Time filter

Source Type

Li L.,Shenzhen National Climate Observatory | Li L.,Shenzhen Key Laboratory of Severe Weather in South China | Chan P.W.,Hong Kong Observatory
Meteorological Applications

Vortex/wave shedding is sometimes observed in the Hong Kong International Airport (HKIA) region by such sophisticated instruments as Doppler LIght Detection And Ranging (LIDAR) systems. During the past three years several vortex/wave shedding cases have been documented, often to the west of HKIA, downwind of the mountains which can block and disturb the prevailing airflow from the southeast. These shedding movements might trigger turbulence and wind shear, threatening aircraft landing from the west. This paper documents, for the first time, that such shedding can also occur at the runway corridor to the east of the airport's south runway, caused by mountains on the eastern side of Lantau Island. It calculates the shedding period and Froude number of the events, comparing these data with results reported in the literature. It also discusses, for the first time, the use of a computational fluid dynamics (CFD) model to simulate these events, based on homogeneous initialization only and using the upper air ascent data closest in time to the events. The simulations were shown to successfully reproduce the main features of the shedding, pointing to the possibility of applying this kind of simulation method in real-time forecasts to provide early warning services for aircraft taking off from HKIA. © 2016 The Authors. Meteorological Applications published by John Wiley © Sons Ltd on behalf of the Royal Meteorological Society. Source

Zhai Y.-H.,University of Science and Technology of China | Huang X.-F.,University of Science and Technology of China | Zhang L.,Shenzhen Key Laboratory of Severe Weather in South China | Li H.-Y.,University of Science and Technology of China | And 4 more authors.
Zhongguo Huanjing Kexue/China Environmental Science

This study established an experimental system, which combined an ultrasonic nebulizer with an Aerosol Chemical Speciation Monitor to measure the chemical composition and size distribution of inorganic ions and water-soluble organic matter of size-segregated aerosol samples collected during the spring of 2013 in Shenzhen, China. The mean water-soluble particle mass concentration was (17.4±2.1) μg/m3 during the campaign, with WSOM and sulfate being the dominant species. Both the fine and coarse mode WSOM was found to be dominated by secondary organic aerosol, and the coarse mode WSOM was inferred to be produced by heterogeneous reaction. The oxidation state (based on the ratio of O/C) of size-segregated WSOM was measured to be 0.46~1.36, corresponding to an OM/OC ratio (mass ratio of organic matter to organic carbon) of 1.76~2.89. The higher oxidation state of the coarse mode WSOM implied its experience of more ageing processes. ©, 2015, Chinese Society for Environmental Sciences. All right reserved. Source

Wei X.,Shenzhen Key Laboratory of Severe Weather in South China | Lam K.-S.,Hong Kong Polytechnic University | Cao C.,Shenzhen Key Laboratory of Severe Weather in South China | Li H.,Shenzhen Key Laboratory of Severe Weather in South China | He J.,Shenzhen Key Laboratory of Severe Weather in South China
Advances in Meteorology

It has been previously established that photochemical smog occurring in the Pearl River Delta Region (PRD) was associated with stagnant meteorological conditions. However, the photochemical smog (17 July to 20 July 2005) induced by typhoon Haitang was associated with moderate wind speed and nonstagnant meteorological conditions. The dynamic process of this ozone episode was studied using an integrated numerical model, that is, a mesoscale meteorological model and Community Multiscale Air Quality (CMAQ) model. Model performance has been evaluated using both ground-based meteorological and air quality observations. Analysis of simulated wind fields and ozone budget has been performed. This dynamic process is summarized into three physical factors. First, the westerly wind placed Hong Kong directly downwind of the PRD emissions. Second, the convergence of wind flow stimulated a vertical local circulation near the surface layer. This recirculation allowed primary and secondary pollutants to accumulate. Third, the conditions of high air temperature and low humidity resulted in active photochemical reactions. These combined effects resulted in the formation of high ozone in this episode. © 2016 Xiaolin Wei et al. Source

Hou T.,CAS Institute of Atmospheric Physics | Hou T.,University of Oklahoma | Kong F.,University of Oklahoma | Chen X.,University of Oklahoma | And 4 more authors.
Advances in Atmospheric Sciences

To improve the accuracy of short-term (0–12 h) forecasts of severe weather in southern China, a real-time storm-scale forecasting system, the Hourly Assimilation and Prediction System (HAPS), has been implemented in Shenzhen, China. The forecasting system is characterized by combining the Advanced Research Weather Research and Forecasting (WRF-ARW) model and the Advanced Regional Prediction System (ARPS) three-dimensional variational data assimilation (3DVAR) package. It is capable of assimilating radar reflectivity and radial velocity data from multiple Doppler radars as well as surface automatic weather station (AWS) data. Experiments are designed to evaluate the impacts of data assimilation on quantitative precipitation forecasting (QPF) by studying a heavy rainfall event in southern China. The forecasts from these experiments are verified against radar, surface, and precipitation observations. Comparison of echo structure and accumulated precipitation suggests that radar data assimilation is useful in improving the short-term forecast by capturing the location and orientation of the band of accumulated rainfall. The assimilation of radar data improves the short-term precipitation forecast skill by up to 9 hours by producing more convection. The slight but generally positive impact that surface AWS data has on the forecast of near-surface variables can last up to 6–9 hours. The assimilation of AWS observations alone has some benefit for improving the Fractions Skill Score (FSS) and bias scores; when radar data are assimilated, the additional AWS data may increase the degree of rainfall overprediction. © 2015, Chinese National Committee for International Association of Meteorology and Atmospheric Sciences, Institute of Atmospheric Physics, Science Press and Springer-Verlag Berlin Heidelberg. Source

Wang M.-J.,Shenzhen Key Laboratory of Severe Weather in South China | Zhang L.,Shenzhen Key Laboratory of Severe Weather in South China | Zhang L.-L.,Shenzhen Key Laboratory of Severe Weather in South China | Xie X.-M.,Shenzhen Key Laboratory of Severe Weather in South China | Li S.-F.,Shenzhen Polytechnic
Zhongguo Huanjing Kexue/China Environmental Science

Based on the Meticulous observational data of hourly haze, visibility and air quality monitoring of Shenzhen during 2010~2013, Seasonal variations of haze, the relationships of the meteorological conditions and air quality to haze were analyzed in order to provide the basis for issuing haze warning and forecast more pointedly. The results suggested that the annual haze days of Shenzhen presented an increasing trend overall and the phase change of a down trend since 2009. The monthly variations of haze days showed "V" type, which implied the haze occurred mainly in autumn and winter rather than in spring and summer. There were more long duration and serious haze processes in autumn and winter but short duration ones in spring and summer. The haze was often accompanied by mainly mild air pollution (35%). PM2.5 was the primary pollutant followed by O3, which indicated that PM2.5 was the main cause of haze weather and photochemical pollution was also serious in Shenzhen. There was significant variation of PM2.5, PM10 and O3 with the seasons. The primary pollutants changed with the seasons that PM2.5 was the main pollutant (above75%) in winter and spring, but O3 and PM2.5 were in summer and autumn. The wind and relative humidity were the important influencing factors of haze. The 80% of moderate and severe haze occurred under the wind speed >2 m/s and relative humidity 70%~90%, which suggested the weaker wind speed and the greater humidity were conductive to the emergence and development of haze. © 2015, Chinese Society for Environmental Sciences. All right reserved. Source

Discover hidden collaborations