Using the recently extended 2D improved Particle Acceleration and Transport in the Heliosphere (iPATH) model, we model an example gradual solar energetic particle event as observed at multiple locations. Protons and ions that are energized via the diffusive shock acceleration mechanism are followed at a 2D coronal mass ejection-driven shock where the shock geometry varies across the shock front. The subsequent transport of energetic particles, including cross-field diffusion, is modeled by a Monte Carlo code that is based on a stochastic differential equation method. Time intensity profiles and particle spectra at multiple locations and different radial distances, separated in longitudes, are presented. The results shown here are relevant to the upcoming Parker Solar Probe mission.
On 2017 September 10, a fast coronal mass ejection (CME) erupted from the active region (AR) 12673, leading to a ground level enhancement (GLE) event at Earth. Using the 2D improved Particle Acceleration and Transport in the Heliosphere (iPATH) model, we model the large solar energetic particle (SEP) event of 2017 September 10 observed at Earth, Mars and STEREO-A. Based on observational evidence, we assume that the CME-driven shock experienced a large lateral expansion shortly after the eruption, which is modeled by a double Gaussian velocity profile in this simulation. We apply the in-situ shock arrival times and the observed CME speeds at multiple spacecraft near Earth and Mars as constraints to adjust the input model parameters. The modeled time intensity profiles and fluence for energetic protons are then compared with observations. Reasonable agreements with observations at Mars and STEREO-A are found. The simulated results at Earth differ from observations of GOES-15. However, the simulated results at a heliocentric longitude 20° west to Earth fit reasonably well with the GOES observation. This can be explained if the pre-event solar wind magnetic field at Earth is not described by a nominal Parker field. Our results suggest that a large lateral expansion of the CME-driven shock and a distorted interplanetary magnetic field due to previous events can be important in understanding this GLE event.
Recent detection of superflares on solar-type stars by Kepler mission raised a possibility that they can be associated with energetic coronal mass ejections (CMEs) and energetic particle events (SEPs). These space weather events can impact habitability of exoplanets around these stars. Here we use the improved Particle Acceleration and Transport in the Heliosphere (iPATH) model, to model the time intensity profile and spectrum of SEPs accelerated at CME-driven shocks from stars of different ages traced by their rotation rates. We consider a solar-like (G-type) star with 6 different rotation rates varying from 0.5Ω to 3.0Ω . In all 6 cases, a fast CME is launched with the same speed of ∼ 1500 km/sec and the resulting time intensity profiles at 3 locations and and energy spectra at 5 locations at 1 AU are obtained. The maximum particle energy at the shock front as a function of r is also shown. Our results suggest that within 0.8 AU the maximum particle energy at the shock front increases with the rotation rate of the star. However, event integrated spectra for the five selected locations along the CME path show complicated patterns. This is because the Parker magnetic field for rapidly rotating stars is more tightly winded. Our results can be used in estimating the radiation environments of terrestrial-type exoplanets around solar-type stars.
In this paper, we study the Galactic cosmic-ray (GCR) variations over the solar cycles 23 and 24, with measurements from NASA’s Advanced Composition Explorer/Cosmic Ray Isotope Spectrometer instrument and the ground-based neutron monitors (NMs). The results show that the maximum GCR intensities of heavy nuclei (5 ≤ Z ≤ 28, 50∼500 MeV nuc−1) at 1 au during the solar minimum in 2019–2020 break their previous records, exceeding those recorded in 1997 and 2009 by ∼25% and ∼6%, respectively, and are at the highest levels since the space age. However, the peak NM count rates are lower than those in late 2009. The difference between GCR intensities and NM count rates still remains to be explained. Furthermore, we find that the GCR modulation environment during the solar minimum P 24/25 are significantly different from previous solar minima in several aspects, including remarkably low sunspot numbers, extremely low inclination of the heliospheric current sheet, rare coronal mass ejections, weak interplanetary magnetic field and turbulence. These changes are conducive to reduce the level of solar modulation, providing a plausible explanation for the record-breaking GCR intensities in interplanetary space.
