Engineering topics

Kelley, M. C.

Publications and source records attributed to Kelley, M. C..

At least 19 records

NASA NTRS2012

On the Distribution of Ion Density Depletion Along Magnetic Field Lines as Deduced Using C-NOFS

To investigate ion density depletion along magnetic field lines, we compare in situ-measured ion density fluctuations as seen from C/NOFS and compare them to the field-line-integrated depletion of the whole bubble as inferred from electric field measurements. Results show that, within C/NOFS' range, local measurement of the normalized density depletion, (Delta)n/n(sub 0), near the apex may be far less than at other points on the same field line. We argue that the distribution of (Delta)n/n(sub 0) is a weighted distribution concentrated at latitudes of the Appleton anomalies and becomes more heavily weighted the closer the field-aligned bubble rises to the peak of the anomalies. A three-dimensional simulation of an ionospheric bubble verifies our arguments.

ion density↗

NASA NTRS2001

Dust Detector

We discuss a recent sounding rocket experiment which found charged dust in the Earth's tropical mesosphere. The dust detector was designed to measure small (5000 - 10000 amu.) charged dust particles, most likely of meteoric origin. A 5 km thick layer of positively charged dust was found at an altitude of 90 km, in the vicinity of an observed sporadic sodium layer and sporadic E layer. The observed dust was positively charged in the bulk of the dust layer, but was negatively charged near the bottom.

Kelley, M. C.↗

NASA NTRS1994

Formation and eruption of Sun-aligned arcs at the polar cap-auroral oval boundary

This paper reports on results from a study of the poleward edge of the auroral oval in the morning sector using a comprehensive blend of in-situ and ground-based measurements. Three rockets, equipped to measure electric and magnetic fields, energetic particles, and plasma density flew into an auroral display whose dynamical features were reorded with a digital image into an auroral display intensified all-sky camera as well as with an incoherent scatter radar. In addition, a number of DMSP satellite measurements bracketed the launch time. Evidence is presented here that in a condition of declining magnetic activity Sun-aligned arcs are injected into the polar cap at velocities approximately 7 km/s from locations of periodic brightening along the morningside of the auroral oval. The multipoint in situ measurements allow some separation of temporal and spatial effects and strongly suggest a poleward contraction of the convention pattern of about 0.25 deg INVL in 70 s. The most equatorward of the two brightest arcs studied erupted into a region which already was characterized by strong sunward convection. The most poleward, however, pushed into a region that had been convecting in an antisunward direction at velocities exceeding 1 km/s less than 2 min earlier, and it is likely that sunward convection subsequently pertained poleward of that arc as well. We believe that these events mark the reconfiguration of the magnetosphere into a system characterized by a smaller polar cap.

Berg, G. A.↗

NASA NTRS1994

VHF radar and rocket observations of equatorial spread F on Kwajalein

VHF radar data from the Summer 1990 Equatorial Spread F campaign on Kwajalein are presented. The Cornell 50 MHz portable radar interferometer (CUPRI) operated concurrently with the Altair UHF incoherent scatter radar throughout July and August and supported two sounding rocket flights on July 30 and August 2. This experiment provided the first opportunity to simultaneously diagnose equatorial spread F using the three prime experimental techniques: VHF/UHF coherent scatter, incoherent scatter, and in situ probe measurements of electric field and density fluctuations. The intensity of the coherent echoes observed was consistent with typical Jicamarca spread F observations, but chains of periodic, large-scale plasma upwellings were observed more often and for much longer durations on Kwajalein than have been seen over Peru. CUPRI also measured Doppler frequencies in one upwelling corresponding to 1200-m/s plasma drift velocities. This measurement agrees with recent observations of supersonic drift rates at the magnetic equator by spacecraft. Near the most active localized plasma upwellings, interferometer data reveal that the zonal drift rate of plasma irregularities can vary sharply in space, as one would expect for two-dimensional incompressible flow. We introduce a semiempirical model of the three-dimensional spectrum of F region irregularities that is consistent with the one-dimensional spectra of density fluctuations observed by sounding rockets and with the axial ratio of irregularities determined recently. Normalized to data from one of the rocket flights on Kwajalein, the model predicts the 3-m scattering cross-section measured by CUPRI to within a few decibels.

