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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

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

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)

Simple Metrics for Representing East asian Winter Monsoon Variability:Urals Blocking and Western pacific Teleconnection Patterns

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Advances in Atmospheric Sciences 2016年第6期33卷 695-705页

作者： Hoffman H.N.CHEUNG Wen ZHOU guy carpenter asia-pacific climate impact centre School of Energy and EnvironmentCity University of Hong KongHong Kong SAR City University of Hong Kong Shenzhen Research Institute Shenzhen 518057

Instead of conventional East asian winter monsoon indices （EAWMIs）, we simply use two large-scale teleconnection patterns to represent long-term variations in the EAWM. First, the Urals blocking pattern index （UBI） is closely related to cold air advection from the high latitudes towards western Siberia, such that it shows an implicit linkage with the Siberian high intensity and the surface air temperature （SAT） variations north of 40°N in the EAWM region. Second, the well-known western pacific teleconnection index （WPI） is connected with the meridional displacement of the East asian jet stream and the East asian trough. This is strongly related to the SAT variations in the coastal area south of 40°N in the EAWM region. The temperature variation in the EAWM region is also represented by the two dominant temperature modes, which are called the northern temperature mode （NTM） and the southern temperature mode （STM）. Compared to 19 existing EAWMIs and other well-known teleconnection patterns, the UBI shows the strongest correlation with the NTM, while the WPI shows an equally strong correlation with the STM as four EAWMIs. The UBI-NTM and WPI-STM relationships are robust when the correlation analysis is repeated by （1） the 31-year running correlation and （2） the 8-year high-pass and low-pass filter. Hence, these results are useful for analyzing the large-scale teleconnections of the EAWM and for evaluating this issue in climate models. Int particular, more studies should focus on the teleconnection patterns over extratropical Eurasia.

关键词： East asian winter monsoon Urals blocking high western pacific teleconnection pattern teleconnection

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

Assessment of Future Drought in Southwest China Based on CMIP5 Multimodel Projections

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Advances in Atmospheric Sciences 2014年第5期31卷 1035-1050页

作者： WANG Lin CHEN Wen ZHOU Wen Center for Monsoon System Research Institute of Atmospheric Physics Chinese Academy of Sciences University of Chinese Academy of Sciences guy carpenter asia-pacific climate impact centre School of Energy and EnvironmentCity University of Hong Kong

In the last decade, a series of severe and extensive droughts have swept across Southwest China, resulting in tremendous economic losses, deaths, and disruption to society. Consequently, this study is motivated by the paramount importance of as- sessing future changes in drought in Southwest China. Precipitation is likely to decrease over most parts of Southwest China around the beginning of the century, followed by widespread precipitation increases; the increase in potential evapotran- spiration （PET）, due to the joint effects of increased temperature and surface net radiation and decreased relative humidity, will overwhelm the whole region throughout the entire 21st century. In comparative terms, the enhancement of PET will outweigh that of precipitation, particularly under Representative Concentration Pathway （RCP） 8.5, resulting in intensified drought. Generally, the drying tendency will be in the southeast portion, whereas the mountainous region in the northwest will become increasingly wetter owing to abundant precipitation increases. Droughts classified as moderate/severe according to historical standards will become the norm in the 2080s under RCP4.5/RCP8.5. Future drought changes will manifest different characteristics depending on the time scale： the magnitude of change at a time scale of 48 months is nearly twice as great as that at 3 months. Furthermore, we will see that not only will incidences of severe and extreme drought increase dramatically in the future, but extremely wet events will also become more probable.

关键词： drought Standardized Precipitation Evapotranspiration Index spatial disaggregation Southwest China

Revisiting the Climatology of Atmospheric Blocking in the Northern Hemisphere

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Advances in Atmospheric Sciences 2013年第2期30卷 397-410页

作者： Ho Nam CHEUNG 周文 Hing Yim MOK Man Chi WU Yaping SHAO City University of Hong Kong Shenzhen Research Institute guy carpenter asia-pacific climate impact centre School of Energy and Environment City University of Hong Kong Hong Kong Observatory Institute for Geophysics and Meteorology University of Cologne

In addition to the occurrence of atmospheric blocking, the climatology of the characteristics of blocking events, including duration, intensity, and extension, in four seasons over the Northern Hemisphere was analyzed for the period 1950-2009. The seasonality and spatial variations of these characteristics were studied according to their longitudinal distributions. In general, there were sharp discrepancies in the blocking characteristics between winter and summer, and these differences were more prominent over the Atlantic and pacific Oceans. The blocking not only occurred more frequently but also underwent stronger amplification in winter; likewise, the blocking occurred less frequently and underwent weaker amplification in summer. There are very strong interrelationships among different blocking characteristics, suggesting that they are supported by similar physical factors. In addition, the relationship between blocking over different regions and East asian circulation was examined. Ural-Siberia is a major blocking formation region in all seasons that may exert a downstream impact on East asia. The impact is generally weak in summer, which is due to its lower intensity and smaller duration. However, the extratropical circulation over East asia in summer can be disturbed persistently by the frequent occurrence of blocking over the asian continent or the Western pacific. In particular, the blocking frequency over the Western pacific significantly increased during the study period. This climatological information provides a background for studying the impact of blocking on East asian circulation under both present and future climate conditions.

关键词： atmospheric blocking climatology seasonality East asian circulation