Engineering topics

Richardson, J. D.

Publications and source records attributed to Richardson, J. D..

At least 19 records

NASA NTRS2018

Interstellar Mapping and Acceleration Probe (IMAP): A New NASA Mission

The Interstellar Mapping and Acceleration Probe (IMAP) is a revolutionary mission that simultaneously investigates two of the most important overarching issues in Heliophysics today: the acceleration of energetic particles and interaction of the solar wind with the local interstellar medium. While seemingly disparate, these are intimately coupled because particles accelerated in the inner heliosphere play critical roles in the outer heliospheric interaction. Selected by NASA in 2018, IMAP is planned to launch in 2024. The IMAP spacecraft is a simple sun-pointed spinner in orbit about the Sun-Earth L1 point. IMAP's ten instruments provide a complete and synergistic set of observations to simultaneously dissect the particle injection and acceleration processes at 1 AU while remotely probing the global heliospheric interaction and its response to particle populations generated by these processes. In situ at 1 AU, IMAP provides detailed observations of solar wind electrons and ions; suprathermal, pickup, and energetic ions; and the interplanetary magnetic field. For the outer heliosphere interaction, IMAP provides advanced global observations of the remote plasma and energetic ions over a broad energy range via energetic neutral atom imaging, and precise observations of interstellar neutral atoms penetrating the heliosphere. Complementary observations of interstellar dust and the ultraviolet glow of interstellar neutrals further deepen the physical understanding from IMAP. IMAP also continuously broadcasts vital real-time space weather observations. Finally, IMAP engages the broader Heliophysics community through a variety of innovative opportunities. This papersummarizes the IMAP mission at the start of Phase A development.

McComas, D. J.↗

NASA NTRS2017

Interplanetary Coronal Mass Ejection Observed at STEREO-A, Mars, Comet 67P/Churyumov-Gerasimenko, Saturn,and New Horizons En Route to Pluto: Comparison of Its Forbush Decreases at 1.4, 3.1, and 9.9 AU

We discuss observations of the journey throughout the Solar System of a large interplanetary coronal mass ejection (ICME) that was ejected at the Sun on 14 October 2014. The ICME hit Mars on 17 October, as observed by the Mars Express, Mars Atmosphere and Volatile EvolutioN Mission (MAVEN), Mars Odyssey, and Mars Science Laboratory (MSL) missions, 44 h before the encounter of the planet with the Siding-Spring comet, for which the space weather context is provided. It reached comet 67P/Churyumov-Gerasimenko, which was perfectly aligned with the Sun and Mars at 3.1 AU, as observed by Rosetta on 22 October. The ICME was also detected by STEREO-A on 16 October at 1 AU, and by Cassini in the solar wind around Saturn on the 12 November at 9.9 AU. Fortuitously, the New Horizons spacecraft was also aligned with the direction of the ICME at 31.6 AU. We investigate whether this ICME has a nonambiguous signature at New Horizons. A potential detection of this ICME by Voyager 2 at 110-111 AU is also discussed. The multispacecraft observations allow the derivation of certain properties of the ICME, such as its large angular extension of at least 116deg, its speed as a function of distance, and its magnetic field structure at four locations from 1 to 10 AU. Observations of the speed data allow two different solar wind propagation models to be validated. Finally, we compare the Forbush decreases (transient decreases followed by gradual recoveries in the galactic cosmic ray intensity) due to the passage of this ICME at Mars, comet 67P, and Saturn.

Witasse, O.↗

NASA NTRS2011

The Solar Wind in the Outer Heliosphere and Heliosheath

The solar wind environment has a large influence on the transport of cosmic rays. This chapter discusses the observations of the solar wind plasma and magnetic field in the outer heliosphere and the heliosheath. In the supersonic solar wind, interaction regions with large magnetic fields form barriers to cosmic ray transport. This effect, the "CR-B" relationship, has been quantified and is shown to be valid everywhere inside the termination shock (TS). In the heliosheath, this relationship breaks down, perhaps because of a change in the nature of the turbulence. Turbulence is compressive in the heliosheath, whereas it was non-compressive in the solar wind. The plasma pressure in the outer heliosphere is dominated by the pickup ions which gain most of the flow energy at the TS. The heliosheath plasma and magnetic field are highly variable on scales as small as ten minutes. The plasma flow turns away from the nose roughly as predicted, but the radial speeds at Voyager 1 are much less than those at Voyager 2, which is not understood. Despite predictions to the contrary, magnetic reconnection is not an important process in the inner heliosheath with only one observed occurrence to date.

