Interplanetary Gas Research Articles

Газодинамика и магнитная гидродинамика взаимодействия межпланетной и межзвездной сред. Теория и эксперимент

Газодинамика и магнитная гидродинамика взаимодействия межпланетной и межзвездной сред. Теория и эксперимент

Hydrogen atom lifetimes in the three‐dimensional heliosphere over the solar cycle

The three‐dimensional (3‐D) structure of the heliosphere is investigated using in situ and remote sensing measurements. The 3‐D structure of both neutral interplanetary gas and solar wind ions are affected by the solar latitude variation of the solar radiation fields (solar wind and solar EUV). Neutral hydrogen atom lifetimes against charge‐exchange with solar wind protons in the 3‐D heliosphere are calculated from measurements of the solar wind proton velocity, density, and mass flux by Ulysses SWOOPS (Solar Wind Observations Over the Poles of the Sun) from 1990–2001. These are compared to in‐ecliptic H atom lifetimes derived from solar wind measurements by the spacecraft IMP (Interplanetary Monitoring Platform) 6, 7, and 8, WIND, and ACE (Advanced Composition Explorer) SWEPAM (Solar Wind Electron Proton Alpha Monitor). Recent observations during the Ulysses rapid solar pole‐to‐solar pole passage (fast‐latitude scan) at solar maximum find a more isotropic rotationally averaged solar wind mass flux (and H atom lifetime) than was found during the previous fast latitude scan at solar minimum. During the solar minimum fast‐latitude scan the 27‐day averaged SWOOPS lifetime passed through two distinct regimes: it doubled from 2 × 106 s at low latitudes to 4 × 106 s at high latitudes in both hemispheres. During the solar maximum pass the 27‐day averaged SWOOPS H atom lifetime (corrected to 1 AU) at all southern latitudes and at all northern latitudes below 60° was (2–2.5) × 106 s, while at the very end of the pass, above 60° N latitude, it rose to 4 × 106 s as polar coronal holes reformed. Remote sensing studies of interplanetary H Lyman‐α emission, white light solar coronal observations, and radio scintillation experiments have also indicated that the time‐averaged solar wind mass flux (and H atom lifetime) is more isotropic at solar maximum than at solar minimum. This enlarges the polar H cavity at solar maximum. Results from in situ measurements are compared to remote sensing data. Ulysses GAS Lyman‐ α maps are modeled, with updated results. Comparisons of the H atom charge exchange loss rate with a weaker H atom loss process, photoionization, are made using the SOLAR2000 model [Tobiska et al., 2000] for in‐ecliptic solar Extreme UltraViolet (EUV) fluxes. The relative latitude invariance of the H atom lifetime at solar maximum is related to the absence of high‐speed solar wind at solar maximum and to the large inclination of the heliospheric current sheet.

The Influence of Fluctuations of the Solar Emission Line Profileon the Doppler Shift of Interplanetary HLyα Lines Observed by the Hubble–Space–Telescope

In an earlier research the employment of a radiation transport model with angle-dependent partial frequency redistribution, self-absorption by interplanetary hydrogen, realistic solar HLyαemission profile, and a time dependent `hot' hydrogen model to analyze 5 interplanetary HLyα glow spectra obtained with theHubble–Space–Telescope–GHRS spectrometer, has not resulted in unequivocal determination of a set of thermodynamical parameters of the interstellar hydrogen The residual discrepancies between the model and the data concern the observations performed within an interval of 1 year close to the solar minimum from very similar lines of sight. In this paper we investigate by calculating interplanetary HLyα lines with the use of a one hydrogen distribution and several solar HLyα line profiles whether this residual may be caused by possible variations in time of the shape of the solar HLyα emission line profile which cause variable illuminations of the interplanetary gas. These variations of illuminations cause variations in Doppler shift of the resonant interplanetary HLyα line that can amount to ≃ 4 km s-1in the line peak. Consequently we conclude that without adequate knowledge of the solar HLyα emission line profile during spectral observations of the interplanetary hydrogen gas it is impossible to obtain an agreement between models and observations better than by this value.

