Engineering topics

Ogilvie, K. W.

Publications and source records attributed to Ogilvie, K. W..

At least 343 records · Page 19

NASA NTRS1994

The subcritical, quasi-parallel, switch-on shock

The conditions that lead to subcritical, quasi-parallel bow shocks are very rare. Even more rarely, a subcritical, quasi-parallel shock can also be termed a switch-on shock, where the tangential component of the magnetic field, which is very small upstream, is said to 'switch on' downstream. The Rankine-Hugoniot conservation relations predict that the jump in the tangential component of the magnetic field across the shock is very large for these upstream conditions. In this study, we find that the measured jumps in the plasma conditions are in accord with predictions made by the Rankine-Hugoniot conservation relations. The structure of the switch-on shock, not predicted by the Rankine-Hugoniot equations, is very similar to that of the subcritical, quasi-perpendicular shock, with the exception that the precursor wave in front of the shock ramp damps more slowly.

Farris, M. H.↗

NASA NTRS1994

Interstellar oxygen, nitrogen and neon in the heliosphere

Oxygen, nitrogen and neon pick-up ions of interstellar origin were detected for the first time with the Solar Wind Ion Spectrometer (SWICS) on board Ulysses. The interstellar origin of these ions is established by the following criteria: (a) they are singly charged, (b) they have the broad velocity distributions characteristic of pick-up ions, with an upper limit of twice the solar wind speed, (c) their relative abundance as a function of distance from the sun corresponds to the theoretical expectation, and (d) there is no relation to a planetary or cometary source. The interstellar abundance ratios He(+)/O(+), N(+)/O(+), Ne(+)/O(+) were investigated. At approximately 5.25 AU in the outermost part of Ulysses' trajectory He(+)/O(+) = 175(sup +70 sub -50) N(+)/O(+) = 0.13(sup +0.05 sub -0.05) and Ne(+)/O(+) = 0.18(sup +0.10 sub -0.07) were determined. For the interstellar gas passing through the termination region and entering the heliosphere (He/O)(sub 0) = 290(sup +190 sub -100), (N/O)(sub 0) = 0.13(sup +0.06 sub -0.06) and (Ne/O)(sub 0) = 0.20(sup +0.12 sub -0.09) were obtained from the pick-up ion measurements. Upper limits for the relative abundances of C(+) and C were also determined.

Geiss, J.↗

NASA NTRS1993

Detection of interstellar pick-up hydrogen in the solar system

Interstellar hydrogen ionized primarily by the solar wind has been detected by the Solar Wind Ion Composition Spectrometer instrument on the Ulysses spacecraft at a distance of 4.8 AUs from the sun. This 'pick-up' hydrogen is identified by its distinct velocity distribution function, which drops abruptly at twice the local solar wind speed. From the measured fluxes of pick-up protons and singly charged helium, the number densities of neutral hydrogen and helium in the distant regions of the solar system are estimated to be 0.077 +/- 0.015 and 0.013 +/- 0.003 per cu cm, respectively.

Gloeckler, G.↗

NASA NTRS1993

High-velocity tails on the velocity distribution of solar wind ions

Recent observations of the solar wind using the SWICS instrument on the Ulysses spacecraft have shown the presence of high-velocity 'tails' on the velocity distribution of protons. Similar features have also been observed on the velocity distributions of helium and oxygen ions. Of the order of 1 percent of the solar wind density is involved in these tails, which are approximately exponential in shape and persist to V = V(B) + 10V(th) or beyond, where VB is the bulk velocity and V(th) the thermal velocity of the solar wind. This paper contains a preliminary description of the phenomenon. It is clear that it is ultimately connected with the passage of interplanetary shocks past the spacecraft and that particle acceleration at oblique shocks is involved.

