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NASA NTRS1983

Pedersen density drift instabilities

This paper describes the linear kinetic theory of electrostatic-drift instabilities driven by Pedersen and density-drift velocities. The model uses a uniform magnetic field B; a weak, uniform density gradient in the x direction; and a weak, uniform electric field in the y direction. Weak charged-neutral collisions are represented by the addition of BGK model terms to the Vlasov equation. The resulting local dispersion equation is used to study the properties of the associated instabilities at ka(i) greater than about 1 (where k is the wave number and a(i) is the ion gyroradius). Results show that the E x B gradient drift instability at ka(i) = about 1 may grow in the auroral ionosphere primarily in the vicinity of 200 km and only if the electron density is sufficiently small.

Gary, S. P.↗

NASA NTRS1984

A simple model for testing the effects of gravity-wave-produced vertical oscillations of scattering irregularities on spaced-antenna, horizontal drift measurements

It has been suggested that the velocities produced by the spaced antenna partial-reflection drift experiment may constitute a measure of the vertical oscillations due to short-period gravity waves rather than the mean horizontal flow. The contention is that the interference between say two scatterers, one of which is traveling upward, and the other down, will create a pattern which sweeps across the ground in the direction (or anti-parallel) of the wave propagation. Since the expected result, viz., spurious drift directions, is seldom, if ever, seen in spaced antenna drift velocities, this speculation is tested in an atmospheric model.

Meek, C. E.↗

NASA NTRS1985

Drift and observations in cosmic-ray modulation, 1

It is illustrated that a relative simple drift model can, in contrast with no drift models, simultaneously fit proton and electron spectra observed in 1965-66 and 1977, using a single set of modulation parameters except for a change in the IMF polarity. This result is interpreted together with the observation of Evenson and Meyer that electrons are recovering more rapidly than protons after 1980, in contrast with what Burger and Swanenburg observed in 1968-72, as a charge sign dependent effect due to the occurrence of drift in cosmic ray modulation. The same set of parameters produces a shift in the phase and amplitude of the diurnal anisotropy vector, consistent with observations in 1969-71 and 1980-81.

Potgieter, M. S.↗

NASA NTRS1985

Drift and observations in cosmic-ray modulation, 2

The significant effect of drift on the radial and latitudinal dependence of cosmic rays for consecutive solar minimum periods is illustrated. Compared with the integral radial gradient observed in 1976, the calculated value seems too small. A detailed comparison will however have to await the forthcoming solar minimum. The same applies to the latitudinal gradient which is as yet inconclusive about drift effects. Searching the literature for observations related to the IMF polarity reversal, distinct differences were found in neutron monitor response functions for consecutive solar minimum periods, and also in the annual variations of cosmic rays observed before and after polarity reversals. Whether drift is the predominant effect is however not yet clear. Better correlation was found between variations in the cosmic ray intensity and solar activity parameters over a much wider range of heliolatitude during 1970-80 compared to before this period.

Potgieter, M. S.↗

NASA NTRS1985

Proportional drift tubes for large area muon detectors

A proportional drift chamber which consists of eight rectangular drift tubes with cross section of 10 cm x 5 cm, a sense wire of 100 micron phi gold-plated tungsten wire and the length of 6 m, was tested using cosmic ray muons. Spatial resolution (rms) is between 0.5 and 1 mm over drift space of 50 mm, depending on incident angle and distance from sense wire.

Cho, C.↗

NASA NTRS1986

Medium and large-scale variations of dynamo-induced electric fields from AE ion drift measurements

Current models of the low latitude electric field are largely based on data from incoherent scatter radars. These observations are extended through the addition of the rather extensive high quality electric field measurements from the Ion Drift Meter (IDM) aboard the Atmosphere Explorer (AE) spacecraft. Some preliminary results obtained from the Unified Abstract files of satellite AE-E are presented. This satellite was active from the end of 1975 through June 1981 in various elliptical and circular orbits having an inclination near 20 deg. The resulting data can be examined for the variation of ion drift with latitude, longitude, season, solar cycle, altitude, and magnetic activity. The results presented deal primarily with latitudinal variations of the drift features. Diagrams of data are given and briefly interpreted. The preliminary results presented here indicate that IDM data from the AE and the more recent Dynamics Explorer B spacecraft should continue to disclose some interesting and previously unobserved dynamical features of the low latitude F region.

Coley, W. R.↗

NASA NTRS1986

The effect of vertical drift on the equatorial F-region stability

Time-dependent ionospheric model calculations for day-time and night-time solutions are presented. The behavior of the growth rate and ion-electron recombination rate for the Rayleigh-Taylor instability on the F-region bottomside is examined as a function of the vertical eastward electric field-magnetic field strength drift velocity. It is observed that on the bottomside F-layer the growth rate exceeds the ion-electron recombination rate even without vertical drift; however, an eastward electric field-magnetic field strength drift can produce an increase in the growth rate by an order of magnitude. The calculated data are compared with previous research and good correlation is detected. The formation of bubbles from a seeding mechanism is investigated.

