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Effects of Solar Variability on the Earth's environment
- The solar output varies on time scales from milliseconds to
centuries.
- Tree-ring and ice-core data indicate that solar variations were
many times greater in
the past.
- Various climatological factors reflect the 11-year solar cycle,
but the nature of the
connection is unclear.
- The Earth is presently warming, and has been for more than
200 years
- Solar variations directly modify global surface temperature,
ozone, and the structure of the middle atmosphere, but the
mechanisms are not understood.
- The mesosphere/lower thermosphere (MLT; ca. 60-150 km) is very
sensitive to chemical, dynamical, and radiational changes. It is the
least explored region of the
atmosphere.
Effect of Solar Variability on the Origin and Evolution of
Life
- The long-term habitability of the Earth depends on sustaining
a hospitable atmosphere.
- Water is a key to life; solar variability affects the ability of
planets to retain hydrogen, and sustain life.
- The atmospheres and radiation environments of Earth and
Mars differ in a number of ways.
- Other solar-like stars have shown brightness variations many
times greater than the Sun.
Safety of Humans in Space
- Astronauts and their equipment are subject to radiation
hazards that include solar energetic particles and photons, trapped
radiation, and galactic cosmic rays.
- These radiation hazards are highly variable, driven by the Sun
and solar wind.
- With adequate warning, astronauts can take measures to
reduce risk.
- The largest solar particle events appear to result from shocks
associated
with coronal mass ejections (CMEs).
- Geomagnetic storms driven by solar activity can facilitate the
access of solar particles to Space Station latitudes.
- The interplanetary radiation environment is even more harsh
than that in Space Station orbit.
- NASA is dedicated to keeping radiation exposure "as low as
reasonably achievable" (ALARA Principle).
Space Weather Hazards to Modern Technological
Systems
Energetic particles in space are a hazard to spacecraft
systems.
Atmospheric heating during solar events increases satellite
drag and magnifies the risk of collisions with orbiting debris.
Large geomagnetic storms can cause power grids to overload.
Communications and navigation are affected by solar activity
and ionospheric disturbances.
Geomagnetic storms are commonly initiated by CMEs with
southward magnetic fields.
Space weather is a concern of many government and
commercial groups.
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