Ogilvie, K. W.↗

NASA NTRS1992

Heat flux dropouts in the solar wind and Coulomb scattering effects

Data on solar wind electrons at the ISEE 3 spacecraft located 0.01 AU upstream from the earth (McComas et al., 1989) showed periods of time when the flux of antisunward suprathermal electrons would decrease suddenly, leading to heat flux dropouts (HFDs). This paper examines data from ISEE 1 at the 1.5 x 10 exp 6 km downstream location to determine whether HFDs identified at ISEE 3 by McComas et al. can be detected at this location and whether the ISEE 1 observations can provide information to one or the other possible interpretations of HFDs: that HFDs are due to enhanced Coulomb scattering, or to disconnection from the sun of the magnetic flux tube. The results of the examination identified the presence of HFD events in the ISEE 1 data, and the findings indicate that Coulomb scattering plays a substantial role in at least some HFD events.

Fitzenreiter, R. J.↗

NASA NTRS1992

Low-energy particle layer outside of the plasma sheet boundary

The ISEE spacecraft in the geomagnetic tail frequently crossed the high-latitude boundary of the plasma sheet. On a number of these crossings on the morningside (between 15 RE and 22 RE) the ISEE instruments detected an enhanced population of low-energy electrons and ions immediately adjacent to the plasma sheet boundary layer (PSBL). The electrons in this low-energy layer (LEL) have energies less than a few hundred eV, and they are aligned along the magnetic field direction propagating in the tailward direction. The ions have energies less than 100 eV and are also streaming along the magnetic field direction but in the earthward direction. These particles are clearly distinguished from the bulk of the particles in the plasma sheet and the PSBL. These observations may help clarify where the various particle features in the geomagnetic tail map to in the ionosphere. It is suggested that the LEL maps to the soft (less than 1 keV) electron precipitation region poleward of the plasma sheet boundary.

Parks, G. K.↗

NASA NTRS1992

Ions with low charges in the solar wind as measured by SWICS on board Ulysses

We present new data on rare ions in the solar wind. Using the Ulysses-SWICS instrument with its very low background we have searched for low-charge ions during a 6-d period of low-speed solar wind and established sensitive upper limits for many species. In the solar wind, we found He(1+)/He(2+) of less than 5 x 10 exp -4. This result and the charge state distributions of heavier elements indicate that all components of the investigated ion population went through a regular coronal expansion and experienced the typical electron temperatures of 1 to 2 million Kelvin. We argue that the virtual absence of low-charge ions demonstrates a very low level of nonsolar contamination in the source region of the solar wind sample we studied. Since this sample showed the FlP effect typical for low-speed solar wind, i.e., an enhancement in the abundances of elements with low first ionization potential, we conclude that this enhancement was caused by an ion-atom separation mechanism operating near the solar surface and not by foreign material in the corona.

Geiss, J.↗

NASA NTRS1992

Solar wind iron and oxygen charge states and relative abundances measured by SWICS on Ulysses

We present the results of a survey of iron and oxygen charge state distributions as detected by the Solar Wind Ion Composition Spectrometer on the Ulysses spacecraft. The results are categorized in terms of the ionization temperature determined every approximately 13 minute instrument cycle from the O(+7) to O(+6) ratio. Our preliminary Fe/O abundance ratio is 0.12 averaged over this 3 month survey. The Fe charge state distributions accumulated during times of high oxygen ionization temperatures are clearly nonisothermal.

Ipavich, F. M.↗

NASA NTRS1992

Solar wind composition from sector boundary crossings and coronal mass ejections

Using the Ion Composition Instrument (ICI) on board the ISEE-3/ICE spacecraft, average abundances of He-4, He-3, O, Ne, Si, and Fe have been determined over extended periods. In this paper the abundances of He-4, O, Ne, Si, and Mg obtained by the ICI in the region of sector boundary crossings (SBCs), magnetic clouds and bidirectional streaming events (BDSs) are compared with the average abundances. Both magnetic clouds and BDSs are associated with coronal mass ejections (CMEs). No variation of abundance is seen to occur at SBCs except for helium, as has already been observed. In CME-related material, the abundance of neon appears to be high and variable, in agreement with recent analysis of spectroscopic observations of active regions. We find that our observations can be correlated with the magnetic topology in the corona.