Hanson, W. B.↗

NASA NTRS1986

An analysis of the role of drift waves in equatorial spread F

An account is given of results of rocket measurements of the wave number spectrum of equatorial spread F irregularities, with emphasis on wavelengths less than 100 m. The measurements were made from two sounding rockets launched from Peru as part of Project Condor. The Condor density fluctuation spectra display a break at a wavelength near 100 m, identical to that found in the PLUMEX experiment (Kelley et al., 1982). The Condor data also confirm a subrange in which the density and the wave potential obey the Boltzmann relation - a strong indication of the presence of low-frequency electrostatic waves with finite wavelength parallel to the magnetic field, perhaps low-frequency drift waves as proposed by Kelley et al. The Condor data are also consistent with the previous conjecture that drift waves only exist above 300 km altitude. To investigate the difference in spectra observed over two altitude ranges, the data must be fitted to a form for the power spectrum taken from Keskinen and Ossakow (1981). The fitted spectrum, along with empirically determined growth and dissipation rates, is used to calculate the energy pumped into the spectrum at long wavelengths as well as the energy dissipated at shorter wavelengths. It is found that the energy is balanced by classical collisional effects in the low-altitude case, but energy balance in the high-altitude case requires an enhanced dissipation of about 500 times that due to classical diffusion. The model is consistent with, but does not uniquely imply, an inverse cascade of drift wave turbulence in equatorial spread F.

Labelle, J.↗

NASA NTRS1986

An assessment of the long-term drift in SBUV total ozone data, based on comparison with the Dobson network

Six years of total ozone data derived from the Nimbus 7 Solar Backscatter Ultraviolet (SBUV) experiment are compared with results from 41 Dobson stations to determine year-to-year changes in addition to the monthly bias change for individual stations and for the network. The SBUV measurements are found to drift against the Dobson stations with a linear trend of .38 + or - .13 percent/yr. The cause of the drift could not be separated between residual uncorrected drift in the SBUV instrument, limited sensitivity of the SBUV to increases in tropospheric ozone, and the effect of local increases in pollution level on individual Dobson stations.

Fleig, Albert J.↗

NASA NTRS1986

Closed-drift thruster investigations

Recent data obtained from a second generation closed-drift thruster design, employing Hall current acceleration is outlined. This type device is emphasized for electric propulsion for geocentric mission applications. Because geocentric mission profiles are best achieved with a specific impulse range of 1000 to 2000 s, closed-drift thrusters are well suited for this application, permitting time payload compromises intermediate of those possible with either electrothermal or electrostatic devices. A discussion is presented of the potential advantages of using a 1000 to 2000 s device for one way orbit raising of nonpower payloads. Because closed-drift thruster operation is not space charge limited, and requires only one power circuit for steady state operation, their application is technically advantageous. Beam, plasma and thrust characteristics are detailed for a range of operating conditions.

Robinson, Raymond S.↗

NASA NTRS1989

High pressure gas scintillation drift chambers with wave shifter fiber readout. I

The authors present results from a prototype xenon-gas scintillation drift chamber. It was operated at pressures up to 20 atm, and the scintillation light yield was measured at various pressures and reduced fields. Scintillation-reduced fields ranged from 1.3 to 3 kV/cm/atm in a 5.4-mm scintillation gap. Drift fields ranged from 45 to 100 V/cm/atm in an 8-cm drift region. The chamber was exposed to an 241Am source in a port either 2.7 or 5.4 cm from the secondary scintillation region. The authors also describe the high-voltage problems encountered during operation at high pressures. Further tests with the wave shifter fiber readout showed that the problem of gas contamination by the fibers is manageable but that the interaction between the optical fibers and the high-pressure xenon gas can lead to fiber damage. A solution to this problem is described.

Parsons, A.↗

NASA NTRS1990

On the length of the drift region in the Ramsey cavity

The interaction of atoms in a beam with the microwave field in a separated field geometry such as a Ramsey cavity is generally described in terms of the three regions traversed successively by the atoms, namely two interaction regions of length (l) separated by a drift, or free precession, region of length L. For a monokinetic beam of velocity v, the linewidth of the central fringe in the Ramsey resonance pattern is usually expressed as delta omega equals pi v/L. A more detailed calculation shows, however, that the linewidth is equal to pi v/L asterisk, where the equivalent drift L asterisk is larger than L by an amount of the order of l/L. The correction depends on the field distribution in the interaction regions. Its origin lies in the fact that atomic precession is not limited to the field-free regions but also occurs in the interaction regions, where atomic coherence builds up or decreases continuously. Although the correction to the equivalent length of the drift region is small, it may be relevant to the evaluation of the second-order Doppler effect bias in primary cesium-beam standards to the extent that the atomic velocity is deduced from the lineshape and from the geometrical parameters of the cavity. It is shown that in current and projected standards with atoms of average thermal velocity, use of corrected dimensions may lead to a change of the calculated bias of the order of 10(exp -14), which is significant at the levels of accuracy considered nowadays.

