Context. Recognizing the transport of Energetic Neutral Atoms (ENA), from their place of birth to Earth orbit, has become an important issue in light of the forthcoming launch of the NASA SMEX ...mission IBEX, which is devoted to imaging of the heliospheric interface by in-situ detection of ENAs. Aims. We investigate the modifications of both energy of survival probability of the hydrogen ENA (H ENA) detectable by IBEX (0.01–6 keV), between the termination shock and Earth orbit. We take into account the influence of the variable and anisotropic solar wind and of solar EUV radiation. Methods. Energy changes of the atoms are calculated by numerical simulations of the orbits of H ENA between ~100 AU from the Sun and Earth orbit, taking into account solar gravity and Lyman-α radiation pressure, which is variable in time and depends on the radial velocity of the atom. To calculate the survival probabilities of the atoms against ionization, a detailed observation-based 3D and time-dependent model of H ENA ionization is constructed, and with the use of this model the probabilities of survival of the atoms are calculated by numerical integration along the previously-calculated orbits. Results. Due to radiation pressure, H ENA reach the Earth orbit practically without energy and direction change, apart from the atoms of energy lower than 0.1 keV, during high solar activity. The survival probability of H ENA increases from just ∼$2\%$ for the slowest detectable ENA at solar minimum to ~$ 80$% for the fastest ENA. For a given energy at Earth orbit we expect fluctuations in the survival probability of amplitude between ∼20 percent at 0.01 keV to just a few percent at 6 keV and a modulation of survival probability as a function of the location at Earth orbit, ecliptic latitude of the arrival direction, and phase of solar cycle with an amplitude of a few dozen percent for 0.1 keV atoms at solar minimum to a few percent for 6 keV atoms at solar maximum. Conclusions. With appropriate account of local transport effects IBEX should be able to discover departures from symmetry in the flux of H ENA from the heliospheric interface at a level of a few percent.
Abstract The latitudinal structure of the solar wind varies during the cycle of solar activity. Analysis of this variation is important for understanding the solar activity and interpretation of ...observations of heliospheric energetic neutral hydrogen atoms and interstellar neutral (ISN) atoms inside the heliosphere, which yield information on the heliosphere and its interaction with the interstellar medium. Existing methods of retrieving this information from indirect remote-sensing measurements of phenomena, including the heliospheric backscatter glow and interplanetary scintillations of remote radio sources, are challenging to apply in real time. Here, we propose a method WawHelioIonMP of approximate retrieval of latitudinal profiles of the ionization rates of ISN H using a machine-learning-based interpretation of the helioglow. Assuming that we know their history during two past solar cycles and have observations of the helioglow for close-to-circumsolar circles with a radius close to 90°, we derive statistically an algebraic relation between the ionization profiles and lightcurves. With the relation reversed, we are then able to derive the ionization rate profiles based on observed light curves, such as those planned for the GLObal solar Wind Structure (GLOWS) experiment on the forthcoming NASA mission Interstellar Mapping and Acceleration Probe (IMAP). The application of this method is straightforward and rapid because complex simulations are no longer needed. We present the method of retrieval of the profiles of the ionization rates, leaving the discussion of details of the decomposition of the retrieved ionization rate profiles into profiles of the solar wind speed and density to a future paper.
Abstract
The solar wind (SW) is an outflow of the solar coronal plasma, which expands supersonically throughout the heliosphere. SW particles interact by charge exchange with interstellar neutral ...atoms; on the one hand, they modify the distribution of this gas in interplanetary space, and, on the other hand, they are the seed populations for heliospheric pickup ions and energetic neutral atoms (ENAs). The heliolatitudinal profiles of the SW’s speed and density evolve during the solar activity cycle. A model of the evolution of the SW’s speed and density is needed to interpret observations of ENAs, pickup ions, the heliospheric backscatter glow, etc. We derive the Warsaw Heliospheric Ionization Model 3DSW—WawHelIon 3DSW—based on interplanetary scintillation (IPS) tomography maps of the SW speed. We use the IPS tomography data from 1985 to 2020, compiled by Tokumaru et al. We derive a novel statistical method of filtering these data against outliers; we present a flexible analytic formula for the latitudinal profiles of the SW speed, based on Legendre polynomials of varying order with additional restraining conditions at the poles; fit this formula to the yearly filtered data; and calculate yearly SW density profiles using the latitudinally invariant SW energy flux observed in the ecliptic plane. Despite the application of a refined IPS data set, a more sophisticated data filtering method, and a more flexible analytic model, the present results mostly agree with those obtained previously, demonstrating the robustness of IPS studies of the SW’s structure.