Interplanetary Neutral Particle Fluxes Influencing the Earth's Atmosphere and the Terrestrial Environment

It is well known that the Solar System is swept over by neutral interstellar gases, primarily hydrogen and helium, entering the heliosphere from the upwind side and penetrating inward, even up to the orbit of the Earth. The Earth on its orbit is thus moving through this density field and is intercepting time-variable hydrogen and helium fluxes. Quantitatively, this is associated with a sensitive reaction of the density fields to time-dependent conditions of the solar radiation pressure and the ionizing solar radiations during the solar activity cycle. As we shall show, the density distribution of interstellar hydrogen along the orbit of the Earth is strongly varying during the solar cycle. In connection with the variation of the mean relative velocity of this gas with respect to the orbiting Earth a highly variable hydrogen inflow into the Earth's atmosphere will be induced. There is also an additional source of hydrogen influencing the Earth's environment due to the fact that neutral interstellar hydrogen and helium are neutralizing solar wind protons by charge exchange inside the orbit of the Earth, thereby producing an antisolar flux of keV-energetic hydrogen atoms impinging onto the Earth's atmosphere. These time-variable fluxes could be directly monitored by gas detectors of an advanced technology. They might also be indicated by indirect terrestrial effects. We are investigating the question of whether and how these time-variable inflows could be recognized by careful studies of relevant upper atmospheric reactions. We study particle-induced energy inputs and ionization rates in the upper atmosphere and analyze influences on the hydrogen geocorona. We also study the process of relaxation of the inflowing hydrogen within the terrestrial atmosphere and investigate the reaction of atmospheric hydrogen densities to these variable inflows. While it is shown that the induced short-period variation of upper atmospheric hydrogen densities is of negligible amplitude at the present epoch, long-periodic variations of the hydrogen inflow like those connected with the entrance of the Solar System into a region of increased interstellar density at earlier or later eons clearly give their imprints even at lower heights and could even be reflected in ozone depletions induced by increased hydrogen densities at heights of around 50 km. At present anomalous variations of the geocoronal H-1216 A and He-584 A glows uncorrelated with the solar resonance line illumination indicate a breathing of the geocorona under variable interplanetary gas inflows.

Oxygen in the heliosphere

Oxygen within the heliosphere, whether neutral or ionized, comes from both the external source in the local interstellar medium (LISM) and internal sources. If transient cometary sources are neglected, Jupiter is the strongest of the internal sources by virtue of its corotation and charge exchange driven neutral wind. O+ pickup ions are born where the penetrating neutrals lose an electron as a result of photoionization, charge exchange with solar wind protons, or solar wind electron impact ionization. The region of the heliosphere from which these pickup ions arise depends on the phase of the solar cycle as well as on the velocities of the neutrals. The present model of neutral O populations and their ionization suggests that Jovian pickup ions can dominate the inner heliospheric O+ population if the LISM neutrals are strongly filtered at the heliopause, or are excluded by strong ionizing fluxes from the Sun. Other heliospheric species such as sulfur and nitrogen may have similar origins. These planetary sources need to be taken into account in the interpretation of interplanetary gas and ion composition observations.

Solar wind latitude variations and multiple scattering from Galileo interplanetary Lyman-α observations

The Galileo Ultraviolet Spectrometer Experiment (UVS) obtained a map of the celestial sphere from interplanetary Lyman-α (IP Lα) on 13,14 December 1990 during the Earth1 encounter. The Galileo spacecraft was near the downwind interstellar axis during the encounter and the map view directions filled the downwind hemisphere. The ratio between the observation and a single scattering model is attributed to a direct measurement of the multiple scattering correction required to model IP Lα in the inner solar system. Analysis of this data set, referred to as an antisun map, shows that the solar wind charge exchange rate with interplanetary gas is 25% less over the solar poles than in the ecliptic at solar maximum. A model of the interstellar wind based on the antisun map observation exhibits a number density of atomic hydrogen far from the solar system, inside the heliosphere, of 0.16 ± 0.05 cm−3.

Expected fluxes of ∼ 1 keV neutral H atoms in interplanetary space; Comparison with the U.V. background and possibility of detection

We estimate the expected signal and the noise (u.v. background) for direct detection of fast ∼ 1 keV neutral H atoms originating in charge exchange of the solar wind on interplanetary gases (H, He). The typical fluxes of fast atoms at Earth orbit are 10 2–10 4cm 2̄ s −1 depending on ecliptic longitude and solar cycle variations. The ratio of the neutral to u.v. fluxes may attain 10 3̄ (particles-to-photons) at solar minimum and 10 −4 at solar maximum conditions. This makes their detection possible if the u.v. suppression factor is better than 10 3, which is easily attainable in the laboratory [see Gruntman and Morozov, 1982, J. Phys. E: Sci. Instrum. 15, 1356 ; Gruntman and Leonas, 1983, Preprint No. 825, Space Research Institute (IKI), Moscow].

