Abstract
Manifestations of severe nighttime equatorial ionospheric disturbances have been observed for decades. It is generally accepted that the phenomena are caused by large depletions, referred to as equatorial plasma bubbles (EPBs), which are initiated on the rising unstable bottom side of the nighttime F layer. Physics-based simulations have enhanced our understanding of the EPB phenomenon. However, until very recently, stochastic structure smaller than ∼ 10 km was not well resolved. Recent high-resolution EPB simulations have extended the resolution to hundreds of meters, which provides a unique opportunity to characterize intermediate-scale EPB structure.This paper presents a summary analysis of simulated high-resolution intermediate-scale EPB structure. Estimation of altitude-dependent power law spectral density function parameters provides an altitude versus time history of the intermediate-scale structure development. Local structure onset is associated with successive bifurcation of rising EPBs. Developed structure characterized by a two-component power law spectral density function ultimately subtends several hundred kilometers in altitude.Two-component inverse power-law structure was first observed in early in situ rocket measurements. It has been observed in diagnostic measurements of beacon-satellite and GPS scintillation data as well as in situ measurements from Atmospheric Explorer and C/NOFS satellites. The EPB simulation data fully support the reported EPB diagnostics as well as a correlation between the turbulent strength and the large-scale spectral index parameter estimates. However, recent analyses have shown that the correlation is an intrinsic property of power-law parameter estimation.
Highlights
The terminology equatorial spread F (ESF), plumes, and equatorial plasma bubbles (EPBs) evolved, respectively, from ionospheric sounder, coherent radar backscatter, and diagnostic measurements
In situ and remote EPB radio-propagation diagnostics are formally time series generated by the motion of the probe or the interrogating propagation path
EPB Cs range is comparable to the reported C/NOFS values when the unscaled C/NOFS values are translated to common electron density units
Summary
The terminology equatorial spread F (ESF), plumes, and equatorial plasma bubbles (EPBs) evolved, respectively, from ionospheric sounder, coherent radar backscatter, and diagnostic measurements. In situ and remote EPB radio-propagation diagnostics are formally time series generated by the motion of the probe or the interrogating propagation path. Interpreting such diagnostic measurements is challenging because altitude, magnetic field, and temporal structure variations are invariably intermingled. Time-to-space conversion depends on an unknown structure drift. Physics-based simulations provide an exceptional opportunity to generate definitive structure development measurements. The underlying physics has been well established for decades, simulating the generation and dissipation of steep gradients that evolve in unstable regions has, until very recently, limited the resolution that could be achieved to kilometer scales. Simulations that exploit advanced computational capabilities have resolved EPB structure to hundreds of meters
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