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Solar energetic particles: is there time to hide?
1NASA/Goddard Space Flight Center, Greenbelt, MD 20771, USA. reames@lheavx.gsfc.nasa.gov
Radiation Measurements
|September 7, 2001
Summary
Large solar energetic particle (SEP) events pose radiation hazards. A 12-hour warning window exists before hazardous particle arrival, allowing astronauts to seek shelter.
Area of Science:
- Space physics
- Astrophysics
- Radiation hazard analysis
Background:
- Solar energetic particle (SEP) events are driven by coronal mass ejections (CMEs).
- A self-regulating wave formation mechanism limits early SEP intensities.
- Hazardous particle levels are associated with shock wave arrival.
Purpose of the Study:
- To understand the temporal dynamics of SEP events.
- To identify potential warning times for astronaut safety.
- To inform strategies for observing rare, high-intensity SEP events.
Main Methods:
- Analysis of particle acceleration at CME-driven shock waves.
- Extrapolation of knowledge from smaller events to predict behavior in larger events.
- Emphasis on in-situ measurements from spacecraft outside Earth's magnetosphere.
Main Results:
- A warning window of approximately 12 hours exists between solar event onset and hazardous particle arrival.
- SEP intensity time histories are influenced by solar event longitude, CME width, and shock speed.
- Hazardous SEP events are rare, necessitating study of smaller events for extrapolation.
Conclusions:
- Astronauts can be warned to take shelter after a solar event begins but before hazardous particles arrive.
- Observing rare, large SEP events requires strategically positioned spacecraft outside the magnetosphere.
- Further research is needed to refine predictions based on limited data from large events.