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NASA NTRS2023

Space Weathering of Genesis Mission Solar-wind Collectors with Inferences for Weathering on Airless Bodies

Samples from the Genesis Solar Wind Sample Return (NASA Discovery 5) are a unique opportunity to study the initial stages of space weathering, i.e., the physical and chemical effects of solar-wind irradiation. Arrays of collectors containing multiple materials were each exposed to a different solar-wind regime (fast, slow, bulk, or coronal mass ejection) at the L1 point for long durations (years). Materials exposed to the solar wind included metals, semiconductors, and insulators. Although the time of exposure was obviously short relative to samples having extraterrestrial origins, optical properties, surface chemical properties, and matrix structure have changed in many collectors due to exposure to solar wind. The thickness of amorphous zones, where present, appears to correspond with the depth of the peak of the solar-wind H distribution in each regime. Damage from high-energy particles was negligible because the collectors were 700 μm or less in thickness and shielded from the back by the spacecraft. Micrometeorite impacts and sputtering were also negligible because of the short exposure times. Our current results are preliminary: We hope future workers will extend this study both to support Genesis characterization efforts and to further understand space-weathering processes on a geologic timescale.

space weathering↗

NASA NTRS1994

Neutral hydrogen in the solar wind acceleration region

Observation of solar Ly alpha radiation scattered by coronal neutral hydrogen atoms can be used to investigate the acceleration region of the solar wind. In this paper we focus on the use of these observations to study Alfven waves, which can accelerate the solar wind plasma to flow speeds observed in high-speed streams if their amplitude at the coronal base is 20 km/s or larger. The wave amplitude is then larger than the proton thermal speed in the outer corona, so that the mean proton speed (averaged over a wave period) is significantly larger than the proton thermal speed. For low-frequency wave the hydrogen atoms follow the proton motion in the waves, while for higher frequencies the protons move relative to the neutrals. Nevertheless, in the higher frequency case, the rates for charge exchange and recombination are high enough to broaden the velocity distribution function of neutral hydrogen. Both the wave motion of the hydrogen atoms in low-frequency Alfven waves and the 'heating' by higher frequency waves lead to a broadening of the scattered solar Ly alpha line. For coronal base amplitues of 20 km/s, the line broadening increases with heliocentric distance beyond 4-5 solar radii.

Olsen, Espen Lyngdal↗

NASA NTRS1977

A reexamination of two-fluid solar wind models

The two-fluid solar-wind equations have been solved by a method which is approximately 50 times faster than any previously developed, through the use of asymptotic expansions which are self-consistently iterated upon to find a solution that passes through the critical point. The energy assumptions in two-fluid solar-wind models are reexamined, and the conclusions are as follows: (1) proton thermal conduction may not be neglected, (2) the Coulomb logarithm must be calculated as a function of radius, and (3) the electron and proton temperatures at the base need not be equal, even when the time scale for energy exchange between the species is an order of magnitude smaller than the expansion time at the base. It is possible to reproduce reasonable quiet-time solar-wind parameters at 1 AU, but only if the proton temperature is approximately twice the electron temperature at 1 solar radius. This may indicate that extended proton heating is important in the outer solar corona. Winds with velocities at 1 AU of 450 km/s are generated without nonthermal energy deposition but require high proton temperatures as well as very low densities at the base. Higher-velocity solutions are not possible in a spherically symmetric geometry for reasonable particle fluxes at 1 AU, and it is suggested that these higher-velocity states probably require additional heating, acceleration mechanisms, or nonradial flow.

Nerney, S.↗

NASA NTRS1978

Pioneer 10 observation of the solar wind proton temperature heliocentric gradient

Solar wind isotropic proton temperatures as measured out to 12.2 AU heliocentric distance by the Ames plasma analyzer aboard Pioneer 10 are presented as consecutive averages over three Carrington solar rotations and discussed. The weighted least-squares fit of average temperature to heliocentric radial distance, R, yields the power law R sup -.52. These average proton temperatures are not correlated as well with Pioneer 10's heliocentric radial distance (-.85) as are the corresponding average Zurich sunspot numbers R sub z (-.95). Consequently, it is difficult to isolate the spatial gradient in the Pioneer 10 solar wind proton temperatures using that data alone.

Mihalov, J. D.↗

NASA NTRS1983

The ISPM solar-wind plasma experiment

The ISPM solar wind plasma experiment accurately characterizes the bulk flow and internal state conditions of the interplanetary plasma in three dimensions at all heliographic distances and heliographic latitudes reached by the spacecraft. Solar wind electrons, protons, alpha particles, and heavier ions are measured. Oxygen, silicon, and iron ions at various charge levels are resolved. Electrons and ions are measured simultaneously with independent curved-plate electrostatic analysers equipped with multiple continuous channel electron multipliers arranged so that particle velocity distributions are suitably resolved without gaps in spacecraft polar-angle space. Electrons with energies between 1 and 900 eV are detected at 7 polar angles and various combinations of azimuth angle to cover the unit sphere comprehensively. Ions are detected between 257 eV/Q and 35 keV/Q. Data matrices are obtained every 4 min when the spacecraft is actively transmitting and every 8 min during storage periods. These matrices contain sufficient energy and angle resolution to permit detailed calculations of ion velocity distributions.

