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We use the idealized tracer experiments and investigate the summertime transport from the surface region of northern India and Tibetan Plateau to the lower stratosphere. It is found that the transport, compared to other surrounding regions, has an overall younger modal age in the northern lower stratosphere away from the tropopause. Analysis of the tracer budget reveals that the tracer is transported to the tropical lower stratosphere rapidly in the first 5 days due to vertical eddy transport and afterward in a month or two advection associated with the Brewer‐Dobson circulation. Meanwhile the tracer is also transported to the northern extratropical lower stratosphere in the first 3 months due to horizontal eddy mixing. The results highlight the uniqueness of the northern India region in the summertime transport to the lower stratosphere and implications for the transport of short‐lived chemical species in the destruction of stratospheric ozone.

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.

The stratospheric influence on summertime high surface ozone (${\mathrm{O}}_3$) events is examined using a twenty-year simulation from the Whole Atmosphere Community Climate Model. We find that${\mathrm{O}}_3$transported from the stratosphere makes a significant contribution to the surface${\mathrm{O}}_3$variability where background surface${\mathrm{O}}_3$exceeds the 95thpercentile, especially over western U.S. Maximum covariance analysis is applied to${\mathrm{O}}_3$anomalies paired with stratospheric${\mathrm{O}}_3$tracer anomalies to identify the stratospheric intrusion and the underlying dynamical mechanism. The first leading mode corresponds to deep stratospheric intrusions in the western and northern tier of the U.S., and intensified northeasterlies in the mid-to-lower troposphere along the west coast, which also facilitate the transport to the eastern Pacific Ocean. The second leading mode corresponds to deep intrusions over the Intermountain Regions. Both modes are associated with eastward propagating baroclinic systems, which are amplified near the end of the North Pacific storm tracks, leading to strong descents over the western U.S.