## 5 Numa Observations by GPM
### AMSR2 and GMI Brightness Temperature Analysis
Specifically, at 00:51 UTC an area of high TBs is found in correspondence of the outer rainfall structures in the northern sector of the cyclone, extending to the Calabria region (visible as an area of slight TB depression over land compared to the background), while at 11:55 UTC, this area is part of the main rainband around the cyclone center, hitting the coast of Salento in Southern Apulia region. Figure 7: Brightness temperature measured at 37 GHz V-pol channel for four overpasses by GMI and AMSR2 radiometers over Numa. (**a**) GMI on 16 November at 13:49 UTC, (**b**) AMSR2 on 17 November at 00:51 UTC, (**c**) AMSR2 on 17 November at 11:55 UTC, and (**d**) GMI on 18 November at 03:59 UTC. The absence of areas of significant TB depression at 37 GHz might be due to one or a combination of the two following factors: (1) the absence of high amounts of large high density ice particles, that significantly scatter the upwelling radiation at 37 GHz; (2) the low spatial resolution of the 37 GHz channels, that cannot distinguish small convective cores. An ambiguity at this frequency comes between the regions of precipitation with no significant contribution of the ice to the scattering (optically thin clouds), and the regions of strong precipitation and significant ice scattering (optically thick clouds). The ambiguity is solved looking at the other channels. For example, maps of TBs at 10 and 19 GHz (not shown), mostly affected by the emission from the rain layers, can be more directly related to rainfall intensity (especially at 10 GHz in Rayleigh regime) with higher values of TBs generally associated with heavier rainfall. However, since they are available at lower spatial resolution (\(24\times 42\) km\({}^{2}\) and \(14\times 22\) km\({}^{2}\) for AMSR2, at 10 GHz and 19 GHz respectively), they do not allow to depict clearly the rainband structure. The TBs measured by GMI and AMSR2 at 89 GHz (V polarization) are shown in Figure 8, along with the LINET strokes registered within 1 h around the time of the overpass. At this frequency water vapor emission increases the TB background values. In correspondence of the clouds, the upwelling  
Figure 8: Brightness temperature measured at 89 GHz V-pol channel for four overpasses of Numa by GMI and AMSR2 radiometers. (**a**) GMI on 16 November at 13:49 UTC; (**b**) AMSR2 on 17 November at 00:51 UTC; (**c**) AMSR2 on 17 November at 11:55 UTC; (**d**) GMI on 18 November at 03:59 UTC. The strokes registered by LINET in one hour interval around the time of the overpass, within a 200 km radius circle from the position of the eye (indicated by a black \(\times\)), are also shown as black crosses. radiation is affected by the emission of cloud liquid water, which tends to further increase the TBs, and by the scattering by the ice hydrometeors (mostly those found in the convective regions) visible as areas of higher or lower TB depression (e.g., [50]). In the development stage, captured by the GMI overpass on 16 November (Figure 8a), most of the clouds in the outer rainbands show significant TB depression compared to the background. The TBs as low as 158 K in the southern portion of the rainband (35.23\({}^{\circ}\)N, 19.07\({}^{\circ}\)E) suggest the presence of strong convective activity [51; 52; 53], associated with significant amounts of ice, presumably either heavily rimed ice or high density graupel. On the other hand, in the two AMSR2 images on 17 November (Figure 8b,c), the area surrounding the cyclone center, exhibiting a symmetric rainfall structure at 37 GHz, does not show any scattering signal (a ring of higher TBs in correspondence of the eyewall is evident in Figure 6c), indicating that rainfall mostly originates from warm rain processes. Scattering signal is evident in some regions of the outer rainbands in the AMSR2 overpasses, including the significant TB depression area over the Ionian Sea and over Calabria region at 00:51 UTC, and over the coast of Salento region at 11:55 UTC.