%0 Journal Article
%A Plöger, F.
%A Konopka, P.
%A Müller, R.
%A Fueglistaler, S.
%A Schmidt, T.
%A Manners, J.C.
%A Grooß, J.-U.
%A Günther, G.
%A Riese, M.
%T Horizontal transport affecting trace gas seasonality in the Tropical Tropopause Layer (TTL)
%J Journal of Geophysical Research
%V 117
%@ 0148-0227
%C Washington, DC
%I Union
%M PreJuSER-17546
%P D09303
%D 2012
%Z We thank M. Volk and Bill Randel for helpful discussions and the ECMWF for providing the reanalysis data. F. Ploeger thanks COST for funding a Short Term Scientific Mission at DAMTP/Cambridge.
%X We analyze horizontal transport from midlatitudes into the tropics (in-mixing) and its impact on seasonal variations of ozone, carbon monoxide and water vapor in the Tropical Tropopause Layer (TTL). For this purpose, we use three-dimensional backward trajectories, driven by ECMWF ERA-Interim winds, and a conceptual one-dimensional model of the chemical composition of the TTL. We find that the fraction of in-mixed midlatitude air shows an annual cycle with maximum during NH summer, resulting from the superposition of two inversely phased annual cycles for in-mixing from the NH and SH, respectively. In-mixing is driven by the monsoonal upper-level anticyclonic circulations. This circulation pattern is dominated by the Southeast Asian summer monsoon and, correspondingly, in-mixing shows an annual cycle. The impact of in-mixing on TTL mixing ratios depends on the in-mixed fraction of midlatitude air and on the meridional gradient of the particular species. For CO the meridional gradient and consequently the effect of in-mixing is weak. For water vapor, in-mixing effects are negligible. For ozone, the meridional gradient is large and the contribution of in-mixing to the ozone maximum during NH summer is about 50%. This in-mixing contribution is not sensitive to the tropical ascent velocity, which is about 40% too fast in ERA-Interim. As photochemically produced ozone in the TTL shows no distinct summer maximum, the ozone annual anomaly in the upper TTL turns out to be mainly forced by in-mixing of ozone-rich extratropical air during NH summer.
%K J (WoSType)
%F PUB:(DE-HGF)16
%9 Journal Article
%U <Go to ISI:>//WOS:000304008600005
%R 10.1029/2011JD017267
%U https://juser.fz-juelich.de/record/17546