Browsing by Author "Swartz, W.E."
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Item Restricted Gravity-wave generation by thunderstorms observed with a vertically-pointing 430 MHz radar(American Geophysical Union, 1982-05) Larsen, M. F.; Swartz, W.E.; Woodman Pollitt, Ronald FranciscoDuring September of 1979, the Arecibo Observatory 430 MHz Doppler radar was used to study the upper troposphere and lower stratosphere during thunderstorm activity in the afternoon hours. It was found that when the olouds developed sufficiently in the vertical direction to reach the height of the tropopause, gravity-wave oscillations in the vertical velocity above the tropopause would develop. The amplitude was 2 m/s, and the period was close to 6 min.Item Open Access Radar observations of the development of tropical thunderstorms and convection cells using the Arecibo radar(Instituto Geofísico del Perú, Radio Observatorio de Jicamarca, 1974) Larsen, M.F.; Swartz, W.E.; Woodman Pollitt, Ronald FranciscoIn the period from 13 Sept to 20 Sept 1979, the 430 MHz radar system at the Arecibo Observatory was used to study profiles of vertical velocity in developing and mature thunderstorms during the afternoon hours. During the eight day period, five days produced significant convective activity. The great sensitivity of the Arecibo radar facility allowed vertical velocities to be measured up to an altitude of 20 km. Since the tropopause over Puerto Rico is at an altitude of approximately 14 km at that time of year, the lower part of the stratosphere was also observed during the period of cloud development. Many studies have been carried out using Doppler radars to probe the interior of convective cells (see Wilson and Miller, 1972 for an excellent review and bibliography; also Battan, 1973). This is particularly true of radars operating at shorter wavelengths of 3 or 10 cm whích are more sensitive to reflections from precipitation within the clouds. The Arecibo radar, operating ata wavelength of 70 cm, receives echoes from variations in the index of refraction with a scale size of half the wavelength, or 35 cm. The fact that vertical velocities could be measured in both the troposphere and lower stratosphere is of particular interest.in view of the theory that the upward flux of mass in the tropical branch of the Hadley cell is concentrated in the cumulus towers (Riehl and Malkus, 1958; Reiter, 1975). Puerto Rico, at approximately 13°N latitude, is in this branch of the Hadley cell.Item Open Access Split-beam studies of the effect of electron collisions on ISR spectra near k ⊥ B(Instituto Geofísico del Perú, 2000) Farley, D.T.; Swartz, W.E.; Chau Chong Shing, Jorge Luis; Woodman Pollitt, Ronald FranciscoIn an effort to test these models, we divided the Jicamarca radar into two beams, each with half the power and half the antenna of the full system, and ran the standard double pulse Faraday/ ACF mode that gives ACFs in the F region. With split beams each beam has only one quarter of the signal-to-noise ratio of the full system, but it allows us to measure at two different aspect angles simultaneously. We have made comparisons between three pointing directions, which at an altitude of 400 km differ from normal to B by 4.8º, 3.4º, and 2.0°. (We compared 4.8 with 3.4 degrees and then with 2.0 degrees.) These angles ali vary slightly with altitude and are significantly smaller than they were when Jicamarca was built because of the slow change in the geomagnetic field. (These beam positions once were called the 6, 4.5, and 3 degree (on axis) positions.)Item Restricted The Condor Equatorial Spread F campaign:Overview and results of the large-scale measurements(American Geophysical Union, 1986-05) Kelley, M.C.; LaBelle, J.; Kudeki, E.; Fejer, B.G.; Basu, Sa.; Basu, Su; Baker, K.D.; Hanuise, C.; Argo, P.; Woodman Pollitt, Ronald Francisco; Swartz, W.E.; Farley, D.T.; Meriwether, J.W.During the Condor campaign a number of instruments were set up in Peru to support the rocket experiments. In this series of papers we report on the results of the experiments designed to study the equatorial F region. In this overview paper we summarize the main results as well as report upon the macroscopic developments of spread F as evidenced by data from backscatter radars, from scintillation observations, and from digital ionosonde meaurements. In this latter regard, we argue here that at least two factors other than the classical gravitational Rayleigh-Taylor plasma instability process must operate to yield the longest-scale horizontal organization of spread F structures. The horizontal scale typical of plume separation distances can be explained by invoking the effect of a shear in the plasma flow, although detailed comparison with theory seems to require shear frequencies a bit higher than observations indicate. On the other hand, the largest-scale organization or modulation of the scattering layer cannot be explained by the shear theory and must be due to local time variations in the ionospheric drift or to gravity wave induced vertical motions. Using simultaneous rocket and radar data, we were also able to confirm the oft quoted hypothesis that rapid overhead height variations in the scattering region over Jicamarca are primarily spatial structures advecting overhead. The detailed rocket-radar comparison verified several other earlier results and speculations, particularly those made in the PLUMEX experiments. In particular, companion papers discuss and extend some of the PLUMEX results to include the role of anomalous diffusion (LaBelle et al., this issue) in the theory of equatorial spread F and to shed light upon the shallow spectral form often observed in the intermediate-scale regime (LaBelle and Kelley, this issue).