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Understanding the fluid dynamics and thermodynamics in the urban atmospheric boundary layer (ABL) is of great practical importance. Based on one-year observations from two advanced remote sensing instruments, namely, the wind lidar and the microwave radiometer, this study investigates the urban ABL structure in a densely built downtown area of Hong Kong. Atmospheric stability, ABL height, wind shear, and wind veer are statistically analyzed. The interconnections among wind speed profiles, wind direction profiles, ABL stability, and ABL height are comprehensively examined. Some features of the wind and thermodynamic structure are observed, such as the prevalence of unstable conditions in the urban ABL and the increase in wind shear and veer with ABL stability. The research outcomes are expected to contribute to the understanding of urban meteorology and offer scientific insights into the influences of urban terrain on the ABL and the vertical and temporal structure of wind and thermodynamic properties in the urban ABL. [ABSTRACT FROM AUTHOR]

Super Typhoon Saola came very close to Hong Kong on 1/2 September 2023, necessitating the issuance of the No. 10 hurricane signal, the highest tropical cyclone warning signal in Hong Kong. While there was widespread damage in Hong Kong, no people were killed in the event with effective early warning. It is rare that a super typhoon comes very close to Hong Kong, and this paper is a part in the series of the documentation of Saola to summarize the interesting observations of Saola near Hong Kong for future reference by weather forecasters. [ABSTRACT FROM AUTHOR]

Severe Typhoon Koinu passed south of Hong Kong on 8 and 9 October 2023, triggering the issuance of the Increasing Gale or Storm Signal No. 9, the second highest tropical cyclone (TC) warning signal in Hong Kong. Koinu was a difficult case for TC warning service due to its compact size and rather erratic movement over the coastal waters of Guangdong. To monitor Koinu's movement and wind structure, the Hong Kong Observatory utilized various observational platforms, including meteorological aircraft, ocean radar, and synthetic aperture radar on polar orbiting satellites. The paper presents major observations derived from these measurements. The aircraft probe and dropsonde data suggested boundary layer inflow, warm core structure, eyewall updraft, and high turbulence in the eyewall of the typhoon. The weather radar observations indicated the occurrence of a waterspout in the vicinity of the typhoon. Additionally, the study highlights the forecasting performance of the AI‐based Pangu‐Weather model, which could outperform the conventional global numerical weather prediction models in forecasting TC track in the region. The documentation of these observations aims to provide valuable references for weather forecasters and stimulate further research on forecasting this type of tropical cyclone. Key Points: Observations from meteorological aircraft, ocean radar, and synthetic aperture radar show the structure of Severe Typhoon KoinuWeather radar observations suggest the occurrence of a waterspout in the vicinity of KoinuAI‐based Pangu‐Weather model could outperform the conventional global numerical weather prediction models in forecasting Koinu's track [ABSTRACT FROM AUTHOR]

Three windshear/microburst detection algorithms are used operationally at the Hong Kong International Airport. Their performance is studied in the present article by assuming the availability of the complete set of meteorological data from numerical weather prediction model output. Only selected tropical cyclone cases are considered. The performance is evaluated using pilot reports of windshear. It turns out that the glide path scan windshear detection algorithm has the best overall performance by considering the area under curve using the relative operating characteristic curves. This may be related to the better geometry in covering the glide paths of the airport for this particular algorithm. [ABSTRACT FROM AUTHOR]

A scanning Doppler LiDAR was set up at King's Park Meteorological Station in 2018 to monitor upper air wind profiles in the atmospheric boundary layer (ABL). Around the period of maximum temperature at King's Park (i.e. 1300-1400 hkt), advection of northerly winds with higher temperatures from the urban area to the north was observed (Figure 1a). This month is special in Hong Kong due to the occurrence of extremely high temperatures in the urban area for many days under generally northerly wind conditions, with daily maximum temperatures reaching 34-35°C at King's Park and the HKO headquarters. The strong northerly winds are believed to cause advection of higher temperature from the urban area to the north of King's Park, which enhanced the upward motion of the ABL above the King's Park Meteorological Station. [Extracted from the article]

Figure 2 shows the location of the radars and the position of the circulation at 04:53:30 when it most likely produced a waterspout, based on the appearance of a small-scale couplet in the velocity data of the nearest radar (Hengqin). ([10]) studied the ability of numerical simulations to predict waterspouts by comparing simulated and observed radar data from a storm producing a weak waterspout near Hong Kong airport. Observational analysis of a waterspout sighted in Macao, China, on 1 June 2021 Waterspout in Macao on 1 June 2021 (provided by radio station of Macao). [Extracted from the article]

A case study of a special event of low‐level windshear and turbulence at the Hong Kong International Airport is performed. The mountainous Lantau Island to the south of the Airport may lead to terrain‐disrupted airflow disturbances in the Airport area in certain wind directions, resulting in low‐level windshear and turbulence to the aircraft. There are a number of novel features in the flow field in the airport region. First, over the seas to the west of the airport, there is sharp convergence between northerly flow and southerly flow within a short distance. Second, in the temperature measurements over this region, there are sharp increases and decreases in temperature. The performance of a high‐resolution numerical weather prediction model in predicting these features is studied. It is shown that, though the model is quite successful in reproducing some features, it may not be able to capture some novel features, such as a sharp rise of temperature and sharp convergence of the airflow. The case study may be a useful reference for aviation weather forecasters and mountain meteorologists. [ABSTRACT FROM AUTHOR]

