Engineering Papers⌕ Search

Engineering topics

Tsurutani, B. T.

Publications and source records attributed to Tsurutani, B. T..

At least 163 records · Page 9
All sourcesNASA NTRSDOE OSTI
NASA NTRS1995

Geomagnetic Response to Large-amplitude Interplanetary Alfven Wave Trains

A review of the geomagnetic response to large-amplitude interplanetary Alfven wave trains is presented, highlighting its dependence on solar activity level and its role in the storm/substorm relationship problem. Also discussed are some recent observations obtained by the Ulysses spacecraft at high heliospheric latitudes dealing with the origin and dynamics of these wave trains.

Space Physics Geomagnetics Alfven Wave Trains Ulys↗
NASA NTRS1994

A detailed examination of a X-line region in the distant tail: ISEE-3 observations of jet flow and B(sub z) reversals and a pair of slow shocks

We report an observation of Petschek-type magnetic reconnection at a distant neutral line (X = -230 R(sub e)) with a full set of signatures of the magnetic merging process. These features include a reversal of plasma flows from earthward to tailward, a pair of slow shocks and the magnetic field X-type line. These two slow shocks are shown to satisfy the shock criteria used by Feldman et al. (1987). The spacecraft first crosses a slow shock to enter the earthward flowing plasmasheet with velocity of about 440 km/s. The embedded magnetic field has a positive B(sub z) component. The spacecraft next enters a region of tailward plasma flow with speed approximately 670 km/s and an embedded negative B(sub z), indicating entry into the plasmasheet tailward of the X-line. These observed velocities are comparable to calculated velocities based on Rankine-Hugoniot conservation relationships. The spacecraft subsequently returns into the south tail lobe by crossing another slow shock. Coplanarity analyses shows that the two slow shocks have orientations consistent with that predicted by the Petschek reconnection model. We note that this event occurs during northward interplanetary magnetic fields. Thus, a magnetic stress built-up in the distant tail may be responsible for this reconnection process.

Ho, C. M.↗
NASA NTRS1994

On the absence of plasma wave emissions and the magnetic field orientation in the distant magnetosheath

In early September, 1983 ISEE-3 made a long traversal of the distant dawnside magnetosheath starting near x = -150 R(sub E) downstream. The distant magnetosheath often contains moderately intense plasma wave emissions at frequencies from several hundred Hz to 5 kHz. However, over time scales of many days, a clear correlation exists between the occurrence of the plasma waves and the cone angle (theta(sub xB)) between the magnetic field and the plasma flow velocity (x-direction). For theta(sub xB) large (small), the plasma wave amplitudes are near background (high). Sudden (less than 1 minute) changes in the local magnetic field orientation produce correspondingly sudden changes in the wave amplitudes. Statistically, the wave amplitudes decrease continuously with increasing theta(sub xB).

Coroniti, F. V.↗
NASA NTRS1994

Whistler mode waves in the Jovian magnetosheath

During the Ulysses flyby of Jupiter in February 1992, the spacecraft traversed the Jovian magnetosheath for a few hours during the inbound pass and for aa few days during the outbound pass. Burstlike electomagnetic waves at frequencies of approximately 0.1-0.4 of the local electron cyclotron frequency have been observed by the Unified Radio and Plasma Wave (URAP) experiement. The waves were more often observed in the regions which were probably the outer or the middle magnetosheath, especially near the bow shock, and rarely seen in the magnetosphere/magnetosheath boundary layer. The propagation angles of the waves are estimated by comparing the measurements of the wave electric and magnetic fields in the spacecraft spin plane with the corresponding values calculated using the cold plasma dispersion relation under local field and plasma conditions. It is found that the waves propagate obliquely with wave angles between approximately 30 deg and 50 deg. These waves are likely to be the whistler mode waves which are excited by suprathermal electrons with a few hundred eV and a slight anisotropy (T(sub perp)/T(sub parallel) approximately 1.1-1.5). They are probably similar in nature to the lion roars observed in the Earth's magnetosheath. Signature of coupling between the mirror and the whistler mode have also been observed. The plasma conditions which favor the excitation of the whistler mode instability during the wave events exists as observed by the plasma experiement of Ulysses.

Lin, Naiguo↗
NASA NTRS1994

The relationship between interplanetary discontinuities and Alfven waves: Ulysses observations

The rate of occurrence of interplanetary discontinuities (ROID) is examined using Ulysses magnetic field and plasma data from 1 to 5 AU radial distance from the Sun and at high heliographic latitudes. We find two regions where the ROID is high: in stream-stream interaction regions and in Alfven wave trains. This latter feature is particularly obvious at high latitudes when Ulysses enters a high speed stream associated with a polar coronal hole. These streams are characterized by the presence of continuous, large-amplitude (Delta (vector 13)/absolute value of B is about 1-2 Alfven waves and an extraordinarily high ROID value (approximately 150 discontinuities/day). In a number of intervals examined, it is found that (rotational) discontinuities are an integral part of the Alfven waves. The nonlinear Alfven waves are spherically polarized, i.e., the tip of the perturbation vector resides on the surface of a sphere (a consequence of constant absolute value of B). The slowly rotating part of the wave rotates approximately 270 deg in phase. There is a slight arc in the B(sub 1) - B(sub 2) hodogram, suggesting an almost linear polarization. The phase rotation associated with the discontinuity is about 90 deg, lies in the same plane as the slowly rotaing part of the Alfven wave, and therefore completes the 360 deg phase rotation. The best description of the overall Alfven wave plus discontinuity is a spherical, arc-polarized, phase-steepened wave.

Tsurutani, B. T.↗
NASA NTRS1994

Ulysses Observations of Latitude Gradients in the Heliospheric Magnetic Field

Several parameters measured by Ulysses as it traveled southward to heliographic latitudes of -50° are presented and analyzed. Three topics of scientific importance are investigated: (1) latitude gradient; (2) extent of agreement between observed and Parker spiral angles near -50°; (3) field variances and their interpretation.

Ulysses↗
NASA NTRS1994

What is a geomagnetic storm?

After a brief review of magnetospheric and interplanetary phenomena for intervals with enhanced solar wind-magnetosphere interaction, an attempt is made to define a geomagnetic storm as an interval of time when a sufficiently intense and long-lasting interplanetary convection electric field leads, through a substantial energization in the magnetosphere-ionosphere system, to an intensified ring current sufficiently strong to exceed some key threshold of the quantifying storm time Dst index. The associated storm/substorm relationship problem is also reviewed. Although the physics of this relationship does not seem to be fully understood at this time, basic and fairly well established mechanisms of this relationship are presented and discussed. Finally, toward the advancement of geomagnetic storm research, some recommendations are given concerning future improvements in monitoring existing geomagnetic indices as well as the solar wind near Earth.

Gonzalez, W. D.↗
NASA NTRS1994

Whistler Mode Waves in the Jovian Magnetosheath

During the flyby of Jupiter in February, 1992, the spacecraft traversed the Jovian magnetosheath for a few hours during the inbound pass and for a few days during the outbound pass.

Ulysses↗