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Carlson, H. C.

Publications and source records attributed to Carlson, H. C..

At least 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1995

Flow-aligned jets in the magnetospheric cusp: Results from the Geospace Environment Modeling Pilot program

The extended flight of the Airborne Ionospheric Observatory during the Geospace Environment Modeling (GEM) Pilot program on January 16, 1990, allowed continuous all-sky monitoring of the two-dimensional ionospheric footprint of the northward interplanetary magnetic field (IMF) cusp in several wavelengths. Especially important in determining the locus of magnetosheath electron precipitation was the 630.0-nm red line emission. The most striking morphological change in the images was the transient appearance of zonally elongated regions of enhanced 630.0-nm emission which resembled 'rays' emanating from the centroid of the precipitation. The appearance of these rays was strongly correlated with the Y component of the IMF: when the magnitude of B(sub y) was large compared to B(sub z), the rays appeared; otherwise, the distribution was relatively unstructured. Late in the flight the field of view of the imager included the field of view of flow measurements from the European incoherent scatter radar (EISCAT). The rays visible in 630.0-nm emission exactly aligned with the position of strong flow jets observed by EISCAT. We attribute this correspondence to the requirement of quasi-neutrality; namely, the soft electrons have their largest precipitating fluxes where the bulk of the ions precipitate. The ions, in regions of strong convective flow, are spread out farther along the flow path than in regions of weaker flow. The occurrence and direction of these flow bursts are controlled by the IMF in a manner consistent with newly opened flux tubes; i.e., when absolute value of B(sub y) greater than absolute value of B(sub z), tension in the reconnected field lines produce east-west flow regions downstream of the ionospheric projection of the x line. We interpret the optical rays (flow bursts), which typically last between 5 and 15 min, as evidence of periods of enhanced dayside (or lobe) reconnection when absolute value of B(sub y) greater than absolute value of B(sub z). The length of the reconnection pulse is difficult to determine, however, since strong zonal flows would be expected to persist until the tension force in the field line has decayed, even if the duration of the enhanced reconnection was relatively short.

Weiss, L. A.↗
NASA NTRS1993

The role of ring current nose events in producing stable auroral red arc intensifications during the main phase - Observations during the September 19-24, 1984, equinox transition study

A set of observations describing ionospheric conditions, magnetospheric populations, and 6300-A emission intensities on stable auroral red (SAR) arc field lines during the solar minimum 19-24 Sept. 1984 magnetic storm period prompted a study of solar cycle and magnetic storm phase variations in SAR arc emissions and their magnetospheric energy source. It was found that medium-energy H(+) was significantly enhanced during the main phase compared to the late recovery phase of the 19-20 Sept. 1984 storm. Enhanced heating of the thermal electron plasma caused by this population resulted in more than an order of magnitude greater SAR arc emissions in the main phase compared to the recovery phase. O(+) was found to be the dominant energy source for SAR arcs in the late recovery phases of storms in the 19-24 Sept. period.

Kozyra, J. U.↗
NASA NTRS1989

Rocket measurements within a polar cap arc - Plasma, particle, and electric circuit parameters

Results are presented from the Polar Ionospheric Irregularities Experiment (PIIE), conducted from Sondrestrom, Greenland, on March 15, 1985, designed for an investigation of processes which lead to the generation of small-scale (less than 1 km) ionospheric irregularities within polar-cap F-layer auroras. An instrumented rocket was launched into a polar cap F layer aurora to measure energetic electron flux, plasma, and electric circuit parameters of a sun-aligned arc, coordinated with simultaneous measurements from the Sondrestrom incoherent scatter radar and the AFGL Airborne Ionospheric Observatory. Results indicated the existence of two different generation mechanisms on the dawnside and duskside of the arc. On the duskside, parameters are suggestive of an interchange process, while on the dawnside, fluctuation parameters are consistent with a velocity shear instability.

