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Register a new userCME Magnetic Structure and IMF Preconditioning Affecting SEP Transport
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Coronal mass ejections (CMEs) and solar energetic particles (SEPs) are two phenomena that can cause severe space weather effects throughout the heliosphere. The evolution of CMEs, especially in terms of their magnetic structure, and the configuration of the interplanetary magnetic field (IMF) that influences the transport of SEPs are currently areas of active research. These two aspects are not necessarily independent of each other, especially during solar maximum when multiple eruptive events can occur close in time. Accordingly, we present the analysis of a CME that erupted on 2012 May 11 (SOL2012-05-11) and an SEP event following an eruption that took place on 2012 May 17 (SOL2012-05-17). After observing the May 11 CME using remote-sensing data from three viewpoints, we evaluate its propagation through interplanetary space using several models. Then, we analyse in-situ measurements from five predicted impact locations (Venus, Earth, the Spitzer Space Telescope, the Mars Science Laboratory en route to Mars, and Mars) in order to search for CME signatures. We find that all in-situ locations detect signatures of an SEP event, which we trace back to the May 17 eruption. These findings suggest that the May 11 CME provided a direct magnetic connectivity for the efficient transport of SEPs. We discuss the space weather implications of CME evolution, regarding in particular its magnetic structure, and CME-driven IMF preconditioning that facilitates SEP transport. Finally, this work remarks the importance of using data from multiple spacecraft, even those that do not include space weather research as their primary objective.
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We address the effect of particle scattering on the energy spectra of solar energetic electron events using i) an observational and ii) a modeling approach. i) We statistically study observations of the STEREO spacecraft making use of directional electron measurements made with the SEPT instrument in the range of 45 -- 425 keV. We compare the energy spectra of the anti-sunward propagating beam with that one of the backward scattered population and find that, on average, the backward scattered population shows a harder spectrum with the effect being stronger at higher energies. ii) We use a numerical SEP transport model to simulate the effect of particle scattering (both in terms of pitch-angle and perpendicular to the mean field) on the spectrum. We find that pitch-angle scattering can lead to spectral changes at higher energies (E $>100$ keV) and further away from the Sun (r $> 1$ au) which are also often observed. At lower energies, and closer to the Sun the effect of pitch-angle scattering is much reduced so that the simulated energy spectra still resemble the injected power-law functions. When examining pitch-angle dependent spectra, we find, in agreement with the observational results, that the spectra of the backward propagating electrons are harder than that of the forward (from the Sun) propagating population. {We conclude that {it Solar Orbiter} and {it Parker Solar Probe} will be able to observe the unmodulated omni-directional SEP electron spectrum close to the Sun at higher energies, giving a direct indication of the accelerated spectrum. }
We analyze the Suns shadow observed with the Tibet-III air shower array and find that the shadows center deviates northward (southward) from the optical solar disc center in the Away (Toward) IMF sector. By comparing with numerical simulations based on the solar magnetic field model, we find that the average IMF strength in the Away (Toward) sector is $1.54 pm 0.21_{rm stat} pm 0.20_{rm syst}$ ($1.62 pm 0.15_{rm stat} pm 0.22_{rm syst}$) times larger than the model prediction. These demonstrate that the observed Suns shadow is a useful tool for the quantitative evaluation of the average solar magnetic field.
We calculate the interplanetary magnetic field path lengths traveled by electrons in solar electron events detected by the WIND 3DP instrument from $1994$ to $2016$. The velocity dispersion analysis method is applied for electrons at energies of $sim$ $27$ keV to $310$ keV. Previous velocity dispersion analyses employ the onset times, which are often affected by instrumental effects and the pre-existing background flux, leading to large uncertainties. We propose a new method here. Instead of using the peak or onset time, we apply the velocity dispersion analysis to the times that correspond to the rising phase of the fluxes that are a fraction, $eta$, of the peak flux. We perform statistical analysis on selected events whose calculated path lengths have uncertainties smaller than $0.1$ AU. The mean and standard deviation, ($mu$, $sigma$), of the calculated path lengths corresponding to $eta=$ $3/4$, $1/2$, and $1/3$ of the peak flux is ($1.17$ AU, $0.17$ AU), ($1.11$ AU, $0.14$ AU), and ($1.06$ AU, $0.15$ AU). The distribution of the calculated path lengths is also well fitted by a Gaussian distribution for the $eta=3/4$ and $1/3$ cases. These results suggest that in these electron events the interplanetary magnetic field topology is close to the nominal Parker spiral with little field line meandering. Our results have important implications for particles perpendicular diffusion.
A new, efficient, and highly accurate method for tracing magnetic separators in global magnetospheric simulations with arbitrary clock angle is presented. The technique is to begin at a magnetic null and iteratively march along the separator by finding where four magnetic topologies meet on a spherical surface. The technique is verified using exact solutions for separators resulting from an analytic magnetic field model that superposes dipolar and uniform magnetic fields. Global resistive magnetohydrodynamic simulations are performed using the three-dimensional BATS-R-US code with a uniform resistivity, in eight distinct simulations with interplanetary magnetic field (IMF) clock angles ranging from 0 (parallel) to 180 degrees (anti-parallel). Magnetic nulls and separators are found in the simulations, and it is shown that separators traced here are accurate for any clock angle, unlike the last closed field line on the Sun-Earth line that fails for southward IMF. Trends in magnetic null locations and the structure of magnetic separators as a function of clock angle are presented and compared with those from the analytic field model. There are many qualitative similarities between the two models, but quantitative differences are also noted. Dependence on solar wind density is briefly investigated.
Protoplanetary disks composed of dust and gas are ubiquitous around young stars and are commonly recognized as nurseries of planetary systems. Their lifetime, appearance, and structure are determined by an interplay between stellar radiation, gravity, thermal pressure, magnetic field, gas viscosity, turbulence, and rotation. Molecules and dust serve as major heating and cooling agents in disks. Dust grains dominate the disk opacities, reprocess most of the stellar radiation, and shield molecules from ionizing UV/X-ray photons. Disks also dynamically evolve by building up planetary systems which drastically change their gas and dust density structures. Over the past decade significant progress has been achieved in our understanding of disk chemical composition thanks to the upgrade or advent of new millimeter/Infrared facilities (SMA, PdBI, CARMA, Herschel, e-VLA, ALMA). Some major breakthroughs in our comprehension of the disk physics and chemistry have been done since PPV. This review will present and discuss the impact of such improvements on our understanding of the disk physical structure and chemical composition.
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