Statistical study of low‐energy heliosphere particle fluxes from 1.4 to 5 AU over a solar cycle

Abstract

Throughout the entire Ulysses mission, the Heliosphere Instrument for Spectra, Composition, and Anisotropy at Low Energies (HI‐SCALE) has collected measurements of low‐energy interplanetary ions and electrons. Time series of electron, proton, and ion fluxes have been obtained since 1990. We present statistical studies of high‐resolution ion and electron energy spectra (∼50 keV to ∼5 MeV) as measured by the HI‐SCALE instrument on the Ulysses spacecraft over a time interval longer than a solar cycle (1990 to 2004). Ulysses is the only spacecraft that continually measured the inner (∼1.4 to ∼5 AU) heliosphere particle population during these years. The data thus provide measures of the lower‐energy population of particles that a spacecraft traveling outward from Earth would have encountered and that also could have impacted the atmosphere and surface of Mars and of its satellites during this interval. Comparisons of Ulysses particle fluxes with those from the Electron, Proton, and Alpha Monitor (EPAM) instrument on the Advanced Composition Explorer (ACE) spacecraft (the HI‐SCALE backup instrument) have shown that azimuthal and heliolatitude dependencies of particle fluxes in the inner heliosphere following solar events are not as extreme as might be expected. Thus the Ulysses measurements, while taken over a range of heliolatitudes, can provide important statistical information that can be used to estimate the low‐energy radiation dosages and potential sputtering fluxes to planetary surfaces and to heliosphere spacecraft surfaces and solar arrays over a solar cycle.

Modeling proton intensity gradients and radiation dose equivalents in the inner heliosphere using EMMREM: May 2003 solar events

“…Substantial effort has already been made to study the propagation and radial gradients of SEP intensities and fluences in the heliosphere [e.g., Hamilton et al , 1990; Shea , 1988; Ng and Reames , 1994; Boufaida and Armstrong , 1997; Kallenrode , 1993; Smart and Shea , 2003; Ruzmaikin et al , 2005; Foullon et al , 2005; Lario et al , 2006, 2007; Denker et al , 2007]. However, the scarcity of simultaneous SEP measurements by multiple spacecraft at different locations in the heliosphere, severely limits our ability to compare observations and model results.…”

Thermal and Suprathermal Particles: A Prime Science Targets for an Interstellar Probe Mission

“…This ion population shows energy distributions that can be approximated by power laws j ∝ E γ (with the differential intensity j and the kinetic energy E). The suprathermal exponent has been observed inward of about 10 AU to be γ ≈ −1.5 (see Gloeckler & Geiss 1998;Denker et al 2007;Hill & Hamilton 2010;Mason & Gloeckler 2012) and of a similar energies of ~100 keV in the heliosheath (Decker et al 2005;Krimigis et al 2013;Fisk & Gloeckler 2014). The acceleration mechanism is still debated and there is a variety of theories ranging from adiabatic compressions (Fisk & Gleockler 2012) to contracting islands (Drake et al, 2013), damping of MHD waves (Le Roux 1998,) and reflection and acceleration at the cross-shock potential (Zank et al, 1996).…”

Survival of Deinococcus radiodurans Against Laboratory-Simulated Solar Wind Charged Particles

“…These may be produced during some solar flares where solar protons that have energies on the order of 100 keV, corresponding to a penetration depth of about 1 lm, are produced. Current estimates about the flux of these ions vary from 2.8 · 10 10 protons$cm -2 $year -1 , based on the Ulysses spacecraft measurements averaged for more than 1 solar cycle (1990)(1991)(1992)(1993)(1994)(1995)(1996)(1997)(1998)(1999)(2000)(2001)(2002)(2003)(2004) (Denker et al, 2007), to 4 · 10 10 protons$cm -2 $year -1 , as calculated by the Space Environment Information System from the European Space Agency (ESA, 2011) with a cumulative solar proton event model (Xapsos et al, 2000) that averages over 30 years, from the solar maximum of 1981 to 2011. Biological effects of low-energy charged particle irradiation on plants and microbes, especially with energies in the range of several to hundreds of kiloelectronvolts, have been the subject of several studies (Yang et al, 1991;Yu, 1998).…”

“…In the case of more energetic protons produced during solar flares with an average energy on the order of 100 keV, current estimates vary from 2.8 · 10 10 protons$cm -2 $year -1 (Denker et al, 2007) to 4 · 10 10 protons$cm -2 $year -1 (Xapsos et al, 2000;ESA, 2011) with a penetration path of the order of a few microns. The maximum fluence tested here with 200 keV protons (2.75 · 10 13 protons $ cm -2 ) corresponds to that delivered over more than 100 years at Earth orbit (1 AU).…”