Prediction of High-Energy Proton Hazards from CME Shocks: Contributions from Ultraviolet Coronagraph Spectroscopy

Discussion:

• The greatest hazard to astronauts and their equipment in interplanetary space is believed to be relativistic protons produced by Coronal Mass Ejections (CMEs) and Solar Flares.

• This radiation hazard is produced by the CME shock as it propagates through interplanetary space and at the sites of solar flares during flare events.

• Ultraviolet Spectroscopy by SOHO has revealed a means for: 1) detecting and characterizing the CME shocks, which are believed to produce most of the relativistic protons, and 2) characterizing the conditions in the pre-CME corona (see Raymond et al. [2000], and Raymond [2002]).

• Such remote sensing combined with models of relativistic proton acceleration and transport can be used to predict the levels and production sites of the radiation.

• Solar Flare/CME events observed in October and November 2003 produced highly elevated levels of relativistic protons for one to two days after each event. Most of these protons are believed to have been accelerated by the CME shock as it traveled at speeds up to 2000 km/second into interplanetary space, taking one to two days to reach the vicinity of the Earth.

• The CME characteristics near the Sun in the initial phases of the event are the inputs needed for theoretical models that predict the following one to two days of proton production including its location and geometrical extent.

• High-energy particles also are emitted on the Sun at the sites of strong solar flares. RHESSI observations have shown that protons and electrons are accelerated at different locations within flares ( Lin et al. [2003]).

Current Status:

• Initial testing of predictions can utilize GOES satellite data and existing data from the SOHO Ultraviolet Coronagraph Spectrometer (UVCS) operated by the Harvard-Smithsonian Center for Astrophysics (see Kohl et al. [1995]) in concert with ground-based radio observations that help to identify the electron density at the shock front ( Mancuso & Raymond [2004]).

• Feasibility of next-generation instrumentation with greater capability for such measurements has been established by Harvard-Smithsonian during Medium Class Explorer Phase A studies.

• Recent theoretical efforts have been devoted to modeling particle (mainly proton) acceleration at CME-driven shocks and the subsequent particle transport in the interplanetary medium (see, e.g., Li, Zank, and Rice [2003]).

• The spectroscopic measurements can determine the speed and Mach number of the shock, the temperature and amount of associated plasma heating, the handedness (chirality) of the associated magnetic field, and inferred information about the local Alfven speed and associated magnetic field strength. In addition to the production of relativistic proton radiation, the same instrumentation can characterize fast solar wind streams that are a known source of the energetic electron hazard. This instrumentation determines the speed, densities, energetics and particle abundances at the solar wind source regions.

Methodology:

• The specific means by which the remote-sensing data will be used as inputs and boundary conditions for the energetic particle codes are described in more detail on the following page.

Additional information about UVCS/SOHO and theoretical models of relativistic proton production can be found at:

http://cfa-www.harvard.edu/uvcs/
http://www.igpp.ucr.edu/Particle_transport.htm