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Stratospheric Circulation Simulation

Almost all air enters the stratosphere over the tropics. A slow, mean vertical circulation, called the Brewer-Dobson circulation, lofts air over the tropics from the troposphere into the stratosphere. Air lofted into the stratosphere then moves either to the north or the south where it drops back down to the troposphere, completing the circulation by moving back towards the tropics.

A second, faster, horizontal circulation is active in the stratosphere. This stratospheric circulation moves from east to west around the equator and changes directions to west-to-east towards the poles. The net result is that particles transported out of the tropics may cover the globe in only two months time.


Simulated Particle Trajectories at 400K Potential Temperature


400K vs. 500K


QuickTime | MPEG 60 MB


This simulation shows the trajectories of weightless particles released into the troposphere over the tropics at an altitude of 400K potential temperature levels (~17 kilometers). The particles are pseudo colored according to their initial temperature. Red particles are warmer and blue ones are cooler. A key result depicted in this animation is that global mixing occurs in the lower stratosphere in only 60 days.

QuickTime | MPEG 38 MB


Simulation data from particles released at 400K (upper image) is compared with data from 500K (~20 kilometers) in the lower image. The 400K particles mix much more rapidly than the higher elevation particles. More rapid mixing occurs at lower levels due to greater interaction of tropospheric weather systems which extend into the lower stratosphere. Mixing is asymmetric from north to south in the 500K simulation. This is due to the interaction of planetary waves that are stronger in the wintertime months than in the summer.
July 1
Time Evolution:
90 days
John Clyne, NCAR/CISL

William Randel, NCAR/ACD

Date Created:
Date Catalogued:
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