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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
NASA NTRS1988

Origin of interplanetary southward magnetic fields responsible for major magnetic storms near solar maximum (1978-1979)

Simultaneous ISEE-3 field and plasma data were used to examine interplanetary phenomena associated with 10 major magnetic storms detected from August 16, 1978, to December 28, 1979, in a study of Gonzalez and Tsurutani (1987), and, in particular to determine the origins of the southward magnetic fields which caused the storms. In nine of the 10 cases, the responsible interplanetary events were found, as expected, to be associated with the high magnetic fields in the stream-stream interaction regions (sheaths) or driver gases, with the events following the interplanetary shocks. The tenth event was found to be associated not with a high-speed stream, but with a noncompressional density-enhancement event. The results of this study indicate the equal importance of both the sheath fields or draped fields and the driver gas fields for the generation of major geomagnetic storms.

Tsurutani, Bruce T.↗
NASA NTRS2001

Low-Latitude Auroras: The Magnetic Storm of 14-15 May 1921

We review solar geophysical data relating to the great magnetic storm of 14-15 May 1921, with emphasis on observations of the low-latitude visual aurora. From the reports we have gathered for this event the lowest geomagnetic latitude of definite overhead aurora (coronal form) was 40 deg and the lowest geomagnetic latitude from which auroras were observed on the poleward horizon in the northern hemisphere was 30 deg. For comparison, corresponding overhead/low-latitude values of 48 deg/32 deg and 41 deg/20 deg were reported for the great auroras on 28-29 August and 1-2 September 1859, respectively. However for the 1921 event, there is a report of aurora from Apia, Samoa, in the southern hemisphere, within 13 deg of the geomagnetic equator. This report by professional observers appears to be credible, based on the aurora description and timing, but is puzzling because of the discrepancy with the lowest latitude of observation in the northern hemisphere and the great implied aurora height (approximately 2000 km, assuming overhead aurora at Auckland, New Zealand). We discuss various possibilities that might account for this observation.

Silverman, S. M.↗
NASA NTRS1994

Ionospheric convection during the magnetic storm of 20-21 March 1991

We report on the response of high-latitude ionospheric convection during the magnetic storm of March 20-21 1990. IMP-8 measurements of solar wind plasma and interplanetary magnetic field (IMF), ionospheric convection flow measurements from the Wick and Goose Bay coherent radars, EISCAT, Millstone Hill and Sondrestorm incoherent radars and three digisondes at Millstone Hill, Goose Bay and Qaanaaq are presented. Two intervals of particular interest have been indentified. The first starts with a storm sudden commencement at 2243 UT on March 20 and includes the ionospheric activity in the following 7 h. The response time of the ionospheric convection to the southward tuning of the IMF in the dusk to midnight local times is found to be approximately half that measured in a similar study at comparable local times during more normal solar wind conditions. A subsequent reconfiguration of the nightside convection pattern was also observed, although it was not possible to distinguish between effects due to possible changes in B(sub y) and effects due to substorm activity. The second interval, 1200-2100 UT 21 March 1990, included a southward turning of the IMF which resulted in the B(sub z) component becoming -10 nT. The response time on the dayside to this change in the IMF at the magnetopause was approximately 15 min to 30 min which is a factor of approximately 2 greater than those previously measured at higher latitudes. A movement of the nightside flow reversal, possibly driven by current systems associated with the substorm expansion phases, was observed, implying that the nightside convection pattern can be dominated by substorm activity.

Taylor, J. R.↗
NASA NTRS1974

Seasonal and magnetic storm related changes in the thermosphere induced by eddy mixing

The possibility of explaining the seasonal and magnetic storm related changes in the thermosphere and the ionosphere through variation in eddy diffusion coefficient in the lower thermosphere is investigated theoretically by obtaining simultaneous numerical solutions of the relevant continuity, momentum, and energy balance equations in a self-consistent manner. It is shown that various important features of thermospheric seasonal behavior, including the winter helium bulge phenomenon, can be explained by assuming effective reduction in the winter-time eddy diffusion coefficient by about one order of magnitude. Storm related changes in the thermal structure and composition are seen to arise by assuming a downward shift of turbulence. Physical implications and relative significance of variation in thermospheric turbulence and large scale inter-hemispheric circulation are briefly discussed.

Sinha, A. K.↗
NASA NTRS2016

Magnetopause Erosion During the 17 March 2015 Magnetic Storm: Combined Field-Aligned Currents, Auroral Oval, and Magnetopause Observations

We present multimission observations of field-aligned currents, auroral oval, and magnetopause crossings during the 17 March 2015 magnetic storm. Dayside reconnection is expected to transport magnetic flux, strengthen field-aligned currents, lead to polar cap expansion and magnetopause erosion. Our multimission observations assemble evidence for all these manifestations. After a prolonged period of strongly southward interplanetary magnetic field, Swarm and AMPERE observe significant intensification of field-aligned currents .The dayside auroral oval, as seen by DMSP, appears as a thin arc associated with ongoing dayside reconnection. Both the field-aligned currents and the auroral arc move equatorward reaching as low as approx. 60 deg. magnetic latitude. Strong magnetopause erosion is evident in the in situ measurements of the magnetopause crossings by GOES 13/15 and MMS. The coordinated Swarm, AMPERE, DMSP, MMS and GOES observations, with both global and in situ coverage of the key regions, provide a clear demonstration of the effects of dayside reconnection on the entire magnetosphere.

Le, G.↗
NASA NTRS1982

Computer simulation of inner magnetospheric dynamics for the magnetic storm of July 29, 1977

The Rice University convection model is applied to the early main phase of the July 29, 1977 magnetic storm through a computer implementation that self-consistently calculates electric fields, currents, and plasma distributions and velocities in the inner magnetosphere/ionosphere system. On the basis of solar wind parameters and AL index as inputs, the model predicts the injection of plasma sheet plasma to form a substantial storm time ring current whose total predicted strength agrees with the observed Dst index. The possibility that the magnetic field may be sufficiently inflated to make 60 deg field lines extend to the outer magnetosphere is examined. In the model, distortion of the plasma sheet inner edge by magnetospheric compression associated with the sudden commencement temporarily disrupts the normal Birkeland current pattern. Normal Birkeland currents and shielding reassert themselves in about an hour.

Wolf, R. A.↗
NASA NTRS1975

The SAR arc event observed during the December 1971 magnetic storm

Observations from five separate experiments on the Isis 2 spacecraft are used to study the atmosphere/ionosphere during the magnetic storm of December 16-20, 1971. The data are most complete in the midlatitude region, permitting a study of the SAR arc (subauroral red arc) which developed during the night of December 17-18. Ion composition and temperature, electron temperature, electron-density height profiles from the spacecraft to the F region, and the intensity of the 6300-A oxygen emission are all presented for the region of interest. It is found that the H(+) concentration had sharp gradients near the SAR arc and that the plasma temperature was significantly enhanced over typical nighttime values, reaching nearly 7000 K at 1400 km on the field line which intersected the arc. A system of time-dependent equations for atmospheric/ionospheric composition and temperature is solved using boundary conditions which were selected so that the solutions are in agreement with the observations. From these solutions, an assessment is made of the influence of (1) the efflux of plasma from the ionosphere to the magnetosphere, (2) the decrease in O/N2 at the turbopause, (3) the increase in the loss coefficient as a result of an increase in the vibrational temperature of N2, and (4) the conduction of thermal energy into the ionosphere.

Maier, E. J.↗