Browsing by Author "Fejer, B.G."
Now showing 1 - 4 of 4
Results Per Page
Sort Options
Item Restricted Climatology of F region zonal plasma drifts over Jicamarca(American Geophysical Union, 2005-12) Fejer, B.G.; Souza, J.R.; Santos, A.S.; Costa Pereira, A. E.We use extensive incoherent scatter radar observations made at the Jicamarca Radio Observatory between 1970 and 2003 to study and model empirically the equatorial zonal plasma drifts near the F region peak using Bernstein polynomials as base functions. Our quiet-time model results confirm that the daytime drifts are westward and are nearly season and solar cycle independent. The nighttime drifts are eastward, have larger magnitudes, and increase strongly with solar flux, particularly near equinox and December solstice. Enhanced geomagnetic activity drives small eastward perturbation drifts during the day and much larger westward disturbance drifts at night. The nighttime drift perturbations are largest near midnight and increase strongly with solar flux near equinox and December solstice but are essentially absent near June solstice. The Jicamarca zonal disturbance drifts can be largely accounted for by disturbance dynamo electric fields with a dominant time delay of about 3–15 hours following enhanced geomagnetic activity. In the postmidnight sector, there are also smaller westward disturbance drifts associated with time delays of about 15–24 hours and perhaps even longer. Our results strongly suggest that the longitudinal dependence of both the quiet and disturbed equatorial nighttime zonal drifts varies with season.Item Restricted Processes in the quiet and disturbed equatorial-low latitude ionosphere: Sundial campaign, 1984(European Geosciences Union, 1987-04) Abdu, M. A.; Reddy, B.M.; Walker, G. O.; Hanbaba, R.; Fejer, B.G.; Woodman Pollitt, Ronald Francisco; Schunk, R.W.; Szuszczewicz, E.P.A network of ionospheric diagnostic instruments was operated on a world wide basis during the October 5-13. 1984 SUNDIAL campaign. The network provided a unique opportunity for a truly multiple technique global analysis of the equatorial-low latitude ionospheric behavior during the campaign period. The SUNDIAL equatorial-low latitude data set included electric field and spread F data from Jicamarca radar, ionosonde data from 15 stations and magnetograms from 5 stations operated in the American, African, Asian and Indian sectors. Also included are data from electronic polarimeters at 8razilian low-latitude sites. The data analysis has focused attention on the global scale steady state ionospheric behavior and its predictability by global theoretical model of Sojka and Schunk (1985) and by the lnternational Reference lonospheric (IRI). The results are suggestive of the need to modify existing quiet time electric field and neutral wind models in varying degrees for different longitude sectors. The analysis also concerns global scale ionospheric transient behavior in response to exo-ionospheric variabilities under disturbed conditions, in an approach towards a hotter understanding of the factors that effect short-term prediction schemes. Among the important outcomes of this study is the possibility of using longitude chains of equatorial region ionosondes (and magnetometers) for investigation of equatorial ionospheric response to magnetospheric electric field penetration events and disturbance dynamo effects.Item Open Access Studies of the low latitude electrodynamics during world days(Instituto Geofísico del Perú, 1984) Fejer, B.G.; Woodman Pollitt, Ronald FranciscoWe propose to use Jicamarca radar observations during the World Day periods together with data from the San Marco satellite for the study of equatorial electrodynamics. These incoherent scatter World Day experiments are usually conducted during two or three yearly campaigns of two to three days each, and about 10 campaigns of about a day. These periods are selected from the times when the IMP-6 satellite is in the solar wind and can therefore provide the interplanetary magnetic field parameters.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).