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Chen L.S.,Chinese Academy of Meteorological Sciences | Li Y.,Chinese Academy of Meteorological Sciences | Cheng Z.Q.,Guangzhou Central Meteorological Observatory
Advances in Atmospheric Sciences | Year: 2010

The ability to forecast heavy rainfall associated with landfalling tropical cyclones (LTCs) can be improved with a better understanding of the mechanism of rainfall rates and distributions of LTCs. Research in the area of LTCs has shown that associated heavy rainfall is related closely to mechanisms such as moisture transport, extratropical transition (ET), interaction with monsoon surge, land surface processes or topographic effects, mesoscale convective system activities within the LTC, and boundary layer energy transfer etc.. LTCs interacting with environmental weather systems, especially the westerly trough and mei-yu front, could change the rainfall rate and distribution associated with these mid-latitude weather systems. Recently improved technologies have contributed to advancements within the areas of quantitative precipitation estimation (QPE) and quantitative precipitation forecasting (QPF). More specifically, progress has been due primarily to remote sensing observations and mesoscale numerical models which incorporate advanced assimilation techniques. Such progress may provide the tools necessary to improve rainfall forecasting techniques associated with LTCs in the future. © 2010 Chinese National Committee for International Association of Meteorology and Atmospheric Sciences, Institute of Atmospheric Physics, Science Press and Springer-Verlag Berlin Heidelberg.

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

The relationship between the intensity of the South China Sea summer monsoon (SCSSM) and the Nino3.4 index and anomalous atmospheric circulation patterns associated with a strong and weak SCSSM are investigated using the NCEP/NCAR reanalysis data, Extended Reconstructed Sea Surface Temperature (ERSST) data and Climate Prediction Center Merged Analysis of Precipitation (CMAP) data. The SCSSM is significantly positively correlated with the Nino3.4 index in the succeeding northern autumn and winter. In the strong minus weak SCSSM composite, a positive East Asia-Pacific teleconnection (EAP) pattern and a negative Europe-Asian-Pacific teleconnection (EUP) pattern appear in the 500 hPa height difference field; low-level cross-equatorial flows are strengthened over the Maritime Continent (MC) region; positive (negative) precipitation anomalies occur in the South China Sea and western north Pacific (MC). A possible mechanism through which SCSSM affects ENSO is proposed. A strong (weak) SCSSM strengthens (weakens) cross-equatorial flows over the MC. The anomalous cross-equatorial flows cool (warm) the SST around the MC through enhanced (reduced) surface latent heat fluxes. The cooling (warming) further leads to suppressed (enhanced) convection over the MC, and causes the anomalous westerly (easterly) in the equatorial western Pacific, which favors the onset of El Niño (La Niña) through modulating the positive air-sea feedback process.

Deng H.,Guangdong Ecological Meteorology Center | Tan H.,Guangdong Ecological Meteorology Center | Tan H.,Guangzhou Institute of Tropical and Marine Meteorology | Li F.,Guangzhou Institute of Tropical and Marine Meteorology | And 5 more authors.
Science of the Total Environment | Year: 2016

Light scattering of aerosols depends on ambient relative humidity (RH) since hygroscopic particles absorb significant water at high RH, and this results in low visibility. This paper used custom-made parallel nephelometers (PNEPs) to measure aerosol light scattering enhancement factor f(RH), and utilized data including visibility, PM2.5, black carbon, water-soluble ions mass concentrations and surface meteorological parameters, in conjunction with background weather conditions, to analyze a haze event in Guangzhou during 8th-15th Dec. 2013. Unfavorable weather conditions, such as high RH and low wind speed, were observed during the haze event. The hourly average mass concentration of PM2.5 was 127μg/m3, with concentration of 192.4μg/m3 on 9th and 196μg/m3 on 13th. The f(RH) did not exhibit significant changes during this haze process, with value of f(80%)=1.58±0.07. Although the mass fraction of water-soluble ions to PM2.5 decreased after 12th Dec., the aerosol hygroscopicity might not have changed significantly since the mass fraction of nitrate became more dominant, which has stronger ability to take up water. The best-fitted parameterized function for f(RH) is f(RH)=0.731+0.1375*(1-RH/100)-1 +0.00719*(1-RH/100)-2. Combining the fixed parameterization of f(RH) above, the visibility was calculated with the measured light scattering and absorption coefficient of particles and gas under dry condition, as well as ambient RH. The predicted visibility range agrees well with the measurements without precipitation. Using ISORROPIA II model, the calculated aerosol liquid water content (ALWC) at ambient RH varied consistently with the PM2.5 under lower RH, while it was more influenced by high RH. This work also show that high RH accompanied with precipitation will enhance aerosol hygroscopic growth effect, leading to further visibility degradation, even if PM2.5 mass decreased due to precipitation. © 2016 Elsevier B.V.