Bame, S. J.↗

NASA NTRS1995

Solar wind eddies and the heliospheric current sheet

Ulysses has collected data between 1 and 5 AU during, and just following solar maximum, when the heliospheric current sheet (HCS) can be thought of as reaching its maximum tilt and being subject to the maximum amount of turbulence in the solar wind. The Ulysses solar wind plasma instrument measures the vector velocity and can be used to estimate the flow speed and direction in turbulent 'eddies' in the solar wind that are a fraction of an astronomical unit in size and last (have either a turnover or dynamical interaction time of) several hours to more than a day. Here, in a simple exercise, these solar wind eddies at the HCS are characterized using Ulysses data. This character is then used to define a model flow field with eddies that is imposed on an ideal HCS to estimate how the HCS will be deformed by the flow. This model inherently results in the complexity of the HCS increasing with heliocentric distance, but the result is a measure of the degree to which the observed change in complexity is a measure of the importance of solar wind flows in deforming the HCS. By comparison with randomly selected intervals not located on the HCS, it appears that eddies on the HCS are similar to those elsewhere at this time during the solar cycle, as is the resultant deformation of the interplanetary magnetic field (IMF). The IMF deformation is analogous to what is often termed the 'random walk' of interplanetary magnetic field lines.

Suess, S. T.↗

NASA NTRS1986

The solar wind interaction with Venus

The relation between Venus and the solar wind is analyzed. The effects of the intrinsic field, neutral atmosphere, and ionosphere of Venus on the solar wind are examined. The solar wind interaction phenomena is studied; consideration is given to the free-stream solar wind, bow shock, magnetosheath, boundary layer, ionospheric features, neutral atmosphere features, and wake and magnetotail. Further research on the boundary layer and tail formation, global models, and high-dynamic pressure interaction is proposed.

Luhmann, J. G.↗

NASA NTRS1967

The angular momentum of the solar wind.

Steady state model of solar wind flow in equatorial plane solved for radial and azimuthal motions, taking into account pressure gradient, magnetic field and gravitational effects

PRESSURE GRADIENT↗

NASA NTRS1976

Coronal holes as sources of solar wind

We investigate the association of high-speed solar wind with coronal holes during the Skylab mission by: (1) direct comparison of solar wind and coronal X-ray data; (2) comparison of near-equatorial coronal hole area with maximum solar wind velocity in the associated streams; and (3) examination of the correlation between solar and interplanetary magnetic polarities. We find that all large near-equatorial coronal holes seen during the Skylab period were associated with high-velocity solar wind streams observed at 1 AU.

Nolte, J. T.↗

NASA NTRS1988

Simulation and non-linear stage of the electrostatic waves observed during the AMPTE lithium release in the solar wind

During the AMPTE lithium releases in the solar wind intense electrostatic waves with frequencies between a few tens of Hz to several kHz were observed outside the diamagnetic cavity. The results of linear Vlasov theory have suggested that these waves may be generated through two types of instabilities. One is the ion-ion instability associated with the relative drift between the lithium ions and the solar wind protons, and the other is the ion-acoustic instability due to the relative drift between the electrons and the ions. In order to look at the non-linear behavior of the wave-particle interactions, and discern the effect of waves on the particles, full particle electrostatic simulations have been performed, and the results are presented here. It is shown that the ion-ion instability whose phase velocity is oblique to the solar wind velocity can cause considerable anisotropic 'heating' of both the lithium ions and the solar wind protons.

Omidi, N.↗

NASA NTRS2013

Plan for Subdividing Genesis Mission Diamond-on-Silicon 60000 Solar Wind Collector

NASA's Genesis solar wind sample return mission experienced an off nominal landing resulting in broken, albeit useful collectors. Sample 60000 from the collector is comprised of diamond-like-carbon film on a float zone (FZ) silicon wafer substrate Diamond-on-Silicon (DOS), and is highly prized for its higher concentration of solar wind (SW) atoms. A team of scientist at the Johnson Space Center was charged with determining the best, nondestructive and noncontaminating method to subdivide the specimen that would result in a 1 sq. cm subsample for allocation and analysis. Previous work included imaging of the SW side of 60000, identifying the crystallographic orientation of adjacent fragments, and devising an initial cutting plan.

Burkett, Patti J.↗

NASA NTRS1992

A parameter study of the two-fluid solar wind

A two-fluid model of the solar wind was introduced by Sturrock and Hartle (1966) and Hartle and Sturrock (1968). In these studies the proton energy equation was integrated neglecting the heat conductive term. Later several authors solved the equations for the two-fluid solar wind model keeping the proton heat conductive term. Methods where the equations are integrated simultaneously outward and inward from the critical point were used. The equations were also integrated inward from a large heliocentric distance. These methods have been applied to cases with low coronal base electron densities and high base temperatures. In this paper we present a method of integrating the two-fluid solar wind equations using an iteration procedure where the equations are integrated separately and the proton flux is kept constant during the integrations. The technique is applicable for a wide range of coronal base densities and temperatures. The method is used to carry out a parameter study of the two-fluid solar wind.

