Zonal mean meridional circulation in the low to middle latitude of MLT region: A numerical simulation by a general circulation model Original Research Article

Zonal mean meridional circulation in the MLT region is investigated using a General Circulation Model at Kyushu University (Kyushu-GCM). A systematic meridional wind from the summer hemisphere to the winter hemisphere associated with ozone heating in the middle atmosphere is balanced with zonal forcing to close off zonal mean zonal wind in the upper mesosphere and the mesopause regions. On the other hand, in the lower thermosphere (ca. 90 km to 130 km) a systematic cellular structure is found throughout a year in the low to middle latitude region. The meridional wind system is induced by momentum depositions by migrating diurnal and semidiurnal tides. The lower part of these meridional winds is induced by dissipating upward propagating migrating diurnal tides, while the upper part is induced by dissipating upward propagating migrating semidiurnal tides. It is found that the effect of non-migrating tides on the meridional wind is one order smaller than that of the migrating tides.