Atmospheric & Oceanic Science Research Works

Permanent URI for this collectionhttp://hdl.handle.net/1903/1596

Formerly known as the Department of Meteorology.

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Author: search.filters.author.Cribb, Maureen

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    Understanding the Effects of Aerosols on Electrification and Lightning Polarity in an Idealized Supercell Thunderstorm via Model Emulation
    (Wiley, 2023-12-29) Sun, Mengyu; Li, Zhanqing; Wang, Tao; Mansell, Edward R.; Qie, Xiushu; Shan, Siyu; Liu, Dongxia; Cribb, Maureen
    Aerosol effects on the lightning intensity and polarity of a continental supercell storm were investigated using a three-dimensional lightning scheme within the Weather Research and Forecasting model. We find that both intra-cloud (IC) and cloud-to-ground (CG) flashes are enhanced by the increasing number of cloud condensation nuclei (CCN), especially the percentage of positive CG (+CG) strokes peaking at 42%. Electrical characteristics of the storm varied in different aerosol scenarios through microphysical processes. Added aerosols increase the number of cloud droplets and ice-phase hydrometeors. The greater ice-crystal concentration and larger graupel size ensure sufficient charge separation, leading to higher charge density and more lightning discharges. In addition, an inverted polarity charge structure with a strong positive-charge region in the mid-levels was formed mainly due to the positively charged graupel in the presence of higher supercooled cloud water content. Positive lightning channels originating from this positive-charge region propagated to the ground, producing more +CG strokes. When the aerosol concentration was low, the charge density in the upper positive-charge region was much lower due to smaller ice-particle content. Consequently, there were barely any +CG strokes. Most of the negative CG flashes deposited positive charge in the lower negative-charge region.
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    Hygroscopicity of Different Types of Aerosol Particles: Case Studies Using Multi-Instrument Data in Megacity Beijing, China
    (MDPI, 2020-03-01) Wu, Tong; Li, Zhanqing; Chen, Jun; Wang, Yuying; Wu, Hao; Jin, Xiao'ai; Liang, Chen; Li, Shangze; Wang, Wei; Cribb, Maureen
    Water uptake by aerosol particles alters its light-scattering characteristics significantly. However, the hygroscopicities of different aerosol particles are not the same due to their different chemical and physical properties. Such differences are explored by making use of extensive measurements concerning aerosol optical and microphysical properties made during a field experiment from December 2018 to March 2019 in Beijing. The aerosol hygroscopic growth was captured by the aerosol optical characteristics obtained from micropulse lidar, aerosol chemical composition, and aerosol particle size distribution information from ground monitoring, together with conventional meteorological measurements. Aerosol hygroscopicity behaves rather distinctly for mineral dust coarse-mode aerosol (Case I) and non-dust fine-mode aerosol (Case II) in terms of the hygroscopic enhancement factor, 𝑓𝛽(𝑅𝐻,𝜆532), calculated for the same humidity range. The two types of aerosols were identified by applying the polarization lidar photometer networking method (POLIPHON). The hygroscopicity for non-dust aerosol was much higher than that for dust conditions with the 𝑓𝛽(𝑅𝐻,𝜆532) being around 1.4 and 3.1, respectively, at the relative humidity of 86% for the two cases identified in this study. To study the effect of dust particles on the hygroscopicity of the overall atmospheric aerosol, the two types of aerosols were identified and separated by applying the polarization lidar photometer networking method in Case I. The hygroscopic enhancement factor of separated non-dust fine-mode particles in Case I had been significantly strengthened, getting closer to that of the total aerosol in Case II. These results were verified by the hygroscopicity parameter, κ (Case I non-dust particles: 0.357 ± 0.024; Case II total: 0.344 ± 0.026), based on the chemical components obtained by an aerosol chemical speciation instrument, both of which showed strong hygroscopicity. It was found that non-dust fine-mode aerosol contributes more during hygroscopic growth and that non-hygroscopic mineral dust aerosol may reduce the total hygroscopicity per unit volume in Beijing.
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    The Urban–Rural Heterogeneity of Air Pollution in 35 Metropolitan Regions across China
    (MDPI, 2020-07-19) Han, Wenchao; Li, Zhanqing; Guo, Jianping; Su, Tianning; Chen, Tianmeng; Wei, Jing; Cribb, Maureen
