## 4 Results and Discussion
### Fitting Parameter Comparison  
The fitting parameters allow a quantitative intercity comparison of different SUHI features. We will show the footprint area Ar61%, magnitude a0, orientation angle \(\varphi\), and central location (x\({}_{0}\), y\({}_{0}\)) as mean values and standard deviations (std) computed over the years 2003-2016. In the figures below, the seasonal behavior (summer/winter) and the diurnal variation (10:00, 14:00, 22:00, and 02:00) are reported for each city. Figure 7 shows Ar61%. For BG and CM, the footprint area during daytime is greater than during nighttime, without significant seasonality differences. In addition, the two daytime values (10:00 and 14:00) are similar, as are the two nighttime ones (22:00 and 02:00). The std values suggest a moderate parameter variability across the years. As pointed out previously, the parameters for NR daytime, KK summer daytime, and UR winter nighttime were not evaluated. As expected, the three smallest cities (UR, KK, and UT) exhibit smaller Ar61% footprints. The increased nighttime area of UR and KK reflects the behavior described in Section 4.1. Figure 6: SUHI (\({}^{\circ}\)C) and Gaussian fitting during 2014 for Ubon Ratchathani (UR), Khon Kaen (KK), and Udon Thani (UT) for summer and winter, considering the diurnal variation at 10:00, 14:00, 22:00, and 02:00. Figure 8 shows the mean magnitude a0 over the 14 years. All the cities demonstrate a cooling effect at nighttime. The SUHI magnitude during daytime is always higher than at night, again without seasonality differences. The nighttime mitigation of SUHI is evident for BG and CM. Indeed, as for UR and UT, the winter daytime a0 can be greater than the summer one. This is mainly ascribed to the winter cooling effect of the rural buffer, which exerts a consequent increasing of the SUHI (Equation (1)), even if the winter urban LST is lower than in summer. The magnitude peak is reached at 14:00 in BG with 6.5\({}^{\circ}\)C both in summer 2012 and in winter 2011. For all the cities, the a0 results at 14:00 confirm an interesting phenomenon discussed in [38]. Daytime SUHI magnitude generally increases as the background LST rises, showing an intensity peak at 14:00. When background LST increases from 10:00 to 14:00, the urban area absorbs more radiation compared to near rural areas, and urban LST experiences a faster increase than the rural surroundings. The a0 results also point out the different underlying mechanisms between day and night SUHI, as discussed later, considering that the background LST is more correlated to daytime SUHI compared to nighttime, as proved in [38]. Figure 8: Intercity comparison of Gaussian magnitude a0 (\({}^{\circ}\)C) during summer (**upper panel**) and winter (**bottom panel**); a0 is averaged over the 14 years, considering the diurnal variation at 10:00, 14:00, 22:00, and 02:00. The black bar is the standard deviation across the years. Figure 7: Intercity comparison of Gaussian footprint area Ar61% (km\({}^{2}\)) during summer (**upper panel**) and winter (**bottom panel**). Ar61% is averaged over the 14 years, considering the diurnal variation at 10:00, 14:00, 22:00, and 02:00. The black bar is the standard deviation across the years. Mean and std of orientation angle \(\varphi\) are reported in Figure 9. This parameter depicts the layout of the Gaussian footprint in each map. The results highlight how the orientation keeps the same behavior for both the seasons, but exhibits differences between daytime and nighttime for some cities. For instance, the daytime footprint orientation of BG is about \(65^{\circ}\) (i.e., along the NE-SW quarters) and follows the urban area constituted by residential and commercial zones, distinctly deployed in the NE-SW quarters [28; 39]. These urban features, combined with the traffic congestion in the road network due to intense human activities, generate for BG the significant daytime SUHI pattern, both in summer and winter.