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Benbrook, J. R.

Publications and source records attributed to Benbrook, J. R..

At least 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1995

Statistical studies of impulsive events at high latitudes

A statistical study has been made of the high-latitude impulsive events that were observed during the 1985-1986 South Pole Balloon Campaign. The events were selected by searching for unipolar pulses greater than or equal to 10 nT above background in the vertical component of the magnetic field on the ground and/or pedestal or 'W' shaped horizontal electric field perturbations greater than or equal to 10 mV/m in amplitude and accompanied by perturbations in the vertical electric field at balloon altitude. A main event list comprising 112 events was compiled from the 468 hours of data available. Three aspects of the events were examined: the solar wind conditions prior to the event, local time of observation, and intrinsic properties of the events. The local time distribution was obtained from the 112 entry main event list and was found to be nearly uniform across the dayside, with no midday gap. The event rate found using our low-amplitude selection criteria was 0.7 event/hr, comparable to expectations based on in situ studies of the magnetopause. A total of 42 events were found for which data were available from Interplanetary Monitoring Platform (IMP) 8. Of these events, 12 occurred when the Z(sub GSM) component (B(sub Z)) of the interplanetary magnetic field (IMF) was northward and 30 occurred when B(sub Z) was southward or fluctuating. Only three of the B(sub Z) northward cases and only five of the B(sub Z) southward cases were preceded by pressure pulses greater than 0.4 nPa in amplitude. Ten of the events were studied in detail by means of a model-fitting method discussed elsewhere. This method infers values of several parameters, including the total current flowing in a coaxial or monopole system and a two-dimensional dipole system. The intrinsic properties of the events showed that only approximately 10% of the total current contributed to momentum transfer to the high-latitude ionosphere, that the direction of the motion depended more on local time of observation than IMF B(sub y), and that events were usually several hundred kilometers in size. The observed B(sub z) control found in the 42 event list and the prevalence of coaxial current dominated events are inconsistent with the predictions of the pressure pulse model.

Lin, Z. M.↗
NASA NTRS1994

Investigation of S3-2 satellite data for local time variation of energetic electron precipitation

Data on precipitating electrons from the S3-2 satellite were investigated for local time variation at four L = 4 stations in the southern hemisphere. The equatorial pitch angles of electrons mirroring at 100 km, assumed to be the edge of the bounce loss cone, are calculated for L = 4 using the International Geomagnetic Reference Field for the epoch of the S3-2 data, along with the variation in mirror altitude per degree of equatorial pitch angle. The largest obstacle to the investigation was uneven sampling in terms of local time for all of the stations. However, this situation was improved upon by the use of S3-2 measurements at the conjugate locations of the four stations which provided additional data on electrons in the southern hemisphere bounce loss cone. Evidence for an effect of the dawn-to-dusk geoelectric field was found at two of the stations, Halley Bay and Siple, in the form of a minimum in electron precipitation at dusk. However, the present study does not completely resolve the question of local time modulation of electron precipitation at L = 4 in the southern hemisphere. Furthermore, while the average precipitation was lowest at the Kerguelen site, as would be expected on the basis of drift loss cone (DLC) theories, the intensity at that site exceeds the level that is expected on the basis of these DLC theories.

Robbe, S.↗
NASA NTRS1993

Ground-based instrumentation for measurements of atmospheric conduction current and electric field at the South Pole

Attention is given to instruments constructed to measure the atmospheric conduction current and the atmospheric electric field - two fundamental parameters of the global-electric circuit. The instruments were deployed at the Amundsen-Scott South Pole Station in January 1991 and are designed to operate continuously for up to one year without operator intervention. The atmospheric current flows into one hemisphere, through the electronics where it is measured, and out the other hemisphere. The electric field is measured by a field mill of the rotating dipole type. Sample data from the first days of operation at the South Pole indicate variations in the global circuit over time scales from minutes to hours to days.

Byrne, G. J.↗
NASA NTRS1990

A mid-latitude balloon-borne observation of total odd nitrogen

A balloon-borne instrument to measure total odd nitrogen NO(y) has been developed. A converter which enables catalytic conversion of NO(y) into nitric oxide on a heated gold surface is combined with a chemiluminescence detector. The conversion efficiency for NO2 was measured to be close to 100 percent at pressures between 60 and 7 mb. The major source of errors in the balloon-borne measurements are the uncertainties in the estimates of the sample flow rate and the zero level of the instrument. The NO(y) concentration was measured at altitudes between 12 and 28 km with a precision of about 25 percent on a balloon experiment conducted at latitude 44 deg N in June 1989. The NO(y) concentration has been measured to be 1.5 + or - 0.4, 3 + or - 0.7, 10 + or - 3, and 14 + or - 4 ppbv at altitudes of 17, 20, 25, and 28 km, respectively.

