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Large-scale Circulation Control of the Occurrence of Low-level Turbulence at Hong Kong International Airport

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Advances in Atmospheric Sciences 2018年第4期35卷 435-444页

作者： Marco Y. T. LEUNG Wen ZHOU Chi-Ming SHUN Pak-Wai CHAN guy carpenter asia-pacific climate impact center School of Energy and Environment City University of Hong Kong Hong Kong China Hong Kong Observatory Hong Kong China

This study identifies the atmospheric circulation features that are favorable for the occurrence of low-level turbulence at Hong Kong International Airport [below 1600 feet （around 500 m）]. By using LIDAR data at the airport, turbulence and nonturbulence cases are selected. It is found that the occurrence of turbulence is significantly related to the strength of the southerly wind at 850 hPa over the South China coast. On the other hand, the east-west wihd at this height demonstrates a weak relation to the occurrence. This suggests that turbulence is generated by flow passing Lantau Island from the south. The southerly wind also transports moisture from the South China Sea to Hong Kong, reducing local stability. This is favorable for the development of strong turbulence. It is also noted that the strong southerly wind during the occurrence of low-level turbulence is contributed by an anomalous zonal gradient of geopotential in the lower troposphere over the South China Sea. This gradient is caused by the combination of variations at different timescales. These are the passage of synoptic extratropical cyclones and anticyclones and the intraseasonal variation in the western North pacific subtropical high. The seasonal variation in geopotential east of the Tibetan Plateau leads to a seasonal change in meridional wind, by which the frequency of low-level turbulence is maximized in spring and minimized in autumn.

关键词： LIDAR temperate cyclone and anticyclone western North pacific subtropical high seasonal cycle topography effect

Changes in the East asian Cold Season since 2000

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Advances in Atmospheric Sciences 2011年第1期28卷 69-79页

作者：魏科陈文周文 center for Monsoon System Research Institute of Atmospheric PhysicsChinese Academy of Sciences guy carpenter asia-pacific climate impact Centre School of Energy and EnvironmentCity University of Hong Kong

Using NCEP-NCAR reanalysis data and observational data from meteorological stations in China, the evolution of the East asian cold season （EACS） and its long-term changes after 2000 were studied. A monsoon tendency index （MTI）, defined as the temporal di？erence of the East asian monsoon index, indi- cates that the winter monsoon setup has been postponed in autumn, while the setup has quickened in early winter. In mid winter, the EACS breakdown process has accelerated, while it has lingered in late winter. The authors suggest that the postponement of monsoon setup in autumn may be caused by strong global warming at the lower levels, which further limits the setup time period and leads to the quickening of the setup process in early winter. Meanwhile, a north-south seesaw of temperature tendency change in China can be observed in December and February, which may be related to large-scale circulation changes in the stratosphere, characterized by a polar warming in mid winter and polar cooling in early spring. This linkage is possibly caused by the dynamical coupling between stratosphere and troposphere, via the variation of planetary wave activities. In spring, the speed of the EACS breakdown has decreased, which favors the revival of the EACS in East asia.

关键词： seasonal evolution East asian winter monsoon stratosphere-troposphere interaction

Variability and Risk Analysis of Hong Kong Air Quality Based on Monsoon and El Nino Conditions

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Advances in Atmospheric Sciences 2013年第2期30卷 280-290页

作者： Jong-Suk KIM ZHOU Wen Ho Nam CHEUNG Chak Hang CHOW school of energy and environment City University of Hong Kong Hong Kong guy carpenter asia-pacific climate impact Centre City University of Hong Kong Hong Kong

This study presents an exploratory analysis aimed at improving understanding of the variability of Hong Kong air quality associated with different climate conditions. Significantly negative correlations were found when Nifio 3 led particulate matter 〈10 p.m PM10） and NO2 by 2 3 months over the Hong Kong territory, while the other pollutants （e.g., Oa, SO2） showed modest correlations. A significant decreasing trend in visibility was observed during the autumn and winter, which has potential implications for the air-quality degradation and the endangerment of human health in Hong Kong. In an E1 Nifio summer, the visibility was relatively better, while visibility in other seasons was diminished. On the other hand, in La Nifia events, significant changes occurred in visibility in winter and autumn. Air pollution indices were less sensitive to the South China Summer Monsoon （SCSM）, but a relatively high correlation existed between the East asian Winter Monsoon （EAWM） and air pollutants. Rainfall was lower during most of the strong EAWM years compared to the weak years. This result suggests that the pollutants that accumulate in Hong Kong are not easy to wash out, so concentrations remain at a higher level. Finally, based on the conditional Air Pollution Index （API） risk assessment, site-specific vulnerabilities were analyzed to facilitate the development of the air-quality warning systems in Hong Kong.