Ogilvie, K. W.↗

NASA NTRS1991

The interaction of a very large interplanetary magnetic cloud with the magnetosphere and with cosmic rays

The observation of one of the largest magnetic clouds ever observed at a distance of 1 AU, with a diameter of greater than about 0.4 AU, is reported. The cloud is shown to be almost unchanged structurally by interaction with the earth bow shock. The first observations are reported of an auroral activity response to the passage of a magnetic cloud, with a nearly immediate increase in auroral activity when the IMF theta(B) angle reversed polarity to negative near the cloud center. The results provide strong evidence that turbulent magnetic fields behind interplanetary shocks are a possible cause of Forbush decreases, but contest the idea that relatively smooth, strong fields in clouds are a cause of such decreases. The cloud field modeling supports the existence of magnetic force-free fields in describing cloud structure.

Lepping, R. P.↗

NASA NTRS1991

Modeling the effects of fast shocks on solar winds ions

Observations show that, when alpha particles and other minor ions in the solar wind plasma encounter fast shocks, they are heated more than protons and their bulk motion is decelerated less than protons. These effects have been studied using a three-fluid model, and the model predictions have been compared with observations. The comparison indicates that, for supercritical fast shocks, the three-fluid model can explain cross-shock minor ion heating which is significantly greater than that of protons. When the ratio of specific heats for minor ions, gamma (alpha), equals 2, both the lesser cross-shock deceleration and the greater heating of minor ions than of protons can be predicted by the model; thus, the minor ion heating through the shock transition region is consistent with the involvement of two degrees of freedom. Because the analysis is formulated in the de Heffmann-Teller frame of reference, the method is not valid for perpendicular shocks or when the angle is large. These results agree with the few extant observations and might be confirmed by further observations at the earth's bow shock.

Zhao, Xuepu↗

NASA NTRS1990

Heating of minor ions by the coronal slow shock

The coronal slow shock has been predicted to exist embedded in large coronal holes at 4-10 solar radii. In this paper, a three-fluid model is used to study the jumps in minor ion properties across a slow shock such as the coronal slow shock. The jump conditions are formulated in the de Hoffmann-Teller frame of reference. The Rankine-Hugoniot solution determines the MHD flow and the magnetic field across the shocks. For each minor ion species, the fluid equations for the conservation of mass, momentum, and energy can be solved to determine the velocity and the temperature of the ions across the shock. Also obtained is a similarity solution for heavy ions. The results show that, on the downstream side of the slow shock, the ion temperatures are nearly proportional to the ion masses for He, O, Si, and Fe, in agreement with observed ion temperatures in the inner solar wind. This indicates that the possibly existing coronal slow shock can be responsible for the observed heating of minor ions in the solar wind.

Whang, Y. C.↗

NASA NTRS1990

Space-based measurements of elemental abundances and their relation to solar abundances

The Ion Composition Instrument (ICI) aboard the ISEE-3/ICE spacecraft was in the solar wind continuously from August 1978 to December 1982. The results made it possible to establish long-term average solar wind abundance values for helium, oxygen, neon, silicon, and iron. The Charge-Energy-Mass instrument aboard the CCE spacecraft of the AMPTE mission has measured the abundance of these elements in the magnetosheath and has also added carbon, nitrogen, magnesium, and sulfur to the list. There is strong evidence that these magnetosheath abundances are representative of the solar wind. Other sources of solar wind abundances are Solar Energetic Particle experiments and Apollo lunar foils. When comparing the abundances from all of these sources with photospheric abundances, it is clear that helium is depleted in the solar wind while silicon and iron are enhanced. Solar wind abundances for carbon, nitrogen, oxygen, and neon correlate well with the photospheric values. The incorporation of minor ions into the solar wind appears to depend upon both the ionization times for the elements and the Coulomb drag exerted by the outflowing proton flux.

Coplan, M. A.↗

NASA NTRS1989

Plasma observations near Neptune - Initial results from Voyager 2

The plasma science experiment on Voyager 2 made observations of the plasma environment in Neptune's magnetosphere and in the surrounding solar wind. Because of the large tilt of the magnetic dipole and fortuitous timing, Voyager entered Neptune's magnetosphere through the cusp region, the first cusp observations at an outer planet. Thus the transition from the magnetosheath to the magnetosphere observed by Voyager 2 was not sharp but rather appeared as a gradual decrease in plasma density and temperature. The maximum plasma density observed in the magnetosphere is inferred to be 1.4 per cubic centimeter (the exact value depends on the composition), the smallest observed by Voyager in any magnetosphere. The plasma has at least two components; light ions (mass, 1 to 5) and heavy ions (mass, 10 to 40), but more precise species identification is not yet available. Most of the plasma is concentrated in a plasma sheet or plasma torus and near closest approach to the planet. A likely source of the heavy ions is Triton's atmosphere or ionosphere, whereas the light ions probably escape from Neptune. The large tilt of Neptune's magnetic dipole produces a dynamic magnetosphere that changes configuration every 16 hours as the planet rotates.