Richardson, J. D.↗

NASA NTRS2010

Observations of the Magnetic Field and Plasma in the Heliosheath by Voyager 2 from 2007.7 to 2009.4

The density and temperature profiles of the plasma measured by Voyager 2 (V2) behind the termination shock changed abruptly near 2008.6 from relatively large average values and large fluctuations during 2007.7 to 2008.6 (interval A) to relatively low average values and very small-amplitude fluctuations during 2008.6 to 2009.4 (interval B). This paper shows that the change in the magnetic field strength B(t) was less abrupt than the plasma changes, and the fluctuations of the magnetic field strength in interval B were of moderate amplitude, with indications of a quasiperiodic structure in part of the interval. The magnetic field was directed away from the sun (positive polarity) approx. 78% +/- 5% of the time in both interval A and interval B, changing in an irregular way from positive to negative polarities throughout the interval. The polarity distribution indicates that the minimum latitudinal extent of the heliospheric current sheet (HCS) was near V2 throughout the interval, consistent with the extrapolated minimum latitudes of the HCS computed from solar magnetic field observations. Thus, V2 was observing magnetic fields from the southern polar coronal hole most of the time. The distribution of B was lognormal in interval A and Gaussian interval B.

Burlaga, L. F.↗

NASA NTRS2008

Saturn's Auroral Response to the Solar Wind: Centrifugal Instability Model

We describe a model initially presented by Sittler et al. [2006] which attempts to explain the global response of Saturn's magnetosphere and its corresponding auroral behavior to variations in the solar wind. The model was derived from published simultaneous Hubble Space Telescope (HST) auroral images and Cassini upstream measurements taken during the month of January 2004. These observations show a direct correlation between solar wind dynamic pressure and (1) auroral brightening toward dawn local time, (2) an increase of rotational movement of auroral features to as much as 75% of the corotation speed, (3) the movement of the auroral oval to higher latitudes and (4) an increase in the intensity of Saturn Kilometric Radiation (SKR). This model is an alternative to the reconnection model of Cowley et al. [2004a,b; 2005] which is more Earth-like while ours stresses rotation. If angular momentum is conserved in a global sense, then when compressed the magnetosphere will tend to spin up and when it expands will tend to spin down. With the plasma sheet outer boundary at L approximates 15 we argue this region to be the dominant source region for the precipitating particles. If radial transport is dominated by centrifugal driven flux tube interchange motions, then when the magnetosphere spins up, outward transport will increase, the precipitating particles will move radially outward and cause the auroral oval to move to higher latitudes as observed. The Kelvin-Helmholtz instability may contribute to the enhanced emission along the dawn meridian as observed by HST. We present this model in the context of presently published observations by Cassini.

Sittler, Edward C.↗

NASA NTRS2008

Impact of Universal Plasma and Energetic Particle Processes on Icy Bodies of the Kuiper Belt and the Oort Cloud

Modeling of space plasma and energetic particle interactions with icy bodies of the outer solar system is simplified when there is commonality of the underlying source, acceleration, and transport processes in spatially distinct regions from the supersonic heliosphere through the heliosheath into the local interstellar medium (LISM). Current trends in the Voyager heliosheath measurements suggest strong commonality to processes in the LISM. The Fisk-Gloeckler "universal" spectrum at suprathermal energies apparently plays a strong role in coupling the plasma and high energy particle regimes in the spatial and energetic transitions from the outer heliosphere to the LISM. Dominant processes in consecutive energy regimes project to varying effects versus irradiation depth on exposed upper surfaces of airless small icy bodies and to upper atmospheres of larger bodies such as Titan and Pluto. Relative absence of the universal suprathermal spectrum in the mid-heliospheric region of the classical Kuiper Belt may profoundly affect surface color diversity of icy bodies in this region.

