## 3 Results and Discussion of Two Reported Windshear Events
### Windshear Event of 12 February 2024
The simulated three-degree PPI image of Doppler velocity at around 14 UTC does not appear to be similar to the actual observations. An earlier time was selected, namely, at around 13:04 UTC, when the turbulence in the model had already been fully developed (not shown). The simulated PPI image is shown in Figure 5a. It can be seen that 07 LA is located in an area of weaker wind (color brown) between two east-southeasterly jets (yellow to orange). If we trace back carefully, the weaker wind area appears to be related to eastern part of the U-shaped mountains on Lantau Island, namely, the northern part of Yi Tung Shan (location in Figure 1b). This observation is more apparent from the two-dimensional wind field at a height of about 100 m above sea level (Figure 5b). As such, the mountain could have a wake extending to about 7 km downstream to affect the 07 LA runway corridor, resulting in terrain-induced windshear to the aircraft. The simulated EDR plot of the three-degree PPI scan of the central LIDAR is shown in Figure 6a. The EDR map is generally consistent with the actual observations (Figure 3b). It can be seen that the moderate turbulence (colored green) at about the 1 nautical mile region of 07 LA is mostly related to the wake from [PERSON]. The EDR map further depicts the impact of the wake of this mountain on the winds over the 07 LA runway corridor. The simulated six-degree PPI Doppler velocity image of the north runway LIDAR (Figure 6b) does not show reverse flow (colored green) or a wake feature over the 07 LA runway corridor, which is consistent with actual observation (Figure 3a). This shows that  
Figure 3: The graph (**a**) on top is the GLYGA panel for the windshear case of 12 February 2024, and (**b**) is the corresponding EDR map from a three-degree PPI scan of the central LIDAR. All the figures are north–south oriented. the wake of [PERSON] at the 07 LA runway corridor is already rather shallow and does not have a high vertical extent. Figure 4: Graph (**a**) is the Sha Lo Wan wind profile, (**b**) is the RASS virtual temperature, and (**c**) shows selected temperature profiles. Times are in HKT. Figure 5: Graph (**a**) shows the simulated three-degree PPI Doppler velocity image of the central LIDAR, and (**b**) is the two-dimensional wind at a height of around 100 m above sea level. The wake of [PERSON] appears between the two broken straight lines. All the figures are north–south oriented. The simulated headwind profiles at the 07 LA and 07 RA runway corridors are shown in Figures 7a and 7b, respectively. The wake at about 1 nautical mile shows up in the 07 LA headwind profile, but the magnitude of the wake is smaller than actual observations, so the headwind change is smaller in the simulation. The simulated 07 RA headwind profile is quite consistent with the actual observations (Figure 3a), in particular, the southeasterly peak between around 1.5 nautical miles to 2 nautical miles over this runway corridor. Figure 2.0 Graph (**a**) is the simulated EDR map, and (**b**) is the simulated six-degree PPI Doppler velocity image of the north LIDAR. All the figures are north–south oriented. The simulated Sha Lo Wan wind profiler/RASS data are shown in Figure 2.1 Comparing between 13 UTC of simulation and 14 UTC of actual observations, the heights of the southeasterly jet and the downward motion at Sha Lo Wan are reproduced reasonably well in Figure 8a,b. For the virtual temperature, Figure 8c, the shape of the vertical profile is simulated quite well, though the absolute value of the virtual temperature is off from the actual observations by 2 to 3 degrees K.  
Figure 2.2 Graph (**a,b**) are the simulated headwind profiles and detected windshear (marked by pink boxes) for 07 LA and 07 RA, respectively, for the windshear case of 12 February 2024. Figure 2.3 _Cont._