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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 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
NASA NTRS2000

Energy Characteristics of Auroral Electron Precipitation: A Comparison of Substorms and Pressure Pulse Related Auroral Activity

The Polar Ultraviolet Imager (UVI) observes auroral responses to incident solar wind pressure pulses and interplanetary shocks such as those associated with coronal mass ejections. The arrival of a CME pressure pulse at the front of the magnetosphere results in highly disturbed geomagnetic conditions and a substantial increase in both dayside and nightside auroral precipitation. Our observations show a simultaneous brightening over broad areas of the dayside and nightside aurora in response to a pressure pulse, indicating that more magnetospheric regions participate as sources for auroral precipitation than during isolated substorms. We estimate the average energies of incident auroral electrons using Polar UVI images and compare the precipitation energies during pressure pulse associated events to those during isolated auroral substorms. Electron precipitation during substorms has average energies greater than 10 keV and is structured both in local time and magnetic latitude. For auroral intensifications following the arrival of a pressure pulse or interplanetary shock, electron precipitation is less spatially structured and has greater ux of lower energy electrons (Eave _ 7 keV) than during isolated substorm, onsets. The average energies of the precipitating electrons inferred from UVI are consistent with those measured in-situ by the FAST spacecraft. These observations quantify the differences between global and local auroral precipitation processes and will provide a valuable experimental check for models of sudden storm commencements and magnetospheric response to perturbations in the solar wind.

Chua, D.↗
NASA NTRS1973

Simultaneous observations of auroras from the South Pole Station and of precipitating electrons by Isis 1.

On the basis of the simultaneous observations of auroras from the South Pole and of precipitating electrons by the Isis 1 satellite it is shown that (1) a midday auroral arc (photographed on black and white film) occurs within the cleft (cusp) region projected to the appropriate auroral height along the geomagnetic field; (2) in the evening sector an aurora, observed by Isis 1 and the South Pole all-sky camera, extended for at least 5 hours of local geomagnetic time in the expected position of the auroral oval; and (3) during a period of extreme magnetic quiet, cleftlike electrons were observed just poleward of a narrow region of intense precipitation in the midnight sector. An earth-sun oriented arc was seen at the projected location of the intense electron flux.

Winningham, J. D.↗
NASA NTRS1984

Electron precipitation zones around major ground-based VLF signal sources

The spatial distribution of electron precipitation induced by VLF signals from ground-based transmitters is determined by using a test particle computer model of the gyroresonant wave-particle interaction (Inan et al., 1982). The results are presented as contours of energy flux on a map of the region around each transmitter. It is shown that the size of the precipitation zones is a strong function of the geographic location of the transmitter, as well as its radiated power and operating frequency. In general, the precipitation zones are much wider in longitude than in latitude and are oriented along lines of constant geomagnetic latitude. Assuming backscatter and/or wave echoing, precipitation zones around the points that are magnetically conjugate to the sources are also estimated. The results presented can be used to interpret satellite- or ground-based measurements of the precipitation induced by ground-based VLF transmitters.

Inan, U. S.↗
NASA NTRS1988

Longitudinal differences in electron precipitation near L = 4

The origin of the significant differences revealed in data on electron precipitation characteristics obtained above Siple Station, Antarctica, and Kerguelen Islands was investigated. The two stations are both in the Southern Hemisphere at nearly the same magnetic latitude (L=4) and at longitudes that place them roughly at equal distances east and west of the center of the South Atlantic magnetic anomaly. The primary data used in the study were counting rates from rocket-borne parachute-deployed scintillation counters and VLF data from ground-based and rocket-borne receivers. The two locations were found to differ in two major respects: (1) the precipitation background at Kerguelen Islands is very low, with high levels of wave activity being required to produce any detectable precipitation, and (2) X-ray microbursts, very common at Siple, were found to be essentially absent at Kerguelen. This observation supports models of the microburst generation process which predict maximum pitch angle scatterings of only a few tenths of a degree.

Bering, E. A., III↗
NASA NTRS1973

Dependence of field-aligned electron precipitation on season, altitude and pitch angle

The occurrence of field-aligned 2.3 keV electron precipitation was examined by using data from more than 7500 orbits of the polar-orbiting satellite, OGO-4. The frequency of occurrence of field aligned precipitation was highest at actual pitch angles between 7 and 10 deg, being highest in the winter months, at highest satellite altitudes. Acceleration by a localized parallel electric field established by electrostatic charge layers is proposed to explain particle observations.

Berko, F. W.↗
NASA NTRS1979

Time structure of postmidnight energetic electron precipitation and the limit of stable trapping

The paper examines the detailed time structure of high-energy (over 30 keV) electron precipitation along the morningside and dayside of the auroral zone. To this end, available high time resolution data from the Ogo 6 energetic electron experiment are analyzed. The relationship between trapped flux levels and degree of precipitation observed is studied from an observational standpoint and compared with the critical flux levels estimated by Kennel and Petschek (1966). A possible explanation within the general framework of the Kennel-Petschek theory of the observed burstlike precipitation episodes is presented, and the implications of these features for the average lifetime of electrons in drifting clouds are discussed.