The wavy sea breeze front can be seen at the interface between easterly and westerly over and to the north of the airport. gl The model simulation result provides further information about the structure of the sea breeze front. This article provides a novel report of the following observations of sea breezes at this airport: The wavy pattern of the sea breeze front (the convergence zone between background wind and the sea breeze). As a result, it is important for the operation of the airport that it receives an accurate forecast/nowcast of the occurrence of a sea breeze, including the timing of any change in wind direction, the strength of the sea breeze and the wind direction change that may occur. This article considers three cases of sea breezes as observed at Hong Kong International Airport, together with the results of numerical simulations, including wavy structures within the sea breeze, vortices along the sea breeze front and large jumps in temperature and relative humidity associated with the sea breeze. [Extracted from the article]

I Rai i broke a number of tropical cyclone (TC) records over the South China Sea, necessitating the issuance of a TC warning signal in Hong Kong. The maximum 10-min mean wind data over Hong Kong, when the TC signal for I Rai i was in force, is shown in Figure 10 (the red number shows the gale force winds at Tai Mo Shan and Bluff Head). The key meteorological observations of a very late-season super typhoon over the northern South China Sea, namely, I Rai i in December 2021, are documented in this article for later reference. An observational study of Super Typhoon Rai, a very late-season typhoon necessitating the issuance of a tropical cyclone warning signal for Hong Kong in December 2021. [Extracted from the article]

A tornado/waterspout associated with a supercell thunderstorm was observed in the adjacent waters of southern China on the evening of 18 April 2019. The case was documented using surface weather observations and Doppler radar data. A weather station near the tornado/waterspout, recorded wind gusts corresponding to hurricane intensity for a few seconds, never observed before in the region. The Doppler velocity associated with the tornado/waterspout was analysed and the vertical profile of the velocity could be very useful for wind engineering applications in the region. Dual‐polarization observations also were analysed and exhibited some similar signatures documented in supercell tornadoes in other parts of the world. Predictability of the tornado/waterspout was studied using a numerical weather prediction model. It showed that the location and timing of the waterspout/tornado could be roughly reproduced, and the model might be used to give earlier alerting to the vessels operating in the south China coastal waters. [ABSTRACT FROM AUTHOR]

Horizontal interpolation (along the direction of the cross-section) has been applied to enhance visualisation along this direction. gl GLO:65TF/01jan22:wea3878-fig-0007.jpg PHOTO (COLOR): 7 Vertical cross-sections along C-D in Figure 6(a) showing (a) radial velocity, (b) horizontal speed, and (c) vertical velocity. gl Mountain waves over the central part of the airport island In addition to the western and eastern regions, mountain waves may also occur over the central part of the island, though it is rather rare. Topographic map showing the Hong Kong International Airport (HKIA). Mountain waves to the west of the airport island There are two incidents of mountain waves to the west of the airport island. Mountain waves near Hong Kong International Airport: observations and high-resolution model analysis. [Extracted from the article]

Wind gust characteristics at wind turbine relevant height are closely tied with wind turbine design and wind power generation, however, they have not been detailed and documented. In this study, high-resolution wind data recorded by 3D sonic anemometers at a tall meteorological tower were analyzed to determine 12 descriptors of wind gusts and to identify the parent distributions that best fit these parameters. The main statistics were estimated using wind data from the 160 m height. It is found that the log-logistic distribution is most appropriate for a 10-min mean wind speed, gust magnitude, gust factor, and turbulence intensity; the gamma distribution appears to best fit peak factor, rise magnitude, lapse magnitude, lapse time, and gust length scale, while gust amplitude, rise time, and gust asymmetric factor are typically log-normally distributed. Gust factors tend to decrease with mean wind speed but increase as a function of turbulence intensity. The results also indicate that these wind gust descriptive parameters are height-dependent in which the 10-min mean wind speed, gust magnitude, gust length scale, rise time, and lapse time usually possess larger values at higher heights, whereas the remaining parameters exhibit negative correlation with height. [ABSTRACT FROM AUTHOR]

A case of severe low-level windshear at the Hong Kong International Airport was investigated in this study using large eddy simulation (LES) with a spatial resolution of 40 m. The computer simulation results were compared with the actual observations at the airport, including Doppler light detection and ranging (LIDAR) systems and surface automatic weather stations. The LES was found to be capable of reproducing the tiny vortices associated with the terrain-disrupted airflow. Some interesting features of surface temperature and vertical velocity were also observed in the computer simulation. The simulated and observed meteorological parameters had satisfactory comparison results, although the micro-scale variability of such parameters still could not be captured by the high-resolution LES. Finally, the computer-simulated headwind profiles appeared to have skills in capturing the low-level windshear reports from the pilots. The headwind refers to the component of the wind along the direction of the flight path to be encountered by the arrival/departing aircraft. The study was novel in the use of the rather large domain for LES simulation and in the application to low-level windshear alerting. [ABSTRACT FROM AUTHOR]

Transmission lines (TLs) are vulnerable to wind actions. Notwithstanding the fact that the behavior of transmission lines under strong winds has been investigated in numerous studies, wind-induced failures of TLs are still common worldwide, which are mainly due to the lack of accurate understanding of the tremendous variability in wind speed. The main goal of this paper is to extend the concept of nonlinear dynamic analysis to identify and characterize the dynamic structures hidden in wind speed fluctuation, which are responsible for generating the variability in wind speed. Two well-established nonlinear dynamic analysis techniques, namely, recurrence plot and recurrence quantification analysis, are applied to diagnose the underlying dynamic characteristics. The results indicate that wind speed time series, regardless of the type of wind event, are likely to exhibit chaotic behavior. Often, the dynamics associated with monsoons are more complex than those for tropical cyclone and thunderstorm winds. Moreover, site-to-site variability in wind speed dynamics is also apparent, which is due mainly to the terrain-enhanced effect. The outcomes of this study are expected to provide a new avenue to aid the wind-resistant design of TL systems, and to accelerate the advancement in wind load design codes and climate-adapted decision-making procedures. [ABSTRACT FROM AUTHOR]

