Solar Radio Physics
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last change 2007 March 23, H. Ínel
Solar Radio Physics - Research Branch I de
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Space Weather

What is Space Weather?

The phenomena of the active Sun, like flares and coronal mass ejections (CMEs), have great influence on the Earth and its environment. Flares generate intensive X-rays and accelerate electrons, protons, and heavy ions to high energies, while CMEs also produce highly energetic particles, and can cause geomagnetic storms if they impact on Earth's magnetosphere. These effects of the solar-terrestrial relations are called Space Weather.

The above picture was taken with the coronograph LASCO on board the SOHO spacecraft on  Oktober 28, 2003. It shows a CME that has been released after a strong flare. It is moving towards the observer and thus towards Earth. It has later triggered a geomagnetic storm. The "snow storm" in the picture is caused by energetic protons that hit the camera's CCD chip. The radiation dose would be fatal for astronauts.

The impact of a CME compresses the magnetosphere of Earth and triggers reconnection processes. The rapid change of the magnetic field is called geomagnetic storm. Furthermore, electrons are accelerated inside the magnetosphere. The intrusion if these energetic electrons into the atmosphere is visible as aurora.
Effects of Space Weather
Space Weather has strong consequences for Earth and our technical civilization. The effects can be summarized in the following groups:
  • Enhanced electromagnetic radiation
    This is mainly X-rays from flares. The upper atmosphere of Earth absorbs this radiation and is heated up. Consequently, the atmosphere expands, so that the air density in the range of low satellite orbits, about 400 km altitude, increases. Satellites can deviate from their orbits due to the enhanced aerodynamic drag and eventually crash.
    Since air molecules are ionized by this radiation, the structure of the ionosphere also changes. This has consequences e.g. for short-wave radio communication, but also for navigation systems like GPS, since precise position finding requires exact modeling of the propagation of satellite signals through the ionosphere.
  • Energetic particles
    Energetic protons and electrons that are produced by flares and CMEs can damage the electronics of satellites, and endanger astronauts.
  • Geomagnetic storms
    A geomagnetic storm caused by the impact of a CME on the terrestrial magnetosphere is characterized by a rapid change of the direction and flux density of the magnetic field at Earth's surface. This can induce strong currents in extended electric conductors like high voltage lines or pipelines. The consequence are power outages and damaged transformers, and rapid corrosion of pipelines, respectively.
Space Weather observations
The energetic particles produced by flares and CMEs can be detected directly with satellite instruments, or indirectly through their radio- and X-ray emission. The plasma clouds of CMEs can be observed directly with coronographs, and their properties can be investigated in detail if a CME passes a satellite.

The working group Solar Radio Physics of the AIP operates the Observatory for Solar Radioastronomy (OSRA) at Tremsdorf, and participates in the following missions that enable Space Weather studies:

  • Radio observations
    The radio data of OSRA cover the solar corona, and SWAVES on board STEREO expands the observation range to lower frequencies, that originate from the transition between corona and interplanetary space. The two STEREO spacecraft additionally provide a spatial resolution, so that CMEs can be better traced. In the future, LOFAR will enable imaging observations on frequencies down to 30 MHz, so that CME propagation can be studied in its early phase.
  • X-rays
    The energetic particles produced by a flare emit X-rays if they hit denser layers of the solar atmosphere. With the X-ray telescope RHESSI, X-ray sources can be localized, and their spectrum can be measured simultaneously. This provides new insights into the physics of solar flares.