Quiet Solar Wind Research Articles

High-altitude cusp: INTERBALL observation

The cusp is a funnel-shaped part of the Earth's magnetosphere where the magnetospheric magnetic field lines are directly interconnected with the magnetosheath ones. The magnetic field configuration allows the magnetosheath plasma to precipitate toward the ionosphere. This feature is used for the determination of the cusp position in low altitudes. However, it is often difficult to distinguish different plasma populations in high altitudes. The cusp region is bounded with the low-latitude boundary layer (LLBL), entry layer or cleft on the equatorward side, and by the plasma mantle on the poleward side, but the plasma and magnetic field parameters are similar in all these regions. We have used the INTERBALL-1 and MAGION-4 satellites to study the topology and dynamics of high-altitude cusp regions under quiet solar wind conditions but different directions of the interplanetary magnetic field (IMF). Two-point event studies have shown that (1) the topology of the magnetic field in the high-altitude cusp is controlled by the IMF direction, (2) the cusp plasma source is located near the tailward boundary of the cusp during northward IMF, and (3) magnetosheath fluctuations are correlated with the fluctuations of the cusp precipitation.

Observations of Pi2 pulsations in a near ground state magnetosphere

This paper reports on the observation of Pi2 pulsations under conditions with which they have not previously been associated, namely, extremely quiet solar wind conditions when the magnetosphere is in a near ground state. Three years of data were scanned for extremely quiet intervals on the basis of ap indices and solar wind parameters. Twenty‐four extremely quiet intervals were identified, thirteen of which contained Pi2 pulsation signatures at low latitudes. The Pi2 amplitudes were similar to those typically observed during substorm expansion phases. One interval was studied in greater detail. It exhibited other substorm signatures; however, the high latitude, negative, H‐component bay was extremely weak and spatially localized. During this interval Pi2 pulsations were also observed on the day side at low latitudes.

Strong flow bursts in the nightside ionosphere during extremely quiet solar wind conditions

Results of an HF radar study of convection during an extended quiet solar wind interval on March 10 1997 are presented. After thirty hours during which the solar wind met the criteria for quiet conditions the HF radars at Sanae and Halley in Antarctica showed strong activity on the night side. Flow bursts with velocities of more than 2000 m s−1, corresponding to electric fields exceeding 100 m V m−1 were observed. These occurred quasi‐periodically for almost two hours on the night‐side with a repetition time of several minutes. It is concluded that they map to a region well inside the magnetotail. It is suggested that they are associated with sporadic energy release during reconfiguration of the tail magnetic field, and that this can occur even during an extended quiet solar wind period.

Self‐consistent stochastic preacceleration of interstellar pickup ions in the solar wind including the effects of wave coupling and damping

A self‐consistent model was developed to study the stochastic acceleration (second‐order Fermi) of interstellar pickup ions in the quiet solar wind (SW) and inside corotating merged interaction regions (CMIRs) in the presence of the effects of wave coupling and the damping of magnetohydrodynamic waves by pickup ions. Our simulations of the solar wind wave spectrum show that (1) Pickup H+ is mainly responsible for wave damping at large wave numbers with pickup He+ contributing very little and pickup O+ contributing nothing. (2) Strong wave‐wave interactions wash out wave‐damping effects for radial distances r ≤ 10 AU from the Sun in the quiet solar wind and for r ≤ 23 AU inside corotating merged interaction regions. This is to be contrasted with previous work which calculated strong wave damping inside 10 AU from the Sun in the absence of wave coupling. For the simulated pickup ion spectra the main results are as follows: (1) The pickup He+ and O+ spectra are unaffected by the wave damping. (2) In contrast, the accelerated pickup H+ spectra have concave features for kinetic energies 1–5 KeV which become more pronounced with increasing radial distance. This suppression of the pickup H+ acceleration is attributed to the wave damping caused by the pickup H+. (3) Inside corotating merged interaction regions the preacceleration of pickup ions is stronger because of the enhanced heliospheric magnetic field. The suppression of pickup H+ acceleration is smaller and only starts to show for r > 23 AU. (4) Under the assumption that the seed population of anomalous cosmic rays should have speeds v > 400 km s−1 the H+/He+ density ratio in this population can be as low as ∼2.6 in the quiet solar wind and ∼13 inside corotating merged interaction regions. Compared with the observed ratio of ∼6 for anomalous cosmic rays (ACRs), our conclusion is that if CMIR and quiet SW regions are considered together, then the observed under abundance in ACR H+ could in principle be produced on average.