Wang L.,Fudan University | Du H.,Fudan University | Chen J.,Fudan University | Zhang M.,Fudan University | And 4 more authors.
Atmospheric Research | Year: 2013

The physical and chemical properties of aerosol particles were investigated during two dust storm events that occurred in March 20-21, 2010 (DS1) and April 26-27, 2010 (DS2), respectively, at Shanghai, China. Highest hourly mass concentrations of particulate matters with less than 2.5μm (PM2.5) and 10μm (PM10) in aerodynamic diameter reached 469 and 1700μgm-3, respectively, in DS1, whereas the corresponding highest values for PM2.5 and PM10 were 94 and 236μgm-3, respectively, in DS2. Profiles of hourly concentrations of water soluble ions show that anthropogenic air masses preceded dust plume by an interval of 10h during the two dust storm events. Anthropogenic air masses were characterized with high concentrations of SO4 2-, NO3 -, and NH4 +, whereas dust plume was dominated by Ca2+ in water soluble components. Together with back trajectories of air parcels arriving at Shanghai, analysis of surface weather chart shows that DS1 was characterized with the arrival of a cold front at Shanghai. In contrast, a chief feature of the cold front stimulated DS2 was that the cold-front did not extend to Shanghai, and dust particles traveled following the front and were transported to Shanghai by strong southeastward airstream although the front did not extend to Shanghai. Our results suggest that Asian dust particles are not homogeneously mixed with anthropogenic pollutants and consecutive transport of anthropogenic air masses and dust plumes occurs. •Asian dust particles were not homogeneously mixed with anthropogenic pollutants.•Consecutive transport of anthropogenic and dust plumes occurred by an interval of 10hours.•Dust particles can be transported to Shanghai by strong airstreams between a high and a low. © 2013 Elsevier B.V.

Zeng L.-P.,Sun Yat Sen University | Lin W.-S.,Sun Yat Sen University | Fan Q.,Sun Yat Sen University | Feng Y.-R.,Guangzhou Central Meteorological Observatory
Environmental Modeling and Assessment | Year: 2012

Changes in urban surface areas and population growth have significantly affected the weather and environment. Emissions of nitrogen oxides are increasing in the Pearl River Delta region. Nitrogen compounds emitted by factories and motor vehicles are the major sources of nitric pollution. To study the impacts of urbanization and the relationship between pollutant diffusion and the atmospheric environment, the nonhydrostatic mesoscale forecast model MM5 (v3. 73), which was developed by Penn State University and the National Center of Atmospheric Research, and a mass continuity equation for air pollutants, were used in this study. Two experiments were designed. One experiment (BE) applied horizontal grid resolutions of 27, 9, 3, and 1 km in four nested domains. The other experiment adopted new land-use data (in domain 4) directly retrieved from Landsat Thematic Mapper imagery to replace the 1980s data of the United States Geological Survey in BE. A 48-h simulation (from 0000 UTC on 21 October to 0000 UTC on 23 October 2008) was conducted, with the first 12 h being the spin-up time and the remaining 36 h being the effective simulation, so as to capture the diurnal features of the thermally induced winds associated with the land-sea breeze and urban heat island circulations. The different results obtained from the two tests for wind circulation and air pollution dispersion and transportation in the Pearl River Delta region were analyzed. The simulated results show that the both experiments can well simulate land-sea breeze circulation and remarkable land-sea breeze evolution, comparing with observation data. The height of the PBL had a significant diurnal cycle. The structure of the wind field can obviously impact the dispersion of the NO x in three dimensions. Nitrogen oxides mainly diffused along the dominant wind direction (east or southeast wind), therefore the majority of the pollutants accumulated in the northwest region of the fine domain in both simulation experiments. However, it induced the pollutants concentration in an irregular pattern due to the fine-resolution grid spaces and complicated inland wind field in the northwest area of the inner domain. Moreover, increasing the proportion of urban surface caused sensible heat flux increase, latent heat flux decrease and humility reducing relatively in the region of urban surface characteristics apparently. Urbanization will cause pollution accumulated severely over the urban surface. © 2012 Springer Science+Business Media B.V.

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