Mechanistic analysis of interhemispheric transport

Abstract

After a strong interannual modulation in methyl chloroform was observed at Samoa, it was hypothesized that a mechanism other than convection, namely the propagation of Rossby waves through the tropical westerly ducts, may also be responsible for interhemispheric transport. We assess the role of these mechanisms in this exchange using the National Center for Atmospheric Research (NCAR)'s Community Climate Model 2 (CCM2). In our analysis of Northern Hemisphere wintertime transport we find that convective outflow is the dominant mechanism for cross‐equatorial transport. Rossby wave propagation through westerly ducts contributes significantly less. Furthermore, we find that the observed modulation of methyl chloroform mixing ratio at Samoa is due to a shift in the low level convergence pattern during El Nino, resulting in a more southeasterly flow at the surface over Samoa.