# Advances in Simulating Radiative Transfer in Complex Environments
## 3 Results and Discussion
In IVS, dotted patterns of lower longwave radiation values received by the lower hemisphere can be found in Central Park where trees cast shade and, thus, cool the ground below canopies leading to less longwave emission compared to the open surfaces in other park areas. These patterns are still visible in Figure 5b depicting the same results but for a horizontal cut in 82.5 m height. Furthermore, as the cut is performed in an intermediate height--above some low- and medium-rise buildings of the model area--differences in roof type effects can be examined. In IVS, the rather cold--and thereby not emitting much longwave radiation--cool and green roofs stand out against the traditional hotter low-albedo roofs that strongly contribute to the longwave radiation received in 82.5 m height. In AVF with its averaging approach, these different roof surface temperature differences while being simulated to not translate in differences of emitted longwave radiation as their contribution as specific object is not stored individually. Even differences in longwave radiation values caused by trees in Central Park are still recognized by IVS, even though spatial distances between the grid cells in 82.5 m height and the trees at ground level are quite large. While surface temperature mainly drives the emitted longwave radiation patterns, reflected shortwave radiation is influenced by both albedo and shadowing. Figure 6a clearly demonstrates which areas are shaded during 13:00 when the sun's position is in the South--thus being at the model area's left due to its rotation. Figure 6a,b again show less pronounced differences in AVF. Especially the very small range between 90 and 144 W/m\({}^{2}\) at pedestrian level in AVF shows that most parts of the model area are rather homogenously affected by reflected shortwave radiation. The IVS results, however, accurately account for spatial relationships between objects and, thus, the models minimal reflected shortwave radiation of \(<\)5 W/m\({}^{2}\) for shaded areas but very large contributions of reflected radiation in high-albedo spots, for example above open sand at the ballpark in Central Park. Furthermore, when performing a horizontal cut at 82.5 m height, we again find roofs in IVS to show higher values than other parts of the model area in contrast to AVF. However, their higher albedo, green and especially cool roofs now show higher values, as they reflect more shortwave radiation than the traditional low-albedo roofs. By examining these comparisons in Figures 5 and 6, it becomes clear that both longwave and shortwave contributions to a cell's radiation budget are underestimated by AVF. Urban heating caused by traditional building materials as well as cooling performances of cool or green roof application, hence, probably have been underestimated in previous ENVI-met modeling studies [30]. By using the model area average, AVF does not consider shortwave radiation reflections accurately in general, which is proved by two additional examples. It is firstly shown by the comparison of reflected shortwave radiation patterns for the horizontal cut at 82.5 m at 09:00 where the sun's position is in the east coming from the bottom side of the model area (Figure 7a). Since the circular shaped building at the Columbus Circle features glass facades and, thus, works like a magnifying glass, shortwave radiation is reflected from all sides to the center, which leads to a high accumulation in sum. By using IVS, these reflections are accounted for and values of up to 299 W/m\({}^{2}\) amid the circular-shapedbuilding wall at the Columbus Circle are predicted by the model, whereas AVF only shows very low values around 25 W/m\({}^{2}\) here. Secondly, the pedestrian level horizontal cut of shortwave radiation reflections from the upper hemisphere also shows that, in contrast to AVF, IVS takes the reflection of glass facades into account (Figure 7b).