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Based on decades of single-spacecraft measurements near 1 au as well as data from heliospheric and planetary missions, multi-spacecraft simultaneous measurements in the inner heliosphere on separations of 0.05-0.2 au are required to close existing gaps in our knowledge of solar wind structures, transients, and energetic particles, especially coronal mass ejections (CMEs), stream interaction regions (SIRs), high speed solar wind streams (HSS), and energetic storm particle (ESP) events. The Mission to Investigate Interplanetary Structures and Transients (MIIST) is a concept for a small multi-spacecraft mission to explore the near-Earth heliosphere on these critical scales. It is designed to advance two goals: (a) to determine the spatiotemporal variations and the variability of solar wind structures, transients, and energetic particle fluxes in near-Earth interplanetary (IP) space, and (b) to advance our fundamental knowledge necessary to improve space weather forecasting from in situ data. We present the scientific rationale for this proposed mission, the science requirements, payload, implementation, and concept of mission operation that address a key gap in our knowledge of IP structures and transients within the cost, launch, and schedule limitations of the NASA Heliophysics Small Explorers program.

The accurate knowledge of cosmic ion fluxes is essential for fundamental physics, deep space missions, and exploration activities in the solar system. In the HelMod-4 model the Parker transport equation is solved using a Monte Carlo approach to evaluate the solar modulation effect on local interstellar spectra of Galactic Cosmic Rays (GCRs). This work presents the latest updates to the HelMod-4 model parameters, focusing on the descending phase of solar cycle 24. The updates are motivated by the latest high-precision measurements from the AMS-02 detector which revealed for the first time with high accuracy the features of GCR fluxes' evolution during a period of positive interplanetary magnetic field polarity. Furthermore, we present HelMod-4/CUDA , a GPU-accelerated approach for solving the Parker equation in the heliosphere using a stochastic differential equation method. The code is an evolution of the HelMod-4 code, porting the algorithm to GPU architecture using the CUDA programming language. This approach achieves significant speedup compared to a CPU implementation. The HelMod-4/CUDA code has been validated by comparing its results with the most precise and updated experimental GCR spectra observed during high and low solar activity periods, both in the inner and outer heliosphere, at the Earth location, and outside the ecliptic plane. The comparison shows that HelMod-4 and HelMod-4/CUDA can be equivalently used to provide solar-modulated spectra with a similar degree of accuracy in reproducing observed data. [ABSTRACT FROM AUTHOR]

Abstract The relationship between solar magnetic activity and solar wind parameters, with observed time-delayed mutual coupling, is an outstanding challenge in space physics. In this study, drawing inspiration from recent observations, we propose a reconciliation framework whose fundamentals stand in the Parker model for solar wind expansion. We investigate the effects on fluctuations in solar wind speed when linearly sustained by an oscillating magnetic solar dynamo described via a modified Van der Pol nonlinear oscillator mimicking the magnetic activity at different timescales. Our findings reveal the presence of a “space-climatic feedback” that, in absence of the driving magnetic activity, slows down solar wind velocity fluctuations. The combined action of the slowing down of fluctuations and a periodic driving is the responsible for the time-delay between solar magnetic activity and solar wind dynamics. Furthermore, we also demonstrate how the space-climatic feedback controls the value of the time-delay which depends on the different periodicities of the driving magnetic activity. This holistic approach provides a formal link at the interplay between solar magnetic activity and solar wind dynamics through the interplanetary space which can advance our understanding of long-term effects of solar activity on solar wind variations, and consequently on interactions with planetary environments.

The relationship between solar magnetic activity and solar wind parameters, with observed time-delayed mutual coupling, is an outstanding challenge in space physics. In this study, drawing inspiration from recent observations, we propose a reconciliation framework whose fundamentals stand in the Parker model for solar wind expansion. We investigate the effects on fluctuations in solar wind speed when linearly sustained by an oscillating magnetic solar dynamo described via a modified Van der Pol nonlinear oscillator mimicking the magnetic activity at different timescales. Our findings reveal the presence of a “space-climatic feedback” that, in absence of the driving magnetic activity, slows down solar wind velocity fluctuations. The combined action of the slowing down of fluctuations and a periodic driving is the responsible for the time-delay between solar magnetic activity and solar wind dynamics. Furthermore, we also demonstrate how the space-climatic feedback controls the value of the time-delay which depends on the different periodicities of the driving magnetic activity. This holistic approach provides a formal link at the interplay between solar magnetic activity and solar wind dynamics through the interplanetary space which can advance our understanding of long-term effects of solar activity on solar wind variations, and consequently on interactions with planetary environments. [ABSTRACT FROM AUTHOR]

