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Yang H.,Shenzhen National Climate Observatory | Lu C.,Shenzhen National Climate Observatory | Liu A.,Shenzhen National Climate Observatory | Yang S.,National Meteorological Information Center
Guangxue Xuebao/Acta Optica Sinica | Year: 2013

Atmospheric aerosols are not only a major component of urban air pollution, but also one of the largest sources of uncertainty in the assessment of the climate evaluation. Aerosol optical properties are investigated at Shenzhen in Pearl River Delta of China according to the observation data of aerosol from 2011 to 2012. The aerosol at Shenzhen is characterized by strongly light-absorbing characteristics. Mean values (standard deviation, SD) of scattering and absorption coefficients for the entire period are (175.4±127.8)×10-6 m-1 and (30.5±24.5)×10-6 m-1, respectively. The mean single scattering albedo (SSA) for the entire period is estimated as 0.83, which is higher than the values reported for the domestic cities, such as Beijing and Guangzhou, but lower than that in foreign cities. The absorption, scattering coefficients and SSA values show a seasonal cycle with the lowest values in summer, while the highest values in winter. Their diurnal variations cannot be solely explained with the change of atmospheric boundary layer, and the influence of local wind patterns, variation of pollution, photochemial reaction and the complex chemical reaction at night should also be considered. A trajectory cluster analysis is applied to discern the source characteristics of aerosol optical properties for different air masses. The results show that the values of optical properties are all high when the air masses come from the dense population centers in industrial areas and contaminated regions, especially in winter. The cluster-mean SSA for aerosol coming from the polluted areas is not only higher than those from the "clean" directions, but also higher than the reported values for the regions with high pollution emissions.


Dai W.,Harbin Institute of Technology | Gao J.,Harbin Institute of Technology | Wang B.,Shenzhen national climate observatory | Ouyang F.,Harbin Institute of Technology
Applied Mechanics and Materials | Year: 2013

PM2.5and ionic components have been measured from summer 2009 to winter 2010 in the suburb of Shenzhen. Serious PM2.5pollution was observed, especially in winter. SO42-, NO3 and NH4 in winter were the predominant ions in PM2.5 In summer, the mean contributions of SO42-, NO3 and NH4 to PM2.5 decreased, while the contributions of Cl- and metal ions increased significantly. Furthermore, ion balance, ratio analysis and correlation analysis were conducted to identify the sources of ions in PM2.5. © (2013) Trans Tech Publications, Switzerland.


Wang G.,Shenzhen National Climate Observatory | Ni W.-T.,National Tsing Hua University | Ni W.-T.,Shanghai Normal University
Classical and Quantum Gravity | Year: 2013

eLISA/NGO is a new gravitational wave detection proposal with arm length of 106 km and one interferometer down-scaled from LISA. Just like LISA and ASTROD-GW, in order to attain the requisite sensitivity for eLISA/NGO, laser frequency noise must be suppressed to below the secondary noises such as the optical path noise, acceleration noise, etc. In previous papers, we have performed the numerical simulation of the time delay interferometry (TDI) for LISA and ASTROD-GW with one arm dysfunctional by using the CGC 2.7 ephemeris. The results are well below their respective limits in which the laser frequency noise is required to be suppressed. In this paper, we follow the same procedure to simulate the time delay interferometry numerically. To do this, we work out a set of 1000-day optimized mission orbits of the eLISA/NGO spacecraft starting on 1 January 2021 using the CGC 2.7 ephemeris framework. We then use the numerical method to calculate the residual optical path differences in the second-generation TDI solutions as in our previous papers. The maximum path length difference, for all configurations calculated, is below 13 mm (43 ps). It is well below the limit in which the laser frequency noise is required to be suppressed for eLISA/NGO. We compare and discuss the resulting differences due to the different arm lengths for various mission proposals - eLISA/NGO, an NGO-LISA-type mission with a nominal arm length of 2 × 106 km, LISA and ASTROD-GW. © 2013 IOP Publishing Ltd.


