S3.3 Figure 3/4 Expanded Explanation of Moisture Source Tracers
Fig. 3 of the main text demonstrates the moisture source diagnostic that post-processing of the VSD tracers yields. To produce Figure 3, the footprint of a January 2021 South Pacific AR was used to create two masks – one at ARgenesis, one as the AR hits Chile on 30 January. Next, the 144 VSD tracers within this mask are averaged for only 6 hours on January 21 during ARgenesis (Fig. 3a) and for 6 hours on January 30 (Fig. 3b) – the times when this actual AR occurred. Next, we solve for the source concentration of moisture consistent with the 144 VSD tracers within this mask at those two times by leveraging the fact that the concentration of these tracers during surface evaporations are spherical harmonics basis functions.
For climatology, the 144 VSD tracers within the two pink masks are averaged for every day in January of 2018, 2019, 2020, 2021, and 2022. Next, we solve for the source concentration of moisture consistent with the 144 VSD tracers within these two (a and b) masks. Figure 3c and 3d are that resulting climatology solution minus the AR solution of Figure 3a and 3b respectively. This figure may thus be interpreted as contrasting the climatological moisture (brown shades) from AR moisture (blue shades).
Fig. 3a and 3b shows blue contouring trailing the pink outline, sourcing moisture from upstream and equatorward, particularly in 3b when the AR is mature. Fig. 3b and 3d put this moisture source in context of climatological moisture source for these two AR footprints (pink outlines).
Fig. 4 of the main text has repeated the process for Fig. 3 for each of the ~7500 ARgenesis footprints.