Ground based measurements of thermospheric temperatures from Mawson, Antarctica, often show a marked spatial gradient, with data taken poleward of the discrete auroral oval up to 200 K or more warmer than measurements taken in or equatorward of the oval. This region of increased temperature is identified as the polar cap. We suggest a possible contribution to polar cap heating may be from thermospheric gravity waves. ¿ 1998 American Geophysical Union