# Implications of GNSS-Inferred Tropopause Altitude Associated with Terrestrial Gamma-ray Flashes
## 3 Analyses and Results
### Thermal Structure of TGF-Producing Thunderstorms  
To investigate the thermal structure associated with TGF production, the TGF-related tropopause structure in temperature profiles during the period of 2006-2019 for the NH extra-tropics, tropics, and SH extra-tropics over continent and ocean are shown in Figure 4. The density distribution of observed temperatures is binned in 100 m for altitude and 0.5 \({}^{\circ}\)C for temperature. The temperature typically decreases steadily up to about 17 km, with a sharp transition in the tropics and milder ones in the subtropics. Figure 3: Box-and-whisker plot for monthly tropopause anomaly (km) from 2006 to 2019 for three latitude bands: (**a**) the Northern Hemisphere (NH) subtropics, (**b**) the tropics, and (**c**) the Southern Hemisphere (SH) subtropics. The vertical lines extend to the 5% and the 95% percentiles. The boxes extend from the 25% to the 75% percentiles, with a horizontal line at the median values. Blue, red and black texts indicate the grid samples of the monthly mean TGF-related tropopause altitude over the ocean, land, and globe, respectively. Note that the NH and SH annual cycles are offset by 6 months. Different from previous studies which show a higher tropical tropopause altitude and a lower subtropical one [28], the tropopause altitude over continent for the tropical TGF-producing thunderstorms (16.6 km) is slightly lower than that in the subtropics (>16.6 km), while those approximating to the oceanic tropical TGFs are higher than the subtropical ones. The standard deviations of the tropopause and the corresponding temperature are about 0.7 km and 15 \({}^{\circ}\)C in the tropics, while those increase up to 1.1 km and 17.5 \({}^{\circ}\)C in the subtropics, with the highest variabilities in the SH subtropical ocean. In the tropics, there is no significant difference in the average temperature profiles between continent and ocean, but with a 1 \({}^{\circ}\)C colder and 0.1 km higher tropopause over land than ocean. In the subtropics, the temperature is 2-3 \({}^{\circ}\)C higher in the middle and lower troposphere for the continental TGF thunderstorms, leading to a 0.5-0.6 km higher \(-\)20 \({}^{\circ}\)C-level and 0.8 km higher \(-\)40 \({}^{\circ}\)C-level than the ocean. In the tropopause region, the TGF storms have a colder and higher tropopause over land than ocean. This indicates a stronger latent heat release and a stronger cloud top outflow divergence for the continental TGF-producing storms. The largest difference in the tropopause structure between land and ocean occurs in the SH subtropics, with a 1.5 km higher and 10 \({}^{\circ}\)C colder tropopause. Figure 4: Density distribution of observed temperatures from 2006 to 2019 as a function of altitude from GNSS-RO observations co-located with TGFs (**left:** a**,**c**,**e**) over land and (**right:** b**,**d**,**f**) over ocean in the (top) Northern Hemisphere subtropics (20\({}^{\circ}\) N–45\({}^{\circ}\) N), (middle) tropics (20\({}^{\circ}\) S–20\({}^{\circ}\) N), and (bottom) Southern Hemisphere subtropics (20\({}^{\circ}\) S–45\({}^{\circ}\) S). In both left and right panels, the average profiles for land (red lines) and ocean (yellow lines) are superimposed. Thick horizontal lines represent the mean primary tropopause altitude in each case, with the dashed lines showing its standard deviation. Units are parts per ten thousand. The positive charge layer is thought to lie above the \(-40\)\({}^{\circ}\)C-level, while the negative charge layer generally occurs between the \(-20\)\({}^{\circ}\)C and \(-40\)\({}^{\circ}\)C levels [45]. The larger spacing (0.2-0.3 km) between \(-20\)\({}^{\circ}\)C and \(-40\)\({}^{\circ}\)C levels over land in the subtropics indicates that there might be more room for the development of negatively charged cloud region. Whether this feature will lead to a more extensive main negative cloud region in the thunderstorm merits further investigations.