A. Zahn et al., Identification of extratropical two-way troposphere-stratosphere mixing based on CARIBIC measurements of O-3, CO, and ultrafine particles, J GEO RES-A, 105(D1), 2000, pp. 1527-1535
Simultaneous measurements of O-3, CO, and ultrafine aerosol particles (UFP)
, conducted on board of a Boeing 767-ER passenger aircraft flying from Sri
Lanka to Germany (project CARIBIC), are used to study two-way cross-tropopa
use mixing near a subtropical tropopause fold. On the equatorward side of t
he fold, downward mixing of stratospheric air into the upper troposphere is
identified by enhanced concentrations of O-3 and (CO)-C-14. Very high UFP
number concentrations of up to 1.5 x 10(4) cm(-3) (STP) were encountered in
side the poleward half of the fold. This accumulation of small particles is
explained by recent extensive aerosol nucleation, most likely triggered by
the mixing of stratospheric air with tropospheric air injected into the fo
ld. Further, nine particle formation events were observed outside the fold
which are attributed to isolated cells of deep convection and to rising air
parcels under cyclonic conditions that mix with surrounding air. In the up
per troposphere O-3 and CO were found to be correlated with high Delta O-3/
Delta CO ratios of 0.6 to 1.5. In the fold the correlation was strongly neg
ative with Delta O-3/Delta CO = -3.5; but the high CO mixing ratios of 100
ppb at O-3 mixing ratios of 250 ppb point to earlier injection of troposphe
ric air, in agreement with the UFP measurements.