Evaluating stratospheric tropical width using tracer concentrations

Considerable effort has been placed on quantifying the width of the tropics at tropospheric levels, but substantially less effort has been placed on quantifying the width at stratospheric levels. Here we probe tropical width in the stratosphere using chemical tracers, which are accessible by direct measurement.

Two new tracer-based width metrics are developed, denoted here as the "1 sigma method" and the gradient weighted latitude (GWL) method. We evaluate widths from three tracers, CH4, N2O, and SF6. We demonstrate that unlike previously proposed stratospheric width methods using tracers, these metrics perform consistently throughout the depth of the stratosphere, at all times of year and on coarse temporal data.