There are also weather changes in space, so do astronauts need to check the "weather forecast"?

In the earth's atmosphere, there are weather phenomena that are closely related to us, such as cloudy and sunny days, cold and warm days, wind, rain, snow, lightning, etc. In the vast space, is there also weather? The answer is yes. Scientists call it space weather. So is space weather the same as weather on earth? How to monitor space weather? Can space weather be predicted?

| What is space weather?

Space weather is completely different from the weather in the Earth's atmosphere. Space weather occurs in the space region between the Sun and the Earth more than 30 kilometers above the Earth's surface, including the solar corona, interplanetary space, magnetosphere, ionosphere, and the middle and upper atmosphere above the middle stratosphere from far to near.

In this space region, except for a very small amount of water vapor in the middle and upper stratosphere, there is almost no water vapor in other spaces, so it is impossible to see the weather phenomena we see in the troposphere of the Earth's atmosphere. In this space, particles, energy and electromagnetic radiation are the undisputed "protagonists", and they will change on a short time scale due to the arrival of matter and energy ejected by solar flare activities, and cause strong disturbances in the Earth's space environment such as the Earth's magnetosphere, ionosphere, and middle and upper atmosphere, triggering proton events and ionospheric storms, geomagnetic storms and other effect events, which is space weather.

Solar eruption activity is the main cause of space weather. During solar eruptions, solar flares and coronal mass ejections release short-lived, extremely energetic light waves and particles in three forms: enhanced electromagnetic radiation, high-energy charged particle flows, and plasma clouds, which eventually act on the Earth. Therefore, the "wind" in space weather is solar wind, and the "rain" is charged particles from the sun.

Like the weather on Earth, space weather can also be "unpredictable." In years with low solar activity, space is relatively calm, while in years with high solar activity, there are more solar eruptions and space weather is frequent and complex. For example, on February 23, 2024, my country's National Space Weather Monitoring and Early Warning Center announced a record-breaking solar eruption: "At 06:34 Beijing time on February 23, 2024, an X6.3-class large flare erupted in active area 13590 at 17 degrees north latitude and 26 degrees east longitude on the surface of the sun. Its intensity is the largest in the current 25th solar activity week, and it also broke the flare eruption record since September 10, 2017."

| Why care about space weather?

A solar eruption usually causes three rounds of impacts on the space between the Sun and the Earth and even the space on the surface of the Earth: the first round: the flare of the solar eruption, that is, the enhanced electromagnetic radiation, brings huge radiation energy and propagates in the form of electromagnetic waves. Because it is the speed of light, it takes only about eight and a half minutes for the sun, which is 151 million kilometers away from the earth, to reach the earth. The stability of the ionosphere is broken and the structure changes; the second round is the sudden increase in the flow of solar matter, that is, high-energy charged particles, which takes tens of minutes to more than ten hours to reach the earth, increasing the number of high-energy charged particles around the earth by thousands of times or even tens of thousands of times. Since protons account for more than 90% of the total number of particles, this event is called a solar proton event; the third round of coronal mass ejection, that is, the solar wind, will also carry a lot of energy to impact the earth, arriving at the earth about three days later, causing geomagnetic storms and magnetospheric substorms.

These three rounds of impacts from solar eruptions bring short-term changes to the interplanetary space, the Earth's magnetosphere, the ionosphere, and the middle and upper atmosphere, generating space weather that affects human activities on Earth and the safe operation of spacecraft in orbit, such as:

Solar flares cause ionospheric disturbances, which may cause radio signals to pass through the ionosphere and into the universe, or "swallow" key information sent back to the ground by satellites. Combined with the impact of geomagnetic storms caused by coronal mass ejections, airplanes, ships, cars, and even smartphones will experience errors when using satellite positioning, and in severe cases, they may even be unable to navigate.

When the radio communication system encounters space weather events, the ionospheric disturbance will also affect the call quality. In mild cases, the large amount of noise will make it impossible for the two parties to hear each other clearly. In severe cases, it may even cause signal drowning and communication interruption.

In most cases, we cannot feel the impact of space weather, but the geomagnetic storms and magnetospheric substorms caused by super solar eruptions may affect the orbital height of low-orbit satellites, the safe operation of power grids, and geological exploration, and have a serious impact on daily life. Take the March 1989 super solar eruption as an example. Less than 90 seconds after the geomagnetic storm occurred, the power grid in Quebec, Canada, was completely paralyzed, 6 million households were plunged into darkness, and the power outage lasted for 9 hours.

If a proton event occurs during the second round of solar eruptions, the high-energy charged particle flow will be accelerated to a speed of thousands, tens of thousands, or even hundreds of thousands of kilometers per second. After reaching Earth space, it will bombard the magnetosphere and break through the defenses of the Earth's magnetic field, enter satellite orbits, and even penetrate into the ionosphere, atmosphere, and surface space. A large number of high-energy particles will enter the Earth's atmosphere, and for passengers and flight attendants on the plane, the aviation radiation dose will increase sharply, posing a health risk.

Astronauts who stay in the space station for a long time need to pay more attention to the radiation environment. In years with high solar activity, irregular solar proton events at near-Earth orbit will also cause the radiation environment of the space station to deteriorate. The "outer wall" of the space station can block these high-energy particles, but during the outbreak of super solar proton events, such as the proton events in July 1989 and November 2003, the radiation level of the International Space Station exceeded the standard seriously, and the astronauts were forced to enter the return capsule to avoid it. In addition, astronauts need to avoid solar proton events when they go out of the cabin for "space walks".

With the rapid expansion of low-Earth satellites, the orbit of the space station has become crowded. In particular, with the launch of Starlink satellites, tens of thousands of satellites will cross the orbit of the space station, leaving a large amount of debris that poses the greatest threat to the space station, making the environment of the space station where astronauts are stationed even more dangerous. Therefore, the impact of space debris on space activities has also been listed as part of space weather.

Author | Xun Jiwei is a senior engineer who graduated from Nanjing Institute of Meteorology with a major in Weather Dynamics (now Nanjing University of Information Science and Technology with a major in Atmospheric Science). The author has been engaged in business and management work in weather forecasting and meteorological services for a long time.