Hysell, D. L.↗

NASA NTRS1994

Steepened structures in equatorial spread F. 1: New observations

Sounding rocket data from the 1990 Combined Release and Radiation Effects Satellite (CRRES)/EQUIS equatorial spread F campaign on Kwajalein Atoll are presented. Two Terrier Malamute sounding rockets were launched into active spread F conditions on July 30 and August 2, respectively, and achieved apogee slightly below 500 km, just above the F peak. Plasma frequency probes aboard both rockets showed that the unstable nighttime F region is characterized by propagating steepened structures. Power density spectra for the structures typically exhibit two regions that obey k(exp -n) scaling, where n is approximately equal to 2 at wavelengths greater than 80-100 m and approximately equal to 5 at shorter wavelengths. These spectral indices are quiet variable, and the long-wavelength spectral index in particular seems to decrease with increasing amplitude of density fluctuations. The rocket payloads also measured vector electric fields in the plane perpendicular to B over wavelengths ranging from over 60 km to less than 6 m. Both vector components of the perpendicular electric field are proportional to delta n/n at wavelengths longer than 300 m but assume a Boltzmann relationship (with square of the absolute value of delta E approximately equal to (k(exp2))(square of the absolute value of (delta n/n)) at smaller scales. The perturbed zonal electric field, delta E(sub x), dominates the vertical field, delta E(sub z), at long wavelenghts, but the situation is reversed at smaller scales.

Hysell, D. L.↗

NASA NTRS1994

Steepened structures in equatorial spread F. 2: Theory

This paper investigates the properties of a one-dimensional fluid model of plasma convection in the equatorial F region ionosphere. The model equations are similar in form to Burgers equation except for additional higher-order spatial derivatives. Like Burgers equation, solution to the model have the form of propagating, shocklike structures. Numerical simulations of the model closely resemble the steepened structures observed by sounding rocket plasma density probes within equatorial spread F. Simulated denstiy power spectra, like the spectra computed from in situ data, seem to possess power law forms with a break at wavelengths of about 100 m. The precise wavenumber of the spectral break is determined by the ambipolar diffusion coefficient. The model predicts that electric field fluctuations perpendicular to the direction of plasma steepening should be proportional to the plasma density fluctuations. Electric field fluctuations parallel to the steepening will be due primarily to the ambipolar field and have a Boltzmann relationship with density (square of the absolute value of delta E) approximately equal to (K(exp 2))(square of the absolute value of (delta n/n)). At wavelengths less than about 300 m, the ambipolar field should be the dominant component of the total field intensity.

Hysell, D. L↗

NASA NTRS1993

Evidence for two different structuring and scattering mechanisms and the associated role of aerosols in the polar summer mesosphere

A Super Arcas rocket, MISTI B, was launched as part of the Polar Mesospheric Summer Echoes (PMSE) salvo to measure electron density irregularities using rf and dc probes. Large and small scale structures in the electron density were measured on rocket ascent and descent at the altitudes of 86.5 and 88.5 +/- .5 km. Since the rocket apogee was 89 km, the rocket was in the height range 88.5 +/- .5 km for 30 seconds giving us an unusual measurement of horizontal structure over a distance of 5.5 km. A power spectrum of the fluctuations for the upper layer gives further evidence that turbulent mixing is an important process in PMSE. The power spectrum of the lower layer, however, gives evidence that this layer is characterized by a form of partial or Fresnel scattering. Both spectra are in excellent agreement with similar analysis of electron fluctuation spectra measured in the same layers on the TURBO-B rocket flown 12 minutes later and the analysis of Cornell University Portable Radar Interferometer (CUPRI) data by Cho et al., 1993A. Thus two different structuring and scattering mechanisms exist at altitudes only 1 km apart. Using the simultaneous dc and rf probe measurements of electron depletions and sharp gradients in the lower layer, we speculate on the role of aerosols in creating these depletions and gradients.

Ulwick, J. C.↗

NASA NTRS1993

Spectral evidence for stirring scales and two-dimensional turbulence in the auroral ionosphere

Electric field power spectra from two auroral sounding rocket flights show evidence of a distinct scale size regime for injection of energy into the auroral oval. The signature of this process is a broad plateau in the spectrum, with power law dependences at both shorter and longer scale sizes. We argue that the spectral properties at high k are dominated by processes occurring near the edges of inverted-V electron precipitation regions (auroral arcs). We see no compelling reason to conclude that a linear local plasma instability is occurring but rather, that nonlinear mixing and forward cascade yield the observed velocity field. The spectra of simultaneously observed density irregularities are quite different from those of the electric field, implying that the plasma density does not behave as a passive scalar in the auroral zone during active conditions. At low-k values we show that the rocket spectra are consistent with the power spectra of magnetospheric electric fields measured by the DE, AE-C, and Hilat stallites.

