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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 91 records · Page 5
All sourcesNASA NTRSDOE OSTI
NASA NTRS1994

Multiwavelength study of the magnetically active T Tauri star HD 283447

We observed the luminous T Tauri star HD 283447 = V773 Tauri simultaneously at X-ray, ultraviolet, optical photometric and spectroscopic, and radio wavelengths for several hours on UT 1992 September 11. ROSAT, IUE, Very Large Array (VLA) and an intercontinental Very Long Baseline Interferometry (VLBI) network, and three optical observatories participated in the campaign. The star is known for its unusually high and variable nonthermal radio continuum emission. High levels of soft X-ray and Mg II line emission are discovered, with luminosity L(sub x) = 5.5 x 10(exp 30) ergs/s (0.2 - 2 keV) and L(sub Mg II) = 1 x 10(exp 29) ergs/s, respectively. Optically, the spectrum exhibits rather weak characteristics of `classical' T Tauri stars. A faint, broad emission line component, probably due to a collimated wind or infall, is present. During the campaign, the radio luminosity decreased by a factor of 4, while optical/UV lines and X-ray emission remained strong but constant. The large gyrosynchrotron-emitting regions are therefore decoupled from the chromospheric and coronal emission. Five models for the magnetic geometry around the star are discussed; solar-type activity, dipole magnetosphere, star-disk magnetic coupling, disk magnetic fields, and close binary interaction. The data suggest that two magnetic geometries are simultaneously present: complex multipolar fields like those on the Sun, and a large-scale field possibly associated with the circumstellar disk.

Feigelson, Eric D.↗
NASA NTRS1984

Cosmic rays, solar activity, magnetic coupling, and lightning incidence

A theoretical model is presented and described that unifies the complex influence of several factors on spatial and temporal variation of lightning incidence. These factors include the cosmic radiation, solar activity, and coupling between geomagnetic and interplanetary (solar wind) magnetic fields. Atmospheric electrical conductivity in the 10 km region was shown to be the crucial parameter altered by these factors. The theory reconciles several large scale studies of lightning incidence previously misinterpreted or considered contradictory. The model predicts additional strong effects on variations in lightning incidence, but only small effects on the morphology and rate of thunderstorm development.

Ely, J. T. A.↗
NASA NTRS1977

The large-scale ionospheric electric field - Its variation with magnetic activity and relation to terrestrial kilometric radiation

Four days of simultaneous auroral zone electric field measurements on balloons flown from six sites spanning 180 deg of magnetic longitude have been analyzed. The average electric field behavior during this magnetically quiet epoch is consistent with earlier single-point measurements, although the average auroral zone electric field was more affected by corotation effects than it was during more disturbed times. When these data, which primarily reflect the large-scale (several hundred kilometer) ionospheric electric field, are mapped to the equator, a steady dawn to dusk component is apparent only on the average, while instantaneously the field is quite variable. The ionospheric electric field during isolated substorms is shown to have differing signatures east and west of 2200 LT. A worldwide positive correlation is shown to exist between the auroral zone electric field strength and the intensity of terrestrial kilometric radiation.

Holzworth, R. H.↗
NASA NTRS1993

F region plasma drifts over Arecibo - Solar cycle, seasonal, and magnetic activity effects

Characteristics of low-latitude F region plasma drifts are determined on the basis of Arecibo incoherent scatter measurements from 1981 to 1990. The measurements show large day-to-day variability even during magnetically quiet periods. The average poleward/perpendicular plasma drifts do not change significantly with season and solar cycle except in the midnight-morning sector. The zonal drifts show clear solar cycle and seasonal effects. The plasma drifts along the magnetic field lines exhibit large altitudinal and seasonal variations, particularly near solar minimum, and are generally anticorrelated with the perpendicular/north drifts. The drift patterns observed by the Arecibo and the middle and upper atmosphere radars have significantly different seasonal dependences. This is explained by electrodynamic effects in the corresponding local and conjugate ionospheres.

Fejer, B. G.↗
NASA NTRS1981

Theoretical predictions for ion composition in the high-latitude winter F-region for solar minimum and low magnetic activity

A simple plasma convection model is combined with an ionospheric-atmospheric density model in order to study the ion composition in the high-latitude winter F-region at solar minimum for low geomagnetic activity. The numerical study produces time-dependent, three-dimensional ion density distributions for the ions NO(+), O2(+), N2(+), O(+), N(+), and He(+). The high-latitude ionosphere above 54 deg N magnetic latitude is covered at altitudes between 160 and 800 km for one complete day. Among the conclusions are the following: the ion composition varies significantly with latitude, local time, altitude, and universal time; the variations in the ion composition with latitude and local time are in good agreement with the Atmosphere Explorer measurements both quantitatively and qualitatively; and at times and at certain locations the molecular ion density can be comparable to the O(+) density at 300 km, and at 200 km the O(+) density can be comparable to the molecular ion density.

Sojka, J. J.↗
NASA NTRS1991

Polarimetric mapping of Orion using Millipol - Magnetic activity in BN/KL

The spatial distribution of the polarized component of the thermal dust emission from the core of the Orion molecular cloud has been mapped over 15 positions at a wavelength of 1300 microns using the Millipol instrument on the NRAO 12 m telescope. The polarization directions deduced for the map positions are quite similar, implying that the embedded magnetic field is strong (of the order of 1 mG) and uniform in direction over the core of the cloud. The mean polarization percentage, 4.6 percent, is quite high, and two positions show polarization percentages of nearly 8 percent, the highest yet detected for polarized thermal dust emission. Finally, the polarization of the BN/KL position was found to be significantly lower than the polarizations toward positions 30 arcmin outside BN/KL.

