On the large wind shear and fast meridional transport above the mesopause

Abstract

Unexpectedly strong winds/shears and fast meridional transport above the mesopause have been revealed from previous rocket and satellite observations. Using Richardson number criteria for dynamic stability, we estimate the maximum wind shears allowable by the background static stability, which peaks above the mesopause. These maximum shears are in general agreement with the large wind shears inferred from the rocket measurements at low and mid‐latitudes, indicating the close relationship between the latter and the stability constraint set by the background atmosphere. Diagnostic calculations also indicate that the meridional transport in this region may not be well understood solely by examining the mean meridional circulation, and large amplitude tides/planetary waves can play an important role in the bulk transport of tracers. Strong stochastic winds, presumably due to gravity waves, do not seem to significantly change the large scale pattern of the transport but may extend the range of the tracer movement.