Kondo, Y.↗
NASA NTRS1990

Observations of ionospheric flux ropes above South Pole

Numerical techniques have been used to investigate two different models of the current flow in ionospheric flux ropes, giving attention to the problem of mapping the electric field from the ionosphere down to balloon altitudes and to the isolated event that occurred at about 1625 UT on January 3, 1986. Also examined are Greenland magnetometer chain and Iqaluit magnetometer data, which imply that the isolated event was localized in longitude as well as 'global', in the sense that it occurred at conjugate points. IMP 8 solar wind plasma and IMF data indicate that the even occurred just as a strong southward turning of the IMF passed the earth.

Lin, Z. M.↗
NASA NTRS1988

Comment on 'Highly relativistic magnetospheric electrons: A role in coupling to the middle atmosphere?'

It is argued that Baker et al. (1987) may have underestimated the electron precipitation rate in the southern hemisphere in the region extending west to about 90 deg in longitude from the southern extension of the center of the South Atlantic geomagnetic anomaly (SAGA). In a reply, it is noted that Baker et al. restricted their study to the case of uniform precipitation in latitude and longitude throughout the outer-zone area, thus entailing a great simplification of the real-world situation. Comments are made on the effects of the SAGA on electron precipitation.

Sheldon, W. R.↗
NASA NTRS1988

The effect of mid-latitude electron precipitation on the geoelectric field

A simple model is outlined to describe electron precipitation from the population of charged particles trapped in the earth's magnetic field; almost all of the precipitation is shown to occur in the region of the South Atlantic Anomaly. When the effect of a dawn-to-dusk electric field across the magnetosphere is included in the model, a diurnal modulation of the precipitated electron flux is predicted. Experimental evidence which supports the diurnal modulation model is described.

Sheldon, W. R.↗
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 NTRS1988

Rocket investigations of electron precipitation and VLF waves in the Antarctic upper atmosphere

The results of two Antarctic rocket campaigns, primarily initiated to investigate electron precipitation stimulated by signals from the Siple-Station ground-based VLF transmitter, are presented. While the primary objective of the campaigns was not achieved, the Siple VLF transmitter facilitated a study of the wave environment in the ionosphere. Standing wave patterns in the ionosphere were observed for the first time by detectors flown aboard the Nike-Tomahawk rockets; the same detectors monitored a continuous signal from the transmitter through the neutral atmosphere and into the ionosphere, providing unique data for comparison with theoretical studies of wave propagation. The measurements of penetrating electron precipitation were interpreted in terms of a model of energetic electron precipitation from the trapped radiational belts.

Sheldon, W. R.↗
NASA NTRS1988

Observations of the stratospheric conductivity and its variation at three latitudes

Measurements from nine high-altitude balloon flights at altitudes ranging from 10 to 30 km have been obtained in order to study atmospheric conductivity variations on local and global scales. The conductivity profiles are not correlated with solar or cosmic ray activity, but they exhibit variations which appear to be dominated by local effects. Evidence is provided of stratospheric aerosol layers with number densities of the order of 1000/cu cm. It is suggested that global conductivity models employing latitudinal variations based on cosmic ray ionization alone may be improved by including the effects of latitudinal variations of temperature and aerosols.

Byrne, G. J.↗
NASA NTRS1987

Electron precipitation near L = 4 - Longitudinal variation

Observations of penetrating electron precipitation at two L of about 4 stations in the southern hemisphere, Kerguelen and Siple Station, Antarctica, are summarized. The nearly complete absence of precipitation at Kerguelen and its frequent occurrence at Siple Station is explained in terms of their location with respect to the center of the South Atlantic geomagnetic anomaly at L of about 4. Conclusions which result from this explanation are discussed along with questions which remain concerning penetrating electron precipitation.

