Observations and Modeling of the Upper Mesosphere: Mesopause Characteristics, Inversion Layers, and Bores

摘要

Using data from TIMED/SABER, we studied the global behavior of the mesopause at solstice (northern-hemisphere summer). The existence of the two- level structure with an abrupt altitude transition near 25N is confirmed. Its altitude in the 'summer' zone is shown to increase with increasing (northerly) latitude; in the 'winter' zone, it is found somewhat below the accepted 100-km level at mid-latitudes. Temperatures are in the 165- 180K range throughout the winter zone but north of 25N they fail continuously, reaching approximately 120K at 80N. We show that mesospheric temperature inversion layers (TILs) are very common, and that large TILs affect the mesopause characteristics. We also characterize the occurrence distribution of TILs in latitude and local time. We studied the properties of mesospheric bores by numerically solving the differential equations governing their propagation modes. Using an impulsive forcing function and measured wind and temperature profiles, we determined the vertical displacement as a function of time and horizontal distance for different altitudes within the duct, and thereby were able to study the evolution of the wave. We were able to reproduce the phase speed of an observed bore to a good approximation.