# Implications of GNSS-Inferred Tropopause Altitude Associated with Terrestrial Gamma-ray Flashes
## 4 Discussions and Conclusions  
In this study, we use the instantaneous observations from various TGF detectors (FERMI GBM, RHESSI, and _Insight_-HXMT) and GNSS-RO (SAC-C, COSMIC, GRACE, TerraSAR-X, and MetOp-A) to improve our understanding on the thermal structure associated with the production of TGFs. We used the combined observations of TGF location and temperature profile to identify the altitude of 1917 TGF-related tropopause cases. The main conclusions are summarized as follows:  
1. The TGF-associated tropopause altitudes exhibit a similar geographical distribution over the global scale and seasonal characteristics to the climatology. The regionally averaged tropopause altitude over the Caribbean Sea is 0.1-0.4 km lower than the climatology, and that over the African continent is slightly (\(\leq\)0.1 km) lower than the climatology. The regional tropopause altitudes over the Asian Monsoon are 0.1-0.2 km higher than the climatology. Most of the tropopause altitudes associated with the TGFs are slightly higher than the climatology, while some of them have a slightly negative bias. 2. There is no significant land-ocean difference in the thermal structures for the tropical TGF-producing thunderstorms. In the subtropics, the tropospheric temperature was warmed over land, with a 0.5-0.6 km higher \(-\)20 \({}^{\circ}\)C-level and 0.8 km higher \(-\)40 \({}^{\circ}\)C-level. Meanwhile, the continental TGF-producing thunderstorms have a colder and higher tropopause than the ocean. 3. During the boreal summer season, the TGF-associated tropopause altitudes in the Asian Monsoon region are considerably higher (by about 1.4 km on average) than the Caribbean area, while whether this will lead to a higher incidence rate of TGFs relative to lightning still depends on the altitude of major charge regions of parent thunderstorms. 4. The TGF-producing thunderstorms are characterized by a cold anomaly in the middle (around 7-9 km) and upper troposphere (around 15 km) and tend to have stronger anomalies than deep convection found in previous studies. There is a slightly high incidence rate of double tropopause associated with the TGFs in the tropics, with some higher primary tropopause altitudes and some lower ones. The higher tropopause situations probably result from reduced stability in the lower stratosphere related to the situation of double tropopause, which may facilitate the occurrence of deep convection [46]. Meanwhile, the lower examples may result from the cooling of upper troposphere associated with the convective cloud top [28; 47]. These partly indicate the relationship between deep convection and TGF occurrence, which suggests that deep convection provides favorable conditions for TGF production. From a regional perspective, the TGF-related tropopause over the Asian Monsoon region is 0.2 km higher than the climatology for the same region. Meanwhile, the region surrounding the Tibetan Plateau has a higher altitude for the \(-\)20 \({}^{\circ}\)C and \(-\)40 \({}^{\circ}\)C levels (more than 0.3 km and \(\sim\)1 km, not shown). These raised levels are associated with the Monsoon anticyclone, which is a dynamical response to the Asian monsoon convective heating from late spring to early fall [48; 49]. The spacing between the \(-\)20 \({}^{\circ}\)C and \(-\)40 \({}^{\circ}\)C levels is larger over continents than ocean in the subtropics and indicates a longer distance between the layered charge regions, which accomplishes a favorable condition for TGF production [20]. In addition, the TGF-producing thunderstorms have a cooler temperature than other deep convection in the middle and upper troposphere [27; 28]. The colder environment gives rise to higher concentrations of cloud ice and precipitation ice, which could be a prevalent condition conducive to TGF production [17]. The coordinated ground-based observations with respect to TGF-associated lightning are crucial for examining the physical connection between individual TGFs and their parent lightning [11; 50; 51].