## 3 Results
### Seasonal Features
\begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline  & \multicolumn{4}{c}{\(\rm T_{b}\) (K)} & \multicolumn{4}{c}{CTH (km)} \\ \cline{2-9} Season & \multicolumn{4}{c}{Mean} & \multicolumn{4}{c}{Mean} \\  & \multicolumn{4}{c}{(SD)} & \multicolumn{4}{c}{(SD)} \\  & **\#1** & **\#2** & **\#3** & **\#4** & **\#1** & **\#2** & **\#3** & **\#4** \\ \hline \hline \multirow{2}{*}{**Summer**} & 233 & 259 & 280 & 284 & 11.07 & 6.37 & 2.68 & 1.64 \\  & **(10)** & **(7)** & **(5)** & **(4)** & **(1.66)** & **(1.28)** & **(0.69)** & **(0.57)** \\ \multirow{2}{*}{**Autumn**} & 230 & 255 & 280 & 284 & 11.34 & 6.82 & 2.70 & 1.61 \\  & (9) & (8) & (6) & (5) & (1.52) & (1.35) & (0.72) & (0.55) \\ \hline \multirow{2}{*}{**Winter**} & 232 & 261 & 279 & 279 & 10.43 & 5.39 & 2.06 & 1.40 \\  & **(10)** & **(10)** & **(5)** & **(6)** & **(1.51)** & **(1.27)** & **(0.57)** & **(0.54)** \\ \multirow{2}{*}{**Spring**} & 231 & 256 & 279 & 284 & 10.47 & 5.98 & 2.56 & 1.45 \\  & (10) & (9) & (5) & (6) & (2.06) & (1.38) & (0.67) & (0.49) \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Seasonal brightness temperature (\(\rm T_{b}\)) grand-time means and standard deviations (SDs, in round brackets) for clusters (#) 1–4. indices both on a grand-time seasonal basis and for the entire period, i.e., disregarding season or year. The calculations were carried out using the [PERSON]'s correlation coefficient (\(\rho\)), which acts over the ranks of the pair of correlated variables (rather than over the raw values) and permits establishing whether there exists a relationship between the variables by means of a monotonic increasing or decreasing function [78]. It is worth noting that the method did not disclose the specific functional relationship between the variables, it just assessed the degree of monotonicity. The circulation indices that were chosen for this specific purpose were the Antarctic Oscillation the Dipole Mode Index (DMI) [79], the Madden-Julian Oscillation (MJO) [80] at ten different longitudes, the Pacific Decadal Oscillation (PDO) [81], the Quasi-Biennial Oscillation (QBO) [82] and the Southern Oscillation Index (SOI) [83]. The values of \(\rho\) are presented in Table 4, which only included significant values. The DMI was excluded from the table as the \(\rho\) values resulted as not significant in all cases. Figure 11: As in Figure 10 but for the seasonal frequency distributions. These distributions were prepared including the entire set of 2036 analyzable images. The AAO, otherwise known as the Southern Annular Mode (SAM) [84], has several definitions depending upon the database it is constructed from ([85] and references therein). The AAO monthly time series used here is constructed as the projection of the monthly 700 hPa height field south of 20 \({}^{\circ}\)S onto the leading pattern that results from an Empirical Orthogonal Function analysis using the 700 hPa height over the 1979-2000 period [86]. The leading pattern consists of two components at two different latitudes, namely an arrangement of three centers of action along 45 \({}^{\circ}\)S with one of them extending over Southern SA and the South Atlantic, and anomalies of the opposite sign over Antarctica [87]. The AAO has significant correlations with cluster 2 and with the entropy, in both cases with no signals in any particular season but year-long. The SAM's presence in the troposphere all through the year [88] may explain the reasons why correlations are only significant year-round. The positive \(\rho\) values means that there exists a certain degree of direct association between the AAO signal in cluster 2's number of pixels and in the entropy. The increase (decrease) in the entropy was partly explained by a positive (negative) phase of the AAO. Dynamically, this may be related to the SAM being associated with synoptic transients [89], which tend to create a more disordered troposphere.