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Yu H.,Hong Kong University of Science and Technology | Wu C.,Hong Kong University of Science and Technology | Wu C.,U.S. National Center for Atmospheric Research | Wu D.,Guangzhou Institute of Tropical and Marine Meteorology | Yu J.Z.,Hong Kong University of Science and Technology
Atmospheric Chemistry and Physics | Year: 2010

Elemental carbon (EC) in size-segregated aerosol samples were determined at five urban, one suburban, and one rural locations in the Pearl River Delta region in South China during 2006-2008 period. The size modal characteristics of EC were different at the urban and suburban/rural locations. The urban EC had a dominant condensation mode with a mass median aerodynamic diameter (MMAD) in the 0.36-0.43 μm range and a slightly less abundant mode in the droplet mode size (MMAD: 0.8-1.1 μm), while the suburban/rural EC had a prominent mode in the droplet mode size (MMAD: 0.7-1.1 μm) and a minor condensation mode (MMAD: 0.22-0.33 μm). Calculations using Mie theory and the measured size distributions of EC, organic carbon, and major inorganic ions indicate that EC-containing particles contributed 76±20% of the observed light extinction at the urban sites. Among the EC-containing particles, EC mass alone contributed 21±11% of the observed light extinction while non-EC materials on the EC particles (i.e., organic matter, ammonium sulfate, and water) contributed 55±15%. At the suburban/rural locations, EC-containing particles contributed 37g-48% of the measured light extinction, with EC mass contributing 4-10% and non-EC coating materials contributing the remaining light extinction. Our results suggest that EC-containing particles were important to the overall light extinction in the urban atmospheres due to their more abundant presence from vehicular emissions. The EC-containing particles in the suburban/rural locations had a reduced but still significant contribution to light extinction budget. © Author(s) 2010.

Wu C.,Hong Kong University of Science and Technology | Ng W.M.,Hong Kong University of Science and Technology | Huang J.,Hong Kong University of Science and Technology | Wu D.,Guangzhou Institute of Tropical and Marine Meteorology | Yu J.Z.,Hong Kong University of Science and Technology
Aerosol Science and Technology | Year: 2012

Organic carbon (OC) and elemental carbon (EC) are operationally defined due to the lack of definitive standards. Consequently, their quantification is protocol dependent. IMPROVE and NIOSH are the two widely used thermal/optical protocols for OCEC analysis, differing in temperature programs and in the optical method for charring correction. The IMPROVE protocol is often implemented on a DRI analyzer while the NIOSH protocol is often implemented on a Sunset Laboratory Analyzer. Evaluation of the implementation of the IMPROVE protocol on the Sunset Laboratory analyzer or implementation of the NIOSH or NIOSHderived protocols on the DRI analyzer has rarely been reported. We analyzed OC and EC in about 100 ambient samples collected in the Pearl River Delta in China by implementing the IMPROVE protocol and a NIOSH-derived (ACE-Asia) protocol on both a DRI Model 2001 analyzer and a Sunset Laboratory analyzer. The total carbon (TC) and EC filter loading as determined by the ACE-Asia protocol on the Sunset analyzer varied from 2.6 to 67.0 and 0.2 to 7.4 μg cm -2, respectively. Inter-instrument comparison indicates that the implementation of the IMPROVE protocol on the Sunset analyzer reports TC, EC, and OC measurements to be in good agreement with those made on the DRI analyzer. EC and OC analyzed using the ACE-Asia protocol are also in good agreements for measurements implemented on the Sunset and DRI analyzers. Inter-protocol comparison indicates consistency in TC determination but discrepancies in OC and EC, with the IMPROVE protocol reporting much higher EC than the ACE-Asia protocol. An analysis of different comparison scenarios reveals that the cause of the EC difference could be quantitatively attributed to temperature protocol (thermal effect) and optical pyrolysis correction method (reflectance vs. transmittance). The variation in EC concentrations was more pronounced in samples that produced more charred OC during thermal analysis. Copyright © American Association for Aerosol Research.

Wu M.,Sun Yat Sen University | Wu D.,Sun Yat Sen University | Wu D.,Guangzhou Institute of Tropical and Marine Meteorology | Fan Q.,Sun Yat Sen University | And 3 more authors.
Atmospheric Chemistry and Physics | Year: 2013

The structure of the atmospheric boundary layer (ABL) and its influence on regional air quality over the Pearl River Delta (PRD) were examined through two intensive observations in October 2004 and July 2006. Analytical results show the presence of two types of typical weather conditions associated with poor air quality over the PRD. The first is the warm period before a cold front (WPBCF) and the second is the subsidence period controlled by a tropical cyclone (SPCTC). Two typical low air quality situations, which are affected by WPBCF and SPCTC, and one high air quality situation were analysed in detail. Results showed that continuously low or calm ground winds resulted in the accumulation of pollutants, and sea-land breezes had. © 2013 Author(s).

