We describe mid-latitude plasma density striations (MDS) modulating the evening side of Storm Enhanced Density (SED) by magnetosphere-ionosphere coupling. The MDS are magnetically conjugate, and they consist of elongated density structures [enhancements (plumes) and depletions (troughs)] that extend from the equator to the main trough equatorward boundary. Each density perturbation is associated with a flow channel, and they develop progressively at all latitudes. We present a detailed analysis of the MDS during the 7-8 September 2017 storm, by virtue of remote and in-situ observations of the magnetosphere-ionosphere system. We find that the density plumes are a result of local plasma uplift, and poleward and westward plasma transport guided by the adjacent flow channels. While the MDS’s troughs bear some resemblance to the depletion patterns associated with equatorial plasma bubbles, it has been found to be quite distinct, both in terms of its observational manifestations and its formation mechanism. Namely, the trough is associated with enhanced flow channels peaking at the edges, with elevated electron and ion temperatures. Crucial spacecraft measurements of plasma parameters in the ionosphere and plasmasphere near the equatorial plane ($L\approx1.9$) unambiguously show conjugate nature of the MDS. In particular, the magnetospheric electric field intensifications lie just earthward of the injected $<$200~keV ions at the ion pressure gradient.