Cooper, John F.↗

NASA NTRS2007

Sheaths: A Comparison of Magnetospheric, ICME, and Heliospheric Sheaths

When a supersonic flow encounters an obstacles, shocks form to divert the flow around the obstacle. The region between the shock and the obstacle is the sheath, where the supersonic flow is compressed, heated, decelerated, and deflected. Supersonic flows, obstacles, and thus sheaths are observed on many scales throughout the Universe. We compare three examples seen in the heliosphere, illustrating the interaction of the solar wind with obstacles of three very different scales lengths. Magnetosheaths form behind planetary bow shocks on scales ranging from tens to 100 planetary radii. ICME sheath form behind shocks driven by solar disturbances on scale lengths of a few to tens of AU. The heliosheath forms behind the termination shock due to the obstacle presented by the interstellar medium on scale lengths of tens to a hundred AU. Despite this range in scales some common features have been observed. Magnetic holes, possibly due to mirror mode waves, have been observed in all three of these sheaths. Plasma depletion layers are observed in planetary and ICME sheaths. Other features observed in some sheaths are wave activity (ion cyclotron, plasma), energetic particles, transmission of Alfven waves/shocks, tangential discontinuities turbulence behind quasi-parallel shocks, standing slow mode waves, and reconnection on the obstacle boundary. We compare these sheath regions, discussing similarities and differences and how these may relate to the scale lengths of these regions.

Sibeck, D. G.↗

NASA NTRS2006

Cosmic Ray Mantle Visibility on Kuiper Belt Objects

Optically red objects constitute the dynamically cold, old component of the Classical Kuiper Belt (40 - 47 AU) with heliocentric orbits of low eccentricity and inclination. The red colors likely arise from primordial mixed ices processed by irradiation to meters in surface depth over the past four billion years, since the time of giant planet migration and Kuiper Belt stirring, at relatively moderate dosages of 60 gigarads provided by galactic cosmic ray protons and heavier ions. The red cosmic ray mantle is uniformly visible on the cold classical objects beneath a minimally thin eroded layer of more neutrally colored material arising from cumulative effects of heliospheric particle irradiation. The radiation fluxes are lowest in the middle heliospheric region containing the Classical Kuiper Belt and increase from there both towards and away from the Sun. Despite increasing irradiation at various times of solar system history from increases in solar and interstellar ion fluxes, the red object region has apparently never reached sufficiently high dosage levels to neutralize in color the red mantle material. Erosion processes, including plasma sputtering and micrometeroid impacts, act continuously to reduce thickness of the upper neutral crust and expose the cosmic ray mantle. A deeper layer at tens of meters and more may consist of relatively unprocessed ices that can erupt to the surface by larger impacts or cryovolcanism and account for brighter surfaces of larger objects such as 2003 UB313. Surface colors among the Kuiper Belt and other icy objects of the outer solar system are then a function, assuming uniform primordial composition, of relative thickness for the three layers and of the resurfacing age dependent on the orbital and impact history of each object.

Cooper, John F.↗

NASA NTRS2006

Thermodynamic Structure of Collision-Dominated Expanding Plasma: Heating of Interplanetary Coronal Mass Injections

We investigate the thermodynamic structure of interplanetary coronal mass ejections (ICMEs) using combined surveys of the ejecta between 0.3 and 20 AU. ICMEs are shown to have a moderate expansion in the solar wind compared with theoretical predictions. The expansion seems to be governed by a polytrope with gamma approx. 1.3 in this distance range. We find that Coulomb collisions are important contributors to the ion-ion equilibration process in the ICME plasma. The alpha-proton differential speed quickly drops to below 10 km/s due to strong Coulomb collisions. However, the two species of particles are far from thermal equilibrium with a temperature ratio T(sub alpha/T(sub p) = 4-6, suggestive of a preferential heating of alpha particles. The plasma heating rate as a function of heliocentric &stance required for the temperature profile is deduced by taking into account the expansion and energy transfer between protons and alphas via Coulomb collisions. The turbulence dissipation rate is also inferred from the inertial range power spectrum of magnetic fluctuations within ICMEs. Comparison of the turbulence dissipation rate with the required heating rate shows that turbulence dissipation seems sufficient to explain the ICME heating. Sources powering the turbulence are also investigated by examining the instabilities induced by temperature anisotropies and energy deposition by pickup ions.