Implications of Proton Anisotropy Development Observed by the Erne Instrument During the 9 July 1996 Solar Particle Event

We analysed the solar particle event following the 9 July 1996 solar flare. High-energy protons were detected by the ERNE instrument on board SOHO. Anisotropy of arriving protons revealed very peculiar non-monotonic development. A short period of almost isotropic distribution was imbedded into the prolonged period of beam-like distribution of 14–17 MeV protons. This implies the existence of a narrow magnetic channel with a much smaller mean free path than in the surrounding quiet solar wind plasma. We used Monte Carlo simulations of interplanetary transport to fit the observed anisotropies and intensity–time profiles. Proton injection and transport parameters are estimated. The injection scenario is found to be very close to the scenario of the 24 May 1990 event, but the intensity and the interplanetary transport parameters are different. The extreme anisotropy observed implies prolonged injection of high-energy protons at the Sun and at the interplanetary shock front, and either a very large mean free path (≥ 5 AU) outside the slow transport channel, or alternatively, a somewhat smaller mean free path (≈2 AU) and enhanced focusing between the Sun and the Earth.

Sub-Alfvénic flows in the quiet and recurrent solar winds

Observed instances are given in this paper to show that sub-Alfvénic flow can be formed in the quiet and recurrent low-speed solar wind streams. This kind of flow appears in regions with abnormal enhancement of Alfvénic speed and is associated with a specific type of magnetic configuration.

IPS observations of heliospheric density structures associated with active regions

Interplanetary scintillation (IPS) measurements of the ‘disturbance factor’ g, obtained with the Cambridge (UK) array can be used to explore the heliospheric density structure. We have used these data to construct synoptic (Carrington) maps, representing the large-scale enhancements of the g-factor in the inner heliosphere. These maps emphasize the stable corotating, rather than the transient heliospheric density enhancements. We have compared these maps with Carrington maps of Fe XIV observations (NSO, Sacramento Peak) and maps based on Yohkoh/SXT X-ray observations. Our results indicate that the regions of enhanced g tend to map to active regions rather than the current sheet. The implication is that active regions are the dominant source of the small-scale (≈ 200 km) density variations present in the quiet solar wind.

Synoptic IPS and Yohkoh soft X‐ray observations

Interplanetary scintillation measurements of the disturbance factor, g, from October 1991 to October 1992 are used to construct synoptic Carrington maps. These maps, which show the structure of the quiet solar wind, are compared with X‐ray Carrington maps from the Yohkoh SXT instrument. For the period studied the global structure outlined by (weakly) enhanced g‐values apparent in the IPS maps tends to match the active regions (as shown in the X‐ray maps) significantly better than the heliospheric current sheet. Contrary to traditional opinion, which views active regions as magnetically closed structures that do not have any significant impact on the solar wind flow, our results suggest that density fluctuations in the solar wind are significantly enhanced over active regions. These results support the suggestion by Uchida et al. (1992), based on Yohkoh observations of expanding active regions, that active regions play a role in feeding mass into the quiet solar wind.

Galileo flybys of earth: The nature of the distant shock

We report on observations of the Earth's bow shock at unprecedentedly large downtail distances, some as remote as 360 R(sub E). Suprisingly, we find that even at these large distances, the bow shock signature remains clear. The cases we report are among the weakest shocks ever clearly identified. These shocks reveal patterns of field changes remarkably similar to those observed for stronger shocks. Indeed, several of the shocks could serve as textbook examples because they occur in unusually quiet and steady solar wind conditions. The quasi- perpendicular shocks are, in some cases preceded by whistler wave trains. Several of the shocks which have normal vectors in the transitional region between quasiperpendicular and quasiparallel are associated with large amplitude wave disturbances in the downstream plasma. Although low Mach number, these shocks are the source of large amplitude turbulence. We show a range of fits to the locations of the shock crossings, and argue that, for steady solar wind conditions, there is no sign of tail flapping. The displacement of the shock from the tail axis appears to be governed by the interplanetary magnetic field orientation as previously reported for Venus.