An observation-based galactic cosmic ray (GCR) spectral model for heavy nuclei is developed. Zhao and Qin [J. Geophys. Res. Space Physics, 118, 1837 -1848, 2013 proposed an empirical elemental GCR spectra model for nuclear charge 5 z 28 over the energy range ∼30 to 500 MeV/nuc, which proved successful in predicting yearly averaged GCR heavy nuclei spectra. Based on the latest highly statistically precise measurements from ACE/CRIS, a further elemental GCR model with monthly averaged spectra is presented. The model can reproduce the past and predict the future GCR intensity monthly by correlating model parameters with the continuous sunspot number (SSN) record. The effects of solar activity on GCR modulation are considered separately for odd and even solar cycles. Compared with other comprehensive GCR models, our modeling results are satisfyingly consistent with the GCR spectral measurements from ACE/SIS and IMP-8, and have comparable prediction accuracy as the Badhwar & O'Neill 2014 model. A detailed error analysis is also provided. Finally, the GCR carbon and iron nuclei fluxes for the subsequent two solar cycles (SC 25 and 26) are predicted and they show a potential trend in reduced flux amplitude, which is suspected to be relevant to possible weak solar cycles.
Using quiet-time measurements of element oxygen within the energy range 7.3–237.9 MeV nuc−1 from the ACE spacecraft at 1 au, we compare the energy spectra and intensities of anomalous and Galactic cosmic rays (ACRs and GCRs, respectively) during 1997–2020. Our analysis shows that the transition from the ACR-dominated spectrum to the GCR-dominated spectrum occurs at energies ∼15 to ∼35 MeV nuc−1, and the transition energy E t is found to be well anticorrelated with varying solar activity. This is the first study of ACR–GCR transition energy dependence on the solar cycle variation. At energies below E t , the index of the power-law ACR-dominated spectrum (γ 1) ranges from −2.0 to −0.5, whereas the GCR-dominated spectrum has a power-law index (γ 2) changing from 0.3 to 0.8 at energies ranging from E t to 237.9 MeV nuc−1. Both γ 1 and γ 2 are positively correlated with solar activity. In addition, during the solar cycle 24/25 minimum period, the peak GCR intensity observed by ACE spacecraft is about 8% above its 2009 value, setting a new record since the space age, while the peak ACR intensity is almost similar to that of the previous two solar cycles with the same pattern of solar magnetic polarity, indicating a different modulation mechanism between ACRs and GCRs.
We introduce a statistical model to explain the latitudinal dependence of the occurrence rate and energy flux of the ionospheric escaping ions, taking advantage of advances in the spatial coverage and accuracy of FAST observations. We use a weighted piecewise Gaussian function to fit the dependence, because two probability peaks are located in the dayside polar cusp source region and the nightside auroral oval zone source region. The statistical results show that (1) the Gaussian Mixture Model suitably describes the dayside polar cusp upflows, and the dayside and the nightside auroral oval zone upflows. (2) The magnetic latitudes of the ionospheric upflow source regions expand toward the magnetic equator as Kp increases, from 81° magnetic latitude (MLAT) (cusp upflows) and 63° MLAT (auroral oval upflows) during quiet times to 76° MLAT and 61° MLAT, respectively. (3) The dayside polar cusp region provides only 3–5% O+ upflows among all the source regions, which include the dayside auroral oval zone, dayside polar cusp, nightside auroral oval zone, and even the polar cap. However, observations show that more than 70% of upflows occur in the auroral oval zone and that the occurrence probability increases at the altitudes of 3500–4200 km, which is considered to be the lower altitude boundary of ion beams. This observed result suggests that soft electron precipitation and transverse wave heating are the most efficient ion energization/acceleration mechanisms at the altitudes of FAST orbit, and that the parallel acceleration caused by field‐aligned potential drops becomes effective above that altitude.
Joule heating and radiative cooling usually play key roles in high‐latitude thermospheric temperature changes during geomagnetic storms. In the mesosphere and lower thermosphere (MLT), however, the causes of storm‐time temperature changes at high latitudes are still elusive. Here, we elucidate the nature and mechanisms of MLT temperature variations at high latitudes during the 10 September 2005 storm by diagnostically analyzing the MLT thermodynamics in the Thermosphere Ionosphere Mesosphere Electrodynamics General Circulation Model (TIMEGCM) simulations. In the storm's initial and main phases, the MLT temperature decreases at 0:00 local time (LT)−12:00 LT, but increases in the 12:00 LT–24:00 LT sector at high latitudes. Afterward, the temperature decrease disappears and temperature increase occurs at all local times in the high latitudes. Adiabatic heating/cooling and vertical advection associated with vertical winds are the main drivers of high‐latitude temperature changes in the entire altitude range of the MLT region. However, around the auroral oval and above ∼100 km, the Joule heating rate is comparable to the heating caused by vertical advection and adiabatic heating/cooling associated with vertical winds and becomes one of the major contributors to total heating in the high‐latitude MLT region. The effects of Joule heating can penetrate down to ∼95 km. Horizontal advection also plays a key role in storm‐time MLT temperature changes inside the polar cap and becomes larger than the adiabatic heating/cooling above ∼105 km.
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