HelMod model allows one to describe how solar modulation affects the propagation of galactic cosmic rays (GCRs) through the heliosphere by solving the Parker transport equation. HelMod provides modulated spectra for protons and nuclei during high and low solar activity periods, in the inner and outer heliosphere, at Earth location and outside the ecliptic plane, as well as at different distances from Sun in the inner and outer heliosphere. The GCRs mainly constitute the high-energy population of the so-called space radiation environment. Modulated cosmic-ray spectra of protons and nuclei, obtained from HelMod and other solar modulation codes were compared to the AMS–02 spectra ranging from GeV up to TeV energies. Concerning other commonly used solar modulation models, HelMod modulated spectra are available over the entire rigidity range and observation period of AMS–02 mission. A quantitative comparison among models was carried out using Δ Φ , i.e., the relative difference between the experimental and simulated fluences, and η RMS , i.e., the error-weighted root mean square of the relative difference between AMS–02 experimental data and simulated differential intensities. HelMod was found to achieve a good agreement over the full set of experimental data with, typically, Δ Φ within ± 2.5 % and η RMS within 5%. Usually larger or, in a few cases, much larger values for Δ Φ and η RMS were found for the other models. [ABSTRACT FROM AUTHOR]

HelMod model allows one to describe how solar modulation affects the propagation of galactic cosmic rays (GCR) through the heliosphere with an accuracy of the level of actual experimental uncertainties. The GCRs mainly constitute the high energy population of the so-called space radiation environment. The model treats the physical processes involved in solar modulation, like diffusion, particle drift, convection and adiabatic energy losses, and it embeds a description of both the inner and outer heliosphere. To obtain the modulated intensities, the model requires the knowledge of a few time-dependent heliospheric quantities, i.e., sunspot number, tilt angle of the neutral current sheet, solar wind speed and density, and interplanetary magnetic field. Using historical records, we present a template-based procedure that allows one to predict the heliospheric parameters for coming years, and, in turn, the forecasted modulated spectra. The forecasting templates reconstruct the typical time variation along with solar cycles and may be tuned to the current solar cycle. We estimate that the uncertainty of the forecasted cosmic rays intensity is below 5% (± 10 % at 68% C.L.) on average for short time predictions (up to 4 years), and below 15% (± (20 - 25) % at 68% C.L.) for long time predictions (up to 11 years). [ABSTRACT FROM AUTHOR]

The dependence of Interplanetary Coronal Mass Ejections' (ICMEs) transit speed on the corresponding Coronal Mass Ejections' (CMEs) initial speed is investigated. It is shown that the transit speed and transit time depend not only on the CME's initial speed, but also on the longitude of the solar source. The longitudinal dependence of the expected transit speeds and times are obtained from the analysis of 288 CMEs, associated with solar flares, observed from 1995 to 2020. A model, estimating the transit and maximum speeds, as well as the time of arrival of an ICME to Earth, based on the initial CME speed and the longitude of the associated solar flare has been created. It is shown that taking into account the longitude of the solar source in addition to the initial CME speed significantly improves the quality of the model, especially for events in the central part of the solar disk (E10°–W10°). The simplicity of the described model makes it accessible to a wide range of users and provides opportunities for further improvement as the statistics and the number of input parameters increase. [ABSTRACT FROM AUTHOR]

During solar eruptions, many closed magnetic flux ropes are ejected into interplanetary space, which contribute to the heliospheric magnetic field and have important space weather effect because of their coherent magnetic field. Therefore, understanding the evolution of these closed flux ropes in the interplanetary space is important. In this paper, we examined all the magnetic and plasma data measured in 1997 by the Wind spacecraft and identified 621 reconnection exhausts. Of the 621 reconnection events, 31 were observed at the boundaries of magnetic flux ropes and were thought to cause the opening or disconnection magnetic field lines of the adjacent ropes. Of the 31 magnetic reconnection events, 29 were interchange reconnections and the closed field lines of these related flux ropes were opened by them. Only 2 of the 31 magnetic reconnection events disconnected the opened field lines of the original flux ropes. These observations indicate that interchange reconnection and disconnection may be two important mechanisms changing the magnetic topology of the magnetic flux ropes during their propagation during the interplanetary space.

Thanks to space-borne experiments of cosmic-ray (CR) detection, such as the AMS and PAMELA missions in low-Earth orbit, or the Voyager-1 spacecraft in the interstellar space, a large collection of multi-channel and time-resolved CR data has become available. Recently, the AMS experiment has released new precision data, on the proton and helium fluxes in CRs, measured on monthly basis during its first six years of mission. The AMS data reveal a remarkable long-term behavior in the temporal evolution of the proton-to-helium ratio at rigidity R ≡ p / Z ≲ , 3 GV. As we have argued in a recent work, such a behavior may reflect the transport properties of low-rigidity CRs in the inteplanetary space. In particular, it can be caused by mass/charge dependence of the CR diffusion coefficient. In this paper, we present our developments in the numerical modeling of CR transport in the Milky Way and in the heliosphere. Within our model, and with the help of approximated analytical solutions, we describe in details the relations between the properties of CR diffusion and the time-dependent evolution of the proton-to-helium ratio. [ABSTRACT FROM AUTHOR]

