Space weather is a part of space physics and aeronomy, or heliophysics, that studies changing conditions in the Solar System and its heliosphere. It looks at how the solar wind affects Earth's magnetosphere, ionosphere, thermosphere, and exosphere. Although these are different from Earth's atmosphere, space weather is similar to weather in Earth's troposphere and stratosphere. The term "space weather" was first used in the 1950s and became more widely known in the 1990s. This led to research on "space climate," which focuses on long-term patterns of space weather.

History

For many centuries, people noticed the effects of space weather but did not understand them. Auroras, or glowing lights in the sky, were often seen in areas near the Earth’s poles.

In 1724, George Graham observed that the needle of a magnetic compass moved away from magnetic north during the day. Scientists later discovered that this was caused by electric currents in the ionosphere and magnetosphere. Balfour Stewart made this connection in 1882, and Arthur Schuster confirmed it in 1889 by studying data from magnetic observatories.

In 1852, Edward Sabine, an astronomer and military officer, found that the number of sunspots on the Sun was linked to the chance of geomagnetic storms on Earth. This showed a new connection between the Sun and Earth. A powerful solar storm in 1859 caused bright auroras and disrupted telegraph systems worldwide. Richard Carrington correctly linked this storm to a solar flare he had seen the day before near a large group of sunspots.

Kristian Birkeland studied auroras by creating them in his laboratory and predicted the solar wind.

The invention of radio revealed that solar weather could cause loud static or noise. During a major solar event in 1942, radar interference led to the discovery of solar radio bursts, which are radio waves created by solar flares.

In the 20th century, interest in space weather grew as military and commercial systems became dependent on technologies that could be affected by space weather. Communications satellites are essential for global business. Weather satellites help track Earth’s weather. GPS satellite signals are used in many applications. Space weather can damage satellites or disrupt their radio signals. It can also cause strong electrical surges in power lines and expose airplane passengers and crews to radiation, especially on polar flight paths.

The International Geophysical Year (IGY) increased research into space weather. Data from IGY showed that auroras form in an auroral oval, a glowing area 15 to 25° away from the magnetic poles and 5 to 20° wide. In 1958, the Explorer I satellite discovered the Van Allen belts, regions of radiation trapped by Earth’s magnetic field. In January 1959, the Soviet satellite Luna 1 first directly observed the solar wind and measured its strength. A smaller event called the International Heliophysical Year (IHY) took place in 2007–2008.

In 1969, the satellite INJUN-5 (or Explorer 40) made the first direct observation of the electric field created by the solar wind in Earth’s high-latitude ionosphere. In the early 1970s, data from the Triad mission showed that electric currents flow between the auroral oval and the magnetosphere.

The term “space weather” began being used in the late 1950s as satellites started measuring the space environment. The term became popular again in the 1990s as people recognized the need for better research and management of space weather’s effects on human systems.

Programs

The US National Space Weather Program aims to help researchers study what is needed by businesses and the military, to help researchers and users work together, to organize centers that provide weather data, and to better understand what users need. NOAA runs the National Weather Service's Space Weather Prediction Center.

The idea became a plan in 2000, a detailed plan in 2002, a review in 2006, and a new plan in 2010. A new plan was planned for 2011, followed by another detailed plan in 2012.

The International Civil Aviation Organization (ICAO) started a Space Weather Advisory program in late 2019. This program chose four global space weather service providers:

Space weather is listed as a natural hazard in risk assessments in countries such as:

Phenomena

Space weather in the Solar System is affected by the solar wind and the magnetic field carried by the solar wind plasma. Many physical events are linked to space weather, such as geomagnetic storms and substorms, increased energy in the Van Allen radiation belts, disturbances in the ionosphere, flickering of radio signals between satellites and Earth, changes in long-distance radar signals, auroras, and electric currents caused by space weather at Earth's surface. Coronal mass ejections are important causes of space weather because they can push the magnetosphere and cause geomagnetic storms. Solar energetic particles (SEP), which are sped up by coronal mass ejections or solar flares, can lead to solar particle events. These events are a major cause of space weather that affects humans, as they can harm electronic equipment on spacecraft (e.g., the failure of Galaxy 15), endanger astronauts, and increase radiation risks for flights at high altitudes and near Earth's poles.

