Engineering topics

Saito, Y.

Publications and source records attributed to Saito, Y..

14 records

NASA NTRS2018

Electron Crescent Distributions as a Manifestation of Diamagnetic Drift in an Electron-Scale Current Sheet: Magnetospheric Multiscale Observations Using New 7.5 ms Fast Plasma Investigation Moments

We report Magnetospheric Multiscale observations of electron pressure gradient electric fields near a magnetic reconnection diffusion region using a new technique for extracting 7.5 ms electron moments from the Fast Plasma Investigation. We find that the deviation of the perpendicular electron bulk velocity from E × B drift in the interval where the out-of-plane current density is increasing can be explained by the diamagnetic drift. In the interval where the out-of-plane current is transitioning to in-plane current, the electron momentum equation is not satisfied at 7.5 ms resolution.

fast plasma↗

NASA NTRS2017

Electron Scattering by High-Frequency Whistler Waves at Earth's Bow Shock

Electrons are accelerated to non-thermal energies at shocks in space and astrophysical environments. While different mechanisms of electron acceleration have been proposed, it remains unclear how non-thermal electrons are produced out of the thermal plasma pool. Here, we report in situ evidence of pitch-angle scattering of non-thermal electrons by whistler waves at Earths bow shock. On 2015 November 4, the Magnetospheric Multiscale (MMS) mission crossed the bow shock with an Alfvn Mach number is approximately 11 and a shock angle of approximately 84deg. In the ramp and overshoot regions, MMS revealed bursty enhancements of non-thermal (0.52 keV) electron flux, correlated with high-frequency (0.2 - 0.4 Omega(sub ce), where Omega(sub ce) is the cyclotron frequency) parallel-propagating whistler waves. The electron velocity distribution (measured at 30 ms cadence) showed an enhanced gradient of phase-space density at and around the region where the electron velocity component parallel to the magnetic field matched the resonant energy inferred from the wave frequency range. The flux of 0.5 keV electrons (measured at 1ms cadence) showed fluctuations with the same frequency. These features indicate that non-thermal electrons were pitch-angle scattered by cyclotron resonance with the high-frequency whistler waves. However, the precise role of the pitch-angle scattering by the higher-frequency whistler waves and possible nonlinear effects in the electron acceleration process remains unclear.

Oka, M.↗

NASA NTRS2017

Electron Heating at Kinetic Scales in Magnetosheath Turbulence

We present a statistical study of coherent structures at kinetic scales, using data from the Magnetospheric Multiscale mission in the Earths magnetosheath. We implemented the multi-spacecraft partial variance of increments (PVI) technique to detect these structures, which are associated with intermittency at kinetic scales. We examine the properties of the electron heating occurring within such structures. We find that, statistically, structures with a high PVI index are regions of significant electron heating. We also focus on one such structure, a current sheet, which shows some signatures consistent with magnetic reconnection. Strong parallel electron heating coincides with whistler emissions at the edges of the current sheet.

Chasapis, Alexandros↗

NASA NTRS2016

Magnetic Reconnection and Modification of the Hall Physics Due to Cold Ions at the Magnetopause

Observations by the four Magnetospheric Multiscale spacecraft are used to investigate the Hall physics of a magnetopause magnetic reconnection separatrix layer. Inside this layer of currents and strong normal electric fields, cold (eV) ions of ionospheric origin can remain frozen-in together with the electrons. The cold ions reduce the Hall current. Using a generalized Ohms law, the electric field is balanced by the sum of the terms corresponding to the Hall current, the v x B drifting cold ions, and the divergence of the electron pressure tensor. A mixture of hot and cold ions is common at the subsolar magnetopause. A mixture of length scales caused by a mixture of ion temperatures has significant effects on the Hall physics of magnetic reconnection.

Andre, M.↗

NASA NTRS2016

Thick Escaping Magnetospheric Ion Layer in Magnetopause Reconnection with MMS Observations

The structure of asymmetric magnetopause reconnection is explored with multiple point and high-time-resolution ion velocity distribution observations from the Magnetospheric Multiscale mission. On 9 September 2015, reconnection took place at the magnetopause, which separated the magnetosheath and the magnetosphere with a density ratio of 25:2. The magnetic field intensity was rather constant, even higher in the asymptotic magnetosheath. The reconnected field line region had a width of approximately 540 km. In this region, streaming and gyrating ions are discriminated. The large extension of the reconnected field line region toward the magnetosheath can be identified where a thick layer of escaping magnetospheric ions was formed. The scale of the magnetosheath side of the reconnected field line region relative to the scale of its magnetospheric side was 4.5:1.

