Sporadic-E and GNSS Scintillation

Multiple recent reports have claimed observations from ground-based GNSS measurements of near-equatorial daytime L1 (1.6 GHz) amplitude scintillation associated with sporadic-E.  While there is a long history of detecting ground-based VHF scintillation associated with sporadic-E, if the L1 observations hold up it could say something new about ionospheric structure.  Refractive index fluctuations in the ionosphere decrease as .  Moreover, L1 scintillation measurements respond to smaller irregularity length scales transverse to the line of sight (LOS) than VHF, and the irregularity spectral density function (SDF) for electron density fluctuations typically decreases with decreasing scale size.  The E-region is a thin layer, so there is not a large distance to integrate through to increase the phase effects.  Some of the strongest historical VHF scintillation observed to be associated with sporadic-E layers had an amplitude scintillation index, S₄, of 0.4–0.6.  Using frequency scaling for power-law spectral indices appropriate to E-layer instabilities, this translates to an L1 S₄ of 0.02–0.03, which is typically at or below the S₄ noise floor for GNSS receivers.  Slant-path enhancements could raise this to 0.09 at low elevations.  Could coherent structures, such as discrete edge-diffraction mechanisms, plausibly generate observable S₄ levels at L1?  This talk will explore both random and coherent scintillation mechanisms to assess the physical conditions required to generate an S₄ of 0.2 or higher at 1.6 GHz due to E-region irregularities.  Particularly, are the required electron density fluctuations consistent with what is likely to be associated with sporadic-E?