Browsing by Author "Stoneback, Russell A."
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Item Daytime Zonal Drifts in the Ionospheric 150km and E Regions Estimated Using Ear Observations(Amer Geophysical Union, 2017-08-31) Pavan Chaitanya, P.; Patra, A. K.; Otsuka, Y.; Yokoyama, T.; Yamamoto, M.; Stoneback, Russell A.; Heelis, R. A.; 0000 0000 3175 0999 (Heelis, RA); 0000-0001-7216-4336 (Stoneback, RA); 0000-0002-5543-5357 (Heelis, RA); Stoneback, Russell A.; Heelis, R. A.Multibeam observations of the 150km echoes made using the Equatorial Atmosphere Radar (EAR), located at Kototabang, Indonesia, provide unique opportunity to study both vertical and zonal ExB plasma drifts in the equatorial ionosphere. In this paper, we focus on estimating daytime zonal drifts at the 150km (140-160km) and E (100-110km) regions using multibeam observations of 150km 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 150km and E regions are found to be westward and mostly below -80ms⁻¹ and -60ms⁻¹, respectively. While the zonal drifts in the 150km 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 150km region show seasonal variations with three maxima peaking around May, September, and January. The zonal drifts at the 150km 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 25ms⁻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 150km 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 Identifying Equatorial Ionospheric Irregularities using In Situ Ion Drifts(Copernicus Gesellschaft Mbh, 2014-04-15) Stoneback, Russell A.; Heelis, Roderick A.; 0000 0000 3175 0999 (Heelis, RA); 88021080 (Heelis, RA)Previous climatological investigations of ionospheric irregularity occurrence in the equatorial ionosphere have utilized in situ measurements of plasma density to identify the presence of an irregularity. Here we use the Morlet wavelet and C/NOFS to isolate perturbations in meridional ion drifts and generate irregularity occurrence maps as a function of local time, longitude, season, and solar activity. For the low solar activity levels in 2008, the distributions identified by velocity perturbations follow normalized density perturbation (Delta N/N) maps with large occurrences after midnight into dawn over all longitudes. The velocity and normalized density occurrence maps contract in both local time and longitude with increasing solar activity. By 2011 irregularities are confined to particular longitudes expected by alignment and a few hours of local time after sunset. The variation in the occurrence of the late night irregularities with solar activity is consistent with the presence of gravity wave seeding.Item The Longitudinal Variability of Equatorial Electrojet and Vertical Drift Velocity in the African and American Sectors(Copernicus Gesellschaft Mbh, 2014-03-13) Yizengaw, E.; Moldwin, M. B.; Zesta, E.; Biouele, C. M.; Damtie, B.; Mebrahtu, A.; Rabiu, B.; Valladares, C. F.; Stoneback, Russell A.While the formation of equatorial electrojet (EEJ) and its temporal variation is believed to be fairly well understood, the longitudinal variability at all local times is still unknown. This paper presents a case and statistical study of the longitudinal variability of dayside EEJ for all local times using ground-based observations. We found EEJ is stronger in the west American sector and decreases from west to east longitudinal sectors. We also confirm the presence of significant longitudinal difference in the dusk sector pre-reversal drift, using the ion velocity meter (IVM) instrument on-board the C/NOFS satellite, with stronger pre-reversal drift in the west American sector compared to the African sector. Previous satellite observations have shown that the African sector is home to stronger and year-round ionospheric bubbles/irregularities compared to the American and Asian sectors. This study's results raises the question if the vertical drift, which is believed to be the main cause for the enhancement of Rayleigh-Taylor (RT) instability growth rate, is stronger in the American sector and weaker in the African sector - why are the occurrence and amplitude of equatorial irregularities stronger in the African sector?Item Storm-Time Meridional Flows: A Comparison of CINDI Observations and Model Results(Copernicus Gmbh, 2014-06-17) Hairston, Marc R.; Maruyama, N.; Coley, William R.; Stoneback, Russell A.During a large geomagnetic storm, the electric field from the polar ionosphere can expand far enough to affect the mid-latitude and equatorial electric fields. These changes in the equatorial zonal electric field, called the penetration field, will cause changes in the meridional ion flows that can be observed by radars and spacecraft. In general this E x B ion flow near the equator caused by the penetration field during undershielding conditions will be upward on the dayside and downward on the nightside of the Earth. Previous analysis of the equatorial meridional flows observed by CINDI instrument on the C/NOFS spacecraft during the 26 September 2011 storm showed that all of the response flows on the dayside were excess downward flows instead of the expected upward flows. These observed storm-time responses are compared to a prediction from a physics-based coupled model of thermosphere-ionosphere- inner-magnetosphere in an effort to explain these observations. The model results suggest that the equatorial downward flow could be attributed to a combined effect of the overshielding and disturbance dynamo processes. However, some discrepancy between the model and observation indicates a need for improving our understanding of how sensitive the equatorial electric field is to various model input parameters that describe the magnetosphere-ionosphere coupling processes.Item Topside Equatorial Zonal Ion Velocities Measured by C/NOFS During Rising Solar Activity(Copernicus Gesellschaft Mbh, 2014-02-04) Coley, W. R.; Stoneback, Russell A.; Heelis, Rodney A.; Hairston, M. R.; 0000 0000 3175 0999 (Heelis, RA); 88021080 (Heelis, RA); Coley, W. R.; Stoneback, Russell A.; Heelis, Rodney A.; Hairston, M. R.The Ion Velocity Meter (IVM), a part of the Coupled Ion Neutral Dynamic Investigation (CINDI) instrument package on the Communication/Navigation Outage Forecast System (C/NOFS) spacecraft, has made over 5 yr of in situ measurements of plasma temperatures, composition, densities, and velocities in the 400-850 km altitude range of the equatorial ionosphere. These measured ion velocities are then transformed into a coordinate system with components parallel and perpendicular to the geomagnetic field allowing us to examine the zonal (horizontal and perpendicular to the geomagnetic field) component of plasma motion over the 2009-2012 interval. The general pattern of local time variation of the equatorial zonal ion velocity is well established as westward during the day and eastward during the night, with the larger nighttime velocities leading to a net ionospheric superrotation. Since the C/NOFS launch in April 2008, F10.7 cm radio fluxes have gradually increased from around 70 sfu to levels in the 130-150 sfu range. The comprehensive coverage of C/NOFS over the low-latitude ionosphere allows us to examine variations of the topside zonal ion velocity over a wide level of solar activity as well as the dependence of the zonal velocity on apex altitude (magnetic latitude), longitude, and solar local time. It was found that the zonal ion drifts show longitude dependence with the largest net eastward values in the American sector. The pre-mid-night zonal drifts show definite solar activity (F10.7) dependence. The daytime drifts have a lower dependence on F10.7. The apex altitude (magnetic latitude) variations indicate a more westerly flow at higher altitudes. There is often a net topside subrotation at low F10.7 levels, perhaps indicative of a suppressed F region dynamo due to low field line-integrated conductivity and a low F region altitude at solar minimum.