    Urbanization and air pollution are major anthropogenic impacts on Earth’s environment, weather, and climate. Each has been studied extensively, but their interactions have not. Urbanization leads to a dramatic variation in the spatial distribution of air pollution (fine particles) by altering surface properties and boundary-layer micrometeorology, but it remains unclear, especially between the centers and suburbs of metropolitan regions. Here, we investigated the spatial variation, or inhomogeneity, of air quality in urban and rural areas of 35 major metropolitan regions across China using four different long-term observational datasets from both ground-based and space-borne observations during the period 2001–2015. In general, air pollution in summer in urban areas is more serious than in rural areas. However, it is more homogeneously polluted, and also more severely polluted in winter than that in summer. Four factors are found to play roles in the spatial inhomogeneity of air pollution between urban and rural areas and their seasonal differences: (1) the urban–rural difference in emissions in summer is slightly larger than in winter; (2) urban structures have a more obvious association with the spatial distribution of aerosols in summer; (3) the wind speed, topography, and different reductions in the planetary boundary layer height from clean to polluted conditions have different effects on the density of pollutants in different seasons; and (4) relative humidity can play an important role in affecting the spatial inhomogeneity of air pollution despite the large uncertainties.
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    Effect of Urban Built-Up Area Expansion on the Urban Heat Islands in Different Seasons in 34 Metropolitan Regions across China
    (MDPI, 2022-12-31) Han, Wenchao; Tao, Zhuolin; Li, Zhangqing; Chengg, Miaomiao; Fan, Hao; Cribb, Maureen; Wang, Qi
    The urban heat island (𝑈𝐻𝐼) refers to the land surface temperature (LST) difference between urban areas and their undeveloped or underdeveloped surroundings. It is a measure of the thermal influence of the urban built-up area expansion (𝑈𝐵𝐴𝐸), a topic that has been extensively studied. However, the impact of 𝑈𝐵𝐴𝐸 on the LST differences between urban areas and rural areas (𝑈𝐻𝐼𝑈−𝑅) and between urban areas and emerging urban areas (𝑈𝐻𝐼𝑈−𝑆) in different seasons has seldom been investigated. Here, the 𝑈𝐻𝐼𝑈−𝑆 and 𝑈𝐻𝐼𝑈−𝑅 in 34 major metropolitan regions across China, and their spatiotemporal variations based on long-term space-borne observations during the period 2001–2020 were analyzed. The 𝑈𝐵𝐴𝐸 quantified by the difference in landscape metrics of built-up areas between 2020 and 2000 and their impact on 𝑈𝐻𝐼 was further analyzed. The 𝑈𝐵𝐴𝐸 is impacted by the level of economic development and topography. The 𝑈𝐵𝐴𝐸 of cities located in more developed regions was more significant than that in less developed regions. Coastal cities experienced the most obvious 𝑈𝐵𝐴𝐸, followed by plain and hilly cities. The 𝑈𝐵𝐴𝐸 in mountainous regions was the weakest. On an annual basis, 𝑈𝐻𝐼𝑈−𝑅 was larger than 𝑈𝐻𝐼𝑈−𝑆, decreasing more slowly with 𝑈𝐵𝐴𝐸 than 𝑈𝐻𝐼𝑈−𝑆. In different seasons, the 𝑈𝐻𝐼𝑈−𝑆 and 𝑈𝐻𝐼𝑈−𝑅 were larger, more clearly varying temporally with 𝑈𝐵𝐴𝐸 in summer than in winter, and their temporal variations were significantly correlated with 𝑈𝐵𝐴𝐸 in summer but not in winter. The seasonal difference in 𝑈𝐻𝐼𝑈−𝑅 was larger than that of 𝑈𝐻𝐼𝑈−𝑆. Both the 𝑈𝐻𝐼𝑈−𝑆 and 𝑈𝐻𝐼𝑈−𝑅 in coastal cities were the lowest in summer, decreasing the fastest with 𝑈𝐵𝐴𝐸, while those in mountain cities decreased the slowest. The change in the density of built-up lands was the primary driver affecting the temporal variations in 𝑈𝐻𝐼𝑈−𝑆 and 𝑈𝐻𝐼𝑈−𝑅 during 𝑈𝐵𝐴𝐸, followed by changes in proportion and shape, while the impact of the speed of expansion was the smallest, all of which were more obvious in summer than in winter. The decreased density of built-up lands can reduce 𝑈𝐻𝐼. These findings provide a new perspective for a deeper understanding of the effect of urban expansion on LST in different seasons.
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    Differentiating the Contributions of Particle Concentration, Humidity, and Hygroscopicity to Aerosol Light Scattering at Three Sites in China
    (Wiley, 2022-11-23) Jin, Xiaoai; Li, Zhanqing; Wu, Tong; Wang, Yuying; Su, Tianning; Ren, Rongmin; Wu, Hao; Zhang, Dongmei; Li, Shangze; Cribb, Maureen
    The scattering of light by aerosol particles dictates atmospheric visibility, which is a straightforward indicator of air quality. It is affected by numerous factors, such as particle number size distribution, particle mass concentration (PM2.5), ambient relative humidity (RH), and chemical composition. The latter two factors jointly influence the aerosol liquid water content (ALWC). Here, the particle backscattering coefficient (βp) under ambient RH conditions is investigated to differentiate and quantify the contributions of aerosol properties and meteorology using comprehensive observational datasets acquired at three megacities in China, that is, Beijing (BJ), Nanjing (NJ), and Guangzhou (GZ). Overall, the temporal variations in βp under ambient RH conditions are consistent with those in ALWC at the three sites. The PM2.5 in BJ is systematically higher than in NJ and GZ, while ambient RH and aerosol hygroscopicity in NJ are much higher than in BJ and GZ. Notable differences in the variations of βp with related factors at the three sites are demonstrated. βp is more sensitive to particle hygroscopicity and mass in NJ and ambient RH in BJ. The relative contributions of these factors to βp at the three sites under different pollution conditions are differentiated and quantified. The factor with the largest impact on the variability in βp shifts from particle mass to ambient RH as air quality deteriorated to heavy pollution in BJ. The opposite is true in NJ. In GZ, the contributions of these factors to changes in βp under different pollution conditions are similar, both dominated by PM2.5.