The Hong Kong Observatory conducted six flights in the atmospheric boundary layer of five tropical cyclones: tropical storm Jebi (1309), typhoon Kalmaegi (1415), severe tropical storm Linfa (1510), typhoon Mujigae (1522), and severe typhoon Nida (1604). Three-dimensional wind data with a 20-Hz sampling rate are available for a height range of 500–670 m, with the mean wind speed from these low-level flights ranging from 10 to 62 m s−1. The turbulent momentum flux and turbulence kinetic energy (e) are measured using the eddy-correlation method, while horizontal scales of turbulent eddies, vertical eddy diffusivity (K), and the vertical turbulent mixing length scale are estimated indirectly. The dependence of the momentum flux, e, K, and the vertical mixing length on wind speed and height are compared with previous studies. Both the momentum flux and turbulent kinetic energy increase with the wind speed, although the rate of increase is smaller for higher wind speeds. It is also found that K increases with wind speed according to a power law up to 40 m s−1 before levelling off, while the vertical mixing length is nearly constant at 100 m. The results serve as a reference for evaluating and improving the turbulent parametrizion in tropical-cyclone models, while the observed large turbulent mixing near the top of the inflow layer of the eyewall region should not be neglected in numerical models. [ABSTRACT FROM AUTHOR]

In summer, Hong Kong is affected by tropical cyclones moving northwestwards over the northern part of the South China Sea. They may bring strong southeasterly airflow to the territory. The wind is disturbed by complex terrain to the south of the Hong Kong International Airport, resulting in turbulent airflow in the airport area and leading to the occurrence of low level wind shear and turbulence. This study documents the observations of wind shear at the airport in some recent cases of tropical cyclones in Hong Kong. The alerts from three operational wind shear algorithms are described, based on anemometers, the light detection and ranging system and microwave radar. The situations at the maximum wind shear magnitudes are presented. This is followed by a statistical analysis of the occurrences of wind shear against the wind shear magnitude and sign. A logarithmic relation between the two is found, and it is applicable for all tropical cyclone cases under study and different wind shear algorithms. However, there is no uniform equation for the logarithmic distribution, apart from the case of laser radar wind shear alerts for headwind loss. Finally, the accuracy of wind shear alerts of one tropical cyclone case is presented by comparison with pilot wind shear reports. It is hoped that the documentation in this study could serve as a useful reference to aviation weather forecasters at other airports with similar wind shear situations, as well as contributing to an improved understanding of the statistical behaviour of the wind shear phenomenon. [ABSTRACT FROM AUTHOR]

The quality and applications of vertical velocity data from SODAR and radar wind profilers are examined in this paper. The vertical velocity data from collocated SODAR and boundary layer type wind profilers are compared for a period of 7 months. It is found that the two datasets are well correlated, but the slope of the linear fit to the data has a significant deviation from 1. This may be related to the difference in the sampling volumes of the vertical beams from the two instruments. The correlation for horizontal wind data was found to be much stronger. Three applications of the vertical velocity data are discussed: subsidence in the outer periphery of a tropical cyclone and in hazy weather, and the upward motion of the air in convective weather. Data such as those under study here are found to contribute significantly to the monitoring and understanding of weather conditions, and would be useful for the nowcasting of lowvisibility and convective weather. [ABSTRACT FROM AUTHOR]

This article presents the results of a comparison between several ceilometers. The ceilometers at Hong Kong International Airport are due to be replaced, and this comparison was undertaken to ensure climatological continuity following the installation of a newer model. Cloud base height measurements are examined, and comparisons are made between the results from the different ceilometers, and between the ceilometer data and the data from a human observer. Quantile–quantile (EQQ) plots are also presented. The results provide assurance, through statistical analysis and consideration of case studies, that continuity of measurement can be achieved for clouds that are operationally significant in terms of aviation meteorology. It is also demonstrated that the new model of ceilometer has advantages over the existing models. The use of ceilometers for cloud amount measurement is also studied through comparison with human observations. [ABSTRACT FROM AUTHOR]

Two typical cases of fog in Hong Kong are documented in this paper. The meteorological conditions leading to the occurrence of fog are examined using observations from ground‐based, remote sensing meteorological instruments. An acoustic sounding system and a microwave radiometer were used to monitor the atmospheric boundary layer and nowcast the low visibility weather conditions. The measurements from these instruments provide many interesting observations of both the sea fog and mixing fog, including temperature inversions and changes in the humidity profiles. The skill of the numerical weather prediction models in forecasting fog episodes is also briefly discussed. The global model is found to have skill in predicting the occurrence of low visibility weather up to 2 days in advance. [ABSTRACT FROM AUTHOR]

Presents a study which used explosive-driven hemispherical implosions to generate shock waves for exploring the chemical reactions and diffusion rates in materials. Experiment; Results and discussion; Conclusion.

