Patra, P.K., M. Takigawa, G.S. Dutton, K. Uhse, K. Ishijima,
B. R. Lintner, K. Miyazaki, and J. W. Elkins, 2009:
Atmos. Chem. Phys., 9, 1209-1225.
Paper (PDF 3.9MB)
Supplement Paper (PDF 3.9MB)
Abstract.
We use an atmospheric general circulation model (AGCM) driven
chemistry-transport model (ACTM) to simulate the evolution of sulfur
hexafluoride (SF6) in the troposphere. The model results are
compared with continuous measurements at 6 sites over 71N–90S. These comparisons
demonstrate that the ACTM simulations lie within the measurement uncertainty over the analysis
period (1999–2006) and capture salient features of synoptic,
seasonal and interannual SF6 variability. To understand
transport timescales of SF6 within the troposphere, transport
times of air parcels from the surface to different regions of the
troposphere ("age") are estimated from a simulation of an idealized
tracer. The age estimation error and its sensitivity to the selection of
reanalysis meteorology for ACTM nudging or the tracer transport by deep
cumulus convection as represented in the model are discussed.
Monthly-mean, 2-box model exchange times (tex) are
calculated from both the observed and simulated SF6 time
series at the 6 observing sites and show favorable agreement, suggesting
that the ACTM adequately represents large-scale interhemispheric
transport. The simulated SF6 variability is further
investigated through decomposition of the mixing ratio time-tendency
into advective, convective, and vertical diffusive components. The
transport component analysis illustrates the role of each process in
SF6 synoptic variability at the site level and provides
insight into the seasonality of tex.
Citation. Patra, P.K., M. Takigawa, G. S. Dutton,
K. Uhse, K. Ishijima, B. R. Lintner, K. Miyazaki, and J. W. Elkins,
2009: Transport mechanisms for synoptic, seasonal and interannual
SF6 variations and "age" of air in the troposphere.
Atmos. Chem. Phys., 9, 1209-1225.
Acknowledgments.
This work is partly supported by the Grantsin-
Aid for Creative Scientific Research (2005/17GS0203) of the
Ministry of Education, Science, Sports and Culture, Japan. We
appreciate the support of Takakiyo Nakazawa and Hajime Akimoto
for this research, and we thank Bradley Hall for creating and
maintaining the NOAA/ESRL 2006 SF6 scale. BRL acknowledges
the support of National Science Foundation ATM-0645200
(J. D. Neelin, PI). Comments and suggestions from Jessica Neu, an
anonymous reviewer, and Peter Haynes were helpful for revising
the article.