Weber, E. J.↗
NASA NTRS1988

Coherent mesoscale convection patterns during northward interplanetary magnetic field

Coincident DE 2 satellite plasma-drift and particle measurements and all-sky imaging photometer data were used to construct two-dimensional convection patterns in a study of polar ionospheric convection in the presence of subvisual-intensity soft-particle excited 6300-A sun-aligned polar cap arcs. Results show a highly anisotropic temporally stable convection with greater order than has previously been suspected.

Carlson, H. C.↗
NASA NTRS1986

Millstone Hill measurements and TGCM simulation for the 30 May 1984 annular solar eclipse

On 30 May 1984, the Millstone Hill incoherent scatter radar was operated to gather data on the effects of the annular solar eclipse on the structure and dynamics of the ionosphere and thermosphere. The eclipse path was about 3 deg. south of Millstone which experienced a maximum obscuration of 86% at about 1705 UT. Both the zenith steerable antennas at Millstone were used in the experiment to collect data on the temporal evolution of the eclipse effects. This experiment represented the first opportunity at Millstone to collect data during an eclipse in the absence of a major magnetospheric disturbance which had previously made the unravelling of eclipse effects difficult. In addition, the configuration of the experiment and analysis of the data included a detailed examination of the effects on the neutral atmosphere. A major catalyst for this study was the opportunity to compare the results with the predictions made from the Thermospheric General Circulation Model (TGCM) at NCAR, as a calibration point for the model. The Arecibo and Sondrestrom radars also participated as part of a radar chain experiment. The analysis of the data from these stations is in progress; the initial results from Millstone Hill are presented.

Salah, J. E.↗
NASA NTRS1978

Nighttime dynamics of the F region near Arecibo as mapped by airglow features

A scanning photometer was used to obtain red line airglow measurements at Arecibo in order to determine the direction and phase velocity of propagation of major airglow enhancements. The scans were made in the N-S direction on 13 nights and in the E-W direction on five nights. The most common type of descent begins in the south and progresses northward, with an apparent phase velocity of the order of 300 m/s. Neutral winds are apparently the cause of this type of descent. Observed descents of the equatorial ionosphere are described, and their relation to airglow enhancement is considered. A second type of airglow enhancement was seen occasionally and travels from north to south; this enhancement is probably due to traveling ionospheric disturbances. A third type previously unreported involves sudden descents lasting an hour or so and sometimes ocurring nearly simultaneously over regions extending at least 1000 km in the N-S or E-W direction.

Sobral, J. H. A.↗
NASA NTRS1977

An experiment to measure variations in nighttime E-region neutral concentration

An experimental procedure is demonstrated which holds promise for the nighttime measurement of ion-neutral collision frequencies or net neutral concentration in the E-region by combining incoherent scatter data with appropriate photometric measurements. Data illustrating the technique are applied to comparing relative variations in atomic oxygen concentrations (from the E-region component of the O I 5577 A emission) near 100 km to those in the net neutral concentration obtained from combined incoherent scatter data and neutral temperature data extracted from Fabry-Perot measurement of the O I 5577 A line profile.

Cogger, L. L.↗
NASA NTRS1977

Photoelectron energy loss and spectral features deduced by the plasma line technique

Plasma line data gathered at the Arecibo Observatory are used to examine relative variations in topside F region differential photoelectron fluxes in the 5- to 20-eV range. A spectral feature not found in present theoretically calculated spectra is noted near 15 eV. A new approach to the interpretation of the measured spectra is taken, which allows a qualitative estimate of the relative importance of different energy loss mechanisms. The altitude variation of the observed photoelectron flux energy spectra at the higher altitudes (above 350 km) and the lower energies (less than 10 eV) agrees quantitatively with the expected variation of the spectrum.

