A possible transport mechanism from the tropical troposphere to the lower stratosphere (LS) across the tropical tropopause layer (TTL) is through convective overshooting clouds (COV) that inject air with tropospheric characteristics (high carbon monoxide (CO) and low ozone (O3) concentrations) into the LS over a few days. Evidence of such convective intrusions was observed at the end of January 2010, associated with increased convective activity over the southern African continent following the onset of a sudden stratospheric warming (SSW) in the northern hemisphere, lasting approximately two weeks. The modulation of tropical stratospheric upwelling by SSW appears to have forced stronger and deeper tropical convection, particularly in the Southern Hemisphere tropics. The tropospheric (CO-rich, O3-poor) air injected into the TTL by COV then gradually moved upward via the tropical stratospheric upwelling strengthened by SSW. Meanwhile the O3 decrease started in the middle stratosphere and descended gradually to the TTL, indicating that the effect of stratospheric upwelling reached the TTL. The present results suggest that the direct and indirect (strengthened convective clouds) effects of stratospheric upwelling modulated by SSW can have a large impact on the trace gas fields in the TTL and LS.
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