# Hailstorm Detection by Satellite Microwave Radiometers
## 2 Data Selection
\begin{table}
\begin{tabular}{l c c c c c c} \hline \hline
**Location** & **Date** & \begin{tabular}{c} **Latitude** \\ **(deg)** \\ \end{tabular} & \begin{tabular}{c} **Longitude** \\ **(deg)** \\ \end{tabular} & \
\begin{tabular}{c} **Overpass Time** \\ **(UTC)** \\ \end{tabular} & **SatID \({}^{*}\)** &
\begin{tabular}{c} **Hail Size** \\ **(cm)** \\ \end{tabular} \\ \hline U.S. (Colorado, & & & & & & \\ N. Mexico) & 9 May 2017 & 30.00–45.00 N & 115.00–95.00 W & 0337 & MOA & 3.5 \\ \hline U.S. (Minnesota, & & & & & \\ N. Dakota) & 10 Jun 2017 & 40.00–50.00 N & 110.00–83.00 W & 0237/ & MOA/ & 3.5 \\ Bulgaria (Sofia) & 8 Jul 2014 & 42.00–43.00 N & 22.00–23.50 E & 1337 & N18 & 7.0 \\ Bulgaria (Montana District) & 8 Jul 2014 & 43.00–44.00 N & 23.00–24.00 E & 1928 & MOA & 4.0 \\ Germany (Reutlingen) & 28 Jul 2013 & 48.00–50.00 N & 08.00–11.00 E & 1427 & N18 & 5.0 \\ U.S. (S. Dakota, & & & & & \\ Vivian) & 23 Jul 2010 & 43.00–49.00 N & 104.00.96.00 W & 2254 & N15 & 11 \\ Argentina (Viale Entre Rios) & 7 Sep 2009 & 35.00–30.00 S & 63.00–55.00 W & 0753/ & N15/ & 12 \\ \hline Bosnia-Herzegovina (Gorazde) & 19 Jun 2007 & 43.67–43.71 N & 18.94–18.98 E & 1927/ & MOA/ & N17 & 8.0 \\ U.S. (S. Dakota, & & & & & \\ Charles) & 21 Aug 2007 & 39.00–43.00 N & 104.00–95.00 W & 227/ & N16/ & 14 \\ \hline Argentina (Colonia Liebig’s) & 13 Nov 2007 & 29.00–26.00 S & 60.00–53.00 W & 2045/ & N16/ & 11 \\  & & & & & & N15 & \\ \hline  & & & & & & \\ \end{tabular} \({}^{*}\) MOA,B Metop A,B N15,16,17,18 NOAA15,16,17,18.  
\end{table} 
Table 1: List of the hailstorms used in the study. Figure 1: Brightness temperature distribution along transects crossing the main core of the storm for the analyzed case studies: (**a**) Bosnia-Herzegovina (2018 UTC); (**b**) Bulgaria-Sofia (1337 UTC); (**c**) Bulgaria-Montana (1928 UTC); (**d**) Germany (1427 UTC); (**e**) S. Dakota-Vivian (2254 UTC); (**f**) S. Dakota-Charles (2341 UTC); (**g**) Colorado-N. Mexico (0337 UTC); (**h**) Minnesota-N. Dakota (0110 UTC); (**i**) Argentina-Viale (1239 UTC); (**j**) Argentina-Liebig (2136 UTC). TBs at all frequencies in Figure 1 decrease when approaching the storm core showing high sensitivity to the hail scattering. The contribution by all channels is well differentiated showing different sounding capabilities with respect to the storm intensity (Figure 1a-d). In particular, the 90 GHz channel exhibits high TB with respect to the ones at 150 and 190 GHz possibly indicating low sensitivity to small hailstones. On the contrary, the same frequency triplet strongly reduces the signal when observing hailstorms over the US Great Plains and AR (Figure 1e-j). The intense convections over S. Dakota (Vivian and Charles) largely impact on the MHS measurements by reaching very low values when approaching the storm core: TB90\({}_{\text{min}}\) = 114.31 K, TB150\({}_{\text{min}}\) = 107.67 K, TB184\({}_{\text{min}}\) = 124.07 K, TB186\({}_{\text{min}}\) = 114.53 K, and TB190\({}_{\text{min}}\) = 107.78 K. TB minima for the AR hailstorms (Viale and Liebig) are quite low: TB90\({}_{\text{min}}\) < 140 K, TB150\({}_{\text{min}}\) < 130 K, TB184\({}_{\text{min}}\)\(<\) 160 K, TB186\({}_{\text{min}}\) < 150 K, TB190\({}_{\text{min}}\) < 130 K. Given the importance of defining the impact of hail on the nominal signal to the satellite and then identify a TB interval where hailstorms can be delineated, on the basis of values listed in Table 1, two classes of hail diameters were considered. For each class the average values of TB minima allow to specify the maximum impact of hail diameters (d) on the MHS frequencies. Results are displayed in Table 2. As expected, large hail is often associated with lower TB values than smaller hail. All channels exhibit high sensitivity to the scattering by hail showing large TB reductions from smaller to larger hail.