## 3 Results
### Sample Dates  
#### 3.1.1 Weather Analysis  
In order to provide a detailed description of the cluster classification results, three different sample dates were randomly selected. These dates are 1 August 2011 (austral winter), 4 January 2014 (austral summer) and 12 October 2016 (austral spring). Prior to analyzing the configuration of each cluster it is appropriate to describe at least the more prominent features of the CC that can be seen in the original \(T_{b}\) images for these dates. An exhaustive analysis is however beyond the scope of the present work. Figure 7 shows the original \(T_{b}\) monochromatic images on these three sample dates along with the corresponding colored \(T_{b}\) values. It also shows the CTHs on 1 August 2011. The poleward edge of extensive shields of cirrus clouds (Cis) generally outlines the anticyclonic curvature of the upper tropospheric jet (UTJ) [20]. Such a structure is clearly visible in Figure 7a with Cis in tones corresponding to colder T\({}_{\rm b}\) values approximately located over Southern Brazil and the Atlantic. As shown in Figure 7b, these clouds have T\({}_{\rm b}\) values of approximately 210-220K in the area, in correspondence with CTHs close to 14 km (Figure 7c), and in turn in agreement with the location of the tropical tropopause in connection with the so-called upper tropospheric \"subtropical front\" found at these latitudes [65]. Mounted on a mid-latitude wavetrain, a frontal zone can be easily identified over the southern tip of SA, and there are visible signs of a cut-off circulation north of this front over central  
Figure 7: Monochromatic brightness temperature (T\({}_{\rm b}\)) as calculated from the original IR images (left) and colored T\({}_{\rm b}\) values in Mercator projection (right) for: (**a–c**) 1 August 2011, (**d,e**) 4 January 2014 and (**f,g**) 12 October 2016. Plate (**c**) shows the cloud top heights (CTHs) that correspond to Figure 2a,b. Blank CTH pixels that do not match their colored T\({}_{\rm b}\) counterparts are negative and were excluded. See text for further details. Argentina. Middle-to-high clouds seem to dominate in both of these two cloud systems. Even though Southern SA is under the influence of frontal activity all year round [66], generally speaking winter fronts are typically stronger due to an equatorward advance of baroclinicity, whose main driver is related to a strengthening of UTJs during the season across the entire SH [67]. Frequently associated to cyclogenesis [68], UTJs are more generally connected to the maintenance of the storm tracks due to their baroclinicity [69]. Figure S2 shows the geopotential height at ten different levels from 850 (lower troposphere) to 100 hPa (lower stratosphere) along with the wind field and the kinetic energy on 1 August 2011. It shows the presence of an UTJ, with maximum strength at 200 hPa in the leading part of an upper-level trough that is in a \"tear-off\" stage over central Argentina. In lighter grey tones in Figure 7d, another frontal structure in a northwest-by-southeast position can be seen as a cloud band stretching from the east of the Ande--where several convective systems can be seen in the foreground--towards the South Atlantic. The T\({}_{\rm b}\) values of the convective cells located in North-Western Bolivia and Eastern Brazil were around or below 210 K; convective-related clouds were also visible over Paraguay (Figure 7e). This cloud arrangement is characteristic of summer and is linked to an area of moisture flux convergence [70]. In fact, the region is associated to the local minima of outgoing longwave radiation where the well-known South Atlantic convergence zone (SACZ) develops as a result of the cold fronts reaching the region becoming stationary there ([71] and references therein). The south-easternmost tip of the cloud structure that sits along the SACZ spirals cyclonically (i.e., clockwise in the SH) well over the South Atlantic and bears a strong resemblance with an occlusion in line with the circulation features of the region [66].