# Elliptical Structures of Gravity Waves Produced by Typhoon Soudelor in 2015 near Taiwan
## 3 Overview of TC Soudelor and Model Validation
### Model Validation
Radar reflectivity isocontours of 20 dBZ and 40 dBZ also show the footprint of the TC asymmetry in rainfall, as well as intense rainfall in the inner core at heights below the freezing level and a rapid decrease in reflectivity across the freezing level indicative of intense melting (not shown). The asymmetry increased as the interaction between the orography and the TC outer core became stronger, in the time before landfall. FormoSat-3/COSMIC RO data are useful for observations of TC events above the ocean as well as the validation of numerical simulations [20; 68; 69; 70; 71]. Vertical profiles of temperature are accurate at <1 K from 5 to 25 km and spatial resolution varyies from 100 m at the surface up to 1.4 km at 40 km heights (1 km at the altitude of tropopause). Figure 7a visualizes the geographic distribution of 13 available FormoSat-3/COSMIC RO profiles during the passage of TC Soudelor at latitudes of 20\({}^{\circ}\)-28\({}^{\circ}\) N and longitudes of 119\({}^{\circ}\)-130\({}^{\circ}\) E on 6 and 7 August 2015. The TC eye was located at the lower right corner of the domain at 00:00 UTC on August 6. In particular, four soundings probed the inner and outer TC core when TC Soudelor was at a distance <400 km off the coast of Taiwan at about 08:30 UTC on 7 August 2015. Potential temperatures with 100 m vertical resolution were computed from the <<wetPrf>> FormoSat-3/COSMIC RO profiles of temperature and pressure, and the vertical background was derived using a fourth-order low-pass Butterworth filter with a 7 km vertical wavelength cutoff. The mean WRF profiles of potential temperature within 1\({}^{\circ}\)\(\times\)1\({}^{\circ}\) area were compared with the collocated FormoSat-3/COSMIC RO profile. Absolute differences in mean potential temperatures were <\(\pm\)4 K in the troposphere at heights <16 km. The amount of water vapor was partly responsible for the large differences in temperature in the lower and middle troposphere. Concerning the LS, large absolute deviations above 22 km height were presumably caused by the top lateral boundary conditions imposed by the NCEP FNL 6-hourly analyses. Indeed, the gradient of NCEP FNL potential temperature was slightly smaller than the WRF one above 19 km height. However, the mean potential temperatures were satisfactorily in agreement at heights \(<\)25 km with a small relative bias \(<\)3%. In this study, the mean profile of FormoSat-3/COSMIC RO potential temperature (Figure 7b) was used to compute the Brunt-Vaisala frequency \(N\) in Equation (1). The mean observational values were \(1.23\times 10^{-2}\) s\({}^{-1}\), \(0.8\times 10^{-2}\) s\({}^{-1}\) and \(2.43\times 10^{-2}\) s\({}^{-1}\) at heights of 3-10 km, 8-15 km and 18-25 km, respectively. Finally, the model reasonably reproduces the dynamical structure of a realistic mature TC as well as its global environment at heights up to 25 km at latitudes of 20\({}^{\circ}\)-28\({}^{\circ}\) N and longitudes of 119\({}^{\circ}\)-130\({}^{\circ}\) E on 6 and 7 August prior to landfall. The effects of the topography on the TC structure were weak on 7 August 12:00 UTC when the TC was at a distance \(<\)200 km from the eastern coast of Taiwan. Thus, taking into account the description of the dynamic and thermodynamic structures of TC Soudelor at 12:00 UTC on 7 August, GWs with vertical wavelengths \(<\)7 km were examined at three different vertical layers: the middle of the TC (3-10 km), the upper part of the TC (8-15 km) in the troposphere and LS (18-25 km). Figure 6: Longitude-height cross sections of simulated (**a**) tangential wind speed (m/s) and isocontours (white) every 10 m/s, (**b**) radial wind speed (m/s) and isocontours (white) of \(\pm\)15 and 20 m/s, (**c**) equivalent potential temperature \(\theta_{e}\) (K) and isocontours (white) every 6 K at the latitude 23\({}^{\circ}\) N on 7 August 12:00 UTC. (**d**) Radial-height cross section of temperature anomalies (color shaded, K) and isocontours (white) every 2 K east of the TC center.