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Geomorphological responses of rivers to active tectonics along the Siwalik Hills,Midwestern Nepalese Himalaya

Journal of Mountain Science 2021年第5期18卷 1268-1294页

作者： Indu BHATTARAI Nahid D.GANI Liang XUE Department of earth Environmentaland Atmospheric SciencesWestern Kentucky UniversityBowling GreenKentucky 42101USA earth and Environmental sciences Syracuse UniversitySyracuseNew York 13244USA

The Nepalese Himalaya is well known for ongoing collisional tectonics,witnessed by major historical and recent *** Siwalik Hills in Midwestern Nepalese Himalaya are bounded by eastwest trending Main Frontal Thrust(MFT)to the south and the Main Boundary Thrust(MBT)to the *** area is dissected by numerous southwest to south-flowing bedrock *** study investigates geomorphic metrics of these rivers to unravel landscape evolution and active tectonics of the Siwalik *** Elevation Model(DEM)analysis was conducted to extract structural lineaments and longitudinal river profile and their metrics(knickpoints,Normalized Steepness Index(ksn),concavity index,and chi integral)using steam powerlaw *** of the lineaments trend eