资源环境科技发展态势分析平台

In this paper, an extended nonlinear multiscale interaction model is proposed to examine nonlinear behavior of eddy-driven blocking as a Rossby wave packet in a three-dimensional background flow by dividing the background meridional potential vorticity gradient (PV_y) into dynamical PV_y$⁡(PVyD)$ related to the horizontal (mainly meridional) shear of background westerly wind (BWW) and thermodynamic PV_y$⁡(PVyT)$ associated with the meridional temperature gradient (MTG). It is found that eddy-driven baroclinic blocking with large amplitude in the midtroposphere tends to have a longer lifetime (~20 days) in a baroclinic atmosphere with stratification than eddy-driven barotropic blocking without vertical variation (less than 15 days). It is shown that barotropic blocking shows a northwest–southeast orientation and has long lifetime, large retrogression, and slow decay only for weaker barotropic BWW and $PVyD$ in higher latitudes. In a baroclinic atmosphere with stratification, baroclinic blocking shows long lifetime, strong eastward movement, slow decay, weak strength, and less local persistence for large barotropic BWW and $PVyD$ under $PVyT=0$⁠, but becomes less slow decay, weak retrogression, and large local persistence for small barotropic BWW and $PVyD$⁠. Such a blocking with a north–south antisymmetric dipole, large amplitude, and long local persistence, characterized by a persistent large meander of westerly jet streams, is easily seen when baroclinic BWW and $PVyT$ are small in the lower to midtroposphere. Comparatively, the magnitude of $PVyT$ plays a larger role in the blocking change than that of $PVyD$⁠, whereas the vertical variation of MTG is more important for the blocking change than the MTG itself for some cases.