Discrete arc structures were identified from EISCAT data on March 11, 1984 which were simultaneously recorded on All-Sky camera pictures from the Kilpisj¿rvi station in Finland. From the electric field measurements supplied by the tri-static UHF facility, some privileged orientation has been found through the requirement of a uniform tangential electric field across the arc structure, which corresponds to the preferential arc alignment as deduced from camera pictures. Additional fold structures, resolved by the All-Sky camera, develop along the preexisting arcs which still organize the electric field fluctuations in their vicinity. ¿ American Geophysical Union 1991