The gaseous component of the disk around Beta Pictoris

Optical spectra of alpha Lyr, alpha PsA, and beta Pic have been obtained at a velocity resolution of 3 km/s. No circumstellar absorption lines of Ca II or Na I are detected toward alpha Lyr or alpha PsA at sensitive limits. In the favorable case of beta Pic, where the circumstellar disk imaged by Smith and Terrile (1984) is seen nearly edge-on, a strong, narrow, circumstellar Ca II K absorption line previously reported by Slettebak (1982) and weaker, still narrower circumstellar Na I D lines are detected. Negative results of high sensitivity also are obtained for the Ca I 4226 A and CH(+) 4232 A lines, along with upper limits on the Zn II 2026, 2062 A doublet from archival IUE spectra. Under assumptions which agree with other well-established observations of the gaseous abundances of calcium and zinc, the total gaseous column density of hydrogen along a radius of the circumstellar disk is between 10 to the 18th and 4 x 10 to the 20th/sq cm. Within the boundaries of the dust disk detected by Smith and Terrile (1984) the total gaseous mass then is less than about 2, or less than 1 percent of the mass of the planetary system. A simplified model of the density distribution in the gaseous disk yields a characteristic total density n(H) of about 100,000/cu cm, which exceeds that of all interplanetary gas at earth's position by a factor of about 10,000.

Interplanetary gas. XXVIII - A study of the three-dimensional properties of interplanetary sector boundaries using disconnection events in cometary plasma tails

Studies of the solar wind on the basis of cometary plasma tail observations are considered. Niedner and Brandt (1978, 1979) have concluded that the plasma tail frequently disconnects from the cometary head, and that these disconnection events (DEs) are produced by magnetic reconnection at sector boundary passages. They proposed that the disconnections are a natural combination of Alfven's model and the solar-wind sector structure first discovered by Wilcox and Ness (1965). The DEs can be utilized as probes of interplanetary sector structure. Correlations between DEs and sector boundaries observed at earth are considered, and sector boundary properties deduced from DEs are discussed. Attention is given to a review of the warped sheet model, the latitude extent of sector structure, the sector boundary tilt, and specific sources of error in the tilt angles derived from DEs.

Interplanetary gas. XXVII - A catalog of disconnection events in cometary plasma tails

A catalog of 72 disconnection event (DES) in cometary plasma tails is presented as a basic data source for cometary and solar wind analysis. The events span the period 1892-1976, and are characterized on the basis of photographic observations. From the observed kinematics of rejected tails, methods are derived to calculate an estimated time of tail disconnection for each DE, either from the average law of motion for DEs lacking velocity measurements, or from the observed velocities. The geometric circumstances of each DE at the times of separation and observation are also tabulated, and a brief description of each event is presented.

Interplanetary gas. XXVI - On the reconnection of magnetic fields in cometary ionospheres at interplanetary sector boundary crossings

The reconnection process in the cometary ionosphere believed responsible for the disconnecting plasma tails phenomenon is studied through the basic equations of reconnection theory and current sheet instability criteria. It is proposed that reconnection occurs when the interplanetary magnetic fields incident on a comet that has gone just past a sector boundary are pressed into the fields captured from the previous sector. The fields are of opposite polarity, and the previously captured fields constitute the 'roots' of the plasma tail. An estimated duration of reconnection during a disconnection event (DE) of 0.75 days is used along with estimates of other cometary parameters to construct fusion region dimensions and resistivity with the adopted time scale.

Pioneer 10 ultraviolet photometer observations of the interplanetary glow at heliocentric distances from 2 to 14 AU

An analysis is presented of the observed Pioneer 10 interplanetary data from 1972 to 1977, taking into account the interplanetary glow intensity observed by the Pioneer 10 UV photometer at sun-spacecraft distances of 2-14 AU. On the basis of the obtained data, it was determined that the background intensity for the 200-1400 A band pass of the photometer channel is about 40 + or - 10 R, and that the nearby interstellar density is 0.04 + or - 0.91 per ccm for hydrogen and about 0.01 + or - 0.002 per ccm for helium. Accordingly, the He/H number density is about 0.25 at large distances from the sun. The Pioneer 10 spacecraft is leaving the solar system in the downwind direction, while both Pioneer 11 and Voyager will leave in the upwind direction. The combined UV observations of the interplanetary glow will provide accurate results on the physical status of the inflowing interstellar gas and the variability of background radiation as well.

