December 16, 2011

Earth’s atmosphere includes several distinct layers that can be identified from one another by differences in temperature, chemical composition, density, and other properties. Most of Earth’s weather occurs in the lower layer of the troposphere, with the layer of the stratosphere residing above. The boundary between these two layers is known as the tropopause and shows variation at different latitudes on Earth. A characteristic tropopause shape shows low heights near the poles, high heights near the equator, and a significant jump (or discontinuity) at about 30 degrees latitude. This variation in tropopause height contributes to variations in weather and climate at different latitudes.

We propose an explanation for the shape of the tropopause in our paper published in Journal of the Atmospheric Sciences. Using a computer climate model (a three-dimensional general circulation model), we create a series of climate states that systematically isolate contributions such as moisture or large-scale weather systems. Although differences in moisture have often been cited as the reason for tropopause variation with latitude, we find that large-scale weather systems (known as eddies in fluid dynamics) alone are necessary to create the characteristic tropopause shape. This leads us to suggest that circulation patterns in the stratosphere may actually be a significant contributor to the troposphere. Or to put it another way: weather patterns on the surface of Earth are significantly influenced by processes in the atmospheric layers above.