Since 2011, routine reconnaissance has been carried out whenever there is a tropical cyclone (TC) entering the Flight Information Region of Hong Kong that may pose a threat to the territory. In October 2022, Typhoon Nesat entered the northern part of the South China Sea and aircraft reconnaissance flights were conducted for the storm. This paper presents these interesting data for the meteorological and wind engineering communities. The presented observations would be beneficial for other studies of this cyclone, such as numerical simulations of Nesat for comparison with actual observations. [ABSTRACT FROM AUTHOR]

For the first time, Hong Kong Observatory conducted a full scale dropsonde observation of the circulation of a tropical cyclone, namely, Tropical Storm Aere, on 7 October 2016, over the northern part of the South China Sea. This paper documents the observations and their use in the prediction of the track and strength of the tropical cyclone in a numerical weather prediction model. In addition to the model analysis fields, the dropsonde observations are found to provide further information about the structure of Aere. The quality of the dropsonde data was found to be satisfactory in comparison with the radiosonde data nearby. The dropsonde data were found to have a positive impact on the prediction of the track of the tropical cyclone, improving track location accuracy by about 13%. The prediction of the strength of Aere was found to have a higher dependence on the assimilation of the wind field than the assimilation of the humidity field. [ABSTRACT FROM AUTHOR]

ABSTRACT Severe wind shear (headwind change of 30 kn or more) at Hong Kong International Airport is documented in this study. Its climatology, including the number of reports from pilots each year, captured by the wind shear alerting service, its cause and its magnitude are presented. The purpose of the study is to document the characteristics of severe wind shear at an operating airport. Some typical cases of severe wind shear are also examined, such as observation by remote-sensing instruments and flight data analysis. It is found that the shear magnitudes in pilot reports of severe wind shear, as with pilot reports of wind shear in general, are subjective in nature. They may not be consistent with headwind changes as determined from the flight data. Sometimes, the pilot reports of wind shear may be based on wind trend information available onboard for certain fleets of aircraft. The wind shear can be transient in nature, for which an alert beforehand is difficult. [ABSTRACT FROM AUTHOR]

ABSTRACT At airports with significant economic growth, more and more buildings are being constructed inside and around the airport premises. These buildings may become a source of low level wind disturbances to the aircraft operating at the airport. In assessing such low level wind effects of buildings, objects and structures, a 7 kn crosswind change criterion can be used. This criterion restricts the wind variations along the glide path and above the runway to a crosswind change of less than 7 kn. It was developed in and based on the experience in the Netherlands over the past 20 years. Therefore, the question arises whether this criterion is applicable to airports and buildings elsewhere in the world, and whether it is consistent with other hazardous wind metrics available in the literature. Based on two cases of pilot reported building induced wind disturbances at Hong Kong International Airport, computer simulated wind fields and a flight simulator were employed to study the validity of the 7 kn criterion. It was found that the criterion is in general consistent with the other hazardous wind metrics available in the literature for the cases under consideration. The number of cases considered in the present study is still limited and further studies into the matter should be considered. [ABSTRACT FROM AUTHOR]

Wind measurement offers an essential data source for a wide range of practices in the fields of meteorology and wind engineering. However, records of surface winds are usually influenced by terrain/topographic effects, and direct usage of raw data may bring in nonignorable errors for follow-up applications. A data-driven standardization scheme was recently proposed by the authors to convert the surface wind measurements over rugged terrain into their potential values corresponding to reference conditions, that is, for neutral winds at a height of 10 m above open flat terrain ( z0 = 0.03 m). As a complementary part of the preceding work, this study focuses on the standardization of surface wind speeds with marine exposures. The effect of wind strength on the roughness of the sea surface is further taken into account, with emphasis on the difference between deep-ocean and shallow-water cases. As an application example, wind measurements at a buoy site near the coastal line (water depth is 14 m) are adjusted to their potential values, which are then compared with those at a nearby station. The good agreement between the two sets of results demonstrates the accuracy and effectiveness of the standardization method. It is also found that the behavior of roughness length scale over shallow water may differ noticeably from that over deep ocean, especially under strong wind conditions, and an inappropriate usage of marine roughness predictors may result in significant estimation errors. [ABSTRACT FROM AUTHOR]

Terrain-induced windshear at Hong Kong International Airport (HKIA) could be hazardous to the landing and departing aircraft. Such windshear occurring in a planetary boundary layer without temperature inversions is studied in this paper by using the data from the Terminal Doppler Weather Radar and Light Detection and Ranging systems. A high resolution numerical model, called aviation model (AVM), is also employed to find out its capability to forecast the occurrence of such windshear. The model is found to have skills in capturing the terrain-induced windshear, including the terrain-induced microburst due to the mountains of Lantau Island. Moreover, the windshear detection algorithm as applied to the AVM output, called AVM-GLYGA, is able to give advance alert for the occurrence of low-level windshear. The model also offers new dataset, such as vertical velocity and vertical cross sections across the windshear feature, to study the terrain-induced windshear phenomena with new insights. The AVM is found to have good skills in depicting the terrain-disrupted airflow at the airport area, and more comprehensive study would be conducted to study the skills of AVM-GLYGA as compared with pilot windshear report as sky truth. [ABSTRACT FROM AUTHOR]

ABSTRACT Hong Kong International Airport ( HKIA) is situated in an area of complex terrain. Mountains near the airport can lead to terrain-disrupted airflow disturbances, which may bring about hazardous weather phenomena for aviation, such as low-level windshear and turbulence. Timely forecasting of such airflow disturbances would be useful in providing early warnings to the pilots. The Hong Kong Observatory has been running a super high resolution numerical weather prediction model suite, the aviation model ( AVM), since late 2013, with spatial resolution up to 200 m immediately around HKIA. After testing and tuning over the past year, the performance of the AVM in forecasting terrain-disrupted airflow at the airport area is investigated in this study. Two typical cases of such complex airflow are considered, Foehn wind and mountain wave. The AVM is found to capture successfully some salient features of the airflow as observed around HKIA through comparison with light detection and ranging (LIDAR) and weather buoy observations. The model also helps in shedding new light on the airflow from the vertical cross sections of the winds across the mountains. Limitations of the AVM are also discussed. [ABSTRACT FROM AUTHOR]

