Browsing by Author "Doherty, P."
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Item Restricted Comparison of storm time equatorial ionospheric electrodynamics in the African and American sectors(Elsevier, 2010-08-12) Yizengaw, E.; Moldwin, M. B.; Mebrahtu, A.; Damtie, B.; Zesta, E.; Valladares, C. E.; Doherty, P.The characteristics of storm time (corotating interaction regions (CIR)-driven storm that happened on 9 August 2008) equatorial electrojet (EEJ) phenomena and their effect on the ionospheric density structure at two different longitudinal sectors are presented. Equatorial magnetometer data, occultation density profiles from COSMIC and CHAMP LEO satellites, and ground-based GPS TEC are used. We find unusual density reduction around local noon at the same time when we observe the reversal of electrojet current and thus counter-equatorial electrojet (CEJ) signatures. The continuous energy deposition in to high latitudes due to the CIR-driven storm that triggers the E-region dynamo and the penetrating magnetospheric origin electric field is suggested to be responsible for the reversal of equatorial electrojet current flows. We also compare the magnitude and direction of the driving force (E×B drift) in the American and African sectors for the first time. It was found that at the same local time the E×B drift in the American sector is stronger than that of the African sector. Previously, the uneven distribution of ground-based instruments hindered our ability to obtain a global understanding of the dynamics and structure of the ionosphere. The newly deployed ground-based instruments, primarily in the African sector, provide the opportunity to observe the governing equatorial electrodynamics simultaneously with the ionospheric density structures detected by the instrument onboard low-Earth-orbit (LEO) satellites. To our knowledge this is the first simultaneous observation performed in the African sector. This case study may provide additional input that could be used to explain the unique density irregularities that are often seen from in situ satellite observation in the African sector, a region that has been devoid of ground-based instrumentations.Item Open Access Studies of equatorial spread-F using LISN VIPIR(Instituto Geofísico del Perú, 2009) Gopi Krishna, S.; Valladares, C. E.; Doherty, P.; Bullet, T.; Livingston, R.LISN, the Low Latitude Ionospheric Sensor Network, is a distributed observatory. LISN represents a closely coordinated geophysical instrument set, comprised of GPS receivers providing TEC values and scintillation measurements, magnetometers providing daytime ionospheric electric fields and Vertical Incidence Pulsed Ionospheric Radar (VIPIR) providing ionograms. The LISN Observatory was designed to do continuous measurements using GPS receivers, VIPIR ionosondes and flux gate magnetometers; provide a nowcast of TEC, S4 index, and other derived parameters of the low-latitude ionosphere. The LISN-GPS network of 70 GPS receivers (planned, about 45+ connected now) and 5 VIPIR ionosondes planned in the same field line, will make it possible to address science questions regarding: the effect of E and Es layers on inhibiting ESF, the role of Gravity Waves on seeding plasma bubbles. It will also provide clues to understand the causes of day-to-day variability of the low-latitude ionosphere. The first VIPIR ionosonde has been installed and working temporarily in Jicamarca since October 2008. The VIPIR is able to operate in different modes; we have used high temporal and spatial resolution modes to measure the E and F regions. We carried out a campaign during March 2009 that aimed to measure the effect of gravity waves on the ionospheric densities and to observe the means of gravity waves as a seeding mechanism for spread F. This poster describes the preliminary results on the characteristics of ionospheric density structures, velocities during spread-F conditions from the VIPIR data.