Interplanetary gas. XXV - A solar wind and interplanetary magnetic field interpretation of cometary light outbursts

Possible relationships of cometary brightness outbursts with the solar wind and interplanetary magnetic field are examined. Two types of outburst are distinguished: those which involve a significant brightening of both the head and the tail in a comet with a conspicuous plasma tail (Class I), and those involving the brightening of the central condensation of a previously faint comet with no detectable plasma tail (Class II). Class I bursts, as exemplified by Comet Morehouse 1908c, are attributed to the generation in the head of enhanced amounts of ions and their injection into the tail shortly before it disconnects, with ionization provided by sector boundary crossings. Class II events, as exhibited by Comet P/Tuttle-Giacobini-Kresak 1973b, are interpreted as the result of the bombardment of the nucleus by disturbed solar wind near corotated high-speed streams and sector boundaries, leading to highly exothermic chemical reactions.

Interplanetary gas. XXIV - Are cometary plasma tail disconnections caused by sector boundary crossings or by encounters with high-speed streams

view Abstract Citations (46) References (35) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Interplanetary gas. XXIV. Are cometary plasma tail disconnections caused by boundary crossings or by encounters with high-speed streams? Niedner, M. B., Jr. ; Brandt, J. C. Abstract The paper discusses and compares the original sector boundary model (Niedner and Brandt) and the alternative high-speed stream model (Ip and Mendis) suggested for explaining cometary plasma tail disconnection events (DE) within a largely observational framework not dependent on detailed plasma physics. Among the findings are: (1) the strong solar cycle phase dependence of the amplitude of the Rosenberg-Coleman effect (Svalgaard and Wilcox) yields inferred maximum latitudes of all of the DEs in the original survey to a one-time Rosenberg-Coleman effect measurement made by Pioneer 11, which indicated a disappearance of sectors above 16 deg latitude, and (2) approximately 70% of the post 1926 DEs in the expanded survey show a close association with corotated shorter-term polarity reversals. This result is difficult to reconcile with the predictions of the stream model, in which DEs should correlate more strongly with streams than with sector boundaries. It is concluded that the sector boundary model better describes the disconnection phenomenon and that the use of DEs as unique sector boundary markers is presently justified. Publication: The Astrophysical Journal Pub Date: December 1979 DOI: 10.1086/157549 Bibcode: 1979ApJ...234..723N Keywords: Astronomical Models; Comet Tails; Cosmic Plasma; Interplanetary Gas; Magnetohydrodynamic Flow; Comet Heads; Flow Velocity; High Speed; Morphology; Pioneer 11 Space Probe; Solar Cycles; Solar Wind; Astrophysics; Cometary Tails:Plasma; Comets:Interplanetary Magnetic Field; Interplanetary Magnetic Field:Sector Structure full text sources ADS | Related Materials (23) Part 1: 1959ApJ...130..670B Part 2: 1960ApJ...131...47C Part 3: 1961ApJ...133..675C Part 4: 1961ApJ...133..688B Part 5: 1961ApJ...134..394B Part 6: 1961ApJ...134..975B Part 7: 1962ApJ...136.1023B Part 8: 1966ApJS...13..125B Part 9: 1967ApJ...147..201B Part 10: 1967ApJ...148..905B Part 11: 1970ApJ...159.1057B Part 12: 1969ApJ...156.1117B Part 13: 1972ApJ...177..277B Part 14: 1973ApJ...183.1037B Part 15: 1973ApJ...184...27B Part 16: 1975ApJ...196..877B Part 17: 1975ApJ...199..756P Part 18: 1978ApJ...223..655N Part 19: 1978ApJ...221.1014N Part 21: 1980ApJ...241..820N Part 22: 1981ApJ...245.1159N Part 23: 1981ApJS...46..141N Part 24: 1982ApJS...48....1N

Science aspects of a mission beyond the planets

A mission out of the planetary system, launched about the year 2000, could provide valuable data concerning characteristics of the heliopause, the interstellar medium, stellar distances (by parallax measurements), low-energy cosmic rays, interplanetary gas distribution, and mass of the solar system. Secondary objectives include investigation of Pluto. Candidate science measurements, instruments, and instrument development needs are discussed. The mission should extend from 400 to 1000 AU from the Sun. A heliocentric hyperbolic escape velocity of 50–100 km/sec or more is needed to attain this distance within a reasonable mission duration (20–50 years). The trajectory should be toward the incoming interstellar gas. For a year 2000 launch, a Pluto encounter and orbiter can be included. A second mission targeted parallel to the solar axis would also be worthwhile.

