Three-dimensional nonlinear evolution ofequatorial ionospheric spread-F bubbles

Using numerical simulation techniques, we present the first study of the three-dimensional nonlinear evolution of an equatorial spread-F bubble. The background ionosphere used to initialize the bubble evolution is computed using a time-dependent first-principles equatorial plasma fountain model together with a prereversal enhancement vertical drift model. We find that finite parallel conductivity effects slow down both the linear and nonlinear bubble evolution compared to the two-dimensional evolution. In addition we find that bubble-like structures with extremely sharp density gradients can be generated off the equator at equatorial anomaly latitudes in agreement with recent observations

Equatorial spread <I>F</I> fossil plumes

Behaviour of equatorial spread F (ESF) fossil plumes, i.e., ESF plumes that have stopped rising, is examined using the NRL SAMI3/ESF three-dimensional simulation code. We find that fossil bubbles, plasma density depletions associated with fossil plumes, can persist as high-altitude equatorial depletions even while being "blown" by zonal winds. Corresponding airglow-proxy images of fossil plumes, plots of electron density versus longitude and latitude at a constant altitude of 288 km, are shown to partially "fill in" in most cases, beginning with the highest altitude field lines within the plume. Specifically, field lines upon which the E field has fallen entirely to zero are affected and only the low altitude (≤600 km) portion if each field line fills in. This suggests that it should be possible to observe a bubble at high altitude on a field line for which the corresponding airglow image no longer shows a depletion. In all cases ESF plumes stop rising when the flux-tube-integrated ion mass density inside the upper edge of the bubble is equal to that of the nearby background, further supporting the result of Krall et al. (2010b)

Anomalous Resistivity in Magnetosphere-Ionosphere Current Systems: The Role of Ion Cyclotron Turbulence

Field aligned currents flowing between the auroral zone topside ionosphere and the magnetosphere excite the electrostatic ion cyclotron instability when the electron drift velocity exceeds-1/31 VTe (H+ mode). Typically, this condition is satisfied at altitudes \u3e1000km. We have made numerical estimates of anomalous resistivity due to ion cyclotron turbulence as a function of altitude in such current systems. In order to arrive at these estimates we have assessed the role played by electron-ion collisions, spatial effects such as convection of wate energy, and various competing nonlinear saturation mechanisms (Quasi-linear plateau formation, ion resonance broadening, nonlinear ion Landau damping, etc.) in the ionosphere-magnetosphere environment

Evolution of equatorial ionosphericbubbles during a large auroral electrojet increase in the recovery phase of a magnetic storm

We present a model and observations of the evolution of equatorial ionospheric bubbles during a large auroral electrojet (AE) index increase in the recovery phase of a geomagnetic storm. Using a three-dimensional time-dependent numerical simulation model, we find, for the 19–21 October 1998 storm, that the equatorial bubble evolution is different during storm time as compared to quiet time conditions. We have found that the storm time vertical drift in conjunction with reduced off-equatorial E region shorting is the primary mechanism that distinguishes the large AE increase recovery phase storm time evolution from the quiet time case. Comparison of the simulation model with ground-based storm time radar observations is made