## 4 Results and Discussion
### SM-LST Relationship at the Seasonal Scale  
The correlation of in situ SM at the SMOS morning passes and \(T_{max}\) from the REMEDHUS network for each season is shown in Figure 8 (left). Note that the strongest anticorrelation is obtained in autumn (September-October-November, SON) with R \(\approx-0.68\) in median, followed by spring (March-April-May, MAM) with R \(\approx-0.51\), and summer (June-July-August, JJA) with R \(\approx-0.48\). Hence, the strongest SM-LST relationship is observed in transitional seasons (i.e., autumn and spring) because the SM is sufficiently dynamic to affect air temperature, and also LST. This result agrees with those obtained in [60], where the SM-air temperature coupling was shown to be higher in transitional zones between wet and dry climates. However, a low correlation is obtained in winter (December-January-February, DJF) with R \(\approx+0.30\). This suggests that SM and LST are not coupled during winter. This could also explain the low performance of disaggregated SM products based on soil evaporation efficiency models in winter [33]. Figure 8 (right) shows the correlation of ground-based SM anomaly at the morning passes and \(T_{max}\) anomaly for each season. A low correlation is also observed in winter (R \(\approx+0.27\) in median) and the strongest anticorrelation is obtained in summer (R \(\approx-0.49\)), which is the driest season, followed by spring (R \(\approx-0.43\)) and autumn (R \(\approx-0.31\)). It can be related to the fact that, under very dry conditions, an increase of SM from an individual precipitation event has an important impact on LST, due to its low thermal inertia. Also, since ET is regulated by the SM content under water-limited conditions in summer, the SM increase produces an ET increase and there is enough energy to maintain the high rate of ET until the SM content decreases. Obviously, this effect is less important in wet seasons, specially in winter, due to the lower available energy involved in the ET process and the higher thermal inertia. These results suggest that the annual cycle contains most of the SM-LST relationship  
Figure 7: Normalized occurrence frequency density diagrams of in situ SM at the SMOS morning passes and \(T_{max}\) (**left**), and SMOS SM at the morning passes and MODIS LST Aqua day (**right**). Similar behavior is obtained at the afternoon passes and/or using Terra day. information of transitional seasons, particularly in autumn. By contrast, the anomaly contains most of the SM-LST relationship information during summer. Similar behavior is obtained with emphin situ SM at the SMOS afternoon passes (not shown). Further research is needed to confirm these results in other regions with different climates. The correlation of SMOS SM at the morning passes and MODIS LST Aqua day for each season is displayed in Figure 9 (left). In this case, all correlations are negative, including winter. The anticorrelations sorted from strong to weak are obtained in autumn (R \(\approx-0.69\)), spring (R \(\approx-0.66\)), summer (R \(\approx-0.39\)) and winter (R \(\approx-0.34\)). Thus, the transitional seasons also present the strongest anticorrelation and other seasons the weakest. We hypothesize that differences between in situ and satellite results during winter could be due to the more frequent presence of clouds than during other seasons, which produces a lower coverage and a higher LST uncertainty that could be up to 10 \({}^{\circ}\)C. Another reason may be a side effect of the different spatial scales represented by the remotely sensed data and ground-based data. Figure 9 (right) shows the correlation of the detrended spaceborne time-series. The sorted anticorrelations are obtained in spring (R \(\approx-0.62\)), autumn (R \(\approx-0.61\)), summer (R \(\approx-0.39\)) and winter (R \(\approx-0.26\)). The lowest SM-LST relationship is obtained during winter, in agreement with results of Figure 8 (right). Similar behavior is obtained with the afternoon passes and/or using Terra day (not shown).