On polarized frontal structures, type-1 and quasi-periodic echoes in midlatitude sporadic E

Sporadic-E (E-S) patches in the nighttime midlatitude ionosphere often appear to consist of quasi-periodic (QP) frontal structures, i.e., strips of enhanced conductivity whose cross-sectional dimensions are small compared to their length. Assuming that such E-S patches are usually found at an ion-convergent node in a wind-shear profile, we show that the meridional neutral wind at that node would polarize these strips and produce an intense, electrojet-like current accompanied by an electric field strength in excess of 10 mV/m. The validity of this model seems to be supported by its ability to account for several hitherto unexplained phenomena including type-1 and QP radar echoes from nighttime E-S patches, and the coupled appearance of altitude-modulated isodensity contours in the F region when frontal structures are present in the E region. While much remains to be done to evaluate the importance of this process, this finding is exciting because it makes plausible the commonplace occurrence of what was previously referred to as anomalous energetics in the midlatitude ionosphere.