H el M od is a Monte Carlo code developed to describe the transport of Galactic Cosmic Rays (GCRs) through the heliosphere from the interstellar space to the Earth. In the current H el M od version 4 the modulation process, based on Parker's equation, is applied to the propagation of GCRs in the inner and outer heliosphere, i.e., including the heliosheath. H el M od was proved to reproduce protons, nuclei and electrons cosmic rays spectra observed during solar cycles 23–24 by several detectors, for instance, PAMELA, BESS and AMS-02. In particular, the unprecedented accuracy of AMS-02 observations allowed one a better tuning of the description regarding the solar modulation mechanisms implemented in H el M od. In addition, H el M od demonstrated to be capable of reproducing the fluxes observed by the Voyager probes in the inner and outer regions of heliosphere up to its border. [ABSTRACT FROM AUTHOR]

• High speed streams (HSS) of long period (16 years) are considered. • Relative geo-effectiveness of the HSS of different speeds and different durations are studied. • Differences in the geo-effectiveness of HSS from different speeds observed. • Differences in recovery characteristics of disturbances due to HSS of different durations found. • Observed differences in geo-effectiveness and recovery characteristics are analyzed. We consider high speed streams (HSS) identified from 16 years (1996–2011) of continuous solar wind plasma and field data. We compare the geomagnetic response of the HSS of different speed and different durations based on statistical distribution, the superposed epoch analysis as well as the regression analysis. We analyse the geomagnetic responses of the HSS of different speed and durations together with the solar wind plasma and field data. The observed differences in the amplitudes, time profiles and recovery characteristics of geomagnetic disturbances during the passage of the HSS of different speed and durations are compared with the differences in the simultaneous solar wind plasma/field behaviour. Implications of these results on the solar wind-magnetosphere coupling are discussed. [ABSTRACT FROM AUTHOR]

The Background Particle Detector (BPD) is an important block of the Polish-Ukrainian X-ray spectrophotometer ChemiX under development for the “Interhelioprobe” interplanetary mission. The BPD primary objective is to detect incoming charged particle fluxes, measure particle energy spectra and safeguard the instrument in case of emergency. The present work describes the BPD laboratory prototype and current results of adjustment and measurements of its important characteristics, in particular the analog signal processing unit and the source of secondary power supply unit. Laboratory benches designed for controlling the parameters of analog module and for characterization of small-sized organic and inorganic scintillation detectors of high energy charged particles are presented. The functional block diagram of the experimental model of digital signal processing line and information data streaming line designed using ProASIC3E М1А3РЕ1500 FPGA are introduced and explained. The results of respective digital modules’ tests performed by using experimental ModelISim Microsemi ME 10.2c program simulator are also presented.

Abstract The heliospheric modulation model H el M od is a two dimensional treatment dealing with the helio-colatitude and radial distance from Sun and is employed to solve the transport-equation for the GCR propagation through the heliosphere down to Earth. This work presents the current version 3 of the H el M od model and reviews how main processes involved in GCR propagation were implemented. The treatment includes the so-called particle drift effects – e.g., those resulting, for instance, from the extension of the neutral current sheet inside the heliosphere and from the curvature and gradient of the IMF –, which affect the transport of particles entering the solar cavity as a function of their charge sign. The H el M od model is capable to provide modulated spectra which well agree within the experimental errors with those measured by AMS-01, BESS, PAMELA and AMS-02 during the solar cycles 23 and 24. Furthermore, the counting rate measured by Ulysses at ± 80 ° of solar latitude and 1–5 AU was also found in agreement with that expected by H el M od code version 3. [ABSTRACT FROM AUTHOR]

A coronal mass ejections (CME) is the huge mass of plasma with embedded magnetic field ejected abruptly from the Sun. These CMEs propagate into interplanetary space with different speed. Some of them hit the Earth's magnetosphere and create many types of disturbances; one of them is the disturbance in the geomagnetic field. Individual geomagnetic disturbances differ not only in their magnitudes, but the nature of disturbance is also different. It is, therefore, desirable to understand these differences not only to understand the physics of geomagnetic disturbances but also to understand the properties of solar/interplanetary structures producing these disturbances of different magnitude and nature. In this work, we use the spacecraft measurements of CMEs with distinct magnetic properties propagating in the interplanetary space and generating disturbances of different levels and nature. We utilize their distinct plasma and field properties to search for the interplanetary parameter(s) playing important role in influencing the geomagnetic response of different coronal mass ejections. [ABSTRACT FROM AUTHOR]