Abstract
The solar wind (SW) is a supersonic outflow of plasma from the solar corona, with the latitudinal speed and density profiles varying with the solar activity. The SW protons charge exchange ...with the inflowing interstellar neutral atoms and create energetic neutral atoms (ENAs), which bring information on the physical state of the plasma within the boundary region of the heliosphere. The speed of the ENAs depends on their energies, and consequently observations at different energies provide information on different epochs backward in time. Therefore, understanding the history of the evolution of the SW is important to understand this information. In this paper, we extend the work by Porowski et al., who provided the WawHelioIon 3DSW model of the time evolution of latitudinal profiles of the SW speed and density based on results of analysis of interplanetary scintillations (IPSs). Based on results of principal component analysis, we search for correlation between selected solar proxies and the structure of the SW obtained from IPSs and show that it is possible to reproduce the evolution of the SW structure during the past three solar cycles based on the proxies. With this, we extend the history of the evolution of the SW structure back to 1976, i.e., to the epoch when observations of the key proxies—the inclination of the SW current sheet and the solar polar magnetic fields—became available. We point out the potential of the use of the proxies for forecasting the structure of the SW into the future.
In situ measurements of the heliospheric particle populations by the Voyager spacecraft can only be put in an appropriate context with remote-sensing observations of energetic and interstellar ...neutral atoms (ENAs and ISN, respectively) at 1 au when the time delay between the production and the observation times is taken into account. ENA times of flight from the production regions in the heliosheath are relatively easy to estimate because these atoms follow almost constant speed, force-free trajectories. For the ISN populations, dynamical and ballistic selection effects are important, and times of flight are much longer. We estimate these times for ISN He and H atoms observed by IBEX and in the future by IMAP using the WTPM model with synthesis method. We show that for the primary population atoms, the times of flight are on the order of three solar cycle periods, with a spread equivalent to one solar cycle. For the secondary populations, the times of flight are on the order of ten solar cycle periods, and during the past ten years of observations, IBEX has been collecting secondary He atoms produced in the outer heliosheath during almost the entire 19th century. ISN atoms penetrating the heliopause at the time of Voyager crossing will become gradually visible about 2027, during the planned IMAP observations. Hypothetical variations in the ISN flow in the Local Interstellar Medium are currently not detectable. Nevertheless, we expect steady-state heliosphere models used with appropriately averaged solar wind parameters to be suitable for understanding the ISN observations.
The solar wind (SW) and the extreme ultraviolet (EUV) radiation modulate fluxes of interstellar and heliospheric particles inside the heliosphere both in time and in space. Understanding this ...modulation is necessary to correctly interpret measurements of particles of interstellar origin inside the heliosphere. We present a revision of heliospheric ionization rates and provide the Sun-Heliosphere Observation-based Ionization Rates model based on the currently available data. We calculate the total ionization rates using revised SW and solar EUV data. We study the in-ecliptic variation of the SW parameters, the latitudinal structure of the SW speed and density, and the reconstruction of the photoionization rates. The revision most affects the SW out of the ecliptic plane during solar maximum and the estimation of the photoionization rates, the latter due to a change of the reference data. The revised polar SW is slower and denser during the solar maximum of solar cycle (SC) 24. The current estimated total ionization rates are higher than the previous ones for H, O, and Ne, and lower for He. The changes for the in-ecliptic total ionization rates are less than 10% for H and He, up to 20% for O, and up to 35% for Ne. Additionally, the changes are not constant in time and vary as a function of time and latitude.
