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This paper analyses over 10,000 quality‐controlled pilot reports of low‐level wind shear ('wind shear') at the Hong Kong International Airport (HKIA; ICAO code: VHHH) between 2001 and 2019. HKIA is well known for its susceptibility to wind shear, which is a potential hazard for aircraft during landing and take‐off. Wind shear at HKIA exhibits strong seasonality with double peaks in the middle of the spring and summer months. There is a strong diurnal cycle in report numbers, peaking towards the afternoon, as modulated by air traffic at HKIA. On average, there are 115 days per year with wind shear reported, with possible power law distribution in the number of days with different number of reports. By comparing the background wind distribution during those minutes with pilot reports against the climatological distribution, wind shear is observed to be, on average, favoured under higher wind speeds (≥6 m s−1) and reduced under lower speeds with shifted frequency peak and heavier tail, although statistical behaviour can differ significantly across individual runway corridors. Preferred background wind directions for wind shear occurrence highlight the role of terrain influence upstream of HKIA. While positive shear (65.6%) is more often reported than negative shear (34.4%), both types of wind shear events appear to follow an exponential distribution in shear magnitude, with similar rates of decay. This is by far the largest statistical study of low‐level wind shear at an airport. Results can serve as an important local reference in addition to being a useful example for airports around the world. [ABSTRACT FROM AUTHOR]

Small-scale, fast-evolving airflow disturbances, possibly due to upstream building clusters, are known to affect aircraft landing at corridor 25RA of Hong Kong International Airport (HKIA), China, under southerly or southwesterly winds. The paper presents a new algorithm, based on the concept of coherent integrated differential velocity (CIDV), for the automatic alerting of such hectometric (scale of hundreds of metres) turbulence features using short-range LIDAR (SRL) scans at 30 m radial resolution and an observation frequency of around every 20 s by Hong Kong Observatory (HKO). The CIDV identifies the cumulative effect of coherent patches of radial velocity changes occurring along the landing flight path by comparing two consecutive subminute SRL scans. Verification was conducted between June and September 2017 against a selection of relevant pilot reports, with a positive skill level observed over the whole range of the CIDV thresholds considered. When simulating a realistic setting where the SRL would issue alerts in conjunction with HKO's operational Windshear and Turbulence Warning System (WTWS), the CIDV algorithm would bring a gain in hit rate between 5% and 25%, with a corresponding increase in alert duration between 0.4% and 20%. The chosen CIDV threshold of 0.4 m·s-1 nautical mile (nm) can be physically interpreted as an average radial velocity change of 4.0 m·s-1 sustained over a distance of < 200 m (or between 2 and 3 s of flight), which agrees with reported values of crosswind changes considered significant for a landing aircraft and also pilots' perception of the characteristics of such events. [ABSTRACT FROM AUTHOR]

With the aim of developing a forecasting system for the prediction of adverse meteorological conditions in the vicinity of complex terrain for aircraft landing at Hong Kong International Airport, the linearized, quasi‐empirical FLOWSTAR model has been configured to represent a series of eight landing events (2015–2017); half of these events reported significant wind shear and, for two, the landing attempt was aborted. Meteorological data used as input to the model have been derived from Hong Kong Observatory radiosonde measurements; these are the most reliable available despite being recorded at a location distant from the airport and at one or more hours before or after landing events. In general, the model predicts stronger wind shear for cases where adverse conditions have been reported. Analysis of the magnitude of wind shear generated as a result of wind veering and backing helps to quantify the importance of nonlinear flow features such as trapped lee waves. The model is able to represent strong downslope flows and recirculating flow regions (rotors) generated by the mountainous region located upwind of the airport. Comparisons of model predictions against LIDAR traces indicate that the model replicates wind shear for 50% of cases where it was recorded, although the location and magnitude of the wind shear usually differs between the modelled and measured datasets; the lack of agreement is likely to be because the input meteorological conditions are not wholly representative of the upstream conditions and the LIDAR trace does not exactly coincide with the aircraft trajectory. When airports are located in hilly terrain, near‐ground flow features such as wind shear and turbulence periodically cause disruption to aircraft movements. The FLOWSTAR model has been configured to represent favourable and unfavourable landings at Hong Kong International Airport; the model predicts high wind shear at some locations along the flight path (black dotted line). Quantitative analyses of wind shear generated as a result of wind veering and backing demonstrate the importance of flow features such as trapped lee waves. [ABSTRACT FROM AUTHOR]