The mesopause altitude: Only two distinctive levels worldwide?

A large number of temperature profiles of the altitude range 80 to 105 km were obtained between 71 degrees S and 54 degrees N latitude from late April to early July 1996. The measurements were performed by a shipborne lidar, resolving the Doppler broadening of the K(DI) resonance line. The most notable result of this field campaign is the finding that throughout our observation series the mesopause altitude was located at altitudes of either 100 +/- 3 km or 86 +/- 3 km. The high ''winter'' level extended from 71 degrees S to 23 degrees N, the low ''summer'' level from 24 degrees N until the end of the field observations at 54 degrees N. Our latitudinally distributed observations indicate strongly a worldwide bimodal character of the mesopause altitude. Furthermore, our mesopause temperatures are generally lower than previonsly measured in the Northern hemisphere.