Abstract
We present a study of the influence of solar UV anisotropy on the heliospheric backscatter helioglow generated by resonant scattering of solar Ly
α
photons on interstellar hydrogen atoms ...around the Sun. Simulations based on the WawHelioGlow model suggest that the response of the helioglow pole-to-ecliptic ratio to the anisotropy is linear, but 15% of the anisotropy (polar darkening) generates 30%–40% change in the ratio in the solar minimum and 15%–20% in the solar maximum. We attribute this difference to an interplay between the solar UV anisotropy and the latitudinal structure of the solar wind in solar minima. The solar UV anisotropy also increases the helioglow intensity from the downwind direction by 5%–10%, due to the influence of the anisotropy on the ionization losses and trajectories of atoms passing by the Sun in polar regions. Consequently, midlatitude regions (in the heliographic and ecliptic coordinates) are least affected by the UV anisotropy. By comparison of the simulation results with observations of the Solar and Heliospheric Observatory/SWAN satellite instrument, we derive the day-by-day time evolution of the solar Ly
α
anisotropy for the north and south poles over two solar cycles from 1996 to 2022. The inferred anisotropy is ∼5%–10% in solar minima and ∼15%–25% in solar maxima, the northern anisotropy being stronger than the southern one. Our study suggests that in solar minima a highly structured solar wind is associated with relatively small solar UV anisotropy, while in solar maxima the solar wind is more isotropic but a substantial solar UV anisotropy appears.
The Heliosphere Is Not Round Schwadron, N. A.; Bzowski, M.
The Astrophysical journal,
07/2018, Letnik:
862, Številka:
1
Journal Article
Recenzirano
Observations from the Ion and Neutral Camera (INCA) on the Cassini mission of energetic neutral atoms (ENAs) at ∼10 keV and ∼45 keV showed significant correlated time variations over relatively fast ...2-3 yr timescales. These observed ENA variations have been interpreted as indicating limited scale lengths of ∼80-120 au along the line of sight for the size of the heliosphere. We show here, however, that rather than a heliosphere with a quasi-spherical shape, the INCA line-of-sight observations vary in response to episodic cooling and heating of the inner heliosheath plasma during periods of large-scale expansion and compression.
Models play an important role in our understanding of the global structure of the solar wind and its interaction with the interstellar medium. A critical ingredient in many types of models is the ...charge-exchange collisions between ions and neutrals. Some ambiguity exists in the charge-exchange cross-section for protons and hydrogen atoms, depending on which experimental data is used. The differences are greatest at low energies, and for the plasma-neutral interaction in the outer heliosheath may exceed 50%. In this paper we assess a number of existing data sets and formulae for proton-hydrogen charge exchange. We use a global simulation of the heliosphere to quantify the differences between the currently favored cross-section, and we suggest a formulation that more closely matches the majority of available data. We find that in order to make the resulting two heliospheres the same size, the interstellar proton and hydrogen densities need to be adjusted by 10%-15%, which provides a way to link the uncertainty in the cross-section to the uncertainty in the parameters of the pristine interstellar plasma.
Abstract Direct observations of solar wind are mostly limited to the vicinity of the ecliptic plane. Retrieving the latitudinal structure of solar wind indirectly based on observations of the ...backscatter glow of interstellar neutral hydrogen is complex and requires support from theoretical models. The GLOWS instrument, to operate on the planned IMAP mission, will scan the helioglow along circumsolar rings with an angular distance of ∼75°. Its objective is to retrieve the latitudinal structure of the ionization rate of interstellar hydrogen and with this the structure of the solar wind. In preparation for the future analysis, we studied the sensitivity of the light curves to temporal and latitudinal variation of the ionization rate of interstellar hydrogen and the solar Ly α illumination. Based on carefully planned numerical experiments, we analyze the time delay and relaxation time of the system for variations of the ionization rate and solar illumination in heliolatitude and with time. We found that variations in the solar illumination are reflected in the helioglow without delay, but relaxation takes longer than the variation rise time. By contrast, variations in the ionization rate are anticorrelated with the helioglow brightness with a delay of several months. We also found that the helioglow is not sensitive to variations in the ionization rate at the solar poles, so retrieving the ionization rate and solar wind at the poles requires approximation of the ionization rate profiles with appropriate parametric functions.
PDF