Trefall, H.↗
NASA NTRS2019

Radiation Dose During Relativistic Electron Precipitation Events at the International Space Station

We provide a quantitative estimate of the radiation dose during relativistic electron precipitation (REP) events at the International Space Station (ISS). To this goal, we take advantage of the data collected by the CALorimetric Electron Telescope, the Monitor of All‐sky X‐ray Image, and the Space Environment Data Acquisition equipment‐Attached Payload. The three ISS detectors offer complementary REP observations, including energy spectra and flux directional information, during a period of approximately 2.5 years, from November 2015 to March 2018. We have identified 762 REP events during this period from which we obtain the distribution of radiation dose, relevant to extravehicular activities outside the ISS.

H. Ueno↗
NASA NTRS1975

Echo 2 - Observations at Fort Churchill of a 4-keV peak in low-level electron precipitation

The Echo 2 rocket flight launched from Fort Churchill, Manitoba, offered the opportunity to observe high-latitude low-level electron precipitation during quiet magnetic conditions. Although no visual aurora was evident at the time of the flight, an auroral spectrum sharply peaked at a few keV was observed to have intensities from 1 to 2 orders of magnitude lower than peaked spectra typically associated with bright auroral forms. There is a growing body of evidence that relates peaked electron spectra to discrete aurora. The Echo 2 observations show that whatever the mechanism for peaking the electron spectrum in and above discrete forms, it operates over a range of precipitation intensities covering nearly 3 orders of magnitude down to subvisual or near subvisual events.

Arnoldy, R. L.↗
NASA NTRS2021

Magnetosphere–Ionosphere Coupling of Precipitating Electrons and Ionospheric Conductance

Modeling of electrodynamic coupling between the magnetosphere and ionosphere depends on accurate specification of ionospheric conductances produced by auroral precipitation. Magnetospheric models determine the plasma properties on magnetic field lines connected to the auroral ionosphere, but the precipitation of energetic particles into the ionosphere is the result of a two-step process. The first step is the initiation of electron precipitation into both magnetically conjugate points from Earth’s plasma sheet via wave–particle interactions. The second step consists of the multiple atmospheric reflections of electrons at the two magnetically conjugate points.

George V Khazanov↗
NASA NTRS1990

Search for lightning-induced electron precipitation with rocket-borne photometers

Photometers at 3914 A and 5577 A and an optical imager were part of an experimental package launched on a sounding rocket in the 1987 Wave Induced Particle Precipitation campaign at Wallops Island, Virginia. The objective was to measure lightning-induced electron precipitation (LEP) by means of its optical signature. This was the first attempt to measure LEP using rocket-borne optical instrumentation. Launch criteria included nearby thunderstorm activity and ground-based observations of Trimpi events. Lightning flashes are clearly discernible in the data. The photometer data was also characterized by large spin and precession modulations in the photon count rate, consistent with elevated steady particle fluxes in the northern portion of the instrument field of view. No evidence of LEP was observed by the photometers or onboard particle detectors (Arnoldy and Kintner, 1989). Analysis of the data has made it possible to place an upper limit of 0.0008 ergs/sq cm per sec on any burst precipitation energy flux that may have occurred during the rocket flight in the regions explored by the photometers.

Massey, R. D.↗
NASA NTRS1985

Near-conjugate observations of inverted-V electron precipitation using DE 1 and DE 2

A major focus of auroral research has been related to the inverted-V electron precipitation event, distinguished by the 'inverted-V' variation of peak energy flux in an energy-time spectrogram. Thieman and Hoffman (1984), in an examination of plasma data from near-conjugate DE 1/2 passes in the southern hemisphere, have found that some inverted-V events remain reasonably stable over a time span of up to 18 min, while other events change over shorter time periods. The present investigation has the objective to study quantitatively the energization of inverted-V electron fluxes and to compare the results with predictions from adiabatic acceleration by an electrostatic field. The obtained results suggest that the turbulent processes might contirbute minimally to the energy flux of secondary electrons for some events, but significantly for others.

Lin, C. S.↗
NASA NTRS1981

Mechanisms for intense relativistic electron precipitation

An analysis of data gathered over a period of 14 months by the S3-3 satellite has revealed the detection of 313 relativistic electron precipitation events with isotropic flux over the upward-looking hemisphere, of which the majority occur at night in a narrow latitudinal zone which is embedded within a broader region of intense energetic ion precipitation. Three classes of precipitation are found to be associated with strong, diffusion resonant scattering due to known magnetospheric plasma waves. It is also found that intense electron energy deposition is a major source of middle-atmospheric, odd-hydrogen and odd-nitrogen molecules at sub-auroral latitudes, leading to an observable catalytic destruction of mesospheric ozone.

Thorne, R. M.↗