Transport and mixing of chemical air masses in idealized baroclinic life cycles

Abstract

[1] The transport, mixing, and three-dimensional evolution of chemically distinct air masses within growing baroclinic waves are studied in idealized, high-resolution, life cycle experiments using suitably initialized passive tracers, contrasting the two well-known life cycle paradigms, distinguished by predominantly anticyclonic (LC1) or cyclonic (LC2) flow at upper levels. Stratosphere-troposphere exchange differs significantly between the two life cycles. Specifically, transport from the stratosphere into the troposphere is significantly larger for LC2 (typically by 50%), due to the presence of large and deep cyclonic vortices that create a wider surf zone than for LC1. In contrast, the transport of tropospheric air into the stratosphere is nearly identical between the two life cycles. The mass of boundary layer air uplifted into the free troposphere is similar for both life cycles, but much more is directly injected into the stratosphere in the case of LC1 (fourfold, approximately). However, the total mixing of boundary layer with stratospheric air is larger for LC2, owing to the presence of the deep cyclonic vortices that entrain and mix both boundary layer air from the surface and stratospheric air from the upper levels. For LC1, boundary layer and stratospheric air are brought together by smaller cyclonic structures that develop on the poleward side of the jet in the lower part of the middleworld, resulting in correspondingly weaker mixing. As both the El Niño-Southern Oscillation and the North Atlantic Oscillation are correlated with the relative frequency of life cycle behaviors, corresponding changes in chemical transport and mixing are to be expected.

Synoptic influences on springtime tropospheric O<sub>3</sub> and CO over the North American export region observed by TES

“…Some WCBs originating over North America can transport O 3 and precursors to the free troposphere over Europe within 4-5 days (Stohl et al, 1999(Stohl et al, , 2003a where descending motions carry them back toward the surface causing groundlevel O 3 mixing ratios to rise, but so far this has only been observed at high elevation sites in the Alps (Huntrieser et al, 2005). However, the same cyclones responsible for lofting O 3 -forming anthropogenic pollutants from the continental boundary layer to the free troposphere may also mix down O 3 of stratospheric origin, which inevitably complicates the quantification of the tropospheric O 3 budgets (Cooper et al, 2001(Cooper et al, , 2002Moody et al, 1996;Merrill et al, 1996;Oltmans et al, 1996;Polvani and Esler, 2007). Thus information on the 3-dimensional distribution of O 3 and its precursors as well as the air mass transport history are required to ascertain the contributions of the various sources to observed O 3 levels.…”

Boundary‐layer ventilation by baroclinic life cycles

“…However, these regions are to some degree predictable, and the structure of the WCB is strongly related to the dynamical aspects of the extratropical cyclone, and the background conditions in which it develops. Polvani and Esler (2007) in their paper on transport and mixing in idealised lifecycles have also produced three-dimensional plots of their boundary-layer tracer distributions (their Figure 13). When we compare Figure 11 here to their Figures 13 and 14, we see that the tracer distributions within the free troposphere are very similar.…”

“…However, no boundary-layer parameterization scheme was included and therefore the definition of the boundary-layer depth is arbitrary and is effectively assumed constant in time and space. Additionally, the absence of a boundary-layer scheme means that Polvani and Esler (2007) do not investigate transport within the boundary layer. It is likely that, due to the proximity to the surface, transport processes within the boundary layer will differ considerably from those that have been observed in the free troposphere.…”

“…Currently there are few idealised modelling studies which investigate boundary-layer ventilation. Polvani and Esler (2007) investigate the exchange and mixing of different air masses (boundary layer, free troposphere and stratospheric) during the evolution of two contrasting baroclinic life cycles. They show the WCB to transport a similar amount of tracer out of the boundary layer in both cases.…”

Extreme moisture transport into the Arctic linked to Rossby wave breaking

“…RWB in idealized simulations exhibits rapid large-scale transport and mixing on synoptic time scales [Polvani and Esler, 2007]. In fact, the linkage between atmospheric rivers and RWB has been investigated recently over the North Pacific [Ryoo et al, 2013;Payne and Magnusdottir, 2014].…”