Wu D.,Guangzhou Institute of Tropical and Marine Meteorology | Wu D.,Sun Yat Sen University
Huanjing Kexue Xuebao/Acta Scientiae Circumstantiae | Year: 2012

Systematic research on haze in China has been on-going for a decade. The rapid economic expansion and urbanization has led to worsening particulate matter (PM) pollution and more frequent poor visibility events. A rapid increase in the number of hazy days has been seen over eastern China. The culprit of hazy weather is fine PM pollution. Hazy weather is often associated with photochemical pollution and composition of aerosols responsible for haze is rather complicated. In recent years, hazy weather, due to its significant environmental impacts and climatic effects, has become a hot topic, attracting wide attention from scientific community, government departments and the public. This paper surveys the literature in Chinese in the recent decade to provide a review on the process of understanding haze and research progress in hazy weather. Future research directions are also discussed.

Wan Q.,Guangzhou Institute of Tropical and Marine Meteorology | Xu J.,National Oceanic and Atmospheric Administration
Hydrological Processes | Year: 2011

The evolution and structure of rainstorms associated with a flash-flood event are simulated by the Advanced Weather Research and Forecasting (WRF-ARW) model of the National Center for Atmospheric Research and the Gridpoint Statistical Interpolation (GSI) data assimilation (DA) system of the National Oceanic and Atmospheric Administration (NOAA) of the United States. The event is based on a flash flood that occurred in the central Guangdong Province of south-east China during 20-21 June 2005. Compared to an hourly mixed rain-gauge and satellite-retrieved precipitation data, the model shows the capability to reproduce the intensity and location of rainfall; however, the simulation depends on three conditions to a large extent: model resolution, physical processes schemes and initial condition. In this case, the Eta Ferrier microphysics scheme and the initialization with satellite radiance DA with a fine 4-km grid spacing nested grid and coarse 12-km grid spacing outer grid are the best options. The model-predicted rain rates, however, are slightly overestimated, and the activities of the storms do not precisely correspond with those observed, although peak values are obtained. Abundant moisture brought by the south-westerly winds with a mesoscale low-level jet from the South China Sea or Bay of Bengal and trapped within the XingfengJiang region encompassed by northern Jiulian, southern Lianhua and eastern small mountains are apparently the primary elements responsible for the flood event. All simulated rainstorms were initiated over the southern slopes of the Jiulian Mountain and moved south or north-eastward within the Xingfengjiang region. Meanwhile, the Skew-T/Log-P diagrams show that there is a fairly high convective available potential energy (CAPE) over the active areas of the rainstorms. The higher CAPE provides a beneficial thermodynamic condition for the development of rainstorms, but the higher convective inhibition near the northern, eastern and southern mountains prohibits the storms from moving out of the region and causes heavy rainfall that is trapped within the area. © 2010 John Wiley & Sons, Ltd.

Wang Y.,Texas A&M University | Wan Q.,Guangzhou Institute of Tropical and Marine Meteorology | Meng W.,Guangzhou Institute of Tropical and Marine Meteorology | Liao F.,Guangzhou Institute of Tropical and Marine Meteorology | And 3 more authors.
Atmospheric Chemistry and Physics | Year: 2011

Seven-year measurements of precipitation, lightning flashes, and visibility from 2000 to 2006 have been analyzed in the Pearl River Delta (PRD) region, China, with a focus on the Guangzhou megacity area. Statistical analysis shows that the occurrence of heavy rainfall (>25 mm per day) and frequency of lightning strikes are reversely correlated to visibility during this period. To elucidate the effects of aerosols on cloud processes, precipitation, and lightning activity, a cloud resolving-Weather Research and Forecasting (CR-WRF) model with a two-moment bulk microphysical scheme is employed to simulate a mesoscale convective system occurring on 28 Match 2009 in the Guangzhou megacity area. The model predicted evolutions of composite radar reflectivity and accumulated precipitation are in agreement with measurements from S-band weather radars and automatic gauge stations. The calculated lightning potential index (LPI) exhibits temporal and spatial consistence with lightning flashes recorded by a local lightning detection network. Sensitivity experiments have been performed to reflect aerosol conditions representative of polluted and clean cases. The simulations suggest that precipitation and LPI are enhanced by about 16% and 50%, respectively, under the polluted aerosol condition. Our results suggest that elevated aerosol loading suppresses light and moderate precipitation (less than 25 mm per day), but enhances heavy precipitation. The responses of hydrometeors and latent heat release to different aerosol loadings reveal the physical mechanism for the precipitation and lightning enhancement in the Guangzhou megacity area, showing more efficient mixed phase processes and intensified convection under the polluted aerosol condition. © 2011 Author(s).

