Damaso de Lario

ENERGETIC PARTICLE EVENTS: EFFICIENCY OF INTERPLANETARY SHOCKS AS 50 keV \ E \ 100 MeV PROTON ACCELERATORS

We have studied the injection rate of shock-accelerated protons in long-lasting particle events by tracing back the magnetohydrodynamic conditions at the shock under which protons are accelerated. This tracing back is carried out by -tting the observed Nux and anisotropy pro-les at di†erent energies, considering the magnetic connection between the shock and the observer, and modeling the propagation of the shock and of the particles along the interplanetary magnetic -eld. A focused-di†usion transport equation that includes the e†ects of adiabatic deceleration and solar wind convection has been used to model the evolution of the particle population. The mean free path and the injection rate have been derived by requiring consistency with the observed Nux and anisotropy pro-les for di†erent energies, in the upstream region of the events. We have extended the energy range of previous models down to 50 keV and up to D100 MeV. We have analyzed four proton events, representative of west, central merid- ian, and east scenarios. The spectra of the injection rate of shock-accelerated protons derived for these events show that for energies higher than 2 MeV the shock becomes a less efficient proton accelerator. We have related the derived injection rates to the evolution of the strength of the shock, particularly to the normalized downstream-upstream velocity ratio (VR), the magnetic -eld ratio, and the angle As h Bn . a result, we have derived an empirical relation of the injection rate with respect to the normalized veloc- ity ratio (log Q P VR), but we have not succeeded with the other two parameters. The Q(VR) relation allows us to determine the injection rate of shock-accelerated particles along the shock front and throughout its dynamical expansion, reproducing multispacecraft observations for one of the simulated events. This relation allows us to analyze the inNuence of the corotation e†ect on the modeled particle Nux and anisotropy pro-les. Subject headings: acceleration of particles E interplanetary medium E MHD E shock waves E Sun: particle emission

Modeling the interplanetary propagation of 0.1–20 MeV shock-accelerated protons. II: Energy spectrum and evolution of the injection rate

Abstract Long lasting (i.e., > 2 days) transient proton fluxes associated with interplanetary shocks are generated by particle acceleration at the shock front while it is moving outwards from the Sun and expanding. Therefore, the physical conditions under which the particle acceleration takes place, “the efficiency of the process”, change as the shock does. We have evaluated the evolution of this injection rate on different Energetic Storm Particle events, for protons with energies from 91 keV to 20 MeV, by fitting the fluxes and anisotropies observed in their upstream region. The results are discussed in terms of the large-scale structure of the shock and its MHD strength at the point of the front magnetically connected with the observer.

ENERGY SPECTRUM OF LOW-ENERGY FLUXES OF PARTICLES ACCELERATED BY INTERPLANETARY SHOCKS

Abstract The injection rate of particles at the front of interplanetary shocks has usually been studied locally, around the shock passage by the observers position, but little is known of how the efficiency of the particle-acceleration process evolves as the shock propagates from the Sun to the Earth. In many events accelerated particles are observed long in advance of the arrival of the shock (from 5 hours to 2 days), and they show large anisotropies. We have used a compound shock-particle model to derive the injection rate of particles at the shock front and their energy spectrum, as a function of time, by fitting the observed particle fluxes and anisotropies between 100 and 1000 keV. We have studied three individual low-energy particle events taken as representatives of West, Central Meridian and East events.

Modeling the interplanetary propagation of 0.1–20 MeV shock-accelerated protons. I: Effects of the adiabatic deceleration and solar wind convection

The foc.used transport equation for particle propagation (Roelof, 1969) allows us to model flux and anisotropy profiles when the anisotropy is high for long periods. This equation has been applied to model Energetic Storm Particle events of these characteristics, assuming a source of accelerated protons at the front of the interplanetary shocks (Heras et al., 1992 and 1995). Nevertheless, its application is less accurate for energies below 0.5 MeV since the effects of adiabatic deceleration and solar wind convection are not negligible. We present a numerical code that includes both effects in the transport equation, and we apply different tests to validate it. We shortly discuss the influence of these effects in the flux and anisotropy profiles of Energetic Storm Particle Events. Q 1997 COSPAR. Published by Elsevier Science Ltd.

Proton Flux Prediction: First Version of an Operational Code

Solar energetic particle (SEP) events belong to the major causes of prejudicial effects to space systems and pose a serious hazard to astronauts. The characterization and modelling of flux profiles of SEP events in several locations of interplanetary space are among the key parameters for space weather effects (Feynmann et al., 2000, JGR, 105, 10543). We have developed a preliminary version of an operational code which provides proton flux profiles at 0.5 MeV and 2 MeV as well as the cumulative fluence for gradual SEP events, for spacecrafts located at 1 AU and 0.4 AU. This code is based on the particle transport model by Lario et al. (1998, ApJ, 509, 415) and the 2 1/2-D MHD shock propagation model of Wu et al. (1983, Sol. Phys., 84, 395). SEP events profiles strongly depend on the characteristics of the interplanetary shock and on the position of the observer in space (Cane et al., 1988, JGR, 93, 9555).

Gradual Solar Energetic Particle Events in Space Weather

Gradual Solar Energetic Particle (SEP) events are a well-known phenomenon observed from near the Sun up to several AU. They are associated with interplanetary shocks driven by Coronal Mass Ejections (CMEs). Their main features greatly vary, depending on the relative position of the observer with respect to the Sun, the strength of the shock, and the characteristics of the Interplanetary Magnetic Field (IMF). Predicting fluxes for these events requires information and modeling on the initiation and propagation of CME-driven shocks, as well as about the production of shock-accelerated particles and how these particles propagate along the IMF lines. We shortly review the characteristics of these gradual events, the present efforts made for modeling them up to 1 AU, and the possible application of the models for flux prediction in space weather.