Abreu, V. J.↗
NASA NTRS1977

An experimental estimate of the O/+/-O resonant charge transfer cross section, collision frequency, and energy transfer rate

The resonant-charge-transfer cross section dominates the interaction between neutral and ionized atomic oxygen at temperatures greater than several hundred degrees Kelvin. This cross section is of direct importance to F-region studies of ion diffusion, ion thermal balance, and neutral atmospheric winds and pressure gradients, since it determines collision frequencies and energy and momentum transfer rates. However, the uncertainty in this cross section is roughly 25-40%. Incoherent-scatter measurements allow determination of the product of the atomic oxygen concentration multiplied by the cross section. If present-day atmospheric models are accepted as statistically representative of F-region atomic oxygen concentrations experimental (aeronomical) data presented indicate that the resonant-charge-transfer cross section is about 1.3 times greater than the value presently in general use, though in excellent agreement with the only other available (laboratory) experimental value. This revised cross section has obvious implications for thermospheric studies.

Carlson, H. C.↗
NASA NTRS1977

Electron and ion temperatures - A comparison of ground-based incoherent scatter and AE-C satellite measurements

The paper presents the results of comparisons of AE-C electron temperature of the ionosphere determined from the cylindrical electrostatic probe and the ion temperature of the ionosphere determined from the planar retarding potential analyzer with electron and ion temperatures determined from four incoherent scatter facilities: Arecibo, St. Santin, Millstone Hill, and Chatanika. Good agreement was obtained between the in situ and remote measurements of electron and ion temperatures. Longitudinal variations are found to be very important in the comparison of electron temperatures at some locations.

Benson, R. F.↗
NASA NTRS1976

The excitation of plasma lines in blanketing sporadic E

Enhanced plasma lines in blanketing sporadic E have been excited by a powerful HF radio wave illuminating the E region over the Arecibo Observatory. The plasma lines are observed by the incoherent scatter radar at the observatory. They originate in the sporadic E layer when the blanketing frequency exceeds the exciting frequency, a result which confirms that the plasma is overdense for the exciting frequency. Around the time when the blanketing frequency falls through the exciting frequency, large fluctuations in the plasma line intensities are observed, and thus the possibility of overdense patches drifting through the sampled volume is suggested.

Gordon, W. E.↗
NASA NTRS1974

The 6300 A O/1-D/ airglow and dissociative recombination

Measurements of night-time 6300 A airglow intensities at the Arecibo Observatory have been compared with dissociative recombination calculations based on electron densities derived from simultaneous incoherent backscatter measurements. The agreement indicates that the nightglow can be fully accounted for by dissociative recombination. The comparisons are examined to determine the importance of quenching, heavy ions, ionization above the F-layer peak, and the temperature parameter of the model atmosphere. Comparable fits between the observed and calculated intensities are found for several available model atmospheres. The least-squares fitting process, used to make the comparisons, produces comparable fits over a wide range of combinations of neutral densities and of reaction constants. Yet, the fitting places constraints upon the possible combinations; these constraints indicate that the latest laboratory chemical constants and densities extrapolated to a base altitude are mutually consistent.

Wickwar, V. B.↗
NASA NTRS1973

Comparison of Te and Ti from Ogo 6 and from various incoherent scatter radars.

Langmuir probe and retarding potential analyzer (RPA) data on the electron and ion temperatures Te and Ti obtained from Ogo 6 are compared with Te and Ti values obtained from the incoherent scatter network. The satellite to radar temperature ratio TeS/TeR is 1.15 on the average for these comparisons. This discrepancy is larger than the uncertainties usually placed on the probe and radar Te values. The ion temperature ratio TiS/TiR approximately 1.0, independent of the particular radar examined. This comparison serves as an intercalibration of the incoherent scatter network.

Mcclure, J. P.↗
NASA NTRS1971

Ionospheric heating at Arecibo - First tests.

Ionospheric F-region heating by a high-frequency transmitter (100 kW at 5.62 MHz fed into a 1000-ft dish producing a beam with an angular half-width of 10 deg) was observed with a 430-MHz incoherent scatter radar, an ionosonde, and several photometers. The electron temperature of the ionosphere was increased by as much as 30% at and just below the height where the local plasma frequency was equal to the frequency of the heating transmitter. Calculations show time constants of 40 sec for electron heating and less than 10 sec for the cooling at 308 km when the heating transmitter was operated in a pulsed mode.

Gordon, W. E.↗