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JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 112, D15112, doi:10.1029/2006JD007973, 2007

Three-dimensional SF6 data and tropospheric transport simulations: Signals, modeling accuracy, and implications for inverse modeling

M. Gloor

Earth and Biosphere Institute and School of Geography, University of Leeds, Leeds, UK


E. Dlugokencky

Global Monitoring Division, Earth System Research Laboratory, NOAA, Boulder, Colorado, USA


C. Brenninkmeijer

Max-Planck Institute for Chemistry, Mainz, Germany


L. Horowitz

Geophysical Fluid Dynamics Laboratory, NOAA, Princeton, New Jersey, USA


D. F. Hurst

Global Monitoring Division, Earth System Research Laboratory, NOAA, Boulder, Colorado, USA


G. Dutton

Global Monitoring Division, Earth System Research Laboratory, NOAA, Boulder, Colorado, USA
Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, Colorado, USA.


C. Crevoisier

Atmospheric and Oceanic Sciences Program, Princeton University, Princeton, New Jersey, USA


T. Machida

National Institute for Environmental Studies, Tsukuba, Japan


P. Tans

Global Monitoring Division, Earth System Research Laboratory, NOAA, Boulder, Colorado, USA


Abstract

Surface emissions of SF6 are closely tied to human activity and thus fairly well known. They therefore can and have been used to evaluate tropospheric transport predicted by models. A range of new atmospheric SF6 data permit us to expand on earlier studies. The purpose of this first of two papers is to characterize known and new transport constraints provided by the data and to use them to quantify predictive skill of the MOZART-2 atmospheric chemistry and transport model. Main noteworthy observational constraints are (1) a well-known steep N-S gradient at the surface confined to an ≈40° wide latitude band in the tropics; (2) a fairly uniform N-S gradient in the upper troposphere; (3) an increase in the temporal variation in upper troposphere Northern Hemisphere records with increasing latitude; (4) a negative SF6 gradient in Northern Hemisphere vertical profiles from the surface to 8 km height, but a positive gradient in the Southern Hemisphere; and (5) a clear reflection in surface records of large-scale seasonal atmosphere movements like the undulations of the Intertropical Convergence Zone (ITCZ). Comparison of observations with simulations reveal excellent modeling skills with regards to (1) large-scale annual mean latitudinal gradients at remote surface sites (relative bias of N-S hemisphere difference ≤ 5%) and aloft (≈10 km, relative bias ≤ 25%); (2) seasonality in signals at remote sites caused by large-scale movements of the atmosphere; (3) time variation in upper troposphere records; (4) “faithfulness” of advective transport on timescales up to ≈1 week; and (5) the general shapes and seasonal variation of vertical profiles. The model (1) underestimates the variation in the vertical of profiles, particularly those from locations close to high emissions regions, and (2) overestimates the difference in SF6 between the planetary boundary layer (PBL) and free troposphere over North America, and thus likely Eurasia, during winter by approximately a factor of 2 (STD ≈ 100%). The comparisons permit estimating lower bounds on representation errors which are large for sites close to continental outflow regions. Given the magnitude of the signals and signal variance, SF6 provides a strong constraint on interhemispheric transport, PBL ventilation, dispersion pathways of northern midlatitude surface emissions through the upper troposphere, and large-scale movements of the atmosphere.

Received 26 August 2006; accepted 18 April 2007; published 15 August 2007.

Keywords: tropospheric transport; transport modeling; sulfur hexafluoride.

Index Terms: 0368 Atmospheric Composition and Structure: Troposphere: constituent transport and chemistry; 0322 Atmospheric Composition and Structure: Constituent sources and sinks; 0330 Atmospheric Composition and Structure: Geochemical cycles (1030); 0466 Biogeosciences: Modeling.

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Citation: Gloor, M., E. Dlugokencky, C. Brenninkmeijer, L. Horowitz, D. F. Hurst, G. Dutton, C. Crevoisier, T. Machida, and P. Tans (2007), Three-dimensional SF6 data and tropospheric transport simulations: Signals, modeling accuracy, and implications for inverse modeling, J. Geophys. Res., 112, D15112, doi:10.1029/2006JD007973.