Experimental studies of the temperature and pressure dependence of the ambipolar diffusion coefficient in the mesopause region have been undertaken by studying meteor trail decay times with radars at a variety of sites in North America, with latitudes between 75N and 35N. The site at Resolute Bay, Canada, has proven especially useful, due to the wide range of mesopause temperatures experienced at that site between summer and winter. Theoretical predictions have been confirmed, and an algorithm is outlined which permits meteor decay times to be used to determine absolute measurements of mesospheric temperatures. ¿ 1999 American Geophysical Union