAA Space Weather Scales. Space Weather enthusiasts can subscribe to receive forecasts, warnings, and event summaries. 

Solar Eruptions: Flares and Coronal Mass Ejections

One type of solar event is called a solar flare—flares are short, impulsive bursts of electromagnetic radiation in different frequencies. They can blast x-rays (and also energetic particles) into the interplanetary space. Weak flares are common occurrences on the Sun, while intense flares are among the most energetic events in the solar system and occur a few times per solar cycle.

Another type of solar event are solar eruptions, called coronal mass ejections (CMEs), which are powerful explosions that send giant bubbles  of magnetic field and plasma out into the heliosphere. CMEs fly into space reaching the outer edges of the solar system. Billions of tons of plasma from the Sun’s corona blast into space traveling between 600 to 900 km/s. The most powerful CMEs can reach speeds of a few thousand km/s. Only CMEs that are directed toward Earth will impact us.

Image of eight CME's in rows of four captured by a satellite.
Courtesy of NASA and the SOHO and STEREO missions.

Coronal Holes

Coronal holes are dark regions in the Sun’s atmosphere as detected by ultraviolet and x-ray imaging. They are the source of high-speed solar wind streams. The winds generated by a coronal hole pass virtually unhampered into space. Sometimes present for many months, the holes rotate as the Sun rotates, which is approximately once a month. These high-speed streams collide with the slow solar wind that is generated outside the holes. The visual effect resembles the spiral of a rotating sprinkler, which scientists call the Parker Spiral. The varying solar wind streams in the Parker Spiral can lead to the formation of shockwaves in the solar wind and can produce disturbances to Earth’s magnetosphere, the protective magnetic field that surrounds the planet for thousands of miles above the surface.

Geomagnetic Storms

Flares, CMEs, and high speed streams cause space weather-induced storms near Earth referred to as geomagnetic storms. These near-Earth responses to events from the Sun demonstrate the far-reaching impact of the star’s tremendous power. The Sun’s eruptions, precursors to storms, become problematic once they interact with the Earth’s magnetosphere and ionosphere. Solar storms can temporarily disrupt systems on Earth, from radar to airline navigational tools.

GPS signals are also susceptible to space weather events, which can disturb the ionosphere and change a GPS receiver’s ability to calculate an accurate position from a satellite signal. With more than 2,000 satellites in space and GPS features common in cell phones and vehicles, the implications can be broad if signals are hampered. At home, our telecommunications systems, radio waves, cellular service, and power grids can all be affected by space weather.

In March 1989, millions of people lost power when a geomagnetic storm caused a power grid failure in Quebec and even melted some power transformers in New Jersey. During another incident around Halloween 2003, a geomagnetic storm forced airline rerouting, halted spacecraft instrumentation, and caused power failure in Sweden.

The Northern and Southern Lights come about from particles reacting to the everyday atmospheric matter in Earth’s protective buffer.

The Human Experience

Space weather can reach Earth’s immediate vicinity within a few minutes from the solar event that caused it. Observations from key satellites, including GOES and DSCOVR, help scientists better understand those phenomena and detect potential harm to our technologies. In October 2016, a U.S. presidential executive order required the development of a nationwide strategy to cope with security and disaster issues related to space weather.

Not all outcomes of space weather are negative. Aurorae claim the distinction of being a natural, beautiful consequence of space weather. Aurorae could be considered space weather’s equivalent to the rainbow, except that the shimmering curtains of light have nothing to do with refraction of sunlight by rain droplets. They develop from the collision of charged particles from solar eruptions with Earth’s upper atmosphere. The same space weather event of Halloween 2003 also created a remarkable aurora. That aurora borealis, also known as the Northern Lights, was observed in many regions, even in low latitudes.

Photo of aurora
The Northern Lights come about from particles reacting to the everyday atmospheric matter in Earth’s protective buffer.

Space Weather Data

NCEI archives and scientifically stewards a broad assortment of space weather data for public use. Solar and space environmental data archives include extensive collections from solar observatories and satellites. The datasets include solar radio flux, sunspot numbers, solar imagery, and geomagnetic indices. They are used to produce forecasts, such as the monthly sunspot number forecast. Most notably, sunspot numbers represent one of the longest continuous climate records available. The data give scientists the means to make forecasts and issue space weather advisories and alerts.