Browsing by Author "Roddy, P. A."
Now showing 1 - 4 of 4
Results Per Page
Sort Options
Item Restricted C/NOFS satellite observations of equatorial ionospheric plasma structures supported by multiple ground‐based diagnostics in October 2008(American Geophysical Union, 2011-10-28) Nishioka, M.; Basu, Su.; Basu, S.; Valladares, C. E.; Sheehan, R. E.; Roddy, P. A.; Groves, K. M.In early October 2008, the C/NOFS satellite orbited near the magnetic equator at its perigee altitude of ∼400 km at dusk in the Peruvian sector. This provided an ideal opportunity for a comparison, under the current very low solar flux condition, of equatorial ionospheric disturbances observed with the Communication/Navigation Outage Forecasting System (C/NOFS) in situ measurements and ground‐based observations available near Jicamarca Observatory. The primary objective was the comparison of plasma density disturbances measured by a Planar Langmuir Probe (PLP) instrument on the C/NOFS satellite with VHF scintillation activity at Ancon near Jicamarca for this period. Here we discuss in detail two extreme cases: one in which severe in situ disturbances were accompanied by mild scintillation on a particular day, namely, 10 October while there was little in situ disturbance with strong scintillation on 5 October. This apparent contradiction was diagnosed further by a latitudinal ground‐based GPS network at Peruvian longitudes, a Digisonde, and the incoherent scatter radar (ISR) at Jicamarca. The crucial distinction was provided by the behavior of the equatorial ionization anomaly (EIA). The EIA was well‐developed on the day having severe in situ disturbances (10 Oct). This led to lower equatorial plasma density and total electron content (TEC) at the equator and consequently reduced the scintillations detected at Ancon. On the other hand, on the day with severe scintillations (5 Oct), the EIA was not so well developed as on 10 October, leading to relatively higher equatorial plasma density and TEC. Consequently the severe scintillations at Ancon were likely caused by ionospheric structure located below the altitude of C/NOFS. The NRL SAMI2 model was utilized to gain a greater understanding of the role of neutral winds and electric fields in reproducing the TEC as a function of latitude for both classes of irregularities. Spectral studies with high resolution in situ PLP data were also performed. The power law spectra within the plasma bubbles showed two slopes: the low frequency slope being ∼−5/3 and the high frequency ∼−5 with a break around λ = 70 m. This particular type of two‐slope spectra may be related to the extremely low solar activity and its impact on ion composition and temperature.Item Open Access Comparing F region ionospheric irregularity observations from C/NOFS and Jicamarca(American Geophysical Union, 2009-07-11) Hysell, D. L.; Hedden, R. B.; Chau Chong Shing, Jorge Luis; Galindo, F. R.; Roddy, P. A.; Pfaff, R. F.Observations of plasma density irregularities associated with equatorial spread F (ESF) have been made using the Jicamarca Radio Observatory and the Plasma Langmuir Probe (PLP) and Vector Electric Field Instrument (VEFI) instruments on the Communications Navigation Outage Forecast System (C/NOFS) satellite during a close spatio-temporal conjunction. The radar data resolution is of the order of 1 km and a few sec. in space and time, respectively. We find that coherent scatter intensifications at these scales are coincident and collocated with plasma density depletions as determined by C/NOFS. The Doppler shifts of the localized echoes are also comparable to the vertical components of the E × B plasma drifts. The strongest backscatter does not necessarily come from the deepest or most rapidly convecting depletions. This implies a complex relationship between coherent backscatter and the underlying state parameters in the ionospheric plasma.Item Open Access Comparing Jicamarca and C/NOFS (PLP, VEFI): observations of equatorial spread F irregularities(Instituto Geofísico del Perú, 2009) Hysell, D. L.; Hedden, R. B.; Chau Chong Shing, Jorge Luis; Galindo, F. R.; Roddy, P. A.; Pfaff, R. F.Diapositivas presentadas en The Meeting of the Americas, 2009 Joint Assembly, organizadas por la American Geophysical Union del 24 al 27 mayo de 2009 en Ontario, Canada.Item Restricted Evolution of equatorial ionospheric plasma bubbles and formation of broad plasma depletions measured by the C/NOFS satellite during deep solar minimum(American Geophysical Union, 2011-03-08) Huang, Chao‐Song; de la Beaujardiére, O.; Roddy, P. A.; Hunton, D. E.; Pfaff, R. F.; Valladares, C. E.; Ballenthin, J. O.An unexpected feature revealed by the measurements of the Communication/Navigation Outage Forecasting System (C/NOFS) satellite is the presence of broad plasma depletions in the midnight–dawn sector during deep solar minimum. It has not been well understood what causes the broad plasma depletions and how equatorial plasma bubbles are related to the broad depletions. In this paper we present the C/NOFS measurements of equatorial plasma bubbles and broad depletions in a few cases. The ion density perturbations and enhanced ion vertical velocity are first identified in the topside F region at ∼2200 LT, suggesting that the plasma bubbles start to form earlier at lower altitudes. The observations show that the plasma bubbles observed in the midnight–dawn sector may originate in the evening sector. The plasma bubbles continue growing for more than 3.3 h, and the decay time of the bubbles is also longer than 3.3 h. The continuous growth of the plasma bubbles in the evening sector and the slow decay after midnight determine that most plasma bubbles become fully developed and are easily detected in the midnight–dawn sector. The plasma flow inside the bubbles remains strongly upward throughout the entire nighttime. We propose the following mechanism for the generation of wide plasma bubbles and broad depletions. A series of plasma bubbles is generated through the Rayleigh‐Taylor instability process over a large longitudinal range. These plasma bubbles grow and merge to form a wide bubble (width of ∼700 km as observed), and multiple regular and/or wide bubbles can further merge to form broad plasma depletions (thousands of kilometers in longitude). The ion vertical drift inside each plasma bubble is driven by the polarization electric field and remains large after the bubbles have merged. This mechanism provides a reasonable interpretation of the large upward ion drift velocity inside the broad depletion region.