Leach, Robert W.↗
NASA NTRS2012

The Stellar Imager (SI) - A Mission to Resolve Stellar Surfaces, Interiors, and Magnetic Activity

The Stellar Imager (SI) is a space-based, UV/Optical Interferometer (UVOI) designed to enable 0.1 milli-arcsecond (mas) spectral imaging of stellar surfaces and of the Universe in general. It will also probe via asteroseismology flows and structures in stellar interiors. SI will enable the development and testing of a predictive dynamo model for the Sun, by observing patterns of surface activity and imaging of the structure and differential rotation of stellar interiors in a population study of Sun-like stars to determine the dependence of dynamo action on mass, internal structure and flows, and time. SI's science focuses on the role of magnetism in the Universe and will revolutionize our understanding of the formation of planetary systems, of the habitability and climatology of distant planets, and of many magnetohydrodynamically controlled processes in the Universe. SI is a "LandmarklDiscovery Mission" in the 2005 Heliophysics Roadmap, an implementation of the UVOI in the 2006 Astrophysics Strategic Plan, and a NASA Vision Mission ("NASA Space Science Vision Missions" (2008), ed. M. Allen). We present here the science goals of the SI Mission, a mission architecture that could meet those goals, and the technology development needed to enable this mission

Christensen-Dalsgaard, Jorgen↗
NASA NTRS2023

Deciphering Solar Magnetic Activity: The (Solar) Hale Cycle Terminator of 2021

McIntosh and colleagues identified an event in the solar timeline that appeared to play a role in how Sunspot Cycle 23 (SC23) transitioned into Sunspot Cycle 24 (SC24). The timeframe for this transition was rapid, taking place in as short as time as a solar rotation. M2014 inferred that the transition observed was a critical episode for the Sun’s global-scale magnetic field that was being manifest in the spatially and temporally overlapping and magnetic systems belonging to the Sun’s 22-year (Hale) magnetic cycle. These events have been dubbed as Hale Cycle terminations, or ‘terminators’ for short. Further exploration revealed a relationship between terminator separation (as a measure of overlap in the Hale Cycles) and the upcoming sunspot cycle amplitude. McIntosh and colleagues extrapolated upon this relationship to identify the termination of the SC24 carrying Hale Cycle band in Mid-2020 and inferred that this would result in a very large Sunspot Cycle 25 (SC25). This paper presents observational analysis of the end of SC24 and the initial months of SC25 growth following a terminator that occurred in mid-December 2021 (approximately 12/13/2021). We use the December 2021 terminator to finalize the forecast of SC25 amplitude 184 (±17 with 95% confidence, and ±63 with 68% confidence). Finally, we use other terminator-related superposed epoch analyses to project the timing of SC25 maxima in late 2023 to mid 2024.

Sun↗
NASA NTRS1985

A theoretical study of the global F region for June solstice, solar maximum, and low magnetic activity

A time-dependent, three-dimensional, multi-ion model of the ionospheric F region at 120-800 km altitude is presented. Account is taken of field-aligned diffusion, cross-field electrodynamic drifts in equatorial and high latitude regions, interhemispheric flow, thermospheric winds, polar wind escape, energy-dependent chemical reactions and neutral composition changes. Attention is also given to the effects of ion production by solar EUV radiation and auroral precipitation, thermal conduction, diffusion-thermal heat flow, local heating and cooling processes, offsets between the geomagnetic and geographic poles, and bending of field lines near the magnetic equator. The model incorporates all phenomena described by previous models and can be applied to tracing magnetic storm and substorm disturbances from high to low latitudes on a global scale. Sample results are provided for ionospheric features during a June solstice, the solar maximum and in a period of low geomagnetic activity. The model will eventually be used to study coupled ionosphere-thermosphere activity.

Sojka, J. J.↗
NASA NTRS1972

Variations of atmospheric density near 400 km with magnetic activity during the storm period of 28 September to 2 October 1969

Neutral density data were obtained near 400 km (1600 LT) from a microphone density gage on OGO-6 from 0 to 40 deg N geomagnetic latitude for 25 September through 3 October 1969. Several geomagnetic storms occurred during this period. Least squares fits were made to data points on density scatter diagrams. An equation representing the least squares fit was computed for each delay time. The equation of best fit (and the corresponding time delay between the density and the magnetic index which resulted in this best fit) was found by choosing the equation that gave the minimum standard error. The implications of the time differences associated with the best fits at various latitudes and longitudes are discussed with regard to the time delays involved in geomagnetic heating of the neutral upper atmosphere.

Anderson, A. D.↗
NASA NTRS1989

IUE observations of the M dwarfs CM Draconis and Rossiter 137 B - Magnetic activity at saturated levels

IUE observations of two active M dwarfs with known rotation rate or age and presumed to be almost totally convective are presented. The first of these stars, CM Draconis (Gl 630.1), is an old Population II binary with its components in tidally induced rapid rotation (P = 1.27 d, dM 4 + dM 4). The other one, Rossiter 137 B, forms with HD 36705 (AB Dor) a visual pair of young active stars. The activity of CM Dra is due to the forced rotation in a close binary, while Rst 137 B is assumed to rotate fast enough to generate its magnetica activity. These results are compared with those for M dwarfs, particularly AU Mic and YZ CMi, that have known rotational periods and measured ultraviolet emission line fluxes. The chromospheric-coronal saturation levels of cool dwarfs between 0.3 less than B-V less than 1.6 is determined. It is found that saturated F stars have stronger chromospheres than saturated M stars, but the opposite is true for the corona. Results of these observations seem to favor a rotation-dependent distributed dynamo generating magnetic flux in totally convective stars.

Vilhu, O.↗