On the mixing‐driven formation of the Extratropical Transition Layer (ExTL)

Abstract

[1] We present a case study on the formation and structure of the Extratropical Transition Layer (ExTL) using in situ observations and a Lagrangian chemical transport model. The results show that the model with mixing parameterized from the large-scale flow deformations well reconstructs the observed asymmetric structure of the ExTL with a deeper transition layer on the cyclonic side of the jet stream. Information from the model and observations are integrated using tracer-tracer correlations between ozone (O 3 ) and carbon monoxide (CO). Transport of chemical tracers from the stratospheric or tropospheric background to the ExTL through mixing is identified by the change of the CO-O 3 correlation in the CO-O 3 space. The ExTL formation process simulated by the model, therefore, provides a scenario to connect the mixed air parcels to the history of mixing. An estimate of timescales of ExTL formation is made using model experiments. The results show that the fastest formation of the ExTL occurs on the isentropic levels below the subtropical jet core, e.g. around 3 weeks for 310 K, whereas at 360 K level (jet core) the formation of the ExTL needs around 3 months. Overall, this result demonstrates the important role of mixing in transport of trace gases across the tropopause.

Long-range transport pathways of tropospheric source gases originating in Asia into the northern lower stratosphere during the Asian monsoon season 2012

“…Global geographical location of artificial boundary layer source regions in the CLaMS model, also referred to as "emission tracers" . The latitude and longitude range for each emission tracer is listed in Table 1. reproduce the strong gradients of chemical species found in regions with strong transport barriers, such as the edge of the Asian monsoon anticyclone (e.g., Konopka et al, 2010;Ploeger et al, 2015;Vogel et al, 2015), the extratropical tropopause (e.g., Pan et al, 2006;Vogel et al, 2011b;Konopka and Pan, 2012), and the polar vortex (e.g., Günther et al, 2008;Vogel et al, 2008).…”

“…ECMWF water vapor is prescribed at lower model levels. In CLaMS simulations, both AIRS (Atmospheric Infrared Sounder) and MOPITT (Measurements of Pollution in the Troposphere) were previously used for constructing the boundary for CO in the troposphere (Vogel et al, 2011b;Konopka and Pan, 2012;Pommrich et al, 2014). Here, lower boundary conditions for CO and CH4 (ζ < 200 K) are derived from AIRS version 6 satellite measurements following the approach described by Pommrich et al (2014).…”

“…This allows the origin of the air masses and the detailed transport pathways from Asian source regions into the northern lower stratosphere to be quantified. Further, in CLaMS the irreversible part of transport, i.e., mixing, is controlled by the local horizontal strain and vertical shear rates with mixing parameters deduced from observations , and references therein) and therefore allows mixing processes in the lower stratosphere, as shown in several previous studies, to be characterized (e.g., Pan et al, 2006;Vogel et al, 2011b;Konopka and Pan, 2012). Small-scale structures, indicating the impact of young tropospheric air masses within the lower stratosphere measured during the TACTS/ESMVal aircraft campaign in September 2012, are compared with results of CLaMS model simulations to identify their origin and the associated transport pathways.…”

Airborne limb-imaging measurements of temperature, HNO&lt;sub&gt;3&lt;/sub&gt;, O&lt;sub&gt;3&lt;/sub&gt;, ClONO&lt;sub&gt;2&lt;/sub&gt;, H&lt;sub&gt;2&lt;/sub&gt;O and CFC-12 during the Arctic winter 2015/2016: characterization, in situ validation and comparison to Aura/MLS

“…The UTLS is challenging to observe. Isentropic mixing in this region happens via very long filaments with small vertical and horizontal extent (Konopka and Pan, 2012). This requires a large horizontal coverage on the one hand and high spatial resolution on the other hand.…”

Filamentary structure in chemical tracer distributions near the subtropical jet following a wave breaking event

“…The formation of the observed structure involves both advection and mixing (e.g. Konopka and Pan, 2012). In this case, small-scale processes such as turbulent mixing induced by the shear and strain in the flow, are also expected to contribute to the observed structure, which can be diagnosed using tracer-tracer relationships.…”