Space Radiation Hazards and the Vision for Space Exploration Report of a Workshop (2006) / Chapter Skim
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2 Specifying and Predicting the Space Radiation Environment
2 Specifying and Predicting the Space Radiation Environment
Pages 24-37
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From page 24... ...
Solar activity is most often associated with solar active regions, which generally last for several solar rotations and that are localized regions on the solar surface where sunspots, flares, and other magnetically related phenomena occur. The Sun's magnetic field and its associated activity exhibit a 22 year cycle -- twice the familiar 11 year sunspot cycle, because the dominant polar magnetic fields have opposite polarities for consecutive 11 year sunspot cycles.
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From page 25... ...
This reflects a general, heliospheric depression of the intensity of galactic cosmic rays, which are entering the solar system from the outside. The heliosphere, the bubble with the Sun at its center, is carved out of the interstellar gas by the solar wind, which blows radially outward, carrying with it the solar magnetic field, producing a classical Archimedean spiral magnetic field.
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From page 26... ...
The energy spectrum of the solar energetic particles is softer than that of galactic cosmic rays, and the events typically last for periods of hours to days. The intensities during the events can be quite large, although at energies above several hundred MeV, the time-integrated galactic cosmic ray flux is larger than that of solar cosmic rays.
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From page 27... ...
The composition of these events indicates that the process of acceleration may involve the existence of "seed" particles (low-energy superthermal particles) that were accelerated earlier in prompt solar energetic particle events.
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From page 28... ...
Such a cloud of gas drives a large-scale "bow" shock wave, which precedes the spheroidal cloud through interplanetary space and that accelerates the energetic particles in gradual solar energetic particle events. When this shock wave and cloud strike Earth's magnetosphere, there are usually significant geomagnetic and ionospheric effects.
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From page 29... ...
Solar energetic particles are likely produced from the flare and current sheet and from the shock front near the leading edge in fast CMEs. The disk and coronal images (in red)
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From page 30... ...
2-4 Flares and Active Regions Flares occur during the rapid conversion of energy from the solar magnetic field to the kinetic energy of particles in localized regions at the base of the solar corona.The accelerated particles and their interactions with the surrounding plasmas and fields can also produce electromagnetic emission in a broad range of frequencies, from microwaves to gamma rays. Flares are one of the primary sites for the acceleration of electrons (up to 10 MeV)
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From page 31... ...
Determining which of these flares will produce large SEP fluxes would be of extreme importance for the prediction of the radiation environment in the heliosphere. PROSPECTS FOR LONg- AND SHORT-TERM FORECAST MODELS On the basis of current knowledge and present progress, participants at the workshop expressed optimism that solar and space physics researchers will be able to specify the space radiation environment accurately and will be able to forecast both long-term trends and short-term events.
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From page 32... ...
Other tools for predicting active region eruptions use photospheric magnetograms to determine the degree of nonpotentiality (overall twist and shear) and the amount of free energy in coronal magnetic fields (e.g., Falconer et al., 2003; Beveridge and Longcope, 2006)
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From page 33... ...
. Helioseismology is also being used to track active regions while they are on the back side of the Sun (Braun and Lindsey, 2001)
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From page 34... ...
These numerical models have not yet reached the stage of being able to routinely and reliably forecast solar wind conditions at Earth and other locations, and a major challenge for the models is to specify the north-south component of the interplanetary magnetic field that controls energy transfer at, for example, Earth's magnetopause. Models for Coronal Mass Ejections and Flares and for Solar Energetic Particles CMEs and flares are the primary sources of solar energetic particles, so understanding their onset and evolution are active areas of research.
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From page 35... ...
An NSF-funded project to support an affiliation of researchers within the solar, interplanetary, and heliospheric communities whose goal is to enrich and strengthen both physical understanding and predictive capabilities for connecting events on the Sun with solar wind and disturbances in the inner heliosphere (http://www.shinegroup.org/)
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From page 36... ...
1999. A model for solar coronal mass ejections.
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From page 37... ...
2003. Energetic particle acceleration and transport at coronal mass ejection-driven shocks.
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