Analysing mixing processes in tomographically imaged filaments of Asian Monsoon outflow during the PHILEAS campaign using computer vision

The Asian summer monsoon (ASM) is one of the most important events of the northern winter hemisphere. It represents an effective pathway of tropospheric air originating from the south-Asian continent into the upper troposphere (UT), which is to date only partially understood and quantified.

Through Rossby wave breaking events large filaments of ASM air are transported westward into the mid-latitudes, where they are mixed into the lower stratosphere (LS). The composition of the UTLS, especially with respect to radiatively active trace gas species, is a key factor for the global climate, which the ASM affects directly.

During the PHILEAS (Probing High Latitude Export of Air from the Asian Summer Monsoon) campaign in later summer 2023 a filament of ASM outflow was measured with the airborne limb imager GLORIA on board the German research aircraft HALO on two consecutive days. The edge of the filament was imaged in 3-D during the first flight and its outflow based on CLaMS trajectory calculations was revisited inside a second 3-D retrieval on the following day. The chemical composition of the filamented air was measured in the five different trace gas species water vapor, ozone, peroxyacetyl nitrate (PAN), nitric acid and carbon tetrachloride with unprecedented 3-D spatial resolution unique to the GLORIA instrument. The filament contains a strong tropopause fold, which perturbs its dynamical structure.

We present the tomographic retrievals of the matching flights. We are able to identify the different types of air from their chemical composition using a novel classification method based on mixture models, and are able to resolve the spatial structure of both the filament and the mixing process on the mesoscale. By revisiting the outflow of the filament we are able to directly measure the change in chemical composition and are able to determine and quantify the different possible pathways during mixing. We are able to uniquely link the different types of air to different regions of origin.

GLORIA is an airborne demonstrator for the European Space Agency Earth Explorer 11 candidate CAIRT, currently selected for Phase A. GLORIA observations offer an outlook on how exploring global processes in the UTLS would be possible using CAIRT.