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Abstract:

In order to investigate whether climate models of different complexity have the potential to simulate natural atmospheric circulation regimes, 1000-year-long integrations with constant external forcing have been analysed. Significant non-Gaussian uni-, bi-, and trimodal probability density functions have been found in 100-year segments. © 2001 Royal Meteorological Society.

Abstract:

An examination of zonal asymmetries in meridional momentum flux reaching the mesosphere is made using the Hines Doppler spread parameterization of gravity waves. As expected a general correspondence is seen between wave one wind in the stratosphere and wave one signals in gravity wave momentum flux leaving the stratosphere. However, a significant difference is the presence of wave one features in the gravity-wave momentum flux at 56 km and ∼70°N during mid-summer which contrast with minimal signals in stratospheric wave one wind. The prominence of this feature is accounted for by a significant wave one Brunt-Väisälä feature at the tropopause amplifying a wave one signal in momentum flux which can then propagate to great heights. Such a feature could result in mesospheric planetary waves which are coupled to the tropopause forcing without intervening planetary wave signals in the stratosphere.