Effects

Some spacecraft failures are directly caused by space weather, and many more are affected by it in some way. For example, 46 out of 70 spacecraft failures reported in 2003 happened during a strong geomagnetic storm in October 2003. The two most common problems caused by space weather are radiation damage and spacecraft charging.

Radiation, which is made of high-energy particles, can pass through the outer layer of a spacecraft and reach its electronic parts. Usually, this causes errors in the spacecraft’s systems or changes a single bit of information stored in its memory (called a "single event upset"). In rare cases, radiation can permanently damage part of the spacecraft’s electronics (called a "single-event latchup").

Spacecraft charging happens when low-energy particles collect as an electric charge on nonconducting materials on the spacecraft’s surface. If enough charge builds up, it can cause a spark. This spark might trick the spacecraft’s computer into acting on false signals. Studies show that spacecraft charging is the most common space weather effect on satellites in geosynchronous orbit.

Spacecraft in low Earth orbit (LEO) gradually lose altitude over time because of drag, which is the resistance from the Earth’s atmosphere. Eventually, they fall back to Earth. Many spacecraft launched in recent years can use small rockets to adjust their orbits. These rockets help extend the spacecraft’s lifetime, guide it to re-enter Earth’s atmosphere at a specific location, or avoid collisions with other satellites. Accurate orbit information is needed for these maneuvers. A geomagnetic storm can change a spacecraft’s orbit in just a few days, a change that would normally take a year or more. It also speeds up the re-entry of satellites from LEO by heating the thermosphere, which makes the atmosphere expand and increase drag. The 2009 collision between the Iridium 33 and Cosmos 2251 satellites showed how important it is to track all objects in orbit. Iridium 33 could have avoided the crash if a reliable prediction of the collision had been available.

Human exposure to ionizing radiation, whether from medical X-rays, nuclear power plants, or space, can cause harm. The severity of the harm depends on how long the exposure lasts and the radiation’s energy level. Radiation belts near Earth extend down to the altitude of spacecraft like the International Space Station (ISS) and the Space Shuttle. Under normal conditions, the radiation levels are safe. However, during major space weather events that include solar energetic particle (SEP) bursts, radiation levels can increase dramatically. The ISS has shielding to keep radiation doses within safe limits. For the Space Shuttle, such events would require ending the mission immediately.

The ionosphere bends radio waves in the same way water in a pool bends light. When the ionosphere is disturbed, radio signals can become unclear or unrecognizable. The amount of distortion (called "scintillation") depends on the signal’s frequency. Very high frequency (VHF) radio signals (30 to 300 MHz) can be completely scrambled by a disturbed ionosphere. Ultra high frequency (UHF) signals (300 MHz to 3 GHz) can still pass through, but receivers might lose track of the signal. GPS uses signals at 1575.42 MHz (L1) and 1227.6 MHz (L2), which can be disrupted by a disturbed ionosphere. Major space weather events can cause GPS outages lasting minutes to days. These events can also shift the ionosphere toward the equator and create large changes in ionospheric density, further disrupting GPS signals.

High frequency (HF) radio waves (3 to 30 MHz) are reflected by the ionosphere, allowing them to travel beyond the line of sight around Earth. In the 20th century, HF was the only way for ships or planes far from land to communicate. While newer systems like Iridium now exist, HF remains important for ships without newer equipment and as a backup for others. Space weather can disrupt HF communications by scattering signals instead of reflecting them. Small space weather events near the poles frequently disrupt HF signals, while larger events at mid-latitudes can also cause problems.

