Fast Transport Pathways Into the Northern Hemisphere Upper Troposphere and Lower Stratosphere During Northern Summer

Abstract

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.

Infrequent, Rapid Transport Pathways to the Summer North American Upper Troposphere and Lower Stratosphere

“…(2017)]. Overall, both deep convection and resolved dynamics play principal roles in transport into the NA UTLS region, consistent with the processes of its Asian counterpart (Wu et al., 2020). More precisely, while deep convection determines the gradient of tracer concentrations at the bottom of the UTLS with transport times of several hours to 1–2 days in WACCM5, the resolved large‐scale circulation governs the transport further upward with typical transport times of several weeks.…”

“…Recently, Wu et al. (2020) examined transport pathways linking the surface to the UTLS at 100 hPa using an idealized pulse passive tracer approach to reveal the transport dynamics. Fast transport paths were identified over the southern slope of the Tibetan Plateau, northern India, and Saudi Arabia with a modal age (the most probable transit time; see details in Section 2) of 5–10 days in an average of a large tracer ensemble.…”

Confinement of air in the Asian monsoon anticyclone and pathways of convective air to the stratosphere during the summer season

“…Satellite observations show that tropospheric compounds emitted at the surface, like CO and aerosols generated from these compounds, tend to concentrate within the AMA while it is depleted in stratospherically borne ozone (Randel and Park, 2006;Park et al, 2008;Randel et al, 2010;Vernier et al, 2015;Santee et al, 2017;Luo et al, 2018). These observations have been corroborated by a number of numerical simulations based on Lagrangian or general circulation models which all show confinement of tropospheric tracers within the AMA (James et al, 2008;Park et al, 2009;Tzella and Legras, 2011;Wright et al, 2011;Bergman et al, 2012Bergman et al, , 2013Orbe et al, 2015;Vogel et al, 2015;Yan and Bian, 2015;Tissier and Legras, 2016;Garny and Randel, 2016;Pan et al, 2016;Fan et al, 2017;Ploeger et al, 2017;Vogel et al, 2019;Wu et al, 2020). There is, however, a lack of consensus on the interpretation of what is actually observed.…”

Summertime Transport Pathways From Different Northern Hemisphere Regions Into the Arctic

“…Park et al, 2009;Randel et al, 2010;Hoskins 1996, 2001;Tissier & Legras, 2016;Vogel et al, 2015Vogel et al, , 2019. The strong rising motion directly above the source region of NI and TP tracers in the UTLS, is likely the reason why NI and TP tracers can be most efficiently transported into lower latitude UTLS (Figure 7a; also see Wu et al, 2020) and then into the Arctic (Figure 1g).…”

“…Li et al, 2012;Orbe et al, 2016) to measure the transit time at r independent of when (with respect to t') the tracer was last at the Earth's surface. Similar to Wu et al (2020), our focus here is on quantifying how the tracer distribution at time t and location r is related to tracer source Ω conditioned on its release time.…”