Fast transport pathways into the northern hemisphere upper troposphere and lower stratosphere during northern summer

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This study identifies the fast (i.e., ∼ days–weeks) transport pathways that connect the Northern Hemisphere surface to the upper troposphere and lower stratosphere (UTLS) during northern summer by integrating a large (90 member) ensemble of Boundary Impulse Response tracers in the Whole Atmosphere Community Climate Model version 5. We show that there is a fast transport pathway that occurs over the southern slope of the Tibetan Plateau, northern India, the Arabian Sea, and Saudi Arabia; furthermore, we show that during July this pathway connects the Northern Hemisphere surface to the UTLS on a modal time scale of 5–10 days. A less efficient transport pathway is also identified over the western Pacific. A detailed budget analysis reveals that, while convective processes are responsible for transport to 200–300 hPa, the resolved dynamics, specifically the vertical eddy flux, dominate at 100–150 hPa. Transport variations are analyzed on weekly, monthly, and interannual time scales and are largely related to differences in the resolved dynamics in the UTLS.
© 2020. American Geophysical Union. The authors thank the reviewers for their comments and suggestions. The authors acknowledge the constructive discussion with scientists at the Atmospheric Chemistry Observations and Modeling Lab at NCAR, especially Bill Randel, Laura Pan, and Mijeong Park at the early stage of this work. Y. W. would like to thank Li Song, Joowan Kim, and Walter Robinson for helpful discussions. The computations were carried out with high-performance computing support provided by NCAR's Computational and Information Systems Laboratory, which is sponsored by the National Science Foundation (NSF). The data produced for and analyzed in this paper are available through the IRI/LDEO Climate Data Library ( etal_JGR_2019). Y. W. and X. W. are supported by NSF Award AGS-1802248. M. A. acknowledges funding from the Program Atracción de Talento Comunidad de Madrid (2016-T2/AMB-1405).