Direct usage of raw wind data without modification of topographic and/or terrain effects may result in remarkable errors. Thus, standardization of raw wind datasets is of great importance to remove these influences. But, the existing standardization methods are mainly applicable for flat terrains, which may become inappropriate under complex terrain conditions. This paper presents a data-driven standardization scheme which can be applied for different terrains including complex terrains. Although this scheme is established based on wind profile records at a reference station equipped with both an anemometer at a near-ground height and a Doppler radar profiler system, it can be used for the standardization of surface winds not only at the reference station but also at other surrounding stations with only surface observation instruments. Thus, the proposed data-driven scheme is efficient and economic. As applications of this scheme, correction factors to convert raw wind speeds at about 50 weather stations in Hong Kong to those over a reference terrain are estimated. To verify the effectiveness of the proposed standardization scheme, a wind tunnel testing involved the topographic model of a weather station has been conducted. The standardization results via the proposed scheme and the wind tunnel testing are in good agreement. The proposed methodology and relevant results can be used for the analysis of topographic effects on wind speeds over complex terrains. [ABSTRACT FROM AUTHOR]

The article reports on the observation of weather condition through air reconnaissance within the Severe Typhoon Utor in Hong Kong, China. It mentions the city's observatory (HKO) and its cooperation with the Government Flying Service (GFS) for the installation of a meteorological measuring system to its BAe Jetstream 4100 aircraft. An overview of its flight route is also presented.

A case of vortex/wave shedding at a mountain near Hong Kong International Airport (HKIA) in a tropical cyclone situation is studied in this paper. Compared with similar studies at HKIA in the past, this paper contains novel results by considering both actual observations and numerical simulation of the event, and by studying the shedding in a neutral boundary layer instead of a stably stratified atmosphere in the spring time. The vortex/wave shedding is clearly observed from the radial velocity imagery of Terminal Doppler Weather Radar (TDWR). The shedding period is about 7 min, which is consistent with previous results in the literature. The vortex/wave adjacent to the background strong southeasterly flow also leads to significant wind shear over the arrival runway corridor to the west of the north runway of HKIA. It may also be associated with the significant headwind changes encountered by an arriving aircraft that had to conduct missed approach due to the rapidly fluctuating winds. The shedding event is simulated by using the Regional Atmospheric Modelling System (RAMS) version 4.4 with a horizontal resolution down to 50 m. The model is found to capture the vortex/wave shedding successfully. The simulated shedding period is similar to actual observations, though the associated area of reverse flow is much smaller. As such, with faster computers, it may be possible to forecast the occurrence of significant wind shear associated with vortex/wave shedding in an area of complex terrain and provide earlier alert to the aviation weather forecasters. Copyright © 2012 Royal Meteorological Society [ABSTRACT FROM AUTHOR]

At about 0155 UTC, 22 February 2009, an aircraft departing from the south runway of the Hong Kong International Airport to the east experienced significant wind shear of headwind loss. This may contribute towards the tail strike of the aircraft. This paper documents the meteorological observations in this tail strike event. The case occurs in a background atmosphere with a stable boundary layer and fresh east to southeasterly winds near the surface. The surface anemometer readings do not indicate the occurrence of significant headwind drop over the south runway. The glide-path scan data of a Doppler Light Detection and Ranging (LIDAR) system over the runway corridor concerned also do not indicate significant changes of the headwind due to blind zone of the LIDAR and geometrical constraint. However, the wind data measured on board the aircraft show that the tail strike may be due to a wind change from headwind of 19 knots to a tailwind of 5 knots over the western and middle parts of the south runway when the aircraft was on rotation. The headwind drop appears to be due to a jet of more easterly component near the surface occurring over the western part of the south runway. This drop could be captured if the LIDAR's headwind profiles over different runway corridors could be combined, and the present case suggests that, for wind shear alerting purposes, it may be necessary to try out combinations of headwind profiles over different parts of the same runway. The possibility of forecasting the significant wind shear in this case is also studied using a numerical weather prediction (NWP) model. The model results show that it may not be possible to forecast the event by using the direct model output alone, but would need to consider both the simulated wind direction as well as the forecast gust near the surface. Here the gust is forecast based on a physical approach as applied to the NWP model output. Copyright © 2012 Royal Meteorological Society [ABSTRACT FROM AUTHOR]

In the literature, there is rather limited number of accounts of significant turbulence over the South China Sea, which is an area of busy air traffic. The present paper documents the meteorological observations of an aircraft over the seas west of the Philippines on encountering severe turbulence associated with an area of convection. From the valuable flight data available from this aircraft, it is found that, on encountering the significant turbulence, the aircraft experienced increase in wind speed, strong downdraft, high windshear hazard factor, and, most importantly, high level of eddy dissipation rate, which is a measure of turbulence intensity in civil aviation. The application of numerical weather prediction (NWP) models in the forecasting of this severe turbulence case is also studied. It turns out that the cumulonimbus extent and in-cloud turbulence potential products from World Area Forecast System may have some indication of the occurrence of significant turbulence associated with convection in the area concerned. A mesoscale NWP model even forecasts the possibility of moderate-to-severe turbulence about 24 to 27 hours ahead of the event. [ABSTRACT FROM AUTHOR]

Hong Kong Observatory currently uses a series of meteorological instruments, including long-range LIDAR (light detection and ranging) systems, to provide alerting services of low-level windshear and turbulence for Hong Kong International Airport. For some events that are smaller in spatial dimensions and are rapidly changing, such as low altitude windshear and turbulence associated with buildings or man-made structures, it would be necessary to involve meteorological instruments that offer greater spatial resolution. Therefore, the Observatory has set up a short-range LIDAR on the roof of the AsiaWorld-Expo during the summers over the past several years, conducting field research on the feasibility of strengthening early alerting for windshear and turbulence over the north runway's eastern arrival runway (Runway 25RA) and developing an automated early alerting algorithm. This paper takes the pilot reports for Runway 25RA during the 2013 field research as verification samples, using different thresholds for radial wind velocity spatial and temporal changes detected by the short-range LIDAR to calculate the relative operating characteristic (ROC) curve, and analyzes its early alerting performance. [ABSTRACT FROM AUTHOR]