Earle, G. D.↗

NASA NTRS1993

Long-lived artificial ion clouds in the earth's ionosphere

In two barium releases made over the Caribbean during the summer of 1991, the ion cloud was observed to last more than 10 hours. Observations were made with a low light level TV imager and a TV spectrograph operated onboard a Russian research vessel conducting ionospheric research and participating in the NASA-CRRES mission. The two clouds were observed near the release region for 15 to 25 minutes during the twilight following the initial release. One of the releases was made during evening twilight and the ion cloud reappeared the following morning, while the other was a morning release and the late-time observations made the next evening. The observations are highly surprising since, generally, it has been assumed that the ion cloud would dissipate within a few hours. However, the long life time appears consistent with current knowledge about dissipative processes. The long lifetime of barium ion clouds may provide for the most sensitive experimental testing of ionospheric convection models, a possibility with clear implications for future barium release experiments.

Milinevskij, G. P.↗

NASA NTRS1992

The collective gyration of a heavy ion cloud in a magnetized plasma

Results are reported from the ionospheric barium injection experiments CRIT I and CRIT II, during both of which a long-duration oscillation was observed with a frequency close to the gyrofrequency of barium and a time duration of about 1 sec. A model for the phenomenon which was proposed for CRIT I is compared to the results from CRIT II, which made a much more complete set of measurements. The model follows the motion of a low-beta ion cloud through a larger ambient plasma. As the ions move across the magnetic field, the space charge is continuously neutralized by magnetic-field aligned electron currents from the ambient ionosphere, drawn by the divergence in the perpendicular electric field. These currents yield a perturbation of the magnetic field related to the electric perturbation by Delta-E/Delta-B is approximately equal to V sub A. The possibility of extending the model to the active region, where the ions are produced in this type of self-ionizing injection experiments, is discussed.

Brenning, N.↗

NASA NTRS1991

Electric and magnetic field measurements inside a high-velocity neutral beam undergoing ionization

Vector electric field measurements were made inside two ionizing, high-velocity streams of barium atoms in the earth's ionosphere, and a variety of electrical phenomena across the frequency spectrum are reported. A very large quasi-dc electric field was detected antiparallel to the beam velocity at a roughly 45 deg angle with the magnetic field B0. A very large component of E is found parallel to B0. The fluctuating electric fields are also quite large, of the same order of magnitude as the quasi-dc pulse. The wave energy maximizes at frequencies below the barium lower hybrid frequency and includes strong signatures of the oxygen cyclotron frequency. Measurements made on a subpayload separated across B0 by several hundred meters and along B0 by several km do not show the large pulse. Very large amplitude magnetic field fluctuations were observed in both bursts.

Kelley, M. C.↗

NASA NTRS1991

Interpretation of the electric fields measured in an ionospheric critical ionization velocity experiment

The quasi-dc electric fields measured in the CRIT I ionospheric release experiment are studied. In the experiment, two identical barium shaped charges were fired toward a main payload, and three-dimensional measurements of the electric field inside the streams were made. The relevance of proposed mechanisms for electron heating in the critical ionization velocity (CIV) mechanism is addressed. It is concluded that both the 'homogeneous' and the 'ionizing front' models probably are valid, but in different parts of the streams. It is also possible that electrons are directly accelerated by a magnetic field-aligned component of the electric field. The coupling between the ambient ionosphere and the ionized barium stream is more complicated that is usually assumed in CIV theories, with strong magnetic-field-aligned electric fields and probably current limitation as important processes.

Brenning, N.↗

NASA NTRS1990

CRIT II electric, magnetic, and density measurements within an ionizing neutral stream

Measurements from rocket-borne sensors inside a high-velocity neutral barium beam show a-factor-of-six increase in plasma density in a moving ionizing front. This region was colocated with intense fluctuating electric fields at frequencies well under the lower hybrid frequency for a barium plasma. Large quasi-dc electric and magnetic field fluctuations were also detected with a large component of the current and the electric field parallel to B(0). An Alfven wave with a finite electric field component parallel to the geomagnetic field was observed to propagate along B(0), where it was detected by an instrumented subpayload.