Li L.,Shenzhen National Climate Observatory | Yang L.,Shenzhen Meteorological Service Center | Zhang L.-J.,Shenzhen National Climate Observatory | Jiang Y.,Shenzhen National Climate Observatory
Advances in Atmospheric Sciences | Year: 2012

The impact of ground heating on flow fields in street canyons under different ambient wind speed conditions was studied based on numerical methods. A series of numerical tests were performed, and three factors including height-to-width (H/W) ratio, ambient wind speed and ground heating intensity were taken into account. Three types of street canyon with H/W ratios of 0. 5, 1. 0 and 2. 0, respectively, were used in the simulation and seven speed values ranging from 0. 0 to 3. 0 m s -1 were set for the ambient wind speed. The ground heating intensity, which was defined as the difference between the ground temperature and air temperature, ranged from 10 to 40 K with an increase of 10 K in the tests. The results showed that under calm conditions, ground heating could induce circulation with a wind speed of around 1. 0 m s -1, which is enough to disperse pollutants in a street canyon. It was also found that an ambient wind speed threshold may exist for street canyons with a fixed H/W ratio. When ambient wind speed was lower than the threshold identified in this study, the impact of the thermal effect on the flow field was obvious, and there existed a multi-vortex flow pattern in the street canyon. When the ambient wind speed was higher than the threshold, the circulation pattern was basically determined by dynamic effects. The tests on the impact of heating intensity showed that a higher ground heating intensity could strengthen the vortical flow within the street canyon, which would help improve pollutant diffusion capability in street canyons. © 2012 Chinese National Committee for International Association of Meteorology and Atmospheric Sciences, Institute of Atmospheric Physics, Science Press and Springer-Verlag Berlin Heidelberg.


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 | Year: 2016

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.


Li L.,Shenzhen National Climate Observatory | Chan P.W.,Hong Kong Observatory | Wang D.,Shenzhen National Climate Observatory | Tan M.,Shenzhen National Climate Observatory
Climate Research | Year: 2015

An intercomparison of climate trends between 2 adjacent large cities, Shenzhen and Hong Kong, in the past 46 yr (1968-2013) suggests that the rate of urbanization is clearly reflected in the rate of the change in local climate. Since becoming a special economic zone in 1980, Shenzhen has experienced a very rapid urbanization process. In only 30 yr, Shenzhen has transformed from a small town into a metropolis rivaling Hong Kong. The gross domestic product and urban built-up area in Shenzhen have increased rapidly. Climate data analysis over the last 46 yr showed a greater rate of change in climate in Shenzhen than in Hong Kong over the same period. In Shenzhen, average annual temperature warmed by 1.63 ± 0.18°C (∼0.35 ± 0.04°C per decade), average maximum temperature increased by 0.90 ± 0.19°C, average minimum temperature increased by 2.09 ± 0.23°C and the diurnal temperature range (DTR) decreased by 1.18 ± 0.23°C. Over the same period in Hong Kong, average temperature increased by 0.47 ± 0.20°C (∼0.10 ± 0.04°C per decade), maximum temperature increased by 0.12 ± 0.28°C, minimum temperature increased by 0.55 ± 0.20°C and DTR decreased by 0.43 ± 0.27°C. In addition, relative humidity in Shenzhen decreased by 13.13 ± 1.78% in the last 46 yr, while there were no significant changes in Hong Kong. Finally, data analysis showed that urbanization has no significant effect on total rainfall for both cities. © The authors 2015.


Li L.,Shenzhen National Climate Observatory | Li L.,CAS Institute of Atmospheric Physics | Chan P.W.,Hong Kong Observatory
Meteorologische Zeitschrift | Year: 2012

Apart from terrain-induced airflow disturbances and thunderstorms, buildings and artificial structures at airports may bring about sudden wind changes to aircraft in certain weather conditions. In the typhoon situation in the morning of 22 August 2008 under a generally crosswind situation, two aircraft landing at the Hong Kong International Airport reported encountering significant wind changes, which were considered to affect the operation of the aircraft. At the same time, a wind speed difference in the order of 10-15 knots was observed between the anemometers at the north and the south parallel runways of the airport. The cause of the wind changes experienced by the aircraft is studied in this paper by using numerical simulation, namely, using mesoscale meteorological models to provide the background wind fields, and nesting them with a computational fluid dynamics (CFD) model to study the effect of buildings and terrain on the airflow along the glide path of the landing aircraft. It is found that the complete set of simulation (i.e. including both buildings and terrain) successfully captures the wind speed difference between the north and the south runways, and gives the drop of the crosswind along the glide path exceeding the 7-knot criterion as adopted for buildinginduced wind changes affecting the normal operation of the aircraft. The results of the present study suggest that, for the timely warning of wind changes to be encountered by the landing aircraft, it may be necessary to consider examining the low-level wind effects of the buildings on the airfield by performing numerical simulations by mesoscale meteorological models as nested with a CFD model. © 2012 by Gebrüder Borntraeger.


