The slope of surfaces of maximum tracer concentration in the lower stratosphere

The level of maximum concentration of radioactive tracer material injected into the stratosphere is invariably observed to slope from higher altitudes over the equator to lower altitudes and colder potential temperatures near the pole. Six months to a year after injections into the lower stratosphere in equatorial, temperate, and polar latitudes, the configurations of the levels of maximum concentration were almost identical irrespective of the source latitude and possible variations in initial altitude and vertical distribution. For the temperate latitude injection in the summer of 1967 there are sufficient data to examine the details of the genesis of the surface of maximum concentration. The data show a poleward movement of the center of concentration by midfall, a net descent in the late fall and winter poleward of 55°N and subsequent quasi-horizontal mixing the following spring and summer. Tracers originally injected into the upper stratosphere or mesosphere follow similar patterns, as does a tracer injected into the stratosphere of a computer-generated model of the general circulation.