Airline routes that cross the poles are especially affected by space weather because federal rules require reliable communication during the entire flight. Changing such a flight can cost about $100,000.

The magnetosphere directs cosmic rays and solar particles toward Earth’s polar regions. These high-energy particles enter the atmosphere and break apart air molecules, creating lower-energy particles that can travel deep into the atmosphere. All aircraft flying above 8 km (26,200 feet) are exposed to these particles. Radiation exposure is highest near the poles. Many commercial flights travel over polar regions. If space weather causes radiation levels to exceed safety limits, flight paths are changed.

Radiation levels at aircraft altitudes have been measured using instruments that record data on board and send it to Earth later. However, a system called NASA’s Automated Radiation Measurements for Aerospace Safety (ARMAS) now provides real-time radiation data from aircraft. ARMAS has collected data from hundreds of flights since 2013, mostly on research planes, using Iridium satellite links. The goal is to use this data to improve global radiation models, like NASA’s NAIRAS system, to predict radiation conditions in real time.

Magnetic storms can create geoelectric fields in Earth’s crust. These fields can cause uncontrolled electrical currents in power grids, damaging transformers, tripping safety systems, and sometimes causing blackouts. This happened during the March 1989 magnetic storm, which caused the Hydro-Québec power grid to collapse completely.

Observation

Observation of space weather is done for scientific research and practical uses. Scientific observation has changed as scientists learned more, while observation for practical uses grew as people found ways to use the data.

Space weather is watched from Earth by observing changes in Earth's magnetic field over seconds to days, by looking at the Sun's surface, and by listening for radio noise from the Sun's atmosphere.

The Sunspot Number (SSN) counts the number of dark spots on the Sun's visible surface. The number and size of these spots are connected to how bright the Sun is in certain types of light and to events like solar flares and eruptions of solar material.

The 10.7 cm radio flux (F10.7) measures radio waves from the Sun and is related to the Sun's brightness in another type of light. This measurement is taken daily from Earth and has been recorded since 1947. The standard measurements are made by an observatory in Canada and reported in special units. These data are stored by a scientific organization.

Ground-based magnetometers and observatories provide important space weather data. Magnetic storms were first discovered by measuring unusual changes in Earth's magnetic field. These instruments give real-time information for studying space weather events. Observatories have been operating for many years, providing data about long-term changes in space weather patterns.

The Disturbance storm time index (Dst index) estimates changes in Earth's magnetic field caused by electric currents around Earth. This index uses data from four observatories near Earth's equator. The Dst index is collected and stored by a global scientific center.

The Kp/ap index measures how much Earth's magnetic field is disturbed. The 'a' value comes from one observatory's data over three hours, while 'K' is a related number. Kp and ap are averages from many observatories worldwide, showing how much Earth's magnetic field is disturbed by storms and smaller events. These data have been recorded since 1932.

The AE index measures disturbances in Earth's magnetic field near the auroras. It uses data from 12 observatories and is recorded every minute. This data is available with some delay, which limits its use for space weather monitoring. The AE index shows how strong auroral disturbances are, except during major storms when the auroras move closer to Earth.

Radio noise bursts are reported by a network of telescopes to government agencies. These bursts are caused by solar flares interacting with the Sun's atmosphere.

The Sun's surface is watched continuously for signs of solar flares and eruptions. The Global Oscillation Network Group (GONG) studies the Sun's surface and inside by observing sound waves. GONG can find sunspots on the far side of the Sun, a discovery confirmed by other spacecraft.

Neutron monitors on Earth detect cosmic rays from the Sun and other sources. When cosmic rays hit Earth's atmosphere, they create showers of smaller particles. These particles are measured on Earth to study cosmic rays in space.

Total Electron Content (TEC) measures the number of electrons in the ionosphere. This is done by tracking signals from GPS satellites. TEC data is collected in real time by hundreds of stations worldwide.

