SH51A-0261 0800h
Forecasting Interplanetary Shocks Using Energetic Particle Data
A key challenge in NASA's new exploration initiative will be developing the capability to reliably predict the arrival of energetic particles from solar storms. We present a method for detecting the approach of CME-generated shocks, which are often accompanied by orders of magnitude increases in the fluxes of energetic particles and electrons at energies considered harmful to astronauts and electronics. We demonstrate that the upstream particle signature of an approaching shock can be observed up to several days ahead of the shock arrival, and we present algorithms for detecting this signature. Our approach is currently the basis of an operational system using Electron Proton Alpha Monitor (EPAM) data from the Advanced Compositoin Explorer (ACE) spacecraft to give real-time warnings and estimated countdowns of particle events approaching 1 AU - see the URL below. We will present energetic particle data from other spacecraft (Wind, for example) which show similar signatures, indicating that our shock forecasting algorithm could be generalized for use with other particle data covering the energy range of about 50 to 2000 keV. Our approach could provide a crucial space weather monitoring component to Mars-bound spacecraft, since it offers continuous monitoring of approaching shocks, with warnings of up to several days prior to a significant event.
http://sd-www.jhuapl.edu/ACE/EPAM/RUMS/
SH51A-0262 0800h
In situ space weather forecasting with energetic particle spectrometers: RAD and PreSTIM
Forecasting of space weather conditions for the Space Exploration initiative will not rely on L1 monitoring alone. Spacecraft on the way to Mars will be required to depart from the Sun-Earth line. We show that in situ forecasting at the spacecraft is an option for Mars-bound space travel. Our approach of instrument requirement specification, hardware development, and data analysis tackles two possible solutions for this problem: PreSTIM, the Pre-Shock Suprathermal Ion Monitor, provides the observations necessary for interplanetary shock forecasting with low-energy foreshock ions. RAD, the Radiation Assessment Detector, is a light-weight energetic particle instrument that can be used for early radiation warnings by analyzing the onsets of solar energetic particle events. RAD continuously monitors the intensity of the radiation environment, in particular the most hazardous energetic particle species.
SH51A-0263 0800h
Radiation Mitigation at the Moon by the Terrestrial Magnetosphere
During its orbit, the Moon crosses into the terrestrial magnetosphere. The magnetic field from the later can potentially provide radiation shielding from solar energetic particle events, which can be a significant hazard during extra-vehicle activities or during human exploration of the lunar surface. The level of shielding though studied through multi-fluid simulations of the terrestrial and lunar magnetospheres. It is shown that the level of shielding is dependent on magnetospheric conditions and to a lesser extent on interactions of the lunar magnetic anomalies with the magnetic fields of the terrestrial magnetosphere. The differences in shielding capabilities are demonstrated by examining the magnetosphere and its interaction with the Moon during periods of northward and southward interplanetary magnetic field.
SH51A-0264 0800h
A New Evaluation of the Galactic Cosmic Ray Radiation Dose In Interplanetary Space
The radiation dose from galactic cosmic rays (GCRs) during a mission to Mars is expected to be comparable to the allowable limit for astronauts in low Earth orbit. Most of this dose would be due to galactic cosmic rays with energies $<$1 GeV/nucleon, with major contributions from heavy nuclei in spite of their low abundance relative to H and He. Measurements with the CRIS experiment on ACE have provided the first opportunity to make precise measurements of the energy spectra of cosmic rays from Be to Ni during both solar minimum and solar maximum conditions. We have fit these data, along with HEAO-3 data at higher energy, and balloon-borne and satellite measurements of H and He, with a physics-based model of GCR transport and solar modulation. The results of this model were used to evaluate the radiation dose and dose-equivalent of GCRs under both solar minimum and maximum conditions. We find that the solar-minimum radiation dose is somewhat lower than found in previous studies. We also find a smaller difference between solar minimum and solar maximum, due in part to the fact that heavy cosmic rays vary less over the solar cycle than do H and He. Measurements of Be-10 in polar ice cores and other data show that the near-Earth cosmic-ray intensity was significantly greater within the last century. In view of the fact that these conditions could return, we have evaluated the maximum near-Earth cosmic-ray spectra consistent with our model and the Be-10 data. We estimate the radiation dose under these conditions to be more than twice as great as during recent solar minima. The implications of these results for human missions to Mars will be discussed.
SH51A-0265 0800h
NOZOMI/ACE Multispacecraft Observations of Solar Energetic Particles
We report multispacecraft measurements of solar energetic particle (SEP) events using NOZOMI and ACE. During July 1998 to April 2002 while NOZOMI was cruising toward Mars, both NOZOMI and ACE observed many SEP events associated with coronal mass ejections (CMEs) and interplanetary shocks originating from different longitudes. The difference in NOZOMI and ACE longitudes varied from 0 to 180 degrees during this period. These observations can reveal the longitudinal extent of CME-driven shocks and the accelerated particle populations. We use proton and electron data extending from $\sim$40keV to $\sim$1MeV measured with the EIS instruments on NOZOMI and the ULEIS and EPAM instruments on ACE. Comparisons of the time histories from NOZOMI and ACE as a function of the separation longitude, radius, and flare-locations will be presented.