Liu, Y.↗

NASA NTRS2006

Cassini Observations of Saturn's Dawn-Magnetotail Region and their Relation to Models of Saturn's Aurora: Preliminary Results

Using Cassini plasma and magnetic field observations from the dawn meridian of Saturn s outer magnetosphere to Saturn s magnetotail region, we investigate the applicability of the centrifugal instability model by Sittler et al. [2006] for Saturn s auroral response to the solar wind, versus the reconnection model of Saturn s aurora by Cowley et al. [2005]. We use Cassini Plasma Spectrometer (CAPS) Ion Mass Spectrometer (IMS) and Electron Plasma Spectrometer (ELS) observations to characterize the plasma environment. ELS and magnetometer observations are used to map out the morphology of the outer magnetosphere from dawn to midnight local time. IMS observations are used to measure plasma flow velocities from which one can infer rotation versus convective flows. IMS composition measurements are used to trace the source of plasma from the inner magnetosphere (protons, H2 and water group ions) versus an external solar wind source (protons and Heff ions). A critical parameter for both models is the strength of the convection electric field with respect to the rotational electric field for the large scale magnetosphere. Is there a significant return flow from the magnetotail? Pitch angle distributions also play an important role as a discriminator. If the magnetosphere tends to conserve angular momentum as suggested by Sittler et al. [2006], then we expect to see an anti-correlation between rotational flow component and radial flow velocities. All will be investigated.

Sittler, E. C.↗

NASA NTRS2003

[Development Of 25-Year Imp 8 Bow Shock Crossing "List, Ingestion Of This List To Cdaweb, & Enhancement"]

The MIT portion of this project was to use the plasma data from IMP 8 to identify bow shock crossings for construction of a bow shock data base. In collaboration with Goddard, we determined which shock parameters would be included in the catalog and developed a set of flags for characterizing the data. IMP 8 data from 1973-2001 were surveyed for bow shock crossings; the crossings apparent in the plasma data were compared to a list of crossing chosen in the magnetometer data by Goddard. Differences were reconciled to produce a single list. The data were then provided to the NSSDC for archiving. All the work ascribed to MIT in the proposal was completed.

Merka, J.↗

NASA NTRS1995

Coincident 1.3-year Periodicities in the ap Geomagnetic Index and the Solar Wind

Recent observations show an approximately 1.3-year period in the speed of the solar wind detected by the IMP 8 and Voyager 2 spacecraft. A similar period is also seen in the north-south (GSE) component of the magnetic field observed by IMP 8. Since both parameters are commonly used as input to models of geomagnetic activity, the 'ap' index (a measure of geomagnetic disturbance) is examined to look for this periodicity. The Lomb-Scargle periodogram method is used on the ap, plasma, and magnetic field data during the 1973-1994 time range. A dynamic FFT periodogram method is also used to analyze the ap data during this time, as well as to look for periods present between 1932 and 1972. A clear 1.3-year periodicity is present in the post-1986 data when the same period is observed in the plasma and field data. The V(2)B(zsm) and V(2)B(s) proxies for geomagnetic activity also show this periodicity. However, the southward (GSM) component of the magnetic field does not have a 1.3-year period, and neither do solar wind or ap data from 1973-1985. This demonstrates that the ap geomagnetic index can act as a proxy for solar wind periodicities at this time scale. Historic ap data are examined, and show that a similar periodicity in ap exists around 1942. Since auroral data show a 1.4-year periodicity, all these similar periods may result from a common underlying solar mechanism.

Paularena, K. I.↗

NASA NTRS1995

Observations of mirror waves and plasma depletion layer upstream of Saturn's magnetopause

The two inbound traversals of the Saturn's magnetosheath by Voyagers 1 and 2 have been studied using plasma and magnetic field data. In a great portion of the subsolar magnetosheath, large-amplitude compressional waves are observed at low frequency (approximately 0.1 f(sub p)) in a high-beta plasma regime. The fluctuations of the magnetic field magnitude and ion density are anticorrelated, as are those of the magnetic and thermal pressures. The normals to the structures are almost orthogonal to the background field, and the Doppler ratio is on the average small. Even though the data do not allow the determination of the ion thermal anisotropy, the observations are consistent with values of T(sub perpendicular)/T(sub parallel) greater than 1, producing the onset of the mirror instability. All the above features indicate that the waves should be most probably identified with mirror modes. One of the two magnetopause crossings is of the high-shear type and the above described waves are seen until the magnetopause. The other crossing is of the low-shear type and, similarly to what has been observed at Earth, a plasma depletion occurs close to the magnetopause. In this layer, waves with smaller amplitude, presumably of the mirror mode, are present together with higher-frequency waves showing a transverse component.

