Derivation of High-Resolution Meteorological Parameters for Use in Airport Wind Shear Now-Casting Applications

Abstract

Methods for now-casting adverse weather conditions with the potential to cause disruption to aircraft landings often make use of real-time measurements at high temporal resolution. This paper describes processing methodologies developed to derive meteorological parameters from such measurements recorded in the vicinity of Hong Kong International Airport, specifically a radiometer in King’s Park, a wind profiler and surface anemometer on Cheung Chau Island and weather buoys in the Pearl River estuary. These parameters are suitable for use as input to a now-casting application of the computationally efficient airflow model, FLOWSTAR, which has previously been shown to predict mountain waves generated by flow over Lantau Island to the southeast of the airport. Radiosonde data from King’s Park have been used to test the radiometer processing method; the novel approach of using minimum and maximum potential temperature deviations from a series of height-dependent linear profiles to derive radiometer inversion layer parameters generates data that compares well with values derived from corresponding radiosonde profiles. Mountain wave strength depends on the magnitude of wind speed in the inversion layer; wind profiler data can be used to estimate typical and maximum wind speeds and associated wind directions using estimates of inversion layer depth derived from the radiometer data. With estimates of surface sensible heat flux appropriate for the airport’s coastal location calculated using a marine boundary layer scheme, a dataset of meteorological parameters at 20-min resolution has been derived for input into the FLOWSTAR model. The combination of automated meteorological data processing methods and flow field modelling has the potential to form part of a now-casting system for determining strong wind shear conditions at the airport.

Hong Kong Airport Wind Shear Now-Casting System Development and Evaluation

“…Estimates for the The period of 4 January to 30 April 2018 was selected for this study. Note that this is the previous year in relation to that considered in [19], thus allowing for an independent test of the automatic meteorological-processing methodologies developed for that study; the same January-to-April season was considered because wind-shear events are common at HKIA in spring [8]. The pilot wind-shear reporting record for this period contains 154 windshear events occurring 96, 29, 15, and 12 times on runways 07LA, 07RA, 07RD, and 25LD respectively, and once on each of the 25LA and 25RA runways.…”

“…The meteorological-data inputs for the flow-field model were in 20 min resolution, as described in [19], whereas the pilot wind-shear reports could occur at any time. A methodology for assigning each reported wind-shear event to one or more 20 min modelling periods was developed.…”

“…The evaluation process whereby the now-casting system wind-shear outputs are compared to the pilot wind-shear event dataset are described in steps 4 and 5; the methodology for generating the wind-shear event dataset required as input to steps 4 and 5 is described earlier (Section 2.1). The meteorological-data inputs were derived from measurements available in real time using the methodology previously described [19]. A vertical grid of flow-field model output points was defined that aligns with the north and south runways, extending 6 km in either direction from the midpoint of each runway, using the approach outlined in earlier studies of wind-shear modelling using FLOWSTAR [17].…”

“…These skill parameters were analysed to determine which metrics are most effective at identifying wind-shear events and how sensitive the results are to input meteorological conditions, runway corridor, and model-domain extent. The meteorological-data inputs were derived from measurements available in real time using the methodology previously described [19]. A vertical grid of flow-field model output points was defined that aligns with the north and south runways, extending 6 km in either direction from the midpoint of each runway, using the approach outlined in earlier studies of wind-shear modelling using FLOWSTAR [17].…”

“…However, some of the input parameters cannot be measured directly (for example, an estimate of the boundary layer height and the associated temperature jump within the inversion layer, required in order to model trapped waves); instead, they must be estimated from temperature-profile datasets. A recent study [19] describes a methodology for extracting FLOWSTAR input parameters from real-time measurements from the microwave radiometer located at the airport, the wind profiler at the island of Cheung Chau, and the weather buoys deployed in the vicinity of the airport. The temporal resolution of the meteorological data generated has been specified as 20 min; this resolution was specified by the HKO team, based on their experience of observing wind-shear event durations at HKIA.…”