SH51A-0266 0800h
Three-Dimensional Numerical Studies of the Magnetic Topology and Pre-Eruption Conditions for the Halloween Storms from 2003: Computational Challenges Posed by Extreme Space Weather Events
The coronal mass ejections (CMEs), and the solar energetic particle (SEP) events associated with them, are of particular importance for Space Weather since they endanger human life in outer space and pose major hazards for spacecraft in the inner Solar System. The Halloween Storms from 2003 were the most powerful solar events ever recorded. These storms broke all-time records for extreme amount of: peak X-ray intensity ($>$X28); CME speed ($\sim$2700km/s); concentration of energetic CMEs in interplanetary space; concentration of interplanetary radio bursts; SEP flux (33,000pfu); interplanetary CME magnetic field ($\sim$60nT); geo-impact magnetic field (-465nT); and solar wind speed ($\sim$2000km/s). About one third of the total particle radiation emitted by the Sun in the last decade in the deadly 30-50MeV energy range came from these storms, even though the solar activity cycle was well past its maximum. We present preliminary results of a recent numerical investigation of the global magnetic topology and pre-eruption conditions of the active regions that spawned the extreme CME events from last year. We employed the BATS-R-US code to perform global, fully compressional, 3-D numerical MHD computations. High quality magnetic data from MDI are used to drive the MHD simulations. We discuss the obtained numerical results and the computational challenges faced in modeling CME events of that high magnitude. This study is a prerequisite of a more detailed investigation of the series of events associated with the Halloween Storms.
SH51A-0267 0800h
Solar Energetic Particles Acceleration and Transport Model Coupled With a Realistic CME Model.
Solar Energetic Particles (SEPs) accelerated during and after a Coronal Mass Ejection (CME) produce radiation hazards on board manned and unmanned spacecraft that are not shielded by the Earth's magnetic field. To investigate the particle acceleration by the shock wave which arises from the CME and a subsequent SEPs transport in the realistic magnetic field, a realistic magnetic field near the Sun and in the inner heliosphere should be taken into account. To achieve this, we coupled the available MHD model for CME, which is based on the BATSRUS code, to the kinetic code for SEP using Field-Line-Advection Model for a Particle Acceleration (FLAMPA). The FLAMPA assumes coronal and interplanenetary magnetic fields to be ideally frozen into a moving plasma and neglects the cross-field particle diffusion, however it involves the first order Fermi acceleration, particle adiabatic focusing and SEP scattering by a hydromagnetic turbulence. In this presentation we compare the SEP flux at 1 AU obtained with two alternative models for CME dynamics (using the Gibson-Low model or applying a slow sheared plasma motion to create a flux rope) and with two SEP models (averaged or not averaged by the particle pitch-angle). Comparing with the data observed at 1 AU after the 1998 May,2 event, we validate the models. The SEP acceleration in repetitive CME events will be provided too.
SH51A-0268 0800h
The Relative Abundances of H, He, and Heavy Ions in Large Solar Energetic Particle Events
Studies have shown that the heavy element abundances in large solar energetic particle (SEP) events can vary tremendously (e.g., by factors of $\sim$100 for Fe/O) at energies above $\sim$10 MeV/nucleon. The most iron-rich gradual events often have a heavy element composition more typical of impulsive events,supporting the suggestion that flare seed material plays a significant role in these events. However, most of these studies do not include measurements of protons and alpha particles (H and He),which dominate the particle intensities. Using data from ACE, SAMPEX, Wind, and GOES, we have constructed composite spectra of protons, alpha particles, and heavy ions spanning $\sim$0.1 to $\sim$100 MeV/nucleon in energy in many of the large, gradual SEP events of solar cycle 23. We examine the relative abundances and spectral shapes of H and He compared with heavy ions in an effort to better understand the origin of the event-to-event variability. In particular, we test whether the H/Fe ratio in the most iron-rich large events more nearly resembles that in average gradual events or instead approximates the average impulsive event value, which is a factor of $\sim$10 lower. In addition, the variable proton-to-heavy ratio has important space weather implications, which are briefly discussed. This work was supported by NASA under grants NNG04GB55G, NAG5-12929, and NAG5-8877.
SH51A-0269 0800h
Energetic $^{3}$He in the Inner Heliosphere: 1997 to 2004
ACE observations of helium isotopes in solar energetic particles have shown that $^{3}$He was present in the interplanetary medium at 1 AU more than half of the time during the early portion of solar cycle 23 (specifically from August 1997 to April 2002). The observed $^{3}$He particles, with energies in the range 0.2 to 16 MeV/nuc, are believed to be accelerated in numerous small impulsive solar flare events. The suprathermal ions resulting from such events have been shown to provide a seed population which can be further accelerated by shocks in the solar corona or interplanetary medium. We have extended our previous investigation to include the time interval from early 2002 to late 2004, a period during which solar activity declined significantly. In addition to presenting the time dependence of $^{3}$He in the interplanetary medium over a 7-year period, we examine correlations between this energetic particle population and various measures of solar flare activity in order to assess, on a statistical basis, the characteristics of the sources of these particles and to determine the extent to which flare activity can provide a useful indication of the presence of flare suprathermals in the interplanetary medium.
SH51A-0270 0800h
Correlation of Far Ultraviolet Lunar Albedo with Solar Activity
We present a correlative analysis between the variability of the lunar albedo in the far ultraviolet wavelength range (130-190 nm) and various solar activity indices for a two-week period. The albedo is measured using the Ultraviolet Imager on board the Polar spacecraft. We also report lunar albedo measurements in four separate wavelength ranges, corresponding to four filters on the Polar Ultraviolet Imager. To our knowledge this is the first reported long term measurements of the lunar albedo in this wavelength range.