Browsing by Author "Gordon, William E."
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Item An experimental study of electron thermal runaway in the lower ionosphere(1979) Coco, David Stephen; Gordon, William E.; Anderson, Hugh R.; Wolf, Richard A.An ionospheric heating experiment has been performed at the Arecibo Observatory using the 43 MHz incoherent backscatter radar both as a heater and as a diagnostic. Radar pulses up to 9 msec in length were transmitted with 2.5 MW (2.5 x 1^erg/sec) peak: pulse power yielding a peak power flux of approximately 2. x 1 erg/cm sec at 1 km altitude. A 2 microsecond diagnostic pulse offset in frequency from the heating pulse was used to measure the resultant ohmic heating of electrons in the lower ionosphere. Using a model of electron heating and cooling in the lower ionosphere, the ratio of heated electron temperature to unheated electron temperature is calculated as a function of altitude and heating power flux. This model predicts a beam-averaged electron temperature ratio of about 2.25 at 1 km for a transmitted power of 2. MW, pulse length of 9 msec and an antenna efficiency of 5%. When the predicted beamaveraged electron temperature ratios are compared with the observed, the observed are found to be less than the predicted for all values of transmitted power used. Possible sources of the discrepancy between experiment and theory are discussed.Item Artificial heating of the lower ionosphere(1969) Showen, Robert LeRoy; Gordon, William E.The lower ionosphere has been heated in a controlled experiment at the Arecibo ionospheric Observatory. Deposition of energy from a 40 Mhz transmitter has approximately doubled the ambient electron temperature at an altitude of 80 km. Energy from the radio wave is deposited in the ionosphere as a result of collisions of the electrons with the neutral molecules. Cross-modulation experiments (performed elsewhere) have gained information on electron number density and collision frequency between 60 and 90 km. The experiment described here will possibly allow determination of the electron collision frequency and thermal relaxation times between 70 and 120 km, and may increase the understanding of the interaction of plasmas and radio waves. The heating is measured with the 430 Mhz incoherent backscatter radar system. The temperature dependence of the electron backscatter cross-section enables the change in electron temperature to be inferred from backscatter power measurements. Heating with megawatt pulses of 1, 2 and 5 ms duration confirmed predictions of the magnitude of heating.Item Artificial heating paradox of the lower ionosphere(1972) Kantor, Ivan Jelinek; Gordon, William E.An experiment to heat the lower ionosphere by irradiating it by a. 40 MHz transmitter shows an apparent cooling of the ionosphere below 90 km altitude. Considering the interaction of the radio wave with the ionospheric electrons cooling would hardly be unexpected. This apparent paradox, is explained using a two fluid continuum theory of incoherent scattering which includes unequal electron and ion temperatures. This analysis demonstrates the expected heating and permits an electron density and collision frequency profile below 100 km to be obtained. The results are obtained using a library of contour plots prepared for this purpose. The library will be useful in future experiments.Item Artificially produced field-aligned short-scale striations(1980) Frey, Alfred; Gordon, William E.; Chamberlain, Joseph W.; Reiff, Patricia H.HF-radiowaves propagating in the ordinary mode and incident on an overdense ionosphere ( fHF < foF2 ) are known to excite parametric instabilities. Recent experiments showed that under the same conditions short-scale field-aligned striations are formed. The question concerning the interrelation of these two effects is not yet settled. An experiment was performed at the Arecibo Observatory during June 1977 with a 5 MHz radar installed on Guadeloupe island. The Guadeloupe radar had a line of sight perpendicular to the magnetic field lines in the F-region above Arecibo. The 5 MHz radar backscatter measurements from the region where these artificially produced field-aligned striations (AFAS) occur are used to get some insight into the geometry and the temporal behavior of AFAS. The energy density of the HF-field required to produce AFAS is estimated from the experimental data. Plasma-line data on the parametric instability obtained by the 43 MHz incoherent backscatter from the Arecibo Observatory is compared with the Guadeloupe 5 MHz radar data. Several mechanisms which were proposed to produce AFAS are discussed in the light of present and past experimental results.Item Direct measurement of the vertical component of the transport velocity in the ionospheric F region(1968) Behnke, Richard Alan; Gordon, William E.A new technique for measuring the vertical component of the ionospheric ambipolar transport velocity Vz in the topside F region is reported. Incoherent backscatter spectra taken on August 7, 9, and 15 (1967) reveal a slight Doppler shift from which the line-of-sight (vertical) velocity of the plasma under observation is calculated. The measurements v/ere taken from 1800 hrs. L.T. to 2200 hrs. L. T. and demonstrate that the velocities during this period were most negative at times corresponding to the rapid cooling of the F region due to ionospheric sunset. The values of Vz range from 40 meters per second downward to 10 meters per second upward.Item Enhanced plasma wave spectral asymmetries(1976) Duncan, Lewis M.; Gordon, William E.A strong high-frequency radio wave incident on the ionosphere is capable of exciting enhanced electron plasma waves via a parametric wave-plasma coupling interaction. Incoherent backscatter radar is used to obtain detailed power spectra of these enhanced plasma waves. Power and frequency asymmetries are detected between spectra of enhanced plasma waves propagating parallel and antiparallel to the radar line-of-sight at the altitude of observation. The power spectra are corrected for the antenna gain frequency dependence. The power asymmetry is attributed to linear convective amplification of the plasma waves, so that waves observed propagating parallel and antiparallel to the radar line-of-sight have originated at different altitudes, above and below the observation height. The frequency asymmetry is interpreted as a Doppler shift of the power spectra resulting from a downward static drift of the thermal electrons. This drift is necessary to maintain charge neutrality within the wave-plasma