Wang G.,Shenzhen National Climate Observatory | Ni W.-T.,Shanghai Normal University | Ni W.-T.,National Tsing Hua University
Chinese Physics B | Year: 2013

Astrodynamical space test of relativity using optical devices optimized for gravitation wave detection (ASTROD-GW) is an optimization of ASTROD to focus on the goal of detection of gravitation waves. The detection sensitivity is shifted 52 times toward larger wavelength compared with that of laser interferometer space antenna (LISA). The mission orbits of the three spacecrafts forming a nearly equilateral triangular array are chosen to be near the Sun - Earth Lagrange points L3, L4, and L5. The three spacecrafts range interferometrically with one another with an arm length of about 260 million kilometers. In order to attain the required sensitivity for ASTROD-GW, laser frequency noise must be suppressed to below the secondary noises such as the optical path noise, acceleration noise, etc. For suppressing laser frequency noise, we need to use time delay interferometry (TDI) to match the two different optical paths (times of travel). Since planets and other solar-system bodies perturb the orbits of ASTROD-GW spacecraft and affect the TDI, we simulate the time delay numerically using CGC 2.7 (here, CGC stands for center for gravitation and cosmology) ephemeris framework. To conform to the ASTROD-GW planning, we work out a set of 20-year optimized mission orbits of ASTROD-GW spacecraft starting at June 21, 2028, and calculate the differences in optical path in the first and second generation TDIs separately for one-detector case. In our optimized mission orbits of 20 years, changes of arm lengths are less than 0.0003 AU; the relative Doppler velocities are all less than 3 m/s. All the second generation TDI for one-detector case satisfies the ASTROD-GW requirement. © 2013 Chinese Physical Society and IOP Publishing Ltd.


Li L.,Shenzhen National Climate Observatory | Chan P.W.,Hong Kong Observatory | Zhang L.,Shenzhen National Climate Observatory | Hu F.,CAS Institute of Atmospheric Physics
Advances in Meteorology | Year: 2013

This study of a lee wave event over three-dimensional (3D) mountainous terrain in Lantau Island, Hong Kong, using a simulation combining mesoscale model and computational fluid dynamics (CFD) model has shown that (1) 3D steep mountainous terrain can trigger small scale lee waves under strong wind condition, and the horizontal extent of the wave structure is in a dimension of few kilometers and corresponds to the dimension of the horizontal cross-section of the mountain; (2) the life cycle of the lee wave is short, and the wave structures will continuously form roughly in the same location, then gradually move downstream, and dissipate over time; (3) the lee wave triggered by the mountainous terrain in this case can be categorized into "nonsymmetric vortex shedding" or "turbulent wake," as defined before based on water tank experiments; (4) the magnitude of the wave is related to strength of wind shear. This study also shows that a simulation combining mesoscale model and CFD can capture complex wave structure in the boundary layer over realistic 3D steep terrain, and have a potential value for operational jobs on air traffic warning, wind energy utilization, and atmospheric environmental assessment. © 2013 Lei Li et al.


Wang G.,Shenzhen National Climate Observatory | Ni W.-T.,National Tsing Hua University
Chinese Physics B | Year: 2015

ASTROD-GW (ASTROD [astrodynamical space test of relativity using optical devices] optimized for gravitational wave detection) is a gravitational-wave mission with the aim of detecting gravitational waves from massive black holes, extreme mass ratio inspirals (EMRIs) and galactic compact binaries together with testing relativistic gravity and probing dark energy and cosmology. Mission orbits of the 3 spacecrafts forming a nearly equilateral triangular array are chosen to be near the Sun-Earth Lagrange points L3, L4, and L5. The 3 spacecrafts range interferometrically with one another with arm length about 260 million kilometers. For 260 times longer arm length, the detection sensitivity of ASTROD-GW is 260 fold better than that of eLISA/NGO in the lower frequency region by assuming the same acceleration noise. Therefore, ASTROD-GW will be a better cosmological probe. In previous papers, we have worked out the time delay interferometry (TDI) for the ecliptic formation. To resolve the reflection ambiguity about the ecliptic plane in source position determination, we have changed the basic formation into slightly inclined formation with half-year precession-period. In this paper, we optimize a set of 10-year inclined ASTROD-GW mission orbits numerically using ephemeris framework starting at June 21, 2035, including cases of inclination angle with 0° (no inclination), 0.5°, 1.0°, 1.5°, 2.0°, 2.5°, and 3.0°. We simulate the time delays of the first and second generation TDI configurations for the different inclinations, and compare/analyse the numerical results to attain the requisite sensitivity of ASTROD-GW by suppressing laser frequency noise below the secondary noises. To explicate our calculation process for different inclination cases, we take the 1.0° as an example to show the orbit optimization and TDI simulation. © 2015 Chinese Physical Society and IOP Publishing Ltd.

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