Effect of coupled electron-proton thermal conductivities on the two-fluid solutions for the quiet solar wind

view Abstract Citations (12) References (24) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Effect of Coupled Electron-Proton Thermal Conductivities on the Two-Fluid Solutions for the Quiet Solar Wind Cuperman, S. ; Detman, T. ; Dryer, M. Abstract A numerical study of the effect of using coupled electron-proton thermal conduction terms in the two-fluid model equations for the quiet solar wind is presented. Modifications to the standard case solutions at 1 AU which are found to improve the agreement between theoretical predictions and observations include: (1) large increases in the proton temperature and proton thermal conduction energy; (2) a large increase in the bulk (streaming) velocity common to both protons and electrons; and (3) a decrease in the electron temperature and electron thermal conduction energy. A modified shooting-splitting numerical method is discussed. Publication: The Astrophysical Journal Pub Date: July 1988 DOI: 10.1086/166484 Bibcode: 1988ApJ...330..466C Keywords: Coupled Modes; Solar Electrons; Solar Protons; Solar Wind; Thermal Conductivity; Two Fluid Models; Computational Fluid Dynamics; Electron Energy; Flux Vector Splitting; Magnetohydrodynamic Waves; Proton Energy; Solar Wind Velocity; Solar Physics; HYDROMAGNETICS; SUN: SOLAR WIND full text sources ADS |

Magnetic field and current structures in the magnetosphere of Uranus

We compare Voyager 2 magnetic field and plasma data with theoretical model calculations for the magnetosphere of Uranus in order to derive a global picture from the quite limited set of measurements. In two dimensions we use a tilt‐dependent linear MHD equilibrium model for the entire magnetosphere to calculate the plasma parameter β = 8πP/B² and the resulting B field in the tail plasma sheet. The three‐dimensional model satisfies the MHD equilibrium equations in an approximate fashion; it is used to calculate the large‐scale magnetic field structure, the tilt‐dependent shape and position of the Uranian magnetotail plasma sheet, and the influence of the interplanetary magnetic field (IMF). The main results of the model calculations are the following: (1) The actual solar wind pressure at Uranus was found to be about a factor of 5 higher than a calculated solar wind pressure derived from an adiabatically expanding quiet solar wind. This means that the Uranian magnetosphere must have experienced a major magnetic storm prior to the Voyager encounter. (2) The previous conjecture is supported by the fact that the asymptotic plasma beta parameter in the neutral sheet, β0 = β(|x| ≫ 1), relaxes from β0 = 37 to β0 = 14 between the first and second neutral sheet crossings. (3) The excellent agreement between measured and modeled tail lobe magnetic field values suggests that during the time period of the Voyager encounter the Uranian tail plasma sheet, measured in units of planetary radii, was thicker and less stretched than the average Earth's tail plasma sheet. (4) Despite sizable temporal variations suggested by the data and the model, the Uranian magnetosphere seems to reach the state of quasi‐static, i.e., slowly time‐dependent, MHD equilibrium. (5) In relation to a given IMF orientation the magnetosphere changes periodically every 8.62 hours (the Uranian day is 17.24 hours) from an “open” to a “closed” configuration and back. Thus the convection process, driven by the direct influence of the IMF, is periodically interrupted by the planet's rotation, such that the plasma sheet might not experience its full stretching. Consequently, the Uranian magnetosphere might not experience convectively driven, Earth‐type substorms. On the other hand, the possibility of substorms cannot be ruled out either.

The velocity distribution function of the neutral lithium cloud produced by an AMPTE solar wind release

On 20 September 1984 a release of photoionizing lithium neutrals was made in the quiet solar wind, by the AMPTE-IRM spacecraft. The MSSL ion instrument on board the UKS spacecraft that was positioned ∼ 30 km from the release centre enabled measurement of significant fluxes of lithium ions to be made for ∼ 3 min after the release; that is, long after the initial (∼ 25 s) local perturbation to the field and flow had died away. Here, we examine in detail the MSSL on detector response to the release ions, showing that the ion measurements are consistent with injection into a cycloidal orbit. Knowing the ion orbit it is then possible to trace the expansion of the neutral lithium cloud and obtain its initial velocity distribution. Various preliminary analyses suggested a shell-like expansion of the cloud, but disagreed over its velocity. The more detailed analysis of the UKS data presented here shows that it is not possible to determine from this data whether or not the cloud is shell-like, but reveals that significant local anisotropy is present.

Plasma sheet ion composition at various levels of geomagnetic and solar activity

Statistical data obtained by the Plasma Composition Experiment on the ISEE-1 spacecraft, covering energies in the range 0.1-16 keV/e, show that plasma sheet ions fall into two groups which behave differently in response to variations in the geomagnetic and solar activity. One group, most prominently represented by the O+, is to a large extent associated with substorm activity (large AE-index) and also varies in density with the solar cycle. Ions in this group are clearly of terrestrial origin and may increase in numbers as a result of increased electric currents during substorms and of increased EUV radiation during high solar activity. The other group consists mainly of H+ and He2+ ions. These are most numerous during geomagnetically quiet conditions and show no significant response to variations in the solar EUV. Ions in this group are the only ones that vary in energy in a systematic fashion with varying substorm activity, being the least energetic during quiet conditions. When such activity goes to zero the mean (≈ thermal) energy-per-nucleon of these ions approaches the bulk energy-per-nucleon in the quiet solar wind. Ions in this group appear to be largely of solar origin. As a corollary it follows that the capture of solar ions in the plasma sheet is not inherently associated with substorm activity.

