Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “field observation”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 181 records · Page 10
All sourcesNASA NTRSDOE OSTI
NASA NTRS1972

Inferring the interplanetary magnetic field by observing the polar geomagnetic field.

Svalgaard (1968, 1972) and Mansurov (1969) have shown that it is possible to infer the polarity of the interplanetary magnetic field quite reliably from observations of the diurnal variation of polar geomagnetic fields. The effect is most prominent in the vertical component of geomagnetic observatories near the geomagnetic poles during several hours near noon. The interplanetary magnetic field observed with spacecraft near the earth is very similar to the mean solar magnetic field (i.e., the sun observed as though it were a star); thus the fact that observations of the polar geomagnetic field have existed without interruption since 1926 at the Danish Meteorological Institute station at Godhavn, Greenland, means that in effect the inferred solar magnetic field during five sunspot cycles is available for analysis.-

Wilcox, J. M.↗
NASA NTRS1978

Models for quasi-periodic electric fields and associated electron precipitation in the auroral zone

Quasi-periodic electric fields observed in the nighttime auroral oval and in the polar cleft had periods of between 0.5 and 3 s and amplitudes from 2 to 30 mV/m and exhibited left-hand and right-hand elliptical polarization. The events in the auroral oval were associated with substorms and visual auroral activity, and the spectral and polarization properties of the observed fields suggest that they represented the electric components of Pc 1 or Pi 1 micropulsations. One possibility is that the micropulsations result from Birkeland current chopping by an unstable double layer located at an altitude of approximately one earth radius. In this interpretation, the double layer is assumed to accelerate the observed electrons, the electron flux variations being due either to the inherent variations of the double layer or to its interaction with the micropulsations.

Petelski, E. F.↗
NASA NTRS1979

Environmental requirements for flat plate photovoltaic modules for terrestrial applications

The environmental test requirements that have been developed for flat plate modules purchased through Department of Energy funding are described. Concurrent with the selection of the initial qualification tests from space program experience - temperature cycling and humidity - surveys of existing photovoltaic systems in the field revealed that arrays were experiencing the following failure modes: interconnect breakage, delamination, and electrical termination corrosion. These coupled with application-dependent considerations led to the development of additional qualification tests, such as cyclic pressure loading, warped mounting surface, and hail. Rationale for the selection of tests, their levels and durations is described. Comparisons between field-observed degradation and test-induced degradation show a positive correlation with some of the observed field effects. Also, the tests are proving useful for detecting design, process, and workmanship deficiencies. The status of study efforts for the development of environmental requirements for field-related problems is reviewed.

Hoffman, A. R.↗
NASA NTRS1983

Planetary magnetic fields

Observations of planetary magnetic fields are synthesized with current knowledge of the composition and evolution of planets and the sources of planetary magnetism. The observations for earth, Jupiter, Saturn, Mercury, Venus, the moon, Mars, and small bodies and meteorites are summarized. The evolution and structure of the terrestrial planets, of Jupiter and Saturn, and of Uranus and Neptune are discussed in detail. Possible sources of planetary magnetism are discussed, and estimates are established which are sufficient in most cases to identify whether an observed field is likely to be the consequence of dynamo generation. Predictions of the existence or nonexistence of dynamos are offered for each large planet or satellite in the solar system.

Stevenson, D. J.↗
NASA NTRS1982

Observations of magnetic fields on solar-type stars

Magnetic-field observations were carried out for 29 G and K main-sequence stars. The area covering-factors of magnetic regions tends to be greater in the K dwarfs than in the G dwarfs. However, no spectral-type dependence is found for the field strengths, contrary to predictions that pressure equilibrium with the ambient photospheric gas pressure would determine the surface field strengths. Coronal soft X-ray fluxes from the G and K dwarfs correlate well with the fraction of the stellar surface covered by magnetic regions. The dependence of coronal soft X-ray fluxes on photospheric field strengths is consistent with Stein's predicted generation-rates for Alfven waves. These dependences are inconsistent with the one dynamo model for which a specific prediction is offered. Finally, time variability of magnetic fields is seen on the two active stars that have been extensively monitored. Significant changes in magnetic fields are seen to occur on timescales as short as one day.

