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This paper briefly reviews ionospheric irregularities that occur in the E and F regions at mid-latitudes.Sporadic E(Es)is a common ionospheric irregularity phenomenon that is first noticed in the E layer.Es mainly appears during daytime in summer hemispheres,and is formed primarily from neutral wind shear in the mesosphere and lower thermosphere(MLT)region.Field-aligned irregularity(FAI)in the E region is also observed by Very High Frequency(VHF)radar in mid-latitude regions.FAI frequently occurs after sunset in summer hemispheres,and spectrum features of E region FAI echoes suggest that type-2 irregularity is dominant in the nighttime ionosphere.A close relationship between Es and E region FAI implies that Es may be a possible source of E region FAI in the nighttime ionosphere.Strong neutral wind shear,steep Es plasma density gradient,and a polarized electric field are the significant factors affecting the formation of E region FAI.At mid-latitudes,joint observational experiments including ionosonde,VHF radar,Global Positioning System(GPS)stations,and all-sky optical images have revealed strong connections across different scales of ionospheric irregularities in the nighttime F region,such as spread F(SF),medium-scale traveling ionospheric disturbances(MSTID),and F region FAI.Observations suggest that different scales of ionospheric irregularities are generally attributed to the Perkins instability and subsequently excited gradient drift instability.Nighttime MSTID can further evolve into small-scale structures through a nonlinear cascade process when a steep plasma density gradient exists at the bottom of the F region.In addition,the effect of ionospheric electrodynamic coupling processes,including ionospheric E-F coupling and inter-hemispheric coupling on the generation of ionospheric irregularities,becomes more prominent due to the significant dip angle and equipotentiality of magnetic field lines in the mid-latitude ionosphere.Polarized electric fields can map to different ionospheric regions and excite plasma instabilities which form ionospheric irregularities.Nevertheless,the mapping efficiency of a polarized electric field depends on the ionospheric background and spatial scale of the field.