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North Bethesda, MD, United States

Huba J.D.,U.S. Navy | Joyce G.,Icarus Research Inc.
Geophysical Research Letters | Year: 2010

The NRL three-dimensional ionospheric simulation code SAMI3 is used to model the onset and evolution of equatorial spread F (ESF). SAMI3 is a comprehensive ionosphere model that has been modified to self-consistently solve for the global neutral wind driven dynamo electric field as well as the gravity driven electric field associated with plasma bubbles. The latter is achieved with a high resolution longitudinal grid in the pre- to post-sunset sector (i.e., 1630 MLT-2230 MLT). Initial results from the new simulation model are presented. It is shown that ESF can be triggered by pre-sunset ionospheric density perturbations, and that an existing ESF bubble can trigger a new bubble. © 2010 by the American Geophysical Union. Source


Gordon D.F.,U.S. Navy | Hafizi B.,Icarus Research Inc.
Journal of Computational Physics | Year: 2012

A systematic technique for conservatively discretizing the time dependent Schrödinger equation on an arbitrary structured grid is given. Spatial differencing is carried out by finite volumes, and temporal differencing is carried out semi-implicitly. It is shown that the resulting algorithm conserves probability to within a round-off error regardless of the grid geometry. The algorithm is efficient for both serial and parallel computation. The conservative nature of the algorithm, and its phase accuracy, are demonstrated for a bound state, and for a free state in an electromagnetic field. The ionization rate for a hydrogen atom in a strong electromagnetic field is computed, and compared with the rate from tunneling theory. The regime of validity of tunneling theory is clarified. © 2012. Source


Krall J.,U.S. Navy | Huba J.D.,U.S. Navy | Ossakow S.L.,Berkeley Research Associates | Joyce G.,Icarus Research Inc.
Geophysical Research Letters | Year: 2010

The Naval Research Laboratory (NRL) three-dimensional simulation code SAMI3/ESF is used to study the long time evolution of equatorial spread F (ESF) bubbles. The ESF bubbles are modeled until they stop rising and become-gfossils-h with results analyzed to address previously-untested hypotheses. Specifically, it has been suggested that bubbles stop rising when either the local electron density inside the bubble is equal to that of the nearby background or the fluxtube-integrated electron density inside the bubble is equal to that of the nearby background. It is shown that equatorial bubbles stop rising when the magnetic flux-tube-integrated ion mass density inside the bubble equals that of the surrounding background ionosphere. In the case of a singleion ionosphere this reduces to the condition that the fluxtube-integrated electron densities are in balance, consistent with the hypothesis of Mendillo et al. (2005). Copyright © 2010 by the American Geophysical Union. Source


Kuo C.L.,National Central University | Kuo C.L.,National Cheng Kung University | Huba J.D.,U.S. Navy | Joyce G.,Icarus Research Inc. | And 2 more authors.
Journal of Geophysical Research: Space Physics | Year: 2011

Recent ionospheric observations indicate that the total electron content (TEC) may anomalously decrease or increase up to 5-20% before the occurrence of big earthquakes. The ionospheric density variations can be caused by earth surface charges/currents produced from electric currents associated with the stressed rock. We formulate a coupling model for the stressed rock-Earth surface charges-atmosphere-ionosphere system. The stressed-rock acts as the dynamo to provide the currents for the coupling system. The electric fields and currents in the atmosphere and the lower boundary of ionosphere are obtained by solving the current continuity equation, ∇ · J = 0, where J is the current density. A three-dimensional ionosphere simulation code is then used to study the ionospheric dynamics based on the obtained electric fields and currents. The simulation results show that a current density Jrock = 0.2-10 μA/m2 in an earthquake fault zone is required to cause daytime TEC variations of 2-25%. The simulation results also show that a current density Jrock = 0.01-1 μA/m2 can lead to nighttime TEC variations of 1-30% as well as the formation of a nighttime plasma bubble (equatorial spread F) extending over the whole magnetic flux tube containing the earthquake epicenter. We suggest that observations of daytime and nighttime TEC variations and a nighttime plasma bubble within the affected region can be used as precursors for earthquake prediction. Copyright © 2011 by the American Geophysical Union. Source


Krall J.,U.S. Navy | Huba J.D.,U.S. Navy | Joyce G.,Icarus Research Inc. | Yokoyama T.,Cornell University
Annales Geophysicae | Year: 2010

Forces governing the three-dimensional structure of equatorial spread-F (ESF) plumes are examined using the NRL SAMI3/ESF three-dimensional simulation code. As is the case with the equatorial ionization anomaly (IA), density crests within the plume occur where gravitational and diffusive forces are in balance. Large E × B drifts within the ESF plume place these crests on field lines with apex heights higher than those of the background IA crests. Large poleward field-aligned ion velocities within the plume result in large ion-neutral diffusive forces that support these ionization crests at altitudes higher than background IA crest altitudes. We show examples in which density enhancements associated with ESF, also called 'plasma blobs,' can occur within an ESF plume on density-crest field lines, at or above the density crests. Simulated ESF density enhancements reproduce all key features of those that have been observed in situ. Source

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