interaction region, replacing upward-escaping energetic electrons which have been bootstrap accelerated by the enhanced plasma waves.Item High frequency radio heating of the ionosphere(1971) Dias, Luiz Alberto Vieira; Gordon, William E.In this work the effect of a high frequency radio wave incident upon the ionosphere is studied. The changes in the ionospheric parameters are derived, A particular case is examined, namely, the values found for conditions over the Arecibo Observatory, The radio source is a transmitter, with 160 NH, tunable from 5 to 25 MHz, using the dish antenna (305 meters of diameter) of the Arecibo Observatory, The uses of the ordinary or the extraordinary waves are discussed, The different conditions in the non deviative and deviative absorption regions are considered, The probing instruments are: the 430 MHz radar (at the Arecibo Observatory), photometers, and an ionosonde,Item Improved observational programs for the Arecibo ionospheric observatory(1969) Harper, Robert M; Gordon, William E.A new set of ionospheric data taking programs have been completed for the Arecibo Ionospheric Observatory. One will cover the 200-2000 km range and measure electron number densities, temperatures and composition with a time resolution of 25 min. at low altitudes and 1 and one-fourth hrs. at high altitudes. The other program will measure number densities, temperatures, and photo-electron fluxes in the 250-500 km region (i.e., pure 0+ region) with a time resolution of approximately 5 min. By increasing the efficiency of the CDC-3300 computer system, these programs increase the capabilities of the Observatory and improve the value of the data for geophysical studies.Item Induced heating effects in an irregular ionosphere(1975) Misener, Sharon Lynn; Gordon, William E.It is possible to observe and control to a limited extent the changes in characteristic ionospheric parameters such as temperature and density by sending high power, high frequency radio waves into the ionosphere and studying the subsequent effects through incoherent scatter techniques. The high frequency wave deposits energy in the ionosphere through absorption and acceleration of the free electrons; the subsequent collisions of the electrons with ions and neutrals; and Landau damping. Focusing and defocusing of the HP rays may arise because of the existence of two or three dimensional gradients in density in the ionosphere. There can be and are, therefore, two and three dimensional irregularities in the electron density distribution causing local alterations in the index of refraction and, consequently, local deviation of the ray paths of the wave in the vicinity of the perturbation. Relative hot or cold temperature spots should result. These density irregularities may be either natural or induced by the presence of the incident radio wave. It is the purpose of this work to look, in two dimensions, at this focusing effect and to estimate the expected electron temperature changes resulting from it by comparison to calculated changes in a horizontally stratified ionosphere. Calculated temperature changes for two kilometer height intervals with and without density perturbations are found to be from 5% to 25% greater than previously calculated results. However, in order to compare the calculated results of this work with measured temperatures, the calculated changes must be averaged over the height resolution of the radar. Excellent agreement is found between the two when this is done.Item Stratospheric scattering of radio waves and the Jicamarca radio telescope(1977) Fleisch, Daniel Alfred; Gordon, William E.Radar backscatter from the 15 to 35 km height range provides information about the dynamics and turbulent mixing of the stratosphere. The 3-dimensional space spectrum of turbulent fluctuations, the mean wind velocity, and the root-mean-square velocity fluctuations are directly related to the autocorrelation function of the scattered signals. The theory and mechanisms of stratospheric scattering of radio waves is discussed. The equipment and procedures used in previous experiments at the Jicamarca Radio Observatory are examined in detail, and are found to require modification in some cases. The theory of phased arrays is presented, and the correct and complete array factor pertinent to the Jicamarca antenna is derived. Information about the side lobes and precise positions of various beams is considered, and three beams are selected for use in a proposed stratospheric backscatter experiment. The phasing cables needed for the implementation of two off-vertical beams are available at the observatory, while new phasing cables must be manufactured for the realization of the vertical beam.Item The velocities of HF-induced short scale striations(1981) Coster, A. J. (Anthea J.); Gordon, William E.; Chamberlain, Joseph W.; Cloutier, Paul A.Short scale striations are among the phenomena that occur when the ionosphere is heated by high frequency (HF) radio waves with ordinary mode polarization. These striations are electron density irregularities aligned along the magnetic field lines in and near the heated region of the ionosphere. They are a direct consequence of the heating and disappear within seconds after the heater has been turned off. The striations are detected to be moving in the heated region. Experiments were performed in June 1977 to investigate short scale striations. The experiments combined the use of a portable 5 MHz radar located on the island of Guadeloupe with heating facilities at the Arecibo Observatory. The 5 MHz radar had a line of sight that was orthogonal to the magnetic field lines in the F region above Arecibo and was used to detect the striations and their velocities. The 43 MHz radar at Arecibo was used for additional diagnostics. Varying the power of the HF radio wave did not appear to affect the striation velocities. Instead, their velocities appeared to be well correlated with general F-region ionization drifts. On two evenings, shortly after ionospheric sunset, dramatic changes in the striation velocities were observed. These F-region velocity disturbances occur in conjunction with the intensification of existing sporadic-E regions. Only during these disturbed time periods were reflections from sporadic E detected at greater than 5 MHz. A mechanism whereby the sporadic-E regions cause the alternate coupling and decoupling of the E and F regions in the early evening hours is presented. This mechanism can explain changes in local F-region electric fields which would cause the velocity disturbances.