Up 太陽 : 気象 作成: 2021-12-17
更新: 2021-12-17

    NASA より
    1) What kind of weather events occur in space, and when are they likely to strike?
    Quite different from your average terrestrial rain or snow, space weather in our solar system is composed of radiation and particles from the Sun.
    The Sun is made up of superhot electrically charged plasma, the fourth state of matter.
    Plasma constantly streams toward the planets as solar wind, pouring energy into near-Earth space.
    That’s not all the Sun is capable of.
    Sometimes, it hosts much more dramatic events.
    Solar flares are tremendous explosions on the surface of the Sun, releasing energy which travels at the speed of light.
    Their effects on Earth are apparent in eight minutes.
    Coronal mass ejections (CMEs) are eruptions of large clouds of solar plasma and magnetic fields from the Sun.
    The geomagnetic storms resulting from these events may occur one or several days later.
    CMEs and solar flares can also occur at the same time.

    The Sun operates in an eleven-year solar cycle, and CMEs and flares are more common during the middle part of the solar cycle, called solar maximum.
    During solar maximum, the Sun may produce several CMEs per day and a few truly massive explosions per year, said Antti Pulkkinen, director of the Heliophysics Science Division at NASA Goddard.
    In comparison, during solar minimum, the Sun may be relatively quiet for extended periods of time.
    In solar cycle 25, the Sun is expected to hit solar maximum around 2025.

    2) So...why doesn’t space weather just torch us?
    Earth has a strong, large magnetic field produced by charged molten iron churning in its core.
    That field keeps away most of the charged solar wind streaming toward Earth, just like an umbrella works in a rainstorm.
    The area within the safety of Earth’s magnetic field is called the magnetosphere.
    Earth’s magnetosphere is quite large and strong.
    On the side away from the Sun, it extends hundreds of times the length of Earth’s roughly 4,000 mile-radius.
    The magnetosphere faces much more pressure on the side facing the Sun, where it extends 6 to 10 times Earth’s radius (between around 25,000 miles to 40,000 miles).
    “The magnetosphere is this really nice protective shield,” Halford said.
    “It blocks out most of the radiation and bad weather that you get in space, but not all of it.”

    Another barrier is Earth’s thick atmosphere, which blocks harmful light radiation from the Sun from reaching Earth’s surface.

    3) What are the effects of space weather on Earth?
    As Halford explains, protection offered by the magnetosphere isn’t perfect.
    There are three main ways that an explosion on the Sun’s surface can affect Earth.
    • Radio blackout storm:
      It takes light only eight minutes to reach Earth from the Sun, so the effects from this type of event are almost immediate.
      Electromagnetic energy released in flares disrupts Earth’s upper atmosphere –– the region where communication signals travel – and can cause signal blackouts.
      One risk of a radio blackout is that radios are often used for emergency communications, for instance, to direct people amid an earthquake or hurricane.
      Imagine that a solar storm happens to coincide with a natural disaster, when radio communications are essential for keeping people safe.
      This happened during the September 2017 hurricane Irma.
      If operators are notified quickly, Halford says, they can change radio frequencies and avoid an outage.
    • Solar radiation storm:
      At their accelerated speed, these particles carry lots of energy and can permeate the magnetosphere and endanger astronauts and spacecraft in Earth’s orbit.
      To avoid the radiation impact, sensitive systems in satellites may be powered off and astronauts may be instructed to build shelter, or move to better shielded sections within their spacecraft.
      Halford likens it to hiding in a basement during a tornado.
    • Geomagnetic storm:
      The influx of charged particles and electromagnetic fields rippling through Earth’s magnetosphere can induce currents in many important electrical systems on Earth’s surface, including power grids.
      Major blackouts from geomagnetic storms occurred in 1989 and 2003.
      Halford and Pulkkinen said in many countries including the United States, there are safeguards in place to decrease the likelihood of this happening again.