Distant (200–238 Re) magnetotail lobe characteristics during quiet solar wind conditions

The distant ( X = 200–238 R e) tail lobe average properties under quiet solar wind conditions have been determined using simultaneous ISEE-3 magnetic field and IMP-8 magnetic field and plasma observations. Under external solar wind pressuresof P ext = B 2/8 π+ Nk( T e+ T i) ⩽5×10 −10 dynes cm −2, an average tail lobe field strength of 7.1±1.2 nT and average plasma beta (8 π nK T/ B 2) of 0.3 are determined. It is concluded that under quiet solar wind conditions, the distant tail lobes are typically dominated by the magnetic field pressure.

The magnetic field turbulence near interplanetary shock fronts

The power spectra (frequency range 10 −3 to 10 −2 Hz) of the magnetic field fluctuations near i nterplanetary s hock fronts (IPS) are analysed using Venera 13 and Venera 14 data. Ten events in teh period from November, 1981 to February, 1982 typical for IPS passings are evaluated. The event on February 2, 1982 is considered in detail. A sharp increase of the magnetic turbulence downstream the shock front is common to all detected IPS. At a frequency of approx. 10 −3 Hz the spectral density of the IMF fluctuations increases by factors of 50 to 100. The strong field turbulences in the post-shock region last about 6 to 9 hours. The IMF turbulence level decreases significantly (at 10 −3 Hz) within the flare plasma fluxes (driver gas region). In the analysed period four different types of IMF power spectra are found depending on the location of the magnetic turbulence regions: In the post-shock region, near the boundaries of IMF flux tubes, in the quiet solar wind and inside the flare plasma fluxes.

Numerical investigation of fluid models with full electron and proton thermal conduction equations for the quiet solar wind

The effect of using full equations (rather than Fourier law expressions) for the electron and proton thermal conductivities in conjunction with community, momentum, and temperature equations for the description of spherically symmetric quiet solar wind states is investigated numerically. For this purpose a time-dependent method is used, and steady state solutions in both subsonic and supersonic regimes between the sun and 5 AU are obtained and presented. The consequences for one-fluid and two-fluid models for the solar wind are summarized and discussed.

A self-similar flow in Generalized Roche model with increasing energy

The self-similar flow of a gas, moving under the gravitational attraction of a central body of fixed mass behind a spherical shock wave driven out by a propelling contact surface into quiet solar wind region, is investigated. The total energy content between the inner expanding surface and the shock front increases with time. In the last section we briefly pose the self-similar isothermal flow of a gas behind a spherical shock wave.

Self-similar flows behind shock wave with increasing energy in magnetogasdynamics, I

Self-similar solutions for adiabatic and isothermal flows driven out by a propelling contact surface, moving into a quiet solar wind region, are investigated in the presence of magnetic field. The total energy of the flow between the shock and the contact surface is taken to be time-dependent obeying a power-law. The shock is assumed to be strong and propagating into a perfect gas at rest with non uniform density and magnetic field.

Quiet-time solar-wind ionic composition

The ISEE-B EGD solar-wind plasma experiment often observes heavy ions in the solar wind. Selecting two periods of quiet solar wind with no particles observed backstreaming from the Earth’s bow-shock, we show that different ion species follow similar trends in terms of changes in the bulk speed and changes in the particle number density. In particular, quiet-solar-wind ionic abundances in these two cases are (relative to H+)4He2+=(1”5)·10−2,3He2+=1.5·10−4, 0+6=(3”15)·10−4, O+7=3·10−4, Si=1·10−4, Fe=0.5·10−4. We show that, if4He2+ abundance increases, the same occurs for the Si, O+7 and O+6 abundances. Finally the O+6 density fluctuations seem to be anticorrelated with4He2+ density fluctuations.

On the modeling of the three-fluid structure of the quiet solar wind

The reciprocal influence of the electrons and protons, on one side, and the α-particles, on the other side in the quiet solar wind is investigated within the framework of a conductive three-fluid model (with frictional forces included). For this purpose two mathematical methods are used, namely: I. Simultaneous solution of the fluid equations for all three species; and II. Solution of two-fluid equations (for electrons and protons) followed by that of a ‘modified’ one-fluid equation for the α-particles (in which the two-fluid solutions are used for electrons and protons).