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Evaluating Simulations of Interhemispheric Transport: Interhemispheric Exchange Time Versus SF 6 Age
Author(s) -
Yang Huang,
Waugh Darryn W.,
Orbe Clara,
Patra Prabir K.,
Jöckel Patrick,
Lamarque JeanFrancois,
Tilmes Simone,
Kinnison Douglas,
Elkins James W.,
Dlugokencky Edward J.
Publication year - 2019
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/2018gl080960
Subject(s) - southern hemisphere , middle latitudes , northern hemisphere , atmospheric sciences , environmental science , tropics , climatology , annual cycle , geology , biology , ecology
Two recent studies using sulfur hexafluoride (SF 6 ) observations to evaluate interhemispheric transport in two different ensembles of atmospheric chemistry models reached different conclusions on model performance. We show here that the different conclusions are due to the use of different metrics and not differences in the performance of the models. For both model ensembles, the multimodel mean interhemispheric exchange time τ ex agrees well with observations, but in nearly all models the SF 6 age in the southern hemisphere is older than observed. This occurs because transport from the northern extratropics into the tropics is too slow in most models, and the SF 6 age is more sensitive to this bias than τ ex . Thus, simulating τ ex correctly does not necessarily mean that transport from northern midlatitudes into the southern hemisphere is correct. It also suggests that more attention needs to be paid to evaluating transport from northern midlatitudes into the tropics.