## 5 Numa Observations by GPM
### AMSR2 and GMI Brightness Temperature Analysis  
In Figures 7 and 8, the maps of 37 GHz and 89 GHz TBs for four overpasses by AMSR2 and GMI radiometers over Numa are shown. These two radiometers provide measurements at the highest spatial resolution available in the GPM constellation (\(\sim\)5 km at frequencies \(>\) 85 GHz) and are able to depict the precipitation structure with much more detail compared to other MW radiometers [26]. Moreover, the sequence of GMI and AMSR2 measurements and the comparable spatial resolution at each frequency between the two radiometers allow analyzing the evolution of the precipitation at different stages of the storm development. The 37 GHz channel is particularly suitable for the detection of precipitation because TBs are affected by the combined effect of the emission from the rain layers and the scattering from solid-phase hydrometeors, usually associated with intense updraft (e.g., [PERSON] et al. [49]). Over the sea, in most cases (except in presence of deep convection), precipitation areas appear as regions of high TBs compared to the radiatively cold background surface because the emission by the rain layers dominates the scattering effect at this frequency. Over the land, the emission signal by the surface tends to mask the emission signal by the rain layers. Therefore only heavy precipitation is visible as areas of larger or smaller TB depression. Such depression, which depends on the effect of the scattering on the upwelling radiation, is mostly due to large and dense ice particles found in the convective cores. In Figure 7, it is evident how the 37 GHz channel, at spatial resolution around \(7\times 12\) km\({}^{2}\) and \(8.6\times 14\) km\({}^{2}\) for AMSR2 and GMI respectively, depicts quite well the location and structure of the rain bands, visible as areas of warmer TBs with respect to the background. The variability of the TB values across the different rainbands originates from the combined contribution of the liquid and frozen hydrometeors within the cloud. Comparing the different panels, it is possible to see that the precipitation structure has changed throughout the storm evolution. The first GPM-CO overpass on 16 November at 13:49 UTC occurs when the storm is at its development stage, more than 200 km off the  
Figure 6: Temporal evolution of hourly total lightning (magenta line) and mslp minimum (black line) as a function of time. coast of Sicily and Calabria regions (Figure 7a). At the initial phase the cyclone center is hardly visible, surrounded by a whirling rainband with higher TBs at 37 GHz (up to 260 K) in north/northeastern sector and lower TBs (around 230 K) in the southern sector. The outer rainband extends from the north to the south, on the east side of the cyclone center, while other areas of scattered precipitation extend to the north reaching Southern Italian coastal areas. A wide well-defined eye is visible in both AMSR2 overpasses, on 17 November at 00:51 UTC and at 11:55 UTC, and it becomes narrower and well defined in the GMI overpass on 18 November at 03:59 UTC (Figure 7b-d). The difference of the AMSR2 image at 11:55 UTC (Figure 7c) with respect to the MODIS image shown in Figure 1a is worth noting. AMSR2 shows that the rainfall structure is organized and axisymmetric around the cyclone center, as opposed to the upper level clouds which do not show evidence of a well-defined cloud-free eye. On 17 November, the AMSR2 maps at 37 GHz show that the cyclone center moves from 38.5\({}^{\circ}\)N 18.5\({}^{\circ}\)E to 39\({}^{\circ}\)N 18\({}^{\circ}\)E (-70 km) in 12 h, while areas of higher TBs with values around 260 K are found mostly in the northern sector of the storm, over the Ionian Sea.