# Implications of GNSS-Inferred Tropopause Altitude Associated with Terrestrial Gamma-ray Flashes
## 3 Analyses and Results  
### TGF-Related Tropopause Altitude  
The geographic distribution of the TGF-related tropopause altitude observed by GNSS-RO for four seasons from April 2006 to December 2019 is shown in Figure 2. Four seasons are labeled as DJF for December-January-February, MAM for March-April-May, JJA for June-July-August, and SON for September-October-November, respectively. In DJF and MAM, most of the TGF-related tropopauses are higher than 16.4 km. In JJA, active TGF thunderstorms concentrate in the Asian Monsoon region, Northwest Pacific, and the Caribbean Sea, with much higher tropopause altitudes (>17.6 km) in the Asian Monsoon region. This may indicate that the tropopause altitude is raised for thunderstorms. The TGF-related tropopauses show a similar geographic distribution with the climatological results [28]. In the SON season, most of the TGF-related tropopauses vary in the range from 16 to 17 km, with some lower tropopause (<15.5 km) in the Caribbean Sea and extratropics. It is noted that there are some cases of lower tropopause altitudes in Africa. Figure 1: (**a**) Schematic diagram illustrating the combined observations from FERMI and GNSS-RO. (**b**) Temperature profiles from GNSS-RO at 0916 UTC (red) and radiosonde at 1200 UTC (blue) in approximation to a TGF event which occurred in Kunming, Yunnan at 0916:58.391 UTC on 7 June 2016. Colored arrows denote the locations of primary tropopause altitude calculated using each temperature profile. (**c**) NCEP/CPC merged IR brightness temperature at 0900 UTC on 7 June 2016. The location of TGF event is shown by blue square, radiosonde sounding by green diamond, GNSS-RO event by red circle. The regional averaged tropopause altitude for the TGF events and climatology over Africa, Asian Monsoon Anticyclone, and the Caribbean Sea is shown for each season, with blue (red) texts denoting a higher (lower) TGF-related tropopause altitude than the climatology (black). The averaged TGF-related tropopause altitude over Africa and the Caribbean Sea is 0.1-0.4 km lower than the climatology, whereas that over Asia is 0.1-0.2 km higher. The largest difference between the TGF-related and climatology tropopause occurs over Africa (\(-\)0.1 km) and Asian Monsoon Anticyclone (0.2 km) in JJA, and over the Caribbean Sea in MAM (\(-\)0.4 km). Generally speaking, for the boreal summer season, there are two regions with active TGF productions, namely the Asian Monsoon region and the Caribbean area [22]. As we can see from JJA season in Figure 2, the average TGF-associated tropopause altitude in the Asian Monsoon region is considerably higher than that in the Caribbean (by about 1.4 km). The height of tropopause has a substantial impact on the fluences of gamma-rays detected by satellites [42; 43]. If a higher tropopause is also conducive to the development of main charge layers at higher altitudes in a thunderstorm, TGFs produced by thunderstorms in the Asian Monsoon region are likely to be observed by space-born detectors. In addition, there are some double-tropopause cases (indicated by squares in Figure 2) associated with the production of TGFs (e.g., the events in the tropical Atlantic in DJF), with incidence rates for double tropopause of 7.5%, 6.9%, and 21.4% for the NH subtropics (20\({}^{\circ}\) N-45\({}^{\circ}\) N), tropics (20\({}^{\circ}\) S-20\({}^{\circ}\) N), and the Southern Hemisphere (SH) subtropics (20\({}^{\circ}\) S-45\({}^{\circ}\) S), respectively. The incidence rate of tropical double tropopause is slightly higher than that (<5%) found by [44], while the NH subtropical example is much lower than their results (\(\sim\)20%). Considering the similarity in the geographic distributions of associated TGF tropopause altitudes and climatological tropopause altitudes, we used the tropopause altitude anomaly to quantify the difference between TGF-related tropopause and the climatological examples.