Violante, L.↗

NASA NTRS1995

Forward and reverse shocks in the outer heliosphere: Observations from Voyager 2

Observations from Voyager 2 as it moved from 10 to 14 deg S heliographic latitude in the period from 1992 through 1994 were used to gather statistics on the relative number of forward and reverse shocks. These results can be used to compare with observations from the Ulysses spacecraft which moved from 6 deg S to 70 deg S heliographic latitude during that time period. The Ulysses observations are in agreement with a 3-D, MHD model of the evolution of a steady tilted-dipole solar wind flow configuration prevalent in 1993. The model predicts and the Ulysses observations confirm a preponderance of reverse shocks at Ulysses latitudes poleward of streamer-belt latitudes. A preliminary scan of the Voyager data supports the complementary prediction of the model that forward fronts should dominate at large heliocentric distances near the heliographic equatorial plane during the same time period.

Lazarus, A. J.↗

NASA NTRS1995

Plasmas in the outer heliosphere

We review the observed properties of the solar wind in the outer heliosphere, including observations from Voyager and the Pioneers, as well as from inner heliospheric probes as appropriate. These observations are crucial to modeling of the heliosphere and its interactions with the interstellar medium, since the wind ram pressure and its temporal variations are important in understanding the distance to the termination shock and heliopause and how those boundaries might vary in time. We focus on results since Solar Wind 7. Among the issues we will discuss are: (1) the time scales for and statistical properties of variations in the ram pressure in the outer heliosphere, and how those variations might affect the morphology of the heliospheric/interstellar medium interface; (2) the question of possible solar wind slowing in the outer heliosphere due to the pick-up of interstellar ions; (3) the issue of whether there is bulk heating of the solar wind associated either with interstellar ion pick-up or with continued heating due to stream-stream interactions; (4) evidence for latitudinal variations in solar wind properties; and (5) the 1.3 year periodicities apparent in the outer heliosphere, and the close correspondence with similar variations seen with inner heliospheric probes.

Belcher, J. W.↗

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 NTRS1995

Statistical properties of the solar wind

We now have spacecraft observations spanning more than a complete 22-year solar cycle. PVO at Venus, IMP 8 at Earth, and Voyager 2 and Pioneers 10 and 11 in the outer heliosphere provide many years of data from locations scattered through the heliosphere. These large data sets enable us to look at the solar wind velocity, density, temperature and flow angles on a statistical basis. Comparison of results at the different locations will provide information on the evolution of the solar wind with radial distance and variation with latitude.

Richardson, J. D.↗

NASA NTRS1995

The 3-D effects in the long-term solar wind speed rise observed by Voyager 2 in early 1994

In early 1994, Voyager 2 at 42-43 AU near heliolatitude 10 deg S observed over a period of approximately 100 days a remarkable sequence of quasi-recurrent stream fronts, wherein the background (ambient) speed rose steadily from approximately 450 to approximately 550 km/s while the mean period of the streams decreased from the usual 25 days down to approximately 20 days. A qualitative explanation for this effect can be derived from IMP observations, which show that the amplitude of the stream structure at 1 AU increased monotonically in late 1993, concurrent with major secular evolution in the corona. The reduction in period, then, amounts to a doppler shift due to the progressive overtaking of successively faster streams in the sequence. Attempts to model this process quantitatively with 1-D dynamic simulations falter on three accounts: (1) the reduction in period is overestimated, (2) the simulation predicts many more fronts surviving to 43 AU than are observed by Voyager; (3) the density variations are much too large. It is argued that inclusion of the 3-D geometry in the simulation would resolve most all these shortcomings. Using a series of calculations executed with 1-D, 2-D, and 3-D MHD models of hypothetical tilted-dipole flows, we show that: (1) the radial propagation velocities of 3-D fronts are less than those of 1-D or 2-D fronts, owing to the tilt of (and increased shearing across) the interaction surfaces hence the overtaking rate of successive streams is reduced; (2) in a tilted-dipole geometry, the reverse fronts should largely disappear from the equatorial plane by 43 AU, effectively halving the number of fronts to be observed (see companion paper on predominance of forward fronts at Voyager); and (3) the density enhancements would be much smaller than predicted by a 1-D model.

Pizzo, V. J.↗