The Asian monsoon anticyclone (AMA) exhibits a trimodal distribution of sub‐vortices and the western Pacific is one of the preferred locations. Amplification of the western Pacific anticyclone (WPA) is often linked with eastward eddy shedding from the AMA, although the processes are not well understood. This study investigates the dynamics driving eastward eddy shedding associated with the emergence of the WPA in the upper troposphere and lower stratosphere on synoptic scales. Using reanalysis data during 1979–2019, our composite analysis reveals that amplified WPA events are tied to the upstream Silk Road (SR) wave‐train pattern over midlatitude Eurasia as identified in previous studies. The quasi‐stationary eastward propagating eddies result from baroclinic excitation along the westerly jet, as identified by coherent eddy heat fluxes and weakening of the low‐level temperature gradient. The upper‐level westerly jet is important in determining the longitudinal phase‐locking of wave trains, which are anchored and amplify near the jet exit. Occasionally enhanced convection near the Philippines also triggers anticyclonic eddies that propagate upward and northeastward via the Pacific‐Japan (PJ) pattern, forming the WPA in the upper troposphere. Correlation analysis suggests that the SR and PJ mechanisms are not physically correlated.

Ozone in the troposphere is a pollutant and greenhouse gas, and it is crucial to better understand its transport from the ozonerich stratosphere. Tropopause folding, wherein stratospheric air intrudes downward into the troposphere, enables stratosphereto-troposphere ozone transport (STT). However, systematic analysis of the relationship between folding and tropospheric ozone, using data that can both capture folding's spatial scales and accurately represent tropospheric chemistry, is lacking. Here, we compare folding in both high-resolution (0.25°) reanalysis ERA5 and low-resolution (0.75°) chemical reanalysis CAMSRA over one year. High-resolution folding is dramatically more frequent and significantly better-correlated with tropospheric ozone. In particular, folding of deep tropospheric extent is nearly 100% missing at low resolution, and folding-ozone correlations increase most with resolution along midlatitude storm tracks, where deep folding is most common. Our results imply that STT is more attributable to tropopause folding than implied by low-resolution analysis, likely associated with resolving filamentary, deep folding.

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.

Ozone in the stratosphere is beneficial to life on earth, but in the troposphere (where it is much rarer) it is a pollutant hazardous to human health and crops (Krzyzanowski & Cohen, 2008;Monks et al., 2015) and an effective greenhouse gas (Myhre et al., 2013). Understanding the sources of tropospheric ozone is thus societally and climatically important. While photochemical production is the largest source of tropospheric ozone, stratosphere-to-troposphere transport (STT) is a significant contributor (Hess et al., 2015;Neu et al., 2014;Williams et al., 2019), and stratospheric influence on tropospheric ozone is projected to strengthen due both to global-warming-related changes in the stratospheric circulation and to stratospheric ozone recovery (Akritidis