Browsing by Author "Kelley, M.C."
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Item Open Access A San Marco/Jicamarca study of equatorial spread F(Instituto Geofísico del Perú, 1987) Kelley, M.C.; Woodman Pollitt, Ronald FranciscoOver the years at number of experimental technique have been employed to understand equatorial spread F (ESF). The field is by now very advanced as is our understanding of the relationship between the Jicamarca Radar Maps and in situ measurements .This is important since the ground based data is less expensive to obtain and is available over seasonal and even solar cycle time basis.The advanced understanding has come primarily from rocket/radar, satellite/radar and theoretical studies.Item Restricted Comparative in situ studies of the unstable day-time equatorial E region(Elsevier, 1985-10) Pfaff, R.F.; Kelley, M.C.; Fejer, B.Q.; Maynard, N.C.; Brace, L.H.; Ledley, B.Q.; Woodman Pollitt, Ronald Francisco; Smith, L. G.Plasma waves measured by probes on sounding rockets are used to characterize the unstable equatorial E-region and to reflect the changing irregularity morphology with respect to altitude within the layer. We present measurements from three sounding rockets launched at the geomagnetic equator from Punta Lobos. Peru, including both a strong and a mild electrojet experiment conducted at midday and a weak electrojet experiment conducted in the late afternoon. The observed irregularities are analyzed in relation to simultaneous measurements of the electron number density and to either the measured or inferred profiles of the electron current density. The linear growth rate for the combined two-stream and gradient drift instabilities is computed using these profiles and the changing unstable wavenumber regimes are then compared to the power spectra of the wave observations as a function of altitude. We have allowed for long wavelength waves in the growth rate and have included the effect of recombination. In each case, the waves are observed only in the altitude regions, which, on the basis of the growth rate, are predicted to be unstable for horizontally propagating waves. Further, although the conversion of observed frequency to wavenumber is not definitive, the theoretical range of wavenumbers that will be unstable agrees at least qualitatively with the corresponding frequencies which have associated fluctuations displayed in spectrograms of the in situ time series measurements. In the case of the strong electrojet experiment, both the growth rate calculations and the wave observations show a region of high frequency (short wavelength) oscillations in the upper portion of the layer, where the medium was unstable to the primary two-stream instability. In the mild electrojet experiment, current measurements show that the two-stream threshold was not met, which is supported by the absence of observed high frequency oscillations for this flight. The medium may still have been unstable to this process as a secondary mechanism, as suggested in the 3 m backscatter radar data, implying that the large scale wave electric fields were on the order of or greater than, the polarization electric field. Where the payloads encountered a positive (upwards) gradient in electron density, all three rockets show a strong low frequency component which we attribute, in general, to the gradient drift instability.Item Open Access Simultaneous measurements of the electric field in the auroral zone and at the equator during intense magnetic activity(Max-Plank Institute für Aeronomie, 1972) Kelley, M.C.; Gonzáles, C.; Mozer, F.S.; Woodman Pollitt, Ronald FranciscoSimultaneous balloon measurements of the auroral zone electric field in Alaska and of the vertical drift velocity of the region at Jicamarca, Peru during the great flow of August 1972 are presented.· The eastward electric field component at the equator was correlated, with a 20 minute time delay, to the westward component of the auroral zone field at College, Alaska. The equatorial horizontal component actually reversed in sign from the normal westward value and, simultaneously, the electrojet then flowing over the dayside hemisphere (at Trivandrum, India, fer example) was greatly depressed. These results show that intense auroral current systems can grossly affect both the normal dynamo current patterns at low latitudes en the dayside and the polarization fields responsible fer the worldwide low latitude zonal electric field component.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).