## 4 Conclusions  
With the opening of the third runway of HKIA and the rebound of air traffic, it becomes possible to collect actual pilot reports of windshear to determine the nature of headwind changes over the new 07 LA runway corridor, namely, arriving at the new third runway (the north runway) from the west, and whether they could be related to terrain-induced airflow disturbances due to Lantau Island during the east to sotheasterly wind situation in the peak windshear season of springtime in Hong Kong. Based on the limited number of windshear reports so far and the successful reproduction of terrain-induced wind features over the HKIA area using a mesoscale to microscale numerical weather-prediction model, it is evident that the Lantau terrain can still generate significant low-level windshear for the 07 LA runway corridor of the third runway, though it is located about 4 km to the north of the foothills of Lantau Island, which has peaks rising up to about 1 km above mean sea level. For the cases under study, the terrain effect may extend to a distance of at least seven to eight times the local terrain height, which is consistent with the definition of open terrain with a height-over-distance ratio of 1:10. As such, windshear detection equipment, such as Doppler LIDAR, is still an important instrument for safeguarding operation of this runway from the effect of low-level windshear and turbulence, even though it is quite far away from the major mountains of Lantau Island.  
It is noted that the present study is based on a small number of cases only. It would be interesting to compare the frequency of low-level windshear between the old 07 LA (now the central runway) and the new 07 LA (of the three-runway system configuration). However, the mode of operation of the runways has changed. The new 07 LA will be used mainly for landing aircraft, so the number of flights landing on the old 07 LA (now called 07 CA) will reduce. As a result, it would not be meaningful to compare directly between the frequencies of low-level windshear for the new 07 LA and the new 07 CA. One possibility is to compare the frequency for the new 07 LA in the three-runway configuration with that of the original 07 LA in the two-runway configuration. For this to be established, it is still necessary to wait for the full rebound of air traffic at HKIA, assuming that the practice  
Figure 16: The simulated horizontal wind profile (**a**), vertical wind profile (**b**), and virtual temperature (**c**) at the Sha Lo Wan wind profiler/RASS for the 17 February 2024 windshear case.  
of windshear reporting by pilots and the climatology of synoptic and mesoscale weather patterns for low-level windshear (e.g., as documented in [17]) remain unchanged. An update of this study will be presented after report collection in a few years' time.  
Conceptualization, writing, analysis, P.W.C.; data curation, software, K.K.L. All authors have read and agreed to the published version of the manuscript. This research received no external funding.  
Not applicable.  
The data that support the findings of this study are available from the corresponding author upon reasonable request. The data are not publicly available due to privacy.  
The authors declare no conflict of interest.