Doppler spectral profiles of dayside auroral hydrogen show sudden increases in precipitating proton energy by a broadening of the spectral profile towards shorter wavelengths. This coincides with the equatorward motion of the dayside aurora. A model of the expected spectral character and spatial distribution of the H emission shows that the H emission spectrum is a direct measure of the reconnection process at the dayside magnetopause, i.e., 1) the narrow, symmetric spectral profiles are a measure of the magnetospheric velocity filter, 2) the sudden spectral shift of the H emission profiles reflect changes of ion energy due to an increase in the rate of reconnection, 3) spectral H emission observations could be used to map the spatial distribution of the precipitating ion energy, the total reconnection rate, the reconnection sites on the magnetopause, and the direction and intensity of convection. ¿ 1998 American Geophysical Union