ABSTRACT In aviation meteorology, eddy dissipation rate ( EDR) is an internationally-adopted metric for quantifying intensity of low-level turbulence (rapid, irregular headwind fluctuations experienced by an aircraft below 1600 feet/500 m). In this paper, calculations of EDR1/3 profiles along arrival corridors ( 07LA, 25RA) of the Hong Kong International Airport ( HKIA) were performed over a 45 month period ( January to September, 2008-2012) based on radial velocity from a scanning Doppler LIDAR using the azimuthal velocity structure function approach. The quality of the LIDAR-estimated EDR was established by comparison with values calculated from in situ measurements over a 24 month period, which showed that median values of EDR profiles from both sources fell within 0.05 m2/3 s−1 of each other in over 90% (80%) of instances for 07LA ( 25RA). The performance in threshold-based alerting of low-level turbulence at HKIA was then validated against pilot reports. At alert duration of 10%, alerts based on the maximum value of an EDR profile could capture over 90% (80%) of reported events over 07LA ( 25RA), while comparable performance with the wind shear and turbulence warning system ( WTWS) at HKIA was attainable using suitable alert thresholds. Positive skill, albeit inferior to WTWS, was also observed in the alerting of low-level wind shear (sustained headwind change of 15 knots or above below 1600 feet/500 m) with a hit rate of about 70% at alert duration of 10%. This study served to establish the value of EDR derived from ground-based remote-sensing instruments e.g. LIDAR in alerting of low-level turbulence for the aviation community. [ABSTRACT FROM AUTHOR]

ABSTRACT Rapid fluctuations of wind shear hazard factor (or F-factor) calculated from the headwind profile measured by Doppler Light Detection and Ranging ( LIDAR) may make it difficult for use in wind shear alerting at an airport such as Hong Kong International Airport ( HKIA). Preprocessing by flight simulator or post-processing by averaging over a certain length are attempted in this study to smooth the F-factor and enhance its skills on wind shear alerting. The F-factor so obtained is used for alerting of wind shear (headwind change exceeding 15 knots) for departing flights. Through case studies and statistical studies, the LIDAR-based F-factors are found to have good correlation with the F-factor determined from flight data (the Quick Access Recorder, or QAR, data from the commercial jets). Using the relative operating characteristics ( ROC) curves, the LIDAR-based F-factor obtained by smoothing over a window size of 300-500 m is found to have good skills in wind shear alerting, and the performance is comparable with, or even better than, the LIDAR-based F-factor using the flight simulator approach. By choosing an optimal alerting threshold specific for each runway corridor, the F-factor successfully alerts 86% of pilot wind shear reports with the percentage of time on alert of 12%, which is found to be satisfactory for real-time use. The performance of the F-factor on stronger wind shear (headwind change of 25 knots or more) is also studied. [ABSTRACT FROM AUTHOR]

ABSTRACT Two aircraft had to conduct missed approaches in the overnight period of 8-9 September 2010 due to intense thunderstorm activity at the Hong Kong International Airport (HKIA). The missed approach event is studied in detail in this paper using the available flight data and other meteorological measurements. It appeared that the missed approaches were attributable to strong tailwind associated with the downdraft of the thunderstorm. Timely wind shear/microburst alerts had been provided to the pilots in this case based on the measurements from a Terminal Doppler Weather Radar (TDWR) and ground-based anemometer measurements at HKIA. The nowcasting and forecasting aspects for such an event are also discussed. The Aviation Thunderstorm Nowcasting System (ATNS) developed by the Hong Kong Observatory (HKO) is found to provide adequate nowcasting of thunderstorm activity for this particular case and the aviation weather forecasters could be alerted of such intense convective weather at the airport more than half an hour ahead. On the forecasting side, the mesoscale meteorological model used by HKO may provide an indication of the strong tailwind associated with the thunderstorm at 6-7 h ahead, though the exact timing of the tailwind at the airport may be delayed by a couple of hours compared with the actual situation. Using the model the downdraft of the thunderstorm in this event is examined in detail. [ABSTRACT FROM AUTHOR]

ABSTRACT The performance and aviation application of minisodars at Hong Kong International Airport are discussed in this paper. There are two minisodars at the airport and they have been in use for more than 2 years. The data availability at various measurement heights shows that the minisodars in general provide reasonably good coverage for aviation applications. The minisodar's wind data compare well with other measurements, including the anemometer data and LIDAR (light detection and ranging) data. The applications of minisodar data are then described. They are found to provide useful indications of low-level windshear, mechanical turbulence associated with complex terrain, and downburst associated with a thunderstorm. Through these case studies, the minisodars are found to provide good supplementary data to other remote sensing meteorological instruments, such as LIDAR and radar, in the monitoring of low-level wind changes that may be encountered by the aircraft. [ABSTRACT FROM AUTHOR]