Nagai, T.↗

NASA NTRS2016

Shift of the Magnetopause Reconnection Line to the Winter Hemisphere Under Southward IMF Conditions: Geotail and MMS Observations

At 02:13 UT on 18 November 2015 when the geomagnetic dipole was tilted by -27deg, the MMS spacecraft observed southward reconnection jets near the subsolar magnetopause under southward and dawnward interplanetary magnetic field conditions. Based on four-spacecraft estimations of the magnetic field direction near the separatrix and the motion and direction of the current sheet, the location of the reconnection line was estimated to be approx.1.8 R(sub E) or further northward of MMS. The Geotail spacecraft at GSM Z approx. 1.4 R(sub E) also observed southward reconnection jets at the dawnside magnetopause 30-40 min later. The estimated reconnection line location was northward of GSM Z approx.2 R(sub E). This crossing occurred when MMS observed purely southward magnetic fields in the magnetosheath. The simultaneous observations are thus consistent with the hypothesis that the dayside magnetopause reconnection line shifts from the subsolar point toward the northem (winter) hemisphere due to the effect of geomagnetic dipole tilt.

Kitamura, N.↗

NASA NTRS2016

Decay of Mesoscale Flux Transfer Events During Quasi-Continuous Spatially Extended Reconnection at the Magentopause

We present observations on 2 October 201Swhen the Geotail spacecraft, near the Earth's equatorial plane, and the Magnetospheric Multiscale (MMS) spacecraft, at mid-southem latitudes, simultaneously encountered southward jets from dayside magnetopause reconnection under southward interplanetary magnetic field conditions. The observations show that the equatorial reconnection site under modest solar wind Alfven Mach number conditions remained active almost continuously for hours and, at the same time, extended over a wide range of local times (4h). The reconnection jets expanded toward the magnetosphere with distance from the reconnection site. Geotall, closer to the reconnection site, occasionally encountered large-amplitude mesoscale flux transfer events (FTEs) with durations about or less than 1 min. However, MMS subsequently detected no or only smaller-amplitude corresponding FTE signatures. It is suggested that during quasi-continuous spatially extended reconnection, mesoscale FTEs decay as the jet spatially evolves over distances between the two spacecraft of 350 ion inertial lengths.

Hasegawa, H.↗

NASA NTRS2014

Anisotropic Solar Wind Sputtering of the Lunar Surface Induced by Crustal Magnetic Anomalies

The lunar exosphere is generated by several processes each of which generates neutral distributions with different spatial and temporal variability. Solar wind sputtering of the lunar surface is a major process for many regolith-derived species and typically generates neutral distributions with a cosine dependence on solar zenith angle. Complicating this picture are remanent crustal magnetic anomalies on the lunar surface, which decelerate and partially reflect the solar wind before it strikes the surface. We use Kaguya maps of solar wind reflection efficiencies, Lunar Prospector maps of crustal field strengths, and published neutral sputtering yields to calculate anisotropic solar wind sputtering maps. We feed these maps to a Monte Carlo neutral exospheric model to explore three-dimensional exospheric anisotropies and find that significant anisotropies should be present in the neutral exosphere depending on selenographic location and solar wind conditions. Better understanding of solar wind/crustal anomaly interactions could potentially improve our results.

exosphere↗

NASA NTRS2012

Flux Estimates of Ions from the Lunar Exosphere

We compare estimates for the ion fluxes of twelve expected constituents of the lunar exosphere with estimates for the ion fluxes ejected from the lunar surface by solar wind ions and electrons. Our estimates demonstrate that measurements of lunar ions will help constrain the abundances of many undetected species in the lunar exosphere, particularly AI and Si, because the expected ion flux levels from the exosphere exceed those from the surface. To correctly infer the relative abundances of exospheric ions and neutrals from Kaguya Ion Mass Analyzer (IMA) measurements, we must take into account the velocity distributions of local ions. The predicted spectrum underestimates the measured levels of 0+ relative to other lunar ion species, a result that may suggest contributions by molecular ions to the measured 0+ rates.

