School of Natural Sciences and Mathematics
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Browsing School of Natural Sciences and Mathematics by Author "0000 0000 3175 0999 (Heelis, RA)"
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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 Duskside Enhancement of Equatorial Zonal Electric Field Response to Convection Electric Fields During the St. Patrick's Day Storm on 17 March 2015(Blackwell Publishing Ltd, 2016-01-11) Tulasi Ram, S.; Yokoyama, T.; Otsuka, Y.; Shiokawa, K.; Sripathi, S.; Veenadhari, B.; Heelis, Roderick A.; Ajith, K. K.; Gowtam, V. S.; Gurubaran, S.; Supnithi, P.; Le Huy, M.; 0000 0000 3175 0999 (Heelis, RA); Heelis, Roderick A.The equatorial zonal electric field responses to prompt penetration of eastward convection electric fields (PPEF) were compared at closely spaced longitudinal intervals at dusk to premidnight sectors during the intense geomagnetic storm of 17 March 2015. At dusk sector (Indian longitudes), a rapid uplift of equatorial F layer to >550 km and development of intense equatorial plasma bubbles (EPBs) were observed. These EPBs were found to extend up to 27.13⁰N and 25.98⁰S magnetic dip latitudes indicating their altitude development to ~1670 km at apex. In contrast, at few degrees east in the premidnight sector (Thailand-Indonesian longitudes), no significant height rise and/or EPB activity has been observed. The eastward electric field perturbations due to PPEF are greatly dominated at dusk sector despite the existence of background westward ionospheric disturbance dynamo (IDD) fields, whereas they were mostly counter balanced by the IDD fields in the premidnight sector. In situ observations from SWARM-A and SWARM-C and Communication/Navigation Outage Forecasting System satellites detected a large plasma density depletion near Indian equatorial region due to large electrodynamic uplift of F layer to higher than satellite altitudes. Further, this large uplift is found to confine to a narrow longitudinal sector centered on sunset terminator. This study brings out the significantly enhanced equatorial zonal electric field in response to PPEF that is uniquely confined to dusk sector. The responsible mechanisms are discussed in terms of unique electrodynamic conditions prevailing at dusk sector in the presence of convection electric fields associated with the onset of a substorm under southward interplanetary magnetic field B_z.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 Plasma Dynamics Associated with Equatorial Ionospheric Irregularities(Blackwell Publishing Ltd) Smith, Jonathon Matthew; Heelis, Roderick A.; 0000 0000 3175 0999 (Heelis, RA); 0000-0002-5543-5357 (Heelis, RA); Smith, Jonathon Matthew; Heelis, Roderick A.The Communication/Navigation Outage Forecasting System satellite was operational from 2008, a period of deep solar minimum, to 2015, a period of moderate solar conditions. The behavior of the vertical plasma drift and the distribution of plasma depletions during the deep solar minimum of 2009 deviated substantially from the behavior that was observed during the solar moderate conditions encountered by the Communication/Navigation Outage Forecasting System satellite in 2014, which are typical of previous observations. Presented here are observations of the vertical drift of plasma depletions and the background plasma in which they are embedded. We find that depletions detected at local times after 2100 hr during solar minimum are typically found in background drifts that are weakly downward compared to the strongly downward background drifts observed during moderate solar activity levels. Additionally, at solar minimum, the drift within the depletions is upward with respect to the background as compared with observations at the same local times during solar moderate conditions for which the depleted plasma more nearly drifts with the background. We note that weak background plasma drifts observed throughout the night during solar minimum promote the continued growth of depletions that may evolve more slowly or be continuously generated to appear in the topside in the postmidnight hours. ©2018. American Geophysical Union. All Rights Reserved.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.