In the morning of 5 March 2010, an aircraft experienced tail strike when it departed from the south runway of the Hong Kong International Airport to the west. This paper documents the meteorological conditions in the tail strike event, and discusses the alerting and the forecasting aspects of the event. Based on the analysis of the aircraft manufacturer, the tail strike is believed to arise from significant wind shear (headwind loss) experienced by the aircraft. By analysing the surface and the LIDAR observations, it appears that the significant wind shear is related to disruption of the background southwesterly flow by the complex terrain near the airport. From the surface observations, there is a microscale cyclone at the western part of the south runway. The radial velocity image of the LIDAR also depicts an area of reverse flow in that region against the background southerly flow. The alerting of the wind shear based on the two wind shear alerting algorithms developed by the Hong Kong Observatory is discussed, and it turns out that the anemometer-based wind shear algorithm could successfully capture this wind shear occurring close to the ground. On the other hand, due to geometrical constraint, the LIDAR does not pick up the headwind loss experienced by the aircraft. The forecasting of this wind shear event is considered by performing high resolution (down to a horizontal resolution of 50 m) using a mesoscale numerical weather prediction model. The simulated headwind profile at the event time is generally consistent with the aircraft data, though the headwind loss in the simulation is smaller than the reality. Together with the forecast wind gusts, it may be possible to alert the aviation weather forecaster at an earlier time about the occurrence of terrain-induced wind shear over the south runway in this particular event. Copyright © 2011 Royal Meteorological Society [ABSTRACT FROM AUTHOR]

A significant wind shear event occurred in the early morning of 27 December 2009 at the Hong Kong International Airport (HKIA), leading to the diversion of three aircraft to the airport of Shenzhen (about 39 km to the north-northwest of HKIA). This paper documents the meteorological observations and predictions for the event. The significant wind shear arose from disruption of the prevailing easterly to southeasterly flow by the complex terrain to the south of the airport. It was well captured by the Doppler Light Detection and Ranging (LIDAR) systems at HKIA and, as such, the aircraft were given sufficient warning about the occurrence of significant wind shear. The headwind changes along the glide paths as measured by the LIDAR were consistent with the aircraft measurements. The observations of the remote-sensing instruments during the event, including the LIDAR, are described in the paper. Moreover, this paper discusses the possibility of including wind shear forecast information for flight planning purpose for this particular case. The forecast wind field near HKIA based on a high-resolution numerical weather prediction (NWP) model is described. For the present wind shear event, it appears that the occurrence of terrain-disrupted airflow near HKIA may be forecast about 6 h ahead. The timing of significant wind shear is, however, not reproduced well in the NWP forecast. Copyright © 2011 Royal Meteorological Society [ABSTRACT FROM AUTHOR]

Long-range lidar systems have been used operationally at the Hong Kong International Airport for wind shear alerting. They are used for monitoring the headwinds over the last 3 n mi of all of the runway corridors of the Hong Kong International Airport (HKIA). This paper discusses the results of a trial of using short-range lidar (SRL) in the alerting of wind shear over a particular runway corridor by performing more frequently updated wind measurements over a specific section of this corridor in which many wind shear reports are received. The radial resolution of the lidar is 75 m and the data are updated every 20 s. Three different ways of wind shear alerting based on SRL's data are studied, namely, the deviations of the measured radial velocities from the uniform background flow (the 'velocity fluctuation'), eddy dissipation rate (EDR), and autocorrelation of radial velocity. The performance of these methods is studied by comparing with the pilot wind shear reports. The velocity fluctuation has the best skill in capturing the wind shear reports. By combining the wind shear alerts from SRL with those from the Wind Shear and Turbulence Warning System (WTWS), it is possible to achieve a probability of detection (POD) of pilot wind shear reports of about 90%%, with a percentage of time on alert (PTA) of about 10%% only. This even outperforms the existing overall wind shear alerting service (WTWS plus subjective wind shear warnings issued by aviation weather forecasters) by significantly reducing PTA. As such, the present study shows that it is possible to combine wind shear alerts from SRL and WTWS for automatic wind shear alerting without the need of human intervention, at least for a particular runway corridor of HKIA. [ABSTRACT FROM AUTHOR]

Turbulent airflow mostly occurs at Hong Kong International Airport (HKIA) when winds blow off the hills on the Lantau Island (with peaks rising to almost 1000 m to the south of the airport) from the east to the southwest. In a previous study by Chan et al., turbulence intensity in terms of cube root of eddy dissipation rate (EDR1/3) was measured directly using a staring lidar beam. This paper extends the previous study to calculate the spatial distribution of EDR1/3 (the so-called EDR map), with the ultimate goal of monitoring the turbulence over all of the runway corridors of HKIA using the lidar. The EDR map is calculated based on plan position indicator (PPI) scans of the lidar. The whole scan area is divided into a number of small sectors, each having a size of about 1 km in range and 20°° in azimuth. Velocity structure function is evaluated in every sector and compared with the theoretical von Káármáán model to estimate the EDR1/3. This paper gives an overview of the calculation method, shows some examples of EDR map in terrain-disrupted turbulent airflow at HKIA, and examines the quality of the EDR1/3 value thus obtained by comparing against the measurements of a ground-based anemometer. [ABSTRACT FROM AUTHOR]

In December 2005, operational wind shear alerting at the Hong Kong International Airport (HKIA) reached an important milestone with the launch of the automatic Lidar (light detection and ranging) Windshear Alerting System (LIWAS). This signifies that the anemometer-based and radar-based wind shear detection technologies deployed worldwide in the twentieth century have been further advanced by the addition of the lidar—a step closer to all-weather coverage. Unlike the microburst and gust front, which have a well-defined coherent vertical structure in the lowest several hundred meters of the atmosphere, terrain-induced wind shear tends to have high spatial and temporal variability. To detect the highly changeable winds to be encountered by the aircraft under terrain-induced wind shear situations, the Hong Kong Observatory devises an innovative glide path scan (GPScan) strategy for the lidar, pointing the laser beam toward the approach and departure glide paths, with the changes in azimuth and elevation angles concerted. The purpose of the GPScans is to derive the headwind profiles and hence the wind shear along the glide paths. Developed based on these GPScans, LIWAS is able to capture about 76% of the wind shear events reported by pilots over the most-used approach corridor under clear-air conditions. During the past two years, further developments of the lidar took place at HKIA, including the use of runway-specific lidar to further enhance the wind shear detection performance. [ABSTRACT FROM AUTHOR]