Swenson, C. M.↗

NASA NTRS1990

Intense ionospheric electric and magnetic field pulses generated by lightning

Electric and magnetic field measurements have been made in the ionosphere over an active thunderstorm and an optical detector onboard the same rocket yielded an excellent time base for the study of waves radiated into space from the discharge. In addition to detection of intense, but generally well understood whistler mode waves, very unusual electric and magnetic field pulses preceded the 1-10 kHz component of the radiated signal. These pulses lasted several ms and had a significant electric field component parallel to the magnetic field. No known propagating wave mode has this polarization nor a signal propagation velocity as high as those measured here. This study investigated and rejected an explanation based on an anomalous skin depth effect. Although only a hypothesis at this time, a more promising explanation involving the generation of the pulse via a nonlinear decay of whistler mode waves in the frequency range 10-80 kHz is being investigated.

Kelley, M. C.↗

NASA NTRS1990

Consistency of rocket and radar electron density observations - Implications about the anisotropy of mesospheric turbulence

Quantitative comparisons are made between rocketborne measurements of electron density fluctuations and simultaneous 53.5 MHz radar measurements obtained during the Summer in Northern Europe campaign. Rocketborne radar reflectivity results are of the order of 10 dB greater than would be expected in the case of isotropic electron density fluctuations. There results can be reconciled by assuming isotropic turbulence. A relation is derived between rocket and radar observations which covers the entire range from isotropic turbulent scatter to Fresnel scatter at horizontal density stratifications. The anisotropy is greatest at heights where the electron density displays deep 'bite-outs'.

Inhester, B.↗

NASA NTRS1990

Intense turbulence in the polar mesosphere - Rocket and radar measurements

Two radars respectively operating at 53.5 MHz and 224 MHz have been used to simultaneously measure the polar mesospheric summer echoes (PMSEs) during the launch of a sounding rocket designed to measure the fluctuations in the electron density in the same height range. Some features of the data obtained are consistent with nearly isotropic, intense, meter-scale turbulence on the day of the observations. A dissipation rate is derived from the spectral width of the 53.5 MHz backscatter signal and from the rocket electron density fluctuation data; the diffusive subrange occurs at a wavelength which is a factor of 10 greater than the viscous subrange. This corresponds to a Schmidt number of about 100.

Kelley, M. C.↗

NASA NTRS1990

The collective gyration of a heavy ion cloud in a magnetized plasma

In both the ionospheric barium injection experiments CRIT 1 and CRIT 2, a long duration oscillation was seen with a frequency close to the gyro frequency of barium and a time duration of about one second. A model for the phenomena which was proposed for the CRIT 1 experiment is compared to the results from CRIT 2 which made a much more complete set of measurements. The model follows the motion of a low Beta ion cloud through a larger ambient plasma. The internal field of the model is close to antiparallel to the injection direction v sub i but slightly tilted towards the self polarization direction E sub p = -V sub i by B. As the ions move across the magnetic field, the space charge is continuously neutralized by magnetic field aligned electron currents from the ambient ionosphere, drawn by the divergence in the perpendicular electric field. These currents give a perturbation of the magnetic field related to the electric field perturbation by Delta E/Delta B approximately equal to V sub A. The model predictions agree quite well with the observed vector directions, field strengths, and decay times of the electric and magnetic fields in CRIT 2. The possibility to extend the model to the active region, where the ions are produces in this type of self-ionizing injection experiments, is discussed.

Brenning, N.↗

NASA NTRS1990

Low- and mid-latitude ionospheric electric fields during the January 1984 GISMOS campaign

The electrical coupling between the high-, middle-, and low-latitude ionospheres during January 17-19, 1984 is examined, using interplanetary and high-latitude magnetic field data together with F region plasma drift measurements from the EISCAT, Sondre Stromfjord, Millstone Hill, Saint-Santin, Arecibo, and Jicamarca incoherent scatter radars. The penetration both the zonal and meridional electric field components of high-latitude origin into the low-latitude and the equatorial ionospheres are studied. The observations in the postmidnight sector are used to compare the longitudinal variations of the zonal perturbation electric field with predictions made from global convection models. The results show that the meridional electric field perturbations are considerably more attenuated with decreasing latitude than the zonal fluctuations. It is concluded that variations in the meridional electric field at low latitudes are largely due to dynamo effects.

Fejer, B. G.↗