Sarantos, M.↗

NASA NTRS2009

Lunar Neutral Exposphere Properties from Pickup Ion Analysis

Composition and structure of neutral constituents in the lunar exosphere can be determined through measurements of phase space distributions of pickup ions borne from the exosphere [1]. An essential point made in an early study [ 1 ] and inferred by recent pickup ion measurements [2, 3] is that much lower neutral exosphere densities can be derived from ion mass spectrometer measurements of pickup ions than can be determined by conventional neutral mass spectrometers or remote sensing instruments. One approach for deriving properties of neutral exospheric source gasses is to first compare observed ion spectra with pickup ion model phase space distributions. Neutral exosphere properties are then inferred by adjusting exosphere model parameters to obtain the best fit between the resulting model pickup ion distributions and the observed ion spectra. Adopting this path, we obtain ion distributions from a new general pickup ion model, an extension of a simpler analytic description obtained from the Vlasov equation with an ion source [4]. In turn, the ion source is formed from a three-dimensional exospheric density distribution, which can range from the classical Chamberlain type distribution to one with variable exobase temperatures and nonthermal constituents as well as those empirically derived. The initial stage of this approach uses the Moon's known neutral He and Na exospheres to deriv e He+ and Na+ pickup ion exospheres, including their phase space distributions, densities and fluxes. The neutral exospheres used are those based on existing models and remote sensing studies. As mentioned, future ion measurements can be used to constrain the pickup ion model and subsequently improve the neutral exosphere descriptions. The pickup ion model is also used to estimate the exosphere sources of recently observed pickup ions on KAGUYA [3]. Future missions carrying ion spectrometers (e.g., ARTEMIS) will be able to study the lunar neutral exosphere with great sensitivity, yielding the necessary ion velocity spectra needed to further analysis of parent neutral exosphere properties.

Hartle, R. E.↗

NASA NTRS1999

The Relationship Between Magnetotail Dynamics and Substorm Onset Longitudes Determined from Spacecraft Images

Geotail plasma and magnetic field observations of plasmoids between 25 and 30 Re have been compared to Polar UVI observations of auroral brightenings. Plasmoids almost always corresponded to brightenings but the brightenings were sometimes weak and spatially limited and did not always grow to a global substorm. Even a case where a plasmoid event occurred with fast post-plasmoid flow corresponded to a weak brightening but no substorm. Some brightenings did not correspond to plasmoids, but these events were observed away from the longitude of Geotail. The plasmoids are observed 0-2 min after the brightenings in most cases. It seems likely that formation of a near-Earth neutral line causes each brightening in the polar ionosphere, but these formations do not have a one-to-one relationship with a substorm onset. What causes development of the full, large-scale substorm remains an open question.

Ieda, A.↗

NASA NTRS1996

Average energetic ion flux variations associated with geomagnetic activity from EPIC/STICS on Geotail

The magnetotail ion flux measurements from the Geotail spacecraft are analyzed both with and without the application of selection criteria that identify the plasma regime in which an observation is obtained. The different results are compared with each other. The initial results on the changes of energetic ion flux and composition correlated to average substorm activity in different magnetotail plasma regimes are discussed. The energetic ions are measured using the energetic particles and ion composition (EPIC) experiment and the suprathermal ion composition spectrometer (STICS). The plasma, wave and field instruments of the Geotail satellite were used to identify the principle magnetotail plasma regimes of plasma sheet, lobe, and magnetospheric boundary layer, as well as the magnetosheath and solar wind. Energetic O and H ions were observed in all the plasma regimes.

Christon, S. P.↗

NASA NTRS1992

A range-resolved bistatic lidar using a high-sensitive CCD-camera

Until now monostatic type lidar systems have been mainly utilized in the field of lidar measurements of the atmosphere. We propose here a range-resolved bistatic lidar system using a high-sensitive cooled charge coupled device (CCD) camera. This system has the ability to measure the three dimensional distributions of aerosol, atmospheric density, and cloud by processing the image data of the laser beam trajectory obtained by a CCD camera. Also, this lidar system has a feature that allows dual utilization of continuous wave (CW) lasers and pulse lasers. The scheme of measurement with this bistatic lidar is shown. A laser beam is emitted vertically and the image of its trajectory is taken with a remote high-sensitive CCD detector using an interference filter and a camera lens. The specifications of the bistatic lidar system used in the experiments are shown. The preliminary experimental results of our range-resolved bistatic lidar system suggest potential applications in the field of lidar measurements of the atmosphere.

Yamaguchi, K.↗

NASA NTRS1987

Interannual differences in the regressions of the polar caps of Mars

Analyses of the behavior of the Martian polar caps in the recent spacecraft and ground based observations seem to reveal the existence of year to year variations on their regressions. In order to investigate the interannual differences in the regressions of the polar caps, the earlier data by Fischbacher et al., were reexamined, which were based on the measurements of the large number of high quality photographic plates and films collected from 1905 to 1965 at the Lowell Observatory. The results are reported and discussed.

Iwasaki, K.↗