A multi-platform investigation of midlatitude sporadic E and its ties to E–F coupling and meteor activity
- US Naval Research Laboratory, Code 7213, 4555 Overlook Ave. SW, Washington, DC 20375, USA
Abstract. This paper describes the results of a multi-platform observing campaign aimed at studying midlatitude sporadic E (Es) and associated ionospheric phenomena. The assets used were the digisonde in Boulder, Colorado; the first station of the Long Wavelength Array, LWA1, in New Mexico; the transmitters of the radio station WWV in Colorado; and 61 continuously operating GPS receivers between LWA1 and WWV. The results show that southwestward-directed medium-scale traveling ionospheric disturbances (MSTIDs) were substantially more prevalent when Es was detected. The amplitudes of these correlate with a plasma frequency up to about 4.5 MHz. For fp ≳ 5 MHz, the MSTIDs become significantly weaker and basically vanish above ∼ 6.5 MHz. The prevalence of meteor trail reflections observed with LWA1 also correlates with fp up to about 4.5 MHz; above this limit, the relationship exhibits a significant turnover. The observed intensity of coherent backscatter from Es field-aligned irregularities (FAIs) also correlates with inferred plasma frequency. However, this trend continues to higher frequencies with a peak near 6 MHz, followed by a much more subtle turnover. The reflected power from Es structures observed with LWA1 is significantly more correlated on spatial scales between 10 and 40 km. The magnitude of this correlation increases with fp up to ∼ 6 MHz, above which it drops. These results are consistent with the following: (1) southwestward-directed MSTIDs are produced via E–F coupling; (2) this coupling is stronger when the Es layer, seeded by meteor ablation, is more dense; (3) the coupling is substantially diminished for Es layers harboring extremely dense structures (fp ≳ 5 MHz).