Solar terminator wave and its relation to the atmospheric tide

Observations by the CHAMP satellite have recently revealed wave structure of the neutral density near the solar terminator in the upper atmosphere. The amplitude of the neutral density perturbation associated with a solar terminator wave is of order ± 3-6%, and the horizontal wavelength is of order 3000 km. In this study, we examine the excitation mechanism of the solar terminator wave using a general circulation model (GCM) that extends from the ground surface to the exobase. Our result reveals that waves similar to the solar terminator wave observed by the CHAMP satellite are found not only in the thermosphere but also in the stratosphere and mesosphere. The terminator wave is excited in the stratosphere and/or troposphere and propagates upward into the upper thermosphere. Specifically, the solar terminator wave is mainly generated by superposition of the upward propagating migrating tides from zonal wave number 4 to zonal wave number 6. The terminator wave is more prominent during solstice than during equinox. This seasonal variability of the terminator wave is also studied using a GCM simulation. In addition, the maximum temperature perturbation at low latitudes occurs near midnight, indicating a contribution to the midnight temperature maximum in the upper thermosphere. The effect of the terminator wave on the generation of the midnight temperature maximum is examined. The relation between the midnight temperature maximum and the upward propagating migrating tides is also discussed.