Browsing by Author "Aveiro, H. C."
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Item Restricted Fine structure in midlatitude sporadic E layers(Elsevier, 2013-01-03) Hysell, D. L.; Nossa, E.; Aveiro, H. C.; Larsen, M. F.; Munro, J.; Sulzer, M. P.; González, S. A.Fine structure in midlatitude sporadic E layer patches or “clouds” is apparent in incoherent scatter observations from the Arecibo Radio Telescope. The fine structure is wavelike with predominant horizontal wavelengths as large as about 2–3 km. We attribute the structure to a drift wave instability operating in the collisional regime. A linear, local dispersion relation for the waves is described which predicts growth driven by polarization electric fields in the cloud. A numerical simulation produces wave growth and other features consistent with the dispersion relation, including finite parallel wavenumbers. The kilometric irregularities are thought to be the primary waves from which secondary, meter-scale waves in the layers can form.Item Restricted Forecast assessment of topside spread F at Jicamarca(American Geophysical Union, 2010-12-22) Aveiro, H. C.; Hysell, D. L.The Jicamarca Unattended Long Term Investigations of the Ionosphere and Atmosphere (JULIA) radar operated from August 1996 through the present time, making a total of approximately 1500 nights of ionospheric irregularities associated with equatorial spread F (ESF) observations under different seasons, solar flux levels, and geomagnetic conditions. The climatology, persistence, and correlation with the phase of the Moon of premidnight and postmidnight irregularities are evaluated, and different forecasting tools are compared. During equinox, 1 day persistence information improves the forecast over climatology alone for most solar flux and geomagnetic activity conditions, with a significant improvement during periods at low solar flux. December solstice ESF observations show a high correlation with the lunar phase, with periods close to the full Moon presenting the highest probability of ESF occurrence. Using this information for geomagnetically quiet periods during December solstice, we further improve the forecast over the climatological model. For postmidnight and premidnight June solstice ESF, however, climatology still gives the best forecasting results.Item Restricted Implications of the equipotential field line approximation for equatorial spread F analysis(American Geophysical Union, 2012-06-13) Aveiro, H. C.; Hysell, D. L.Three different approaches to the evaluation of the electrostatic potential in the ionosphere under equatorial spread F(ESF) conditions are considered. First, we calculate the potential using an analytical approach, applying force balance laws to a simplified ionosphere. Second, we compute the potential around a cylinder‐like plasma depletion in an idealized ionosphere using both the equipotential field line (EFL) approach and the full 3‐D solution to the electrostatic potential problem. Our third approach involves an initial boundary value simulation in a realistic ionosphere using both EFL and 3‐D potential solutions. The results show that the equipotential field line assumption does not fully capture the 3‐D structure of the ionospheric current system and leads to an underestimation of the growth rate of ESF irregularities in numerical simulations.Item Restricted Ionospheric Irregularities: Frontiers(American Geophysical Union, 2014-03-14) Hysell, D. L.; Aveiro, H. C.; Chau Chong Shing, Jorge LuisThere are several thermosphere ionosphere models with bottom boundaries somewhere in the middle atmosphere. Achieving a true whole atmosphere modeling capability requires the specification of atmospheric conditions at a boundary. This chapter discusses the use of the Navy Operational Global Atmospheric Prediction System‐Advanced Level Physics High Altitude (NOGAPS‐ALPHA) model as a bottom boundary for the thermosphere ionosphere electrodynamics general circulation model (TIEGCM). The results are compared with Sounding of the Atmosphere with Broadband Emission Radiometry (SABER) observations and previously published model results. The chapter presents an evaluation of the behavior of tidal components at the interface between the two models, and suggests a method to reduce the discontinuities. Consistent with previous models, a marked decrease is found in the semidiurnal tide after the dramatic sudden stratospheric warming in late January 2009.Item Restricted Three‐dimensional numerical simulation of equatorial F region plasma irregularities with bottomside shear flow(American Geophysical Union, 2010-11-20) Aveiro, H. C.; Hysell, D. L.A three‐dimensional numerical simulation of plasma density irregularities in the postsunset equatorial F region ionosphere leading to equatorial spread F (ESF) is described. The simulation advances the plasma number density and electrostatic potential forward in time by enforcing the constraints of quasi‐neutrality and momentum conservation. The magnetic field lines are not modeled as equipotentials. Simulations are performed for cases with no background winds, with no background electric field or gravity, and with winds, a background electric field, and gravity all working in concert. The first run produced generalized Rayleigh Taylor (GRT) instability, and the second produced collisional shear instability (CSI). The combined run produced an instability which developed into an intense ESF event more quickly and with more realistic characteristics than the other two. Simulation results are compared with incoherent and coherent scatter radar data from the magnetic equator. A number of signature ESF characteristics are shown to be reproduced by the simulation.