Space Weather

Graphic image of the sun with coronal loops NSO/AURA/NSF

Space weather refers to the day-to-day strength of X-ray photons, charged particles, and magnetic fields that flow from the Sun and interact with the Earth’s magnetic fields, atmosphere, and satellites (or people) in orbit. Normally, there is a rather steady solar “wind” of charged particles and magnetic field that continuously flows from the Sun.  On occasion, an eruptive event on the Sun occurs and can blast the Earth with much larger than average doses of radiation.  These “solar eruptive events” are notoriously difficult to predict.  Like predicting tornadoes on Earth, we know when the conditions near sunspots on the Sun are favorable for eruptive events by using data obtained by the National Solar Observatory, though the prediction of Space Weather events remains an ongoing challenge to researchers.

The NSO Integrated Synoptic Program supplies data for this very purpose from the GONG facilities. GONG produces observations of the Sun’s magnetic field, the solar intensity in the H-α spectral line, and the location of sunspots on the far side of the Sun via helioseismology. These data are sent to the NOAA Space Weather Prediction Center, the US Air Force, and NASA where they are used to forecast events such as geomagnetic storms.

What is Space Weather?

Space weather is the term used to describe the physical processes and events that a) occur in interplanetary space and b) can adversely affect our technology here on Earth. The origins of space weather are on the Sun, where highly energetic explosive events occur in the form of flares and coronal mass ejections (CMEs). These events eject electrically charged particles and radiation into the heliosphere, the region of space surrounding the Sun and including the planets of the solar system. When the ejecta from the solar activity strikes the Earth, there can be several consequences depending on the physical details of what was ejected, when it arrives at our planet, and the area affected. One of these consequences, the Aurora, is beautiful but other consequences not so much. These include loss of telecommunications, increased errors in navigation systems, damage to satellites, radiation exposure of astronauts and airplane passengers and crew, disruption of military operations and widespread power outages.

While it is very unlikely that all these effects would happen with a single space weather event, all of these consequences have happened in the past. The largest known space weather event to affect society was the Carrington event that occurred on Sept. 1-2, 1859. This was also the first space weather event to be observed and it was a doozy – telegraph equipment in England was heated by the electric currents generated by the event in the telegraph wires, to the point that some offices had to extinguish small fires. Since that time there have been other events on the Sun that could have been very destructive but luckily (for us) occurred at solar locations where their ejecta did not strike the Earth.

A solar eruptive event consists of two phenomena:  1) a “coronal mass ejection”, which is a burst of charged particles (with mass) and magnetic fields from the Sun; and 2) a “flare”, which is a burst of electromagnetic radiation (“photons” with no charge or mass).   Sometimes a flare occurs without a coronal mass ejection counterpart, but mostly they occur in tandem when the flares are large.  Solar eruptive events occur when magnetic fields on the Sun’s surface become stretched and twisted; like a rubber band, the field will snap suddenly releasing enormous energy in short time (minutes to hours).

Our space weather is affected differently by flares and coronal mass ejections. First, the flare X-rays arrive at Earth eight minutes after the flare occurs on the Sun because X-rays travel at the speed of light.  These X-rays can cause disturbances in the upper atmosphere of the Earth (at ~80 km, far above the height where planes travel at 10 km), which can cause radio blackouts and affect some types of global military radio communications (e.g., with submarines) and air traffic control.  The X-rays from the flare can also heat up the upper atmosphere of the Earth, causing it to puff out, which leads to unwanted drag on satellites. Second to arrive are charged particles (mostly protons) which typically ramp up between 2-12 hours after the start of the flare. These charged particles stream toward Earth at near (but less than) the speed of light because they were given a giant boost in their energy as the coronal mass ejection erupted from the Sun.  Thanks to the Earth’s magnetic field, most charged particles are trapped and are redirected to the North and South poles. About 18 hours to a day and a half after the flare, the magnetic fields and the shock from the coronal mass ejection itself hit Earth’s magnetic field (if directed at us) creating currents in the ground, which can overload the electric grid if strong enough.  Finally, the beautiful aurora borealis (or “northern/southern lights”) occur due to this impact of the coronal mass ejection on the Earth’s magnetic field.

Space Weather research at NSO

At the NSO, scientists study the origin of space weather on the Sun. Solar flares are analyzed in the optical (visible light) and ultraviolet in order to better understand the underlying physics of the mechanism that causes flares.

By comparing observations to flare models that are run on powerful computers, the scientists at NSO identify aspects of flare physics that are missing from our understanding. We can also gain insight into some of the conditions on the Sun that lead to powerful flares, which improves predictions and alerts.  The state-of-the-art data we use from NSO and NASA facilities provide unique glimpses into the explosive heating and shock waves caused by electron beams that stream into the lowest, densest regions of the Sun’s atmosphere.  For more information about models of these electron beams and their observed signatures during flares.

Flares are also observed from other stars, and some of these flares (the so-called “superflares” or “megaflares”) are 100-1000x as energetic as the largest solar flares.  Megaflares are most often observed from red dwarf stars, which are smaller and less massive than the Sun, but they constitute 70% of the stars in the Universe.  Some red dwarfs have a much larger fraction (~50%) of their surfaces covered by strong magnetic fields than the Sun (which has strong fields in sunspots covering < 1% of the surface), which may give rise to such giant flares.


These movies show the sudden burst of red light originating from the chromosphere during a flare.  The visible light (include the red in these movies) and ultraviolet light does not interact with and disturb the Earth’s atmosphere like the X-rays, but these photons overall constitute 100x greater energy than the collective radiant energy of the X-rays.  The optical photons are seen to flare before the peak X-ray flux, and therefore they carry very important information of the early explosive phase of a flare on the Sun.

Exoplanet Space Weather

We live in the habitable zone around the Sun, which is where liquid water can exist with Earth-like atmospheric conditions.  The habitable zones for red dwarf stars are at least 10x closer to the star, which means that the irradiation on habitable zone planets from flares is hundreds to hundreds of thousands of times larger than what we experience from our Sun’s flares. Scientists are still looking for signatures for coronal mass ejections during flares on other stars, but these eruptions would also be much more damaging to hypothetical advanced societies around red dwarfs.  Scientists at NSO (Kowalski) study the spectra of megaflares on red dwarfs, which allows us to better understand the damaging effects of near-ultraviolet radiation on potential surface biology that might exist on these “exoplanets”.  The nearest star besides the Sun is the red dwarf Proxima Centauri, which is one of the stars studied by Kowalski due to its frequent flaring activity. This stellar system is also the site of the nearest Earth-mass planet in the habitable zone around another star.  A series of ultraviolet flares on Proxima Centauri over 8 hours of observations is shown in the figure below.  Although each flare here is significantly less energetic than a typical large solar flare, Proxima Centauri flares much more often than the Sun while the habitable zone is 20x closer than the Earth-Sun distance.


Dr. Alexei Pevtsov
National Solar Observatory


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