Belcher, J. W.↗

NASA NTRS1989

Solar wind observations with the ion composition instrument aboard the ISEE-3 ICE spacecraft

The principal observations obtained by the Ion Composition Instrument (ICI) flown on the ISEE-3/ICE spacecraft, which was in the solar wind from September 1978 to the end of 1982, before being directed to the far magnetotail of the Earth are discussed. Almost continuous observations were made of the abundances of 3He++, 4He++, O6+, O7+, Ne, Si and Fe in various charge states, and of their bulk speeds and temperatures. The results show that there is a strong tendency in the collisionless solar wind for the ionic temperatures to be proportional to the masses. For heavier ions these temperatures exceed typical coronal electron temperatures. 4He++, especially in high speed streams, moves faster than H+, and travels at the same speed as heavier ions. The mechanism leading to this heating and rapid streaming is still not entirely clear.

Ogilvie, K. W.↗

NASA NTRS1989

Solar wind observations with the ion composition instrument aboard the ISEE-3/ICE spacecraft

The principal observations obtained by the Ion Composition Instrument (ICI) flown on the ISEE-3/ICE spacecraft, which was in the solar wind from September 1978 to the end of 1982, before being directed to the far magnetotail of the Earth are discussed. Almost continuous observations were made of the abundances of 3He++, 4He++, 06+, 07+, Ne, Si and Fe in various charge states, and of their bulk speeds and temperatures. The results show that there is a strong tendency in the collisionless solar wind for the ionic temperatures to be proportional to the masses. For heavier ions these temperatures exceed typical coronal electron temperatures. 4He++, especially in high speed streams, moves faster than H+, and travels at the same speed as heavier ions. The mechanism leading to this heating and rapid streaming is still not entirely clear.

Ogilvie, K. W.↗

NASA NTRS1987

Ion composition and upstream solar wind observations at comet Giacobini-Zinner

The observations by the ion composition instrument (ICI) on the ICE spacecraft made during the encounter with comet P/Giacobini-Zinner (Ogilvie et al., 1986) are discussed in detail. Solar wind He-4(2+) kinetic temperatures, densities, and velocities before, during, and after the encounter are presented. These data combined with He-4(2+) velocity distributions provide evidence for the existence of a thick diffuse shock. Relative abundances of water group ions and CO(+) are derived along with an estimate of the abundance of an ion with M/Q = 24 + or - 1 amu/e. The ICI data are compared with electron data from two other experiments (Bame et al., 1986; Meyer-Vernet et al., 1986) and found to be in reasonable agreement in the region outside the tail. Spectroscopic data for several neutral and ionic species are compared with the ICI results for the water group ions and CO(+). The spectroscopic data are also used to eliminate Mg(+) and CN(+) as candidates for the M/Q = 24 peak. The two most likely candidates are C2(+) and Na(+), but neither photoionization of parent neutrals nor sputtering from dust grains is sufficient to explain the observed abundance relative to H2O(+).

Coplan, M. A.↗

NASA NTRS1986

Origin of metal ions in the coma of P/Giacobini-Zinner

During the crossing of the ICE spacecraft through the coma of the comet Giacobini-Zinner, ions with a mass/charge ratio 24 + or - 1 were unexpectedly found. Na(+) and/or Mg(+) would fit into this mass range. Processes that could lead to high metal ion abundances in cometary comas are discussed and it is concluded that evaporation or sputtering from silicate grains are not likely to be responsible. A remaining possibility is the occurrence of alkali metals in the icy phase as a result of either cometary differentiation or cocondensation of these elements with the icy component prior to the accretion of cometary bodies.

Geiss, J.↗