The behavior of Kelvin waves in the mesosphere and lower thermosphere is examined in three 10-day sequences of high resolution Doppler imager mesospheric and lower thermospheric zonal winds at solstice. Eastward propagating signatures are observed in wavenumbers 1, 2, and 3 of the zonal wind field with periods near 3 and 5 days. These structures are coherent in latitude and altitude, and maximize near or on the equator. In the mesosphere, lines of constant phase move downward in time, implying that these waves are forced from below. Above 90 km the phase lines of Kelvin zonal wavenumbers 2 and 3 traverse upward in time, suggesting in situ or higher-level sources. Estimates of the Eliassen-Palm fluxes indicate that wavenumber 1 may significantly contribute to the eastward momentum budget of the equatorial lower thermosphere. ¿ 1997 American Geophysical Union