Ionospheric anomalies before earthquakes termed as seismo-ionospheric precursors have been extensively discussed due to the importance of earthquake prediction. Electric field driven mechanism is commonly used to explain seismo-ionospheric precursors. Kim et al. (1993) first theoretically demonstrated that seismogenic electric fields could form intensified sporadic E layers in higher altitudes, which is so influential that motivates considerable statistical work on variations of foEs and h'Es before earthquakes. We attempt to establish a physical model of sporadic E layers at middle latitudes based on wind shear theory with the objective to reexamine the influence of seismogenic electric fields on sporadic E layers. The results show that zonal electric fields of several mV/m can influence the formation of higher sporadic E layers: For existing higher sporadic E layers, eastward/westward electric fields are capable of inhibiting/facilitating the existing layers accompanied by ascent/descent in altitude. For normal E region without sporadic E layers, the effect of eastward electric fields is not notable, while westward electric fields are able to form wider sporadic E layers. Taking into account their complicated response and inherently high variability, a suggestion is made about the necessity to be cautious when attributing variations of sporadic E layers to forthcoming earthquakes.
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