Objective: The aim of the study was to determine the clinical profile, aetiology and radiological categories in children diagnosed with bronchiolitis obliterans (BO). Methodology: We undertook a review of the medical records and radiological studies of 14 children with BO. Results: Unresolving cough and wheeze after a short respiratory illness was the commonest presentation. A viral pneumonitis was identified as the initial respiratory event prior to the development of BO in six children and Mycoplasma pneumoniae was the cause in another three children. Chest X-ray findings could be divided into four distinct patterns that were hyperinflation (n = 5), mixed pattern of atelectasis, hyperlucency and bronchial thickening (n = 4), unilateral small hyperlucent lung (n = 3) and unilateral collapse of one lung (n = 2). High resolution computed tomogram (HRCT) chest showing areas of hyperaeration and mosaic ground glass patterns with bronchial thickening were commonly found in patients whose chest X-ray showed bilateral changes. Patients with bilateral lung changes were more likely to have failure to thrive and persistent respiratory symptoms on follow up. Conclusion: A diagnosis of BO can be made from typical clinical features combined with an understanding of the different chest X-ray categories and HRCT of the chest. A viral aetiology was the commonest cause for BO in our series. [ABSTRACT FROM AUTHOR]

Considering that existing theories consider runway lights as markers, neglecting their roles as lighting devices that increase sky background luminance and thus affect runway visual range (RVR) measurements, the actual values of sky background luminance observed by pilots during take-off are calculated and compared with the instrumental RVR measurements in this paper. The RVR measurement errors due to the installation positions of these devices are subsequently analysed. Furthermore, the impacts of different runway light types and positions on sky background luminance are explored, leading to the proposal of an optimized runway lighting scheme. The results show that the representation of sky background luminance sensor data in RVR measurement systems for nighttime airport runways is limited. A deviation of over 90% exists between the sky background luminance of the runway entrance and the RVR measurement equipment location, resulting in a relative error in RVR measurements of over 18%. The centreline and entrance lights contribute significantly to the total sky background luminance. Lights closer to the observer contribute more luminance. In the second proposed scheme, modifying the lighting range to 600 m yields the highest RVR improvement, with an optimization magnitude of over 5% across all visibility ranges. [ABSTRACT FROM AUTHOR]

(2020), and axisymmetric tropical cyclone boundary layer structure was analysed by compositing dropsonde data from multiple tropical cyclones. For the purpose of this study, forecast wind and thermodynamic profiles from the AAMC-WRF at locations corresponding to the dropsonde observations of the tropical cyclones concerned will be generated in the form of "simulated dropsondes". The dropsonde data were not assimilated into the model, but serve as an independent source of data to check the performance of the AAMC-WRF in the forecast of the tropical cyclone, at least in regards to the vertical profiles of the wind and thermodynamic properties of each cyclone. [Extracted from the article]

A new printed structure composed of a dipole and a loop antenna for achieving a unidirectional antenna is proposed. The proposed antenna demonstrates that when an electric dipole and a magnetic dipole are excited simultaneously, a unidirectional radiation pattern can be obtained. With the absence of any ground plane or reflector, this directional printed antenna with single-layer structure can be used nowadays in small directional wireless systems and some handheld devices that need to radiate in a particular direction. The antenna operates at 2.4 GHz with an impedance bandwidth of 7.4% for S11<-10 dB and a peak measured gain of around 4.3 dBi. [ABSTRACT FROM AUTHOR]

The vast majority of current structural design codes and standards do not separately consider the wind and turbulence profiles for different storm types. Based on the 356-m-high Shenzhen Meteorological Gradient Tower, which is the tallest of its kind in Asia, this paper investigates the characteristics and vertical profiles of mean wind and turbulence for different types of strong wind events, including typhoons, monsoons, and thunderstorms, from a comparative perspective. Commonalities and differences among the vertical profiles of mean wind speed, turbulence intensity, and turbulence integral length scale for these storm events are comprehensively investigated. It is observed that the wind and turbulence profiles in typhoons and monsoons can be reasonably described by design codes and standards, while those in thunderstorms substantially deviate from typhoons and monsoons as well as code stipulations. The outcome of this study is expected to facilitate the different forms of wind and turbulence profiles for typhoons, monsoons, and thunderstorms to be taken into consideration in design codes and standards and improve the wind-resistant design of high-rise structures in regions that are prone to these storm events. [ABSTRACT FROM AUTHOR]

Tropical cyclone (TC) wind field models are becoming increasingly sophisticated and complex. This review systematically discusses a range of models capable of simulating TCs in terms of modifications or simplifications of the governing equation, the Navier–Stokes equations, as a starting point. The discussion focuses on linear models, which include slab models, height-resolving models, and numerical simulation methods, respectively. The linear model offers quick calculations and insights into physical mechanisms, while slab models have limitations in capturing important processes and site conditions. The height-resolving model is widely used for Monte Carlo simulations, providing realistic three-dimensional wind structures. Nonlinear simulations yield reliable results for typhoon trajectory prediction, although they require specific boundary and initial conditions. Integration of nonlinear simulation with artificial intelligence and machine learning shows promise for faster typhoon prediction. However, challenges remain in terms of data training for machine learning models. Future advancements in these areas have the potential to enhance hazard assessment and weather forecasting. [ABSTRACT FROM AUTHOR]