Geoeffectiveness measures how strongly space weather affects Earth's magnetic field. This depends on the direction of magnetic fields from the Sun. Scientists are developing new methods using radio waves to study these fields.

Many spacecraft study space weather. Early spacecraft like the Orbiting Geophysical Observatory series helped understand the space environment. Later spacecraft, such as STEREO and the Van Allen Probes, study the Sun and Earth's magnetic field in detail. STEREO spacecraft move away from Earth each year, providing 3D views of the Sun. The Van Allen Probes study radiation belts and storms around Earth.

Some spacecraft with other missions also study the Sun. Early examples include the Applications Technology Satellite (ATS) series, which helped create modern weather satellites. These spacecraft carried instruments to study space conditions.

Many early spacecraft were used for space weather after their original missions. The IMP-8 spacecraft studied the solar wind from 1973 to 2006. Later, the ISEE-3 and WIND spacecraft monitored the solar wind near Earth. The NASA Advanced Composition Explorer continues this work today.

Studying the Sun is important for space weather. Since Earth cannot see the Sun's ultraviolet light, the SOHO spacecraft was launched to provide images of the Sun. SOHO gives real-time data for both research and predicting space weather events.

Models

Space weather models are computer models that show how the space weather environment works. These models use math equations to explain physical processes.

They use a small amount of data to describe parts of the space weather environment or to predict how weather changes over time. Early models were based on experience rather than strict physics. These models needed fewer computer resources compared to more advanced models.

Later models use physics to explain as many space weather events as possible. No model can yet accurately predict the space weather environment from the Sun’s surface to the Earth’s ionosphere. Space weather models differ from weather models on Earth because they use much less input data.

A large part of space weather model research in the past 20 years has been done through the Geospace Environmental Model (GEM) program, which is part of the National Science Foundation. The two main research centers are the Center for Space Environment Modeling (CSEM) and the Center for Integrated Space Weather Modeling (CISM). The Community Coordinated Modeling Center (CCMC) at NASA Goddard Space Flight Center helps scientists develop, test, and prepare models for use in space weather predictions.

Modeling techniques include: (a) magnetohydrodynamics, which treats the space environment as a fluid; (b) particle in cell, which studies small parts of space and connects them to describe the whole environment; (c) first principles, which balance natural rules that govern space; and (d) semi-static modeling, which uses statistical or empirical relationships, or a mix of these methods.

Commercial space weather development

During the first 10 years of the 21st Century, a new commercial sector developed that focused on space weather. This sector provided services and information to government agencies, universities, businesses, and the public. Companies in this field are often small businesses or departments within larger companies. They offer data, models, related products, and services about space weather.

This sector includes scientists, engineers, and people who use space weather information. Most activities focus on how space weather affects technology. For example, space weather can cause problems for satellites, power systems, and communication networks. These issues can lead to effects on society that contribute significantly to a country’s total economic value.

The idea of encouraging private companies to work on space weather was first proposed in 2015 by the American Commercial Space Weather Association (ACSWA). They suggested creating a special area called a "Space Weather Economic Innovation Zone." This zone would help increase economic activity by developing tools to manage risks from space weather. It would also support research at universities and encourage U.S. businesses to invest in space weather services and products. The plan required the government to buy U.S.-made hardware, software, and services when no government capability existed. It also aimed to sell these products to other countries. The plan asked that U.S.-made products be labeled as "Space Weather Economic Innovation Zone" activities and tracked in government reports.

In 2015, the U.S. Congress passed a bill called HR1561, which laid the foundation for studying the social and environmental effects of the Space Weather Economic Innovation Zone. In 2016, a new law called the Space Weather Research and Forecasting Act (S. 2817) was introduced to continue this work. Later, in 2017–2018, the HR3086 Bill combined these ideas with information from studies supported by the Office of Science and Technology Policy’s Space Weather Action Program (SWAP). With support from both political parties, the 116th Congress (2019) is considering passing the Space Weather Coordination Act (S141, 115th Congress).