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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. Source


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. Source


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. Source


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. Source


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. Source

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