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Seasonal Variations of SF 6 , CO 2 , CH 4 , and N 2 O in the UT/LS Region due to Emissions, Transport, and Chemistry
Author(s) -
Bisht Jagat S. H.,
Machida Toshinobu,
Chandra Naveen,
Tsuboi Kazuhiro,
Patra Prabir K.,
Umezawa Taku,
Niwa Yosuke,
Sawa Yousuke,
Morimoto Shinji,
Nakazawa Takakiyo,
Saitoh Naoko,
Takigawa Masayuki
Publication year - 2021
Publication title -
journal of geophysical research: atmospheres
Language(s) - English
Resource type - Journals
eISSN - 2169-8996
pISSN - 2169-897X
DOI - 10.1029/2020jd033541
Subject(s) - seasonality , troposphere , atmospheric sciences , stratosphere , tropopause , atmosphere (unit) , trace gas , environmental science , climatology , atmospheric chemistry , sink (geography) , latitude , mesoscale meteorology , chemistry , ozone , meteorology , geography , geology , statistics , mathematics , cartography , geodesy
Abstract Distributions of trace gases in the atmosphere provide key information on the transport and chemical properties of the Earth's environment. In this study, we examine the observed seasonal variability of SF 6 , CO 2 , CH 4 , and N 2 O from commercial aircraft‐based measurements in the upper troposphere and lower stratosphere (UT/LS) in combination with atmospheric chemistry‐transport model (ACTM) simulations. We used a dynamical tropopause defined based on maximum PV gradient that better allows for model‐observation comparisons in the UT and LS regions separately. The ACTM simulated the following observed features well: (1) smaller seasonality in SF 6 in the UT than in the LS due to seasonal change in the transport processes, (2) large seasonality in CO 2 in the UT, in phase with the source‐sink balance on the Earth's surface, (3) pronounced seasonality in CH 4 in the UT with opposite phase in the subtropics and Eurasian high latitudes as contrasting phases of source and chemical loss seasonality develop, and (4) small N 2 O variability in the UT but stratospheric loss produces distinct seasonality in the LS. Vertical profile comparisons of all the species show that ACTM better simulated the photo‐chemically inert CO 2 vertical gradients in all seasons, suggesting a realistic representation of the Brewer‐Dobson circulation in the model. The seasonal variabilities of the long‐lived species in the LS can be explained based on age of air derived from CO 2 in the older air regime, except for the months of May‐July, when the model mixes UT and LS air more vigorously than suggested by the observations.