关键词： air quality E1 Nifio/La Nifia Monsoon API risk Hong Kong

Recent Decrease in the Difference in Tropical Cyclone Occurrence between the Atlantic and the Western North pacific

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Advances in Atmospheric Sciences 2022年第9期39卷 1387-1397页

作者： Johnny C.L.CHAN Kin Sik LIU guy carpenter asia-pacific climate impact Centre School of Energy and EnvironmentCity University of Hong KongTat Chee Ave.KowloonHong KongChina

Climatologically,among all ocean basins,the western North pacific(WNP)has the largest annual number of tropical cyclones(TCs)of around 26 while the Atlantic has around 13,yielding a difference of ***,the difference is-7 in 2020,with 30 TCs in the Atlantic and 23 in the WNP,which is the most negative difference within the last 46 *** fact,during the last 26 years,the difference in TC number is below 10 in ten years,with four years being *** a decreasing difference in TC number can be attributed to the natural multidecadal variation of the Atlantic Multidecadal Oscillation and Interdecadal pacific Oscillation,as well as other external forcings such as anthropogenic aerosol forcing and increased greenhouse gases,with the additional impact from the La Niña *** result has significant implications on climate model projections of future TC activity in the two ocean basins.

关键词： tropical cyclone frequency Atlantic Multidecadal Oscillation Interdecadal pacific Oscillation climate change

Growing Threat of Rapidly-Intensifying Tropical Cyclones in East asia

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Advances in Atmospheric Sciences 2022年第2期39卷 222-234页

作者： Kin Sik LIU Johnny C.L.CHAN guy carpenter asia-pacific climate impact Centre School of Energy and EnvironmentCity University of Hong KongTat Chee Ave.KowloonHong KongChina

This study examines the long-term change in the threat of landfalling tropical cyclones(TCs) in East asia over the period 1975–2020 with a focus on rapidly intensifying(RI) TCs. The increase in the annual number of RI-TCs over the western North pacific and the northwestward shift of their genesis location lead to an increasing trend in the annual number of landfalling RI-TCs along the coast of East asia. The annual power dissipation index(PDI), a measure of the destructive potential of RI-TCs at landfall, also shows a significant increasing trend due to increases in the annual frequency and mean landfall intensity of landfalling RI-TCs. The increase in mean landfall intensity is related to a higher lifetime maximum intensity(LMI) and the LMI location of the landfalling RI-TCs being closer to the coast. The increase in the annual PDI of East asia is mainly associated with landfalling TCs in the southern(the Philippines, South China, and Vietnam) and northern parts(Japan and the Korean Peninsula) of East asia due to long-term changes in vertical wind shear and TC heat potential. The former leads to a northwestward shift of favorable environments for TC genesis and intensification, resulting in the northwestward shift in the genesis, RI, and LMI locations of RI-TCs. The latter provides more heat energy from the ocean for TC intensification, increasing its chances to undergo RI.

关键词： tropical cyclone landfall tropical cyclone intensity climate change rapid intensification

Projection of the Zhujiang(Pearl) River Delta's potential submerged area due to sea level rise during the 21st century based on CMIP5 simulations

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Acta Oceanologica Sinica 2015年第9期34卷 78-84页

作者： XIA Jiangjiang YAN Zhongwei ZHOU Wen FONG Soi Kun LEONG Ka Cheng TANG Iu Man CHANG S W LEONG W K JIN Shaofei Key Laboratory of Regional climate-environment for Temperate East asia Institute of Atmospheric PhysicsChinese Academy of Sciences guy carpenter asia-pacific climate impact Centre School of Energy and EnvironmentCity University of Hong Kong Macao Meteorological and Geophysical Bureau

Projections of potential submerged area due to sea level rise are helpful for improving understanding of the influence of ongoing global warming on coastal areas. The Ensemble Empirical Mode Decomposition method is used to adaptively decompose the sea level time series in order to extract the secular trend component. Then the linear relationship between the global mean sea level （GMSL） change and the Zhujiang （Pearl） River Delta （PRD） sea level change is calculated： an increase of 1.0 m in the GMSL corresponds to a 1.3 m （uncertainty interval from 1.25 to 1.46 m） increase in the PRD. Based on this relationship and the GMSL rise projected by the Coupled Model Intercomparison Project Phase 5 under three greenhouse gas emission scenarios （representative concentration pathways, or RCPs, from low to high emission scenarios RCP2.6, RCP4.5, and RCP8.5）, the PRD sea level is calculated and projected for the period 2006-2100. By around the year 2050, the PRD sea level will rise 0.29 （0.21 to 0.40） m under RCP2.6, 0.31 （0.22 to 0.42） m under RCP4.5, and 0.34 （0.25 to 0.46） m under RCP8.5, respectively. By 2100, it will rise 0.59 （0.36 to 0.88） m, 0.71 （0.47 to 1.02） m, and 1.0 （0.68 to 1.41） m, respectively. In addition, considering the extreme value of relative sea level due to land subsidence （i.e., 0.20 m） and that obtained from intermonthly variability （i.e., 0.33 m）, the PRD sea level will rise 1.94 m by the year 2100 under the RCP8.5 scenario with the upper uncertainty level （i.e., 1.41 m）. Accordingly, the potential submerged area is 8.57x103 km2 for the PRD, about 1.3 times its present area.

