Embedded Files
Atmospheric blocking is a dynamical phenomenon. Because of the chaotic, turbulent character of the atmospheric flow, fluctuations occur for a large range of time and spatial scales. Blocking could be just one of these. Despite these uncertainties, research suggests that a key-process for initiating atmospheric blocking is Rossby-wave breaking. Broadly speaking, Rossby waves are large scale flow patterns that travel around the globe. As they travel, these Rossby waves modulate their amplitude (by exchanging energy with the background flow), and may even “break”, as seen in the image. This wave-breaking bears similarity to the breaking of surface-waves at sea.
An illustration of the dynamic nature of atmospheric blocking is obtained by studying the evolution of potential temperature on the dynamic tropopause. The dynamic tropopause is defined as the the level where the potential vorticity equals 2 PVU (potential vorticity units). Assuming adiabatic dynamics (which is an approximation), potential temperature is conserved on the 2PVU surface, and is mainly distributed horizontally. In the evolution throughout January 2012 (animation on the right) several wave-breaking events can be distinguished.
Data source: ECMWF
Google Sites
Report abuse