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., st rips of enhanced conductivity whose cross-sectional dimensions are sma ll compared to their length. Assuming that such E-S patches are usuall y found at an ion-convergent node in a wind-shear profile, we show tha t the meridional neutral wind at that node would polarize these strips and produce an intense, electrojet-like current accompanied by an ele ctric 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 u nexplained phenomena including type-1 and QP radar echoes from nightti me E-S patches, and the coupled appearance of altitude-modulated isode nsity 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 anoma lous energetics in the midlatitude ionosphere.