Browsing by Author "Heelis, R. A."
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Item Restricted Comparison of topside equatorial parameters derived from DMSP, Jicamarca, and Another Model of the Ionosphere (SAMI2)(American Geophysical Union, 2005-01-19) Venkatraman, Sarita; Heelis, R. A.; Hysell, D. L.Comparison is made of topside equatorial parameters obtained from DMSP satellites with those measured from Jicamarca radar and those calculated from Another Model of the Ionosphere (SAMI2). To determine acceptable limits for this volume, knowledge of the spatial and temporal gradients in the parameters must be defined. Those can be obtained independently from each data source and are dependent on local time and season. Having described the spatial gradients, a comparison of the ionospheric variables can be made. The present study focuses on simultaneous ground‐based and satellite data obtained for June 2002. Data for days 11, 12, and 13 are compared in this study. Satellite data are obtained from the DMSP satellites F13 (0600–1800 LT) and F15 (0900–2100 LT), respectively. Ground‐based data are obtained from the Jicamarca radar. These are then compared with numerical computations performed by the SAMI2 model for the same period. Good agreement between observation and model is achieved for the total ion concentration during daytime and nighttime, while the ion and electron temperatures agree well at night. The light ion fraction is usually <20% from all three sources except during sunrise where the light ion content can be higher. Accounting for the variables H+ and He+ concentrations in the topside appears to be the major factor affecting the different data sources.Item Restricted Daytime zonal drifts in the ionospheric 150 km and E regions estimated using EAR observations(American Geophysical Union, 2017-08-16) Pavan Chaitanya, P.; Patra, A. K.; Otsuka, Y.; Yokoyama, T.; Yamamoto, M.; Stoneback, R. A.; Heelis, R. A.Multibeam observations of the 150 km echoes made using the Equatorial Atmosphere Radar (EAR), located at Kototabang, Indonesia, provide unique opportunity to study both vertical and zonal E × B plasma drifts in the equatorial ionosphere. In this paper, we focus on estimating daytime zonal drifts at the 150 km (140–160 km) and E (100–110 km) regions using multibeam observations of 150 km and E region echoes made using the EAR and study the daytime zonal drifts covering all seasons not studied before from Kototabang. Zonal drifts in the 150 km and E regions are found to be westward and mostly below −80 m s−1 and −60 m s−1, respectively. While the zonal drifts in the 150 km and E regions do not go hand in hand on a case‐by‐case basis, the seasonal mean drifts in the two height regions are found to be in good agreement with each other. Zonal drifts at the 150 km region show seasonal variations with three maxima peaking around May, September, and January. The zonal drifts at the 150 km region are found to be smaller than the F region drifts obtained from Coupled Ion Neutral Dynamics Investigation (CINDI) onboard Communication and Navigation Outage Forecasting System (C/NOFS) by about 25 m s−1 consistent with the height variations of F region zonal drifts observed by the Jicamarca radar. These results constitute the first comprehensive study of zonal drifts at the 150 km and E regions from Kototabang, Indonesia, and the results are discussed in the light of current understanding on the low‐latitude electrodynamics and coupling.Item Restricted Electrodynamics in the low and middle latitude ionosphere: a tutorial(Elsevier, 2004-03-24) Heelis, R. A.Electric fields in the low and middle latitude ionosphere result from currents driven internally by neutral winds and gravity, and externally by applied potentials. The resulting internal electric polarization fields arise from the need to make the total current divergence free. By considering the current drivers many of the attributes of the observed ion and electron drifts can be understood including the E- and F-region dynamos, the initial growth of ionospheric depletions, and effects from high latitudes. Such an exercise leads to an overall understanding of the governing principles. However, it is necessary to know all the large-scale spatial gradients in the drivers, many of which are presently unknown, in order to unravel the outstanding mysteries of the electrodynamics of the region.Item Restricted Longitudinal ionospheric effects in the South Atlantic evening sector during solar maximum(American Geophysical Union, 2002-07-10) De Paula, E. R.; Souza, J. R.; Fejer, B. G.; Bailey, G. J.; Heelis, R. A.Large-scale horizontal gradients in ion density and vertical drift observed by the Atmospheric Explorer E satellite in the South Atlantic region (latitudes 10S–20S, longitudes 50W–10E) during the June solstice at solar maximum are presented and analyzed. These features occur during the nighttime period. The observations near 450-km altitude show vertically downward ion drift velocities exceeding 120 m s−1 and depleted regions where the ion density is around 2 × 104 cm−3. It is shown, using values modeled by the Sheffield University Plasmasphere Ionosphere Model (SUPIM) along the satellite trajectory, that the large ion density depletions appear as a result of large downward ion drifts driven by large southward winds along the magnetic meridian and by diffusion. During others seasons such behavior is not observed by the AE-E satellite, neither by SUPIM results. The roles played by the different physical processes responsible for the large downward drift velocities are investigated. The model results highlight the relationship between longitudinal variation of the ion densities and the location of the equatorial anomaly crest in the South Atlantic region.