Solar flares could have temporarily worsened the hole in the ozone layer, particularly in the southern hemisphere, says Marc Duldig of the Australian Antarctic Division.
Bursts of energetic particles erupting from the sun during some solar flares can boost levels of ozone-destroying chemicals in our atmosphere. Researchers from the Division are using ground-based sensors to detect the high energy solar particles.
Bullets from the Sun: A Review of Relativistic Solar Cosmic Rays
Australian Antarctic Division, Kingston, TAS 7050, Australia
Cosmic rays generally come from beyond the solar system but rarely they can come from the Sun. This review discusses the solar source, propagation to Earth and impact of highly relativistic solar protons.
The Sun can be a source of the lowest energy cosmic ray protons (>1GeV) but only as a result of major X-Class flare events. The acceleration of the protons to between several and a few tens of GeV is hotly debated but it is clear that they only arise in the most energetic solar processes. The propagation of these protons to Earth is determined by the source location at the Sun and the interplanetary magnetic field which directs their spiral flow out into the solar system. The arrival at Earth is characterized by a spatial asymmetry around an arrival direction and a spectrum deduced from ground based neutron monitor observations. 72 events of this kind, known as Ground Level Enhancements (GLEs) are known since reliable records began in the 1940s.
When GLE particles reach Earth they increase the radiation dose in orbit substantially. To a lesser extent the radiation dose at aircraft altitudes is also increased. The rate of production of cosmogenic isotopes increases and the atmospheric ionization is also increased leading to some chemical changes in the atmosphere.
II. MODELLING THE PARTICLE ARRIVAL
Over many years a model has been developed to determine the arrival direction, spectrum and pitch angle anisotropy of GLE particles [1-4].
This model assists in understanding the impacts at Earth as well as the possible source mechanisms at the Sun and the propagation effects between the Sun and Earth.
III. USING THE MODEL RESULTS
The modeled arrival is incorporated into radiation dose level determinations for aircraft and will be able to produce near real time, location specific, aircraft radiation warnings in the near future.
The model can also be used to deduce the atmospheric ionization profile which is then incorporated into atmospheric chemistry and circulation models that can be tested against ground and satellite observations of particular atmospheric chemical species.
Finally such events may leave traces of enhanced cosmogenic isotopes in the polar ice caps. Investigation to date has only found convincing evidence for solar cycle variations of the cosmogenic isotopes. Atmospheric transport plays a dominant smoothing role and it appears that a much larger event than those seen in the historical cosmic ray record would be necessary before a clear event signature from a GLE could be expected from ice cores.
In this review the modeling process is presented. The conclusions regarding possible solar source mechanisms and interplanetary transport are discussed. Following this the use of the model in aircraft radiation warning systems, atmospheric chemistry changes caused by GLEs and possible signatures of GLEs in ice cores is discussed. The future of each of these applications is also covered.
1. Shea, M. A. and Smart, D. F. (1982) Space Sci. Rev., 32, 251
2. Humble, J. E., Duldig, M. L., Smart, D. and Shea, M. (1991) Geophys. Res. Lett., 18, 737
3. Cramp, J. L., Duldig, M. L., Flückiger, E. O., Humble, J. E., Shea, M. A. and Smart, D. F. (1997) J. Geophys. Res., 102, 24237
4. Bombardieri, D. J., Duldig, M. L., Michael, K. J. and Humble, J. E. (2006), Astrophys. J., 644, 565
Marc Duldig, firstname.lastname@example.org