Signatures of cross-tropopause exchange seen in the oxygen anomaly in CO2

Abstract:

Stratospheric signals, such as oxygen anomaly in CO₂, are distinct from those originated from the Earth’s surface. The stratospheric anomaly in CO₂ was explained as a result of the exchange reaction between CO₂ and O₃ via the excited state oxygen atom O(¹D), produced by the UV photolysis of O₃. The subsequent large scale circulation (Brewer-Dobson circulation) and synoptic eddy mixing bring the anomalous CO₂ to the surface, providing another opportunity for studying biogeochemical cycles involving CO₂. Here, we show that the oxygen anomaly in CO₂ increases during the course of our sampling period (September 2013-February 2014), concordant with the strengthening of winter monsoon and subtropical jet system. The interaction between winter monsoon and jet system could efficiently enhance the vertical mixing between upper troposphere/lower stratosphere and the lower troposphere. Moreover, an attempt to the mid-troposphere CO₂ anomaly is also made. We report for the first time the triple oxygen isotope composition of CO₂ in the middle troposphere collected by the CARRIBIC phase one mission. A clear correlation of D¹⁷O in CO₂ with N₂O mixing ratios is observed which confirms the incursion of stratospheric air to the mid-tropospheric region. This is also supported by the compact correlation with O₃ mixing ratios.