Marcy, G. W.↗
NASA NTRS1984

Observations of magnetic fields on solar-type stars

Magnetic-field observations were carried out for 29 G and K main-sequence stars. The area covering-factors of magnetic regions tends to be greater in the K darfs than in the G dwarfs. However, no spectral-type dependence is found for the field strengths, contrary to predictions that pressure equilibrium with the ambient photospheric gas pressure would determine the surface field strengths. Coronal soft X-ray fluxes from the G and K dwarfs correlate well with the fraction of the stellar surface covered by magnetic regions. The dependence of coronal soft X-ray fluxes on photospheric field strengths is consistent with Stein's predicted generation-rates for Alfven waves. These dependences are inconsistent with the one dynamo model for which a specific prediction is offered. Finally, time variability of magnetic fields is seen on the two active stars that have been extensively monitored. Significant changes in magnetic fields are seen to occur on timescales as short as one day. Previously announced in STAR as N83-24435

Marcy, G. W.↗
NASA NTRS1986

Ionospheric convection signatures observed by DE 2 during northward interplanetary magnetic field

Observations of the ionospheric convection signature at high latitudes are examined during periods of prolonged northward interplanetary magnetic field (IMF). The data from Dynamics Explorer 2 show that a four-cell convection pattern can frequently be observed in a region that is displaced to the sunward side of the dawn-dusk meridian regardless of season. In the eclipsed ionosphere, extremely structured or turbulent flow exists with no identifiable connection to a more coherent pattern that may simultaneously exist in the dayside region. The two highest-latitude convection cells that form part of the coherent dayside pattern show a dependence on the y component of the IMF. This dependence is such that a clockwise circulating cell displaced toward dawn dominates the high-latitude region when B(Y) is positive. Anti-clockwise circulation displaced toward dusk dominates the highest latitudes when B(Y) is negative. Examination of the simultaneously observed energetic particle environment suggests that both open and closed field lines may be associated with the high-latitude convection cells. On occasions these entire cells can exist on open field lines. The existence of closed field lines in regions of sunward flow is also apparent in the data.

Heelis, R. A.↗
NASA NTRS1981

Observations of the magnetic field and plasma flow in Jupiter's magnetosheath

A comprehensive description is given of the Jovian MS magnetic fields, and explanations of these phenomena are proposed. While emphasizing Voyager 1 and 2 magnetic field observations and their relations to the plasma observations, it is also shown that the same phenomena are present in the Pioneer 10 magnetic field data. An unusually high occurrence of nearly north or south fields is observed in the outbound MS, especially in the vicinity of the MP. It is noted that the outbound MS fields and their variations tend to occur in a plane parallel to the local MP, according to large scale MP models.

Lepping, R. P.↗
NASA NTRS1993

Wide field camera observations of Baade's Window

We have observed a field in Baade's Window using the Wide Field Camera (WFC) of the Hubble Space Telescope (HST) and obtain V- and I-band photometry down to V approximately 22.5. These data go several magnitudes fainter than previously obtained from the ground. The location of the break in the luminosity function suggests that there are a significant number of intermediate age (less than 10 Gyr) stars in the Galactic bulge. This conclusion rests on the assumptions that the extinction towards our field is similar to that seen in other parts of Baade's Window, that the distance to the bulge is approximately 8 kpc, and that we can determine fairly accurate zero points for the HST photometry. Changes in any one of these assumptions could increase the inferred age, but a conspiracy of lower reddening, a shorter distance to the bulge, and/or photometric zero-point errors would be needed to imply a population entirely older than 10 Gyr. We infer an initial mass function slope for the main-sequence stars, and find that it is consistent with that measured in the solar neighborhood; unfortunately, the slope is poorly constrained because we sample only a narrow range of stellar mass and because of uncertainties in the observed luminosity function at the faint end.

Holtzman, Jon A.↗
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.↗