Sheldon, W. R.↗
NASA NTRS1986

Convection electric field effects on outer radiation belt electron precipitation

A model is presented for the possible diurnal modulation of outer radiation belt electron precipitation by considering the effect of the convection electric field on geomagnetically trapped electrons. The modulation flux is the flux due to electrons in the drift loss cone, i.e., those which drift into the bounce loss cone. The electron flux in the drift loss cone is related to the time allowable for diffusion from the stably trapped population to the drift loss cone for precipitation at a specific geographic location. This time, which is termed the maximum L-shell lifetime, is obtained by computing electron trajectories, using a realistic magnetic field model and a simple model for the electric field. The maximum L-shell lifetimes are taken to be the times between successive entries into the bounce loss cone. Conservation of the first two adiabatic invariants, as electrons are slowly energized by the convection electric field, leads to variations in pitch angle, maximum L-shell lifetimes, and, consequently, to changes in the electron flux in the drift loss cone. These results are compared with observations of precipitating electrons made with sounding rocket payloads.

Gelpi, C.↗
NASA NTRS1985

X ray microbursts and VLF chorus

On January 4, 1978, at 1140 UT, a SuperArcas sounding rocket was launched from Siple Station, Antarctica (L = 4.2, 76 deg S, 84 deg W), during a geomagnetically disturbed period (Kp = 6-) with intense X-ray and VLF chorus activity. The parachuted payload observed an intense microburst precipitation event of 10-minute duration. These data have been correlated with measurements of FLF chorus by receivers on the ground at both Siple and its magnetic conjugate point, Roberval, Quebec. Detailed one-to-one correspondence between the microbursts and the chorus was not a consistent feature of the data. Time series analysis fo the data did indicate a significant correlation between the Siple X-ray precipitation and the Roberval VLF waves with an arrival time delay of 0.1 + or 0.3.

Roeder, J. L.↗
NASA NTRS1985

Diurnal modulation of the quiet time penetrating electron flux

Three sounding rocket measurements of energetic electron precipitation in the 65 to 80 km altitude range above Siple Station, Antarctica suggest a possible diurnal modulation of the precipitation. Flights made on January 10 and 11, 1981, to investigate this possibility showed that no electrons were present after local noon, while a significant flux of penetrating electrons was observed the following day near local dawn, even though the level of magnetic activity was higher during the postnoon flight. A prevous flight from Siple Station also observed a large flux of penetrating electrons near local dawn. Calculations of electron drift trajectories in a model magnetic field indicate that moderate values of the convection electric field could cause significant local time variations in the penetrating electron flux at the western edge of the South Atlantic anomaly. These calculations indicate that Siple Station is shadowed by eastern Siberia when it is at local noon, but not when it is at local dawn.

Sheldon, W. R.↗
NASA NTRS1983

Quiet-time electron precipitation at L = 4 in the South Atlantic anomaly

A Superarcas sounding rocket was launched from Siple Station, Antarctica in January 1978, during a prolonged geomagnetically quiet period with very low VLF activity. The observed electron flux is the first direct measurement in the high latitude mesosphere of the quiet-time precipitating electrons in the South Atlantic anomaly. The integrated flux agrees resonably well with satellite measurements and predictions. The calculated energy spectrum of the precipitating electrons is much softer than typical measured quiet-time trapped spectra reported from satellite measurements after extended periods of low magnetic activity.

Benbrook, J. R.↗
NASA NTRS1980

The results from the X ray bremsstrahlung experiment of Project Trigger

Analysis of the bremsstrahlung X-ray data produced the following conclusions. The counting rate observed before the explosion was an expected normal quiet background. An unexpected increase in the counting rate below 20 keV was observed after the explosion, which may have been an effect of the explosion. A significant 0.13-H2 peak in the power spectral density of the X-ray flux was observed, which is interpreted as evidence for a particle-wave-particle interaction involving a bounce resonance stimulated by the explosion. Dispersed continuation of this interaction may have been responsible for delayed long-term precipitation.

Bering, E. A.↗
NASA NTRS1980

X-ray measurements during the Araks experiments

Measurements of the X-ray bremsstrahlung precipitation were made during the Araks experiments. The following conclusions were deduced from the data: with several exceptions the ambient X-ray flux observed was the normal quiet background expected for the location and existing conditions. The X-ray flux at energies below 20 keV was in excess of that predicted by theory. No obvious effects of the Araks experiments were seen in the data. However, a superposed epoch analysis of the X-ray data revealed a very small amount of precipitation associated with the electron gun.

Roeder, J. L.↗