“…In recent years, the penetration electric field has been used extensively to interpret various disturbances in the midlatitude and low-latitude ionosphere [e.g., Kelley et al, 2003;Huang et al, 2005;Zhao et al, 2005Zhao et al, , 2008Wei et al, 2008a;Li et al, 2009Li et al, , 2010Guo et al, 2010;Huang, 2009;Zong et al, 2010]. The duskward penetration electric field sometimes can be completely canceled by the dawnward shielding electric field in the ring current, which is called "perfect shielding" [Goldstein, 2006] or "goodshielding" [Wolf et al, 2007].…”