Validation of a 2D model using observed profiles of SF₆ with main focus on the tropics

Abstract

Sulfur hexafluoride (SF₆) is a useful tracer to test the transport behavior of atmospheric models. There have been few measurements of the vertical distribution of SF₆ especially in the tropics, which have restricted the validation of vertical transport in two-dimensional (2D) global models. In an attempt to fill this void, we have used a 2D model in a transient mode to compare the calculated vertical distributions of SF₆ with observations. The gross feature of the simulated vertical profiles compares well with the observations particularly in the tropics. Comparisons with UARS/HALOE CH₄-data show that the sharp vertical gradient above the tropopause and the extremely weak gradient above 25 km in the observations in India are due to the quasi biannual oscillation (QBO). The QBO is not taken into account in the model dynamics but in average between its west and east phase vertical profiles are represented well by the model. We also confirm that global SF₆ source emissions should be distributed on the model grid proportional to electrical power usage.