关键词： sea level Zhujiang (Pearl) River Delta (PRD) representative concentration pathways (RCPs) CMIP5 submerged area Ensemble Empirical Mode Decomposition (EEMD)

Influence of Tropical Cyclones on Hong Kong Air Quality

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Advances in Atmospheric Sciences 2018年第9期35卷 1177-1188页

作者： Eric C.H.CHOW Richard C.Y.LI Wen ZHOU City University of Hong Kong(Shenzhen)Research Institute Shenzhen 518057China guy carpenter asia-pacific climate impact center school of energy and environment City University of Hong KongHong KongChina

Tropical cyclones（TCs） constitute one of the major atmospheric activities affecting the air quality of the Pearl River Delta region. In this study, the impact of TCs on air quality in Hong Kong during the TC active season（July–October） from 2000 to 2015 is investigated. It is found that 57.5% of days with concentration of particulate matter with an aerodynamic diameter 10 μm（PM（10）） above the 90th percentile are related to TC activity. TCs in three regions, located to the east, southeast, and southwest of Hong Kong, have obvious impacts on pollutant concentration. When TCs are located east of Hong Kong near Taiwan, 65.5%/38.7% of the days have high or extremely high PM（10）/ozone（O3） levels, which are associated with northerly wind, sinking motion, and relatively low precipitation. When TCs are located southeast of Hong Kong, 48.1%/58.2% of the days have high pollution levels, associated mainly with continental air mass transport. When TCs are south or west of Hong Kong, only 20.8%/16.9% of the days have high PM（10）/O3 levels, and the air quality in Hong Kong is generally good or normal due to TC-associated precipitation, oceanic air mass transport, and an enhanced rising motion. The higher chance of high O3 days when TCs are present between Hong Kong and Taiwan, possibly due to lower-than-normal precipitation along the east coast of China under TC circulation. The results in this study highlight the important influence of TC position and associated atmospheric circulations on the air quality in Hong Kong.

关键词： PM10 03 air quality HK TC

Intraseasonal Variation of Visibility in Hong Kong

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Advances in Atmospheric Sciences 2017年第1期34卷 26-38页

作者： Wen ZHOU Richard C.Y.LI Eric C.H.CHOW guy carpenter asia-pacific climate impact center School of Energy and EnvironmentCity University of Hong KongHong KongChina City University of Hong Kong Shenzhen Research Institute Shenzhen518057China

Visibility is one of the parameters for indicating air pollution. In this study, visibility variation in Hong Kong during summer and winter is investigated. Visibility in Hong Kong has clear intraseasonai variation. Examination of different environmental parameters suggests that the intraseasonal component dominates the overall circulation anomalies in both summer and winter. Associated with the intraseasonal variation of environmental parameters, obvious variation in visibility impair- ment is found in both summer and winter. In summer, local visibility and air quality are found to be significantly affected by the （MJO） and the 10-30-day intraseasonal oscillation （ISO） through modulation of associated atmospheric circulations. In winter, the modulation effects appear to be weaker due to the southward shift of the associated convection. The results in this study highlight the importance of the ISO in contributing to the overall variation in visibility in Hong Kong, and provide useful implications for the development of possible mitigation strategies associated with visibility impairment and air pollution in Hong Kong.

关键词： visibility intraseasonal oscillation air quality Hong Kong

Analysis of the Role Played by Circulation in the Persistent Precipitation over South China in June 2010

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Advances in Atmospheric Sciences 2012年第4期29卷 769-781页

作者：远芳陈文周文 center for Monsoon System Research Institute of Atmospheric PhysicsChinese Academy of Sciences Graduate University of the Chinese Academy of Sciences guy carpenter asia-pacific climate impact center School of Energy and EnvironmentCity University of Hong Kong

South China （SC） experienced persistent heavy rain in June 2010. The climatic anomalies and related mechanism are analyzed in this study. Results show that the large-scale circulation pattern favorable for precipitation was maintained. In the upper level, the South asian High and westerly jet stream provided a divergent circulation over SC. In the middle and low levels, an anomalous strong subtropical high （STH） extended to the South China Sea. The southwesterly monsoon flow along the northwest flank of the STH transported abundant water vapor from the western North pacific, the Bay of Bengal, and the South China Sea to SC. The precipitation can be classified into two types： the West Siberia low （WSL）-induced low-level cyclone mode, and the STH-induced low-level jet mode. STH and WSL indices are defined to estimate the influence of these two systems, respectively. Analysis shows that both are critical for precipitation, but their respective contributions differ from year to year. In 2010, both were important factors for the heavy rainfall in June.

关键词： South China precipitation circulation the subtropical high the west Siberia low