What Is Space Weather?
Activity on the Sun can cause space weather storms that affect us here on Earth. Solar storms can impact the technology we rely on everyday: Global Positioning Systems (GPS), satellites, and electric power grids. Just as with other types of weather, the National Weather Service forecasts space weather disturbances and serves as the official source for civilian alerts and warnings.
Space weather is a consequence of the behavior of the Sun, the nature of Earth’s magnetic field and atmosphere, and our location in the solar system.
There are various phenomena that originate from the Sun that can result in space weather storms. Outbursts from huge explosions on the Sun—Solar Flares and Coronal Mass Ejections (CME)—send space weather storms hurling outward through our solar system. The Sun also emits a continuous stream of radiation in the form of charged particles that make up the plasma of the solar wind.
Solar Flares are huge explosions on the Sun. A flare appears as a sudden, intense brightening region on the Sun, typically lasting several minutes to hours. Flares are seen as bright areas on the Sun in optical wavelengths and as bursts of noise in radio wavelengths. The primary energy source of flares is the tearing and reconnection of strong magnetic fields. The electromagnetic emission produced during flares travels at the speed of light, taking about 8 minutes—rapidly affecting the day side of Earth.
Coronal Mas Ejections (CME)
Coronal Mas Ejections are explosive outbursts of plasma from the Sun’s outer atmosphere, the Corona. The blast of a CME typically carries roughly a billion tons of material outward from the Sun
at speeds as fast as hundreds of kilometers per second. A CME contains particle radiation (mostly protons and electrons) and powerful magnetic fields. In contrast to solar flares, CMEs are not particularly bright, may take hours to fully erupt from the Sun, and typically take 1-4 days to travel to Earth.
Solar Particle Events
Solar Particle Events release large numbers of high energy charged particles, predominately protons and electrons, which are accelerated to large fractions of the speed of light. These particles may arrive at Earth between 30 minutes and several hours.
Space Weather and the Solar Cycle
The number of sunspots on the surface of the Sun increases and decreases in solar cycles of approximately 11 years. Solar Minimum refers to the several years when the number of sunspots is lowest; Solar Maximum occurs in the years when sunspots are most numerous. The Sun is usually very active when sunspot counts are high, however, severe storms can occur anytime during the solar cycle. Sunspots show where the Sun’s magnetic field energy is building up and where it could release to cause solar flares and CMEs. The Sun gives off more radiation than usual during solar maximum. This extra energy creates changes in the Earth’s upper atmosphere.
Sunspots are dark, cooler areas on the solar surface that contain strong, constantly shifting magnetic fields. A moderate-sized sunspot is many times larger than the size of the Earth. Sunspots form over periods lasting from days to weeks, and can persist for weeks and even months before erupting or dissipating. Sunspots occur when strong magnetic fields emerge through the solar surface and allow the area to cool slightly, from a background value of 6000°C down to about 4200°C. This cooler area appears as a dark spot on the Sun. As the Sun rotates, sunspots on its surface appear to move from left to right. It takes the Sun 27 days to make one complete rotation.
Impacts of Space Weather
Large currents in the ionosphere can induce currents in power lines. Surges from these induced currents can cause massive network failures and permanent damage to electric grid components.
Disturbances in the ionosphere can cause degradation in GPS range measurements and in severe circumstances, loss of lock by the receiver on the GPS signal.
Space weather storms can cause lost or degraded communications, radiation hazards to crew and passengers, unreliable navigational information, and problems with flight-critical electronic systems.
Human Space Exploration
Energetic particles present a health hazard to astronauts on space missions as well as threats to electronic systems. During space missions, astronauts outside spacecraft are less protected and more exposed to space radiation.
Highly energetic ions penetrate electronic components, causing bit-flips in a chain of electronic signals that can result in improper commands within the spacecraft or incorrect data from an instrument. Less energetic particles contribute to a variety of spacecraft surface charging problems, especially during periods of high geomagnetic activity.
Magnetic field changes associated with geomagnetic storms directly affect operations that use the Earth’s magnetic field for guidance, such as magnetic surveys, directional drilling, or the use of magnetic compasses. Ionospheric disturbances cause errors in location obtained from GPS signals.
Communications at all frequencies may be affected by space weather. High frequency (HF) radio communications are more routinely affected because this frequency band depends on reflection by the ionosphere to carry signals great distances.
Space Weather Storms
Radio Blackouts are caused by bursts of X-ray and Extreme Ultra Violet radiation emitted from solar flares. Radio blackouts primarily affect High Frequency (HF) (3-30 MHz) communication, although fading and diminished reception may spill over to Very High Frequency (VHF) (30-300 MHz) and higher frequencies. These storms are a consequence of enhanced electron densities caused by solar flare emissions. The emissions ionize the sunlit side of Earth, which increases the amount of energy lost as radio waves pass through this region.
Radio blackouts are among the most common space weather events to affect Earth. Minor events occur, on average, 2000 times each solar cycle. Blackouts are by far the fastest to impact our planet. The
X-rays creating radio blackouts arrive at the speed of light–8 minutes from Sun to Earth, making advance warnings difficult. When flares occur, however, SWPC measures their intensity and forecasts their
duration. Usually the radio blackouts last for several minutes, but they can last for hours.
The impacts of Radio Blackouts are felt by industries relying on HF radio communication and low frequency signals, primarily the aviation and marine industries.
Solar Radiation Storms
Solar radiation storms occur when large quantities of charged particles, protons and electrons, are accelerated by processes at or near the Sun. When these processes occur, the near-Earth satellite environment is bathed with high energy particles. Earth’s magnetic field and atmosphere offer some protection from this radiation, but the amount of protection is a function of altitude, latitude, and magnetic field strength. The polar regions are most affected by energetic particles because the magnetic field lines at the poles extend vertically downwards, allowing the particles to spiral down the field lines and penetrate into the atmosphere, increasing ionization. Energetic protons reach Earth a half hour to several hours after a solar eruption. Solar radiation storms can last from a few hours to days, depending on the magnitude of the eruption. Solar radiation storms can occur at any time during the solar cycle but tend to be most common around solar maximum.
Solar radiation storm impacts include loss of HF radio communications through the polar regions, navigation position errors, elevated radiation exposure to astronauts, and to passengers and crew in aircraft at high altitudes and latitudes, and damage to satellite systems.
Geomagnetic storms, strong disturbances to Earth’s magnetic field, pose problems for many activities, technological systems, and critical infrastructure. The Earth’s magnetic field changes in the course of a storm as the near-Earth system attempts to adjust to the jolt of energy from the Sun carried in the solar wind. CMEs and their effects can disturb the geomagnetic field for days at a time. The most visible attribute of a geomagnetic storm is the aurora, which becomes brighter and moves closer to the equator. This heightened aurora signals the vigorous electrodynamic processes at play as they respond to the burst of energy.
Geomagnetic storms usually last a few hours to days. The strongest storms may persist for up to a week. A string of CMEs may cause prolonged disturbed periods related to the additional energy being pumped into Earth’s magnetic field. The frequency of geomagnetic storms, in general, depends on where we are in the solar cycle–with most storms occurring near solar maximum; however, these storms are also common in the declining phase due to high speed solar wind streams.
Geomagnetic storms induce currents that can have significant impact on electrical transmission equipment. Electric power companies have procedures in place to mitigate the impact of geomagnetic storms.
Current Space Weather
You can find reports of current space weather at GreendaleWeather.com. Select Space Weather from the menu.
Acknowledgements: Information in this article was obtained from NASA and NOAA.