Quantification of inmixing of Asian Monsoon air by multi-species classification in a match flight experiment

Mixing of air between compartments of the atmosphere is fundamental to atmospheric composition. Such mixing is commonly studied using tracer-tracer correlations. We generalize this approach by statistical classification methods using several tracers to quantify mixing. This paper presents a matching flight-experiment of a filament of Asian monsoon air in the Upper Troposphere/Lower Stratosphere (UTLS) off the Alaskan coast by two flights of the High Altitude and Long Range research aircraft (HALO) conducted during the “Probing High Latitude Export of air from the Asian Summer Monsoon (PHILEAS)” campaign. The 3-D structure of the filament was revealed by tomographic observations by the Gimballed Limb Observer for Radiance Imaging of the Atmosphere (GLORIA) of five trace species. The observed tracer mixing ratios show evidence for a tropopause folding linked to a Rossby wave breaking event. Using a Gaussian mixture model to cluster our observations by similarity we identify five classes of air masses: tropospheric air (both continental and maritime), Asian Summer Monsoon outflow (ASMO), mixed air and stratospheric air. Trajectory calculations are carried out to identify air masses which are observed in both flights.
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The unique 3-D observations allow us to reveal the spatial structure of the mixing processes. Particularly, mixing of ASMO air directly with stratospheric air and into the UTLS are shown. Comparing the classification to simulated artificial surface-origin tracers in the Chemical Lagrangian Model of the Stratosphere (CLaMS), we find strong evidence for distinctly correlated air masses to originate within different source regions within the Asian monsoon region.