Sandbaek, Ornulf↗

NASA NTRS1995

Non-radial flow in the solar wind

Although the radial component of the solar wind dominates the solar wind speed, significant non-radial velocity components are also present. These flows are more difficult to measure accurately, but we now have data sets including the east-west (tangential) and north-south (normal) flows from PVO at Venus, IMP 8 at Earth, and Voyagers 1 and 2 from 1 to 45 AU. We compare the non-radial flow observations from these spacecraft. One of the more interesting features is that the north-south flow angle observed at Earth and Venus oscillates with the period of a local (Earth or Venus) year. These oscillations occur throughout two solar cycles in the IMP 8 data set and are very apparent in the PVO data from 1978 to 1986 but less obvious after this. We will report on the origin of this feature. The tangential flow observed by both IMP 8 and Voyager is on average slightly positive (approximately 1.75 km/s). The magnitudes of the nonradial velocity components decrease with distance from the Sun.

Richardson, J. D.↗

NASA NTRS1976

Solar cycle evolution of high-speed solar wind streams

Large amplitude high-speed solar wind streams and streams with maximum speeds in excess of 700 km/sec are far more common in years of declining and minimum solar activity than near solar maximum. Further, the broadest solar wind streams observed directly with space probes during the years 1962-1974 occurred near solar minimum in 1974. Changes in the frequency and nature of solar wind stream structures at the orbit of earth appear to be directly related to the long-term evolution of regions of low density in the solar corona.

Bame, S. J.↗

NASA NTRSDate not supplied

Global Magnetic Reconnection with Weakly Shocked Solar Wind During Geomagnetic Storms

The solar wind and magnetic field emanating from the sun typically reaches Earth moving at a super-Alfvénic velocity (multiple times the local Alfvén wave speed). This leads to the formation of a bow shock upstream of the planet where the plasma is slowed and heated and the interplanetary magnetic field is compressed before it interacts with Earth's magnetic field. However, a number of recent geomagnetic storm events have been associated with sustained intervals of nearly or indeed fully sub-Alfvénic flows. A weakly- or un-shocked magnetosheath changes the conditions for magnetic reconnection at the magnetopause and subsequently the storm-time evolution of the magnetosphere. We perform Multiscale Atmosphere-Geospace Environment (MAGE) simulations of three different geomagnetic storms each containing a period of nearly or fully sub-Alfvénic solar wind driving and examine the properties of global reconnection. The structure of the night-side magnetosphere and polar cusps are also examined. The dynamical evolution of the global magnetosphere during strong driving represents a key science target for the NASA Heliophysics System Observatory, particularly Magnetospheric Multiscale (MMS) targeting magnetotail/magnetopause reconnection and Tandem Reconnection and Cusp Electrodynamics Reconnaissance Satellites (TRACERS) observing ion dispersion in the cusps.

Brandon Burkholder↗

NASA NTRS2010

Highly Alfvenic Slow Solar Wind

It is commonly thought that fast solar wind tends to be highly Alfvenic, with strong correlations between velocity and magnetic fluctuations, but examples have been known for over 20 years in which slow wind is both Alfvenic and has many other properties more typically expected of fast solar wind. This paper will present a search for examples of such flows from more recent data, and will begin to characterize the general characteristics of them. A very preliminary search suggests that such intervals are more common in the rising phase of the solar cycle. These intervals are important for providing constraints on models of solar wind acceleration, and in particular the role waves might or might not play in that process.

Roberts, D. Aaron↗

NASA NTRS1976

A two-region model of the solar wind including azimuthal velocity

The two-region model of the solar wind divides the interplanetary space into two regions: it assumes that the solar wind is one-fluid in an inner region within 0.4 AU and two-fluid in an outer region beyond 0.4 AU. This paper includes the angular motion of the solar wind in the two-region model. The flow in the one-fluid region is governed by the one-fluid magnetohydrodynamic equations. The second and third moment equations of the Vlasov equation together with other conservation equations are used to describe the solar-wind flow in the two-fluid region. The predicted azimuthal velocity at 1 AU is less than 2 km/s. All other macroscopic and microscopic properties from this model are in good agreement with experimental quiet-time observations at 1 AU. The numerical results also confirm that when the azimuthal velocity is included in the analysis, the amount of magnetic-field energy converted into kinetic energy in the solar wind is only a small fraction of the total expansion energy flux and has little effect upon the final radial expansion velocity.

Acuna, M. H.↗

NASA NTRS1980

Solar wind flows associated with hot heavy ions

Solar wind heavy ion spectra measured with the Vela instrumentation are studied to determine the solar origins of various solar wind structures which contain anomalously high ionization states. The spectra indicating hot coronal conditions were found to occur in 1/7th of all measurements and almost exclusively in postshock flows, nonshock related helium abundance enhancements, or noncompressive density enhancements. The observation of several flared-related helium abundance enhancements suggests that the flare-heated plasma can evolve into the solar wind without producing a noticeable shock at 1 AU.

Fenimore, E. E.↗