Thomann, Pierre↗

NASA NTRS1990

New drift chamber technology for high energy gamma-ray telescopes

Work to develop a low-power amplifier and discriminator for use on space qualifiable drift chambers is discussed. Consideration is given to the goals of the next generation of high-energy gamma-ray telescope design and to how the goals can be achieved using xenon gas drift chambers. The design and construction of a low power drift chamber amplifier and discriminator are described, and the design of a quad-time-to-amplitude converter is outlined.

Hunter, Stanley D.↗

NASA NTRS1989

Efficient detection of a CW signal with a linear frequency drift

An efficient method is presented for the detection of a continuous wave (CW) signal with a frequency drift that is linear in time. Signals of this type occur in transmissions between any two locations that are accelerating relative to one another, e.g., transmissions from the Voyager spacecraft. We assume that both the frequency and the drift are unknown. We also assume that the signal is weak compared to the Gaussian noise. The signal is partitioned into subsequences whose discrete Fourier transforms provide a sequence of instantaneous spectra at equal time intervals. These spectra are then accumulated with a shift that is proportional to time. When the shift is equal to the frequency drift, the signal to noise ratio increases and detection occurs. Here, we show how to compute these accumulations for many shifts in an efficient manner using a variety of Fast Fourier Transformations (FFT). Computing time is proportional to L log L where L is the length of the time series.

Swarztrauber, Paul N.↗

NASA NTRS1992

The temporal evolution of the ionospheric signatures of subauroral ion drifts

The effects of an imposed westward plasma drift on O(+) and molecular ion behavior in the nightside ionosphere are investigated using a model of the ionosphere and plasmasphere. A closed subauroral tube of the plasma is considered, and the velocity input persists for 30 min. The rapid increase in the F-region ion temperature resulting from ion-neutral frictional heating causes an immediate surge in the O(+) field-aligned velocity, upwards in the topside ionosphere and downwards below the F2-peak, but after about 10 min into the event the surge in the topside disappears. After the event there is a return flow of O(+) from the plasmasphere. The relative abundance of O(+) decreases during the event due to the increased rate of conversion of O(+) into NO(+) and O2(+); the decrease is more marked for greater values of the imposed westward ion drift. The implications of these results for satellite observations of subauroral ion drifts events and on EISCAT incoherent scatter radar observations of ion heating events is discussed.

Moffett, R. J.↗

NASA NTRS1992

Observation of non-drifting radio emissions associated with the intense solar activity in March 1991

Three very unusual radio bursts, separated in time by 4 hours and 35 minute-intervals were observed on March 28, 1991 by the radio and plasma wave (URAP) experiment on the Ulysses spacecraft. Although they are preceded by drifting type III bursts at high frequencies, they show no frequency drift at frequencies from 52 kHz down to 16 kHz. In addition, they have extraordinary sawtooth-like profiles; they have a very rapid exponential rise of about 20 minutes independent of frequency and a much longer nonexponential decay which increases with decreasing frequency. The bursts are interpreted as due to synchrotron emission, which seems to fit many of their characteristics. This radio emission appears to be associated with an expanding source region. However, the observed intensity may be somewhat higher than expected and the possible role of the precursor type III radio bursts in triggering the low frequency non-drifting remains unanswered.

Reiner, M. J.↗

NASA NTRS1993

Role of drifts and global merged interaction regions in the long-term modulation of cosmic rays

The paper shows that the long-term modulation of 0.2- to 3-GV galactic and anomalous cosmic rays over the 22-year heliomagnetic cycle is basically a combination of two solar related processes, the cumulative effect of long-lived global merged interaction regions (GMIRs) and large-scale particle gradient and curvature drifts in the interplanetary magnetic field. This paradigm for cosmic ray modulation is based on the observed changes in cosmic ray intensity from solar minimum to solar maximum over successive solar cycles (21 and 22) using data from 1 AU and from the outer heliosphere. For cycle 21, the 1977-1980 modulation is dominated by GMIRs. In cycle 22, it is shown that drifts are an important but not dominant factor for galactic cosmic ray modulation with the current sheet related drift effects decreasing with increasing rigidity and heliocentric distance.

Mcdonald, Frank B.↗

NASA NTRS1993

A proposed production model of rapid subauroral ion drifts and their relationship to substorm evolution

The temporal relationship between subauroral ion drifts (SAIDs) and the phases of an auroral substorm is examined on the basis of multisatellite data. The time of expansive phase onset is identified and the time at which recovery begins is estimated. SAIDs are found to typically occur well after substorm onset (more than 30 min), during the substorm recovery phase. Substantial westward ion drifts and field-aligned currents are observed well equatorward of the auroral oval during the expansion phase of a substorm, but the drifts lack the narrow spike signature associated with SAIDs. A phenomenological model of SAID production that qualitatively agrees with the observed ionospheric signatures and substorm temporal relationship is proposed.

Anderson, P. C.↗