Due to the transport of high-density sunlit plasma from dayside by convection,polar cap tongue of ionization(TOI),polar cap patches and blobs form as common phenomena in polar ionosphere.The steep density gradients at the edges of these structures lead to severe problems in applications involving radio waves traversing the ionosphere.To better understand the evolution of TOI/patches,it is important to know how the transporting sunlit plasma distributed in the whole polar region.Through averaging the hourly TEC(Total electron content)in solar-maximum winter,we found a“Hook-like” pattern of high-density plasmadistribution in polar ionosphere and provided the direct evidence for the plasma source of the dawn-side high-density plasma structures.The combined effects of convection and corotation electric fields are responsible for the dayside sunlit plasma extension from polar cap to dawn side,and the IMF By and Bz components control the transportation pattern through modulating the convection pattern.