Seasonal characteristics of trace gas transport into the extratropical upper troposphere and lower stratosphere
2019
Abstract. To investigate the seasonal characteristics of trace gas
distributions in the extratropical upper troposphere and lower stratosphere
(ExUTLS) as well as stratosphere–troposphere exchange processes, origin
fractions of air masses originating in the stratosphere, tropical
troposphere, midlatitude lower troposphere (LT), and high-latitude LT in the
ExUTLS are estimated using 10-year backward trajectories
calculated with European Centre for Medium-Range Weather Forecasts (ECMWF)
ERA-Interim data as the meteorological input. Time series of trace gases
obtained from ground-based and airborne observations are incorporated into
the trajectories, thus reconstructing spatiotemporal distributions of trace
gases in the ExUTLS. The reconstructed tracer distributions are analyzed with
the origin fractions and the stratospheric age of air (AoA) estimated using
the backward trajectories. The reconstructed distributions of SF 6 and
CO 2 in the ExUTLS are linearly correlated with those of AoA because of
their chemically passive behavior and quasi-stable increasing trends in the
troposphere. Distributions of CH 4 , N 2 O , and CO are
controlled primarily by chemical decay along the transport path from the
source region via the stratosphere and subsequent mixing of such stratospheric
air masses with tropospheric air masses in the ExUTLS.
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