Liu L.,CAS Institute of Atmospheric Physics | Hu F.,CAS Institute of Atmospheric Physics | Cheng X.-L.,CAS Institute of Atmospheric Physics | Song L.-L.,Guangzhou Institute of Tropical and Marine Meteorology
Boundary-Layer Meteorology | Year: 2010

The probability density functions (pdf's) of the wind increments are measured under different weather conditions in the atmospheric boundary layer, including the extreme weather of a typhoon and sand storm. It is found that in each case the measured pdf's with respect to different time lags coincide by suitable scaling transformation. This property is similar to that of the stable distributions. However, fitting results show that the tails of the stable distributions are generally heavier than that of the measured ones. Beside, the stable distributions (except for the Gaussian distribution) have infinite variance, which implies infinite average kinetic energy. In fact, it can be proved that if the tails of the pdf's are heavy enough, the variance will be infinite. Therefore, the tail-truncated stable distributions with finite variances are introduced to fit the data and the fitting results are excellent. © Springer Science+Business Media B.V. 2009.

He C.,Guangzhou Institute of Tropical and Marine Meteorology | Zhou T.,CAS Institute of Atmospheric Physics
Atmospheric Science Letters | Year: 2015

A decadal change has occurred on the relationship between the summertime western North Pacific subtropical High (WNPSH) and the tropical Sea Surface Temperature anomalies (SSTA) in the early 1990s. After this decadal change, the interannual variability of the WNPSH is more strongly regulated by the SSTA over the equatorial central Pacific and the maritime continent. The earlier decay of ElNiño in strong WNPSH years and the earlier development of ElNiño in weak WNPSH years both contributed to this change. Such decadal change is found in the pre-industrial control simulation of a coupled model, suggesting it is probably an internal variability of the climate system. © 2014 Royal Meteorological Society.

Huang H.,Guangzhou Institute of Tropical and Marine Meteorology | Mao W.,Guangzhou Institute of Tropical and Marine Meteorology
Monthly Weather Review | Year: 2015

Knowing the relationship between local convective precipitation and boundary layer processes is critical for forecasting rainstorms. For the South China Sea area, such a forecast is particularly important during the monsoon season. During such a season, the authors examined the boundary layer features at three sites as part of the South China Sea Monsoon Experiment-Boundary Layer Height (SCSMEX-BLH) experiment. The sites are spread from inland to over sea along a 43.4-km line. Here the authors analyze SCSMEX-BLH data from an intensive observing period that includes a convectively suppressed (inactive) period, a period influenced by a tropical storm, and a convectively active monsoon period. Some preliminary findings include the following: 1) The absorption of shortwave radiation over the sea is the primary driver of the land-sea temperature difference. The difference produces a diurnal variation below 400 m, with a warmer surface layer over the coast at night. 2) In the inactive and storm periods, the sensible heat flux is larger than that in the active period, whereas in the active period, the heat flux (primarily latent heat flux) over sea is significant. Also in the active period, the depth of the mixed layer inland is smaller than that in other periods, but the depth on the coast is always higher than that in other periods. 3) In the active period at night, as a monsoon vapor surge advects horizontally over the warm sea surface, a large latent heat flux driven by strong winds aids the growth of marine cumulus, which eventually develop into inland cumulonimbus bringing inland rainfall. © 2015 American Meteorological Society.

Gu D.,Guangzhou Institute of Tropical and Marine Meteorology | Li T.,University of Hawaii at Manoa | Ji Z.,Guangzhou Central Meteorological Observatory | Zheng B.,Guangzhou Institute of Tropical and Marine Meteorology
Journal of Climate | Year: 2010

The phase relationships of the western North Pacific (WNP) summer monsoon (WNPM) with the Australian monsoon (AM) and Indian monsoon (IM) are investigated using observational rainfall, SST, and NCEP reanalysis data for the period of 1979-2005. It is found that a strongWNPMoften follows a strongAM but leads a weak AM, and a significant simultaneous negative correlation appears between WNPM and IM. The in-phase relationship from AM to the succeeding WNPM occurs often during the El Niño decaying phase when the warm eastern Pacific SST anomaly (SSTA) weakens AM through anomalous Walker circulation and the persistence of an anomalous WNP anticyclone from the boreal winter to summer leads to a weak WNPM. The out-of-phase relation from WNPM to the succeeding AM occurs either during the El Niño early onset year when the warm SSTA in June-August (JJA) is strong enough to force a low-level cyclonic flow anomaly in WNP and in December-February (DJF) the same warm SSTA forces a weak AM, or during the El Niño decaying phase when the persistence of theWNP anomalous anticyclone causes a weak WNPMand the transition of a warmto a cold episode causes a strongAMin DJF. The simultaneous negative correlation betweenWNPMand IM often appears either during the El Niño early onset years when the warm eastern Pacific SSTA induces the cyclonic wind shear that strengthens WNPM but suppresses convection over India, or during the El Niño decaying summer when a weakWNPM results from the persistence of the local anomalous anticyclone and a strong IM results from the El Niño-to-La Niña transition or a basin-wide Indian Ocean warming. © 2010 American Meteorological Society.

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