The Sun is a very busy place. Click on the image for the current much larger view. Close inspection through telescopes reveals a surface roiling with activity. There are regions where the temperature is somewhat cooler that the surroundings. These show as darker and are known as sunspots. The sunspots are associated with the magnetic activity of the Sun. The magnetic field of the Sun is not stable or static like that of a permanent magnet. Because of the circulation of huge currents of charged particles within the Sun, there are continuously changing strengths and directions of magnetic field. The magnetic field actually reverses in the middle of the solar cycle. The cycles last about 11 years. We are at the middle now. Reversal is expected any time. Those who monitor the Sun will know when it occurs. You and I will not see anything different with our eyes.
Often, there are eruptions at the surface causing flares to rise and dance controlled by the varying magnetic field. Some of the flares extend out into space as prominences. These are not energetic enough to cause noticeable effects here on Earth. The linked image at the left is a video of some flares and prominences.
Sometimes these eruptions are accompanied by a huge burst of light and radiation whereby a large cloud of solar material is ejected at high speed away from the Sun. These are called Coronal Mass Ejections (CME). If CME are aimed at Earth, they can have significant effects. Scientists monitor these enormous space weather events for geomagnetic storms, solar radiation storms, and radio blackouts that they can cause on Earth.
This post is a short primer on these three effects on Earth associated with CME.
Geomagnetic Storms on Earth
The most common form of space weather effect on Earth is the geomagnetic storm. Earth is protected by a sheath of magnetic field called the magnetosphere. You can see a model of it surrounding Earth in the image at the top of this post. Normally, it is quiet and relatively stable. The magnetic field lines of Earth point northward indicated by a compass if you have used one of them. The interactions of a CME with the Earth’s magnetosphere can cause the visual effect illustrated by the aurora image at the left. Storms are categorized from G1 (minor) to G5 (extreme). In the most extreme cases transformers in power grids may be damaged, spacecraft operation and satellite tracking can be hindered, high frequency radio propagation and satellite navigation systems can be blocked, and auroras may appear much further south than normal.
A CME travels with its own magnetic field. They connect with the field of the Earth on the outside of the magnetosphere for a period of time. If the CME field lines up with Earth’s field, the energy and the particles slide around the Earth and cause little change. If the CME field is opposite of Earth’s field, the disturbance can be dramatic and visual. Charged particles can be caught up in the magnetosphere. The shape of the magnetosphere changes. The particles follow the Earth’s field lines into the polar regions as a sort of loop, or ring of aurora. These energetic particles excite the gases in the upper atmosphere and cause them to emit characteristic colors of green, red, and purple hues. This is a common event over the Canadian provinces and similar latitudes around the world. Sometimes they appear at lower latitudes across the United States. Here is a link to the AuroraMax Project by the Canadian Space Agency in Yellowknife. They have live streaming of aurora and archives of past nights for you to view. Give it a few moments to load the video. It should then auto-play.
Astronaut Don Pettit is a skilled astrophotographer. He has recorded aurora as seen from the ISS. This 3 minute video is an excellent explanation and model of how the aurora form at the poles. It is well worth your time to watch it.
The Solar and Heliospheric Observatory (SOHO) monitors the Sun in multiple wavelengths. The image at left is linked to a video of Sun observations for April 2001. The disc in the center covers the bright image of the Sun so the instruments can see the surrounding material. That was an active phase for the Sun. Multiple CME are seen leaving the region. Most of them were not directed at the Earth. In the latter part of the video, many white speckles appear on the screen from charged particles striking the detector. These CME were directed at Earth and were cause for concern to communications equipment, satellites, and power grids.
A more recent example of a CME is in this video at the right from March 7, 2012. The image is linked to the video. This CME was directed at Earth and produced geomagnetic storms. Notice the large number of white speckles on the screen again.
The SDO spacecraft also viewed this powerful event. A dramatic feature is the way the entire surface of the sun ripples with the force of the eruption. This movement comes from something called EIT waves. They were first discovered with the Extreme ultraviolet Imaging Telescope (EIT) on the SOHO spacecraft. The wave can travel across the full width of the sun and move at over a million miles per hour. They travel from one side of the sun to the other in about an hour. The movie shows two distinct waves. The first seems to spread in all directions. The second is narrower and moves toward the southeast.
This next movie from the Goddard Heliophysics division shows more than 20 M- and X-class flares on the sun between Oct. 23 and Oct. 28, 2013. They were captured by NASA’s Solar Dynamics Observatory SDO. CMEs during that time were captured by the ESA/NASA Solar and Heliospheric Observatory SOHO. Music: “Stella Nova” by Lars Leonhard.
Solar Radiation Storms
A solar radiation storm, also called a solar energetic particle (SEP) event, is an intense inflow to Earth of radiation of protons and other charged particles from the Sun. The radiation is blocked by the magnetosphere and atmosphere and cannot reach humans on Earth. It could harm humans traveling from Earth to the Moon or Mars. It has little to no effect on airplane passengers or astronauts within Earth’s magnetosphere. Solar radiation storms can also disturb the regions where high frequency radio communications travel. During an SEP, airplanes traveling routes near the poles which rely exclusively on radio communications may be re-routed.
Solar radiation storms are rated on a scale from S1 (minor) to S5 (extreme), determined by how many very energetic, fast solar particles move through a given space in the atmosphere. At their most extreme, solar radiation storms can cause complete high frequency radio blackouts, damage to electronics, memory and imaging systems on satellites, and radiation poisoning to astronauts outside of Earth’s magnetosphere.
Radio blackouts can occur when the strong, sudden burst of x-rays from a solar flare hits Earth’s atmosphere. These can jam high and low frequency radio signals. The X-rays disturb a layer of Earth’s atmosphere known as the ionosphere, through which radio waves travel. The disruptions to the ionosphere change the paths of the radio waves and degrade the information they carry. The loss of low frequency radio communication causes Global Positioning System GPS measurements to be off by up to several miles. They can also affect the applications that govern satellite positioning.
Radio blackouts are rated on a scale from R1 (minor) to R5 (extreme). The strongest radio blackouts can result in no radio communication and faulty GPS for hours at a time.
Solar activity has probably reached maximum for the current 11 year cycle. However, it can happen at any time. The Sun is due to reverse its magnetic field now. As of this writing, it has not done that. Fortunately, we don’t appear to have any direct harmful effects on humans to worry about here on the ground. Indirectly, the solar storms and CME could cause a lot of havoc if they are intense enough to disrupt power grids or communication systems. Alerts are issued to the groups who maintain those infrastructures when activity warrants.