Temperature and flow velocity of the interplanetary gases along solar radii

The velocity distributions along solar radii for hydrogen and helium in interplanetary space are calculated by using the Danby-Camm formula modified with a loss function. From these distributions the radial temperature and radial flow velocity of the interplanetary gases are determined. The effects of solar gravitation and ionization loss, due to charge exchange and photoionization, on the gas temperature and velocity are described.

Interplanetary gas. XXII - Plasma tail disconnection events in comets - Evidence for magnetic field line reconnection at interplanetary sector boundaries

Attention is focused on a form of cometary activity which has been known for some time but is poorly understood: the discarding of a plasma tail by a comet. A link is found between plasma-tail rejections and conditions in the solar wind. A model is presented in which a disconnected tail is the end result of magnetic-field-line reconnection in the cometary ionosphere caused by the traversal of a magnetic sector boundary. Observations of plasma tails appear to be the best and only method at present of mapping the interplanetary sector structure out of the ecliptic plane.

Stochastic and dynamic temperature changes in the interplanetary gas

Exact solutions have been found to the Fokker-Planck equations, incorporating stochastic velocity changes and modelling particles moving in an inverse square central force field under an inverse square collision frequency. The solutions for the velocity distribution contain a combination of collisional and dynamical (reversible) heating. At a general position, there are two populations each with three distinct temperatures, one normal to the orbital plane and the others closely parallel and perpendicular to the mean orbit. Collisional heating is strong and most readily detected in the secondary component of gas which reaches upstream directions along indirect orbits (attractive central force). For interplanetary helium gas reaching 1 a.u., the collisional heating ranges from effective transverse increase of 200 K and radial increase of 1500 K in the downstream wake, to several thousand K increase in radial temperature of the secondary component transverse to the initial gas stream. In interpreting 584 Å sky background radiation observations, the dynamical changes in the velocity spread have to be taken into account for helium gas that is initially hot, when Doppler shifts relative to the solar emission line are significant; the present solutions being the thermal approximations to the distribution function reveal the appropriate radial temperature as a function of space.

Interplanetary disturbances in the solar wind produced by density, temperature, or velocity pulses at 0.08 AU

Time-dependent solutions of a one-fluid model of the interplanetary medium are investigated. This set of unsteady hydrodynamic equations has been written in conservation form in order to apply the Lax-Wendroff method for the solution of this problem. The initial disturbance is specified by a pulse at 0.08 AU (astronomical units). Physically, this pulse can be interpreted as having been caused by a solar flare, surge, or any other solar disturbance. The equilibrium condition is determined to be the steady solution of the governing equations and represents the quiet solar wind. The results are presented in terms of density, temperature, and velocity profiles of the interplanetary gas flow at heliocentric distances up to 6 AU at several times. Also, the trajectories of disturbances for various initial pulses are shown. Finally, we have used some June 1972 interplanetary observational data to compare with these theoretical calculations. On the basis of these results, the effects of solar disturbances on the interplanetary environment (such as the generation of large non-linear wave trains in the shocks' wakes) can be inferred.

Interplanetary gas of nonsolar origin

Beginning in 1970 a series of detailed sky maps of the extraterrestrial H I Lyman alpha (Ly α 1216 Å) and He I (584 Å) lines have become available. The observed spatial and temporal properties of the sky brightness provide unambiguous evidence of substantial quantities of neutral gas within the solar system. The view that the majority of these atoms are of interstellar origin is firmly supported by the success of the ‘interstellar wind’ model in explaining the essential features of the maps in terms of backscattering of solar chromospheric 1216‐Å and 584‐Å emission lines. The often hypothesized galactic 1216‐Å emission can now be discounted as a minor, if not negligible, component. These advances have turned attention to such questions as: What are the physical and kinematic properties of the nearby interstellar medium? Is the average solar wind emitted isotropically from the sun? What is the nature and location of the termination region of the solar wind in the interstellar medium? How important is the interstellar gas in heating the solar wind? Reviews of this new field of interplanetary studies were given by Tinsley [1971], Axford [1972], Fahr [1974], Thomas [1974], and Holzer [1974]. This will be a brief summary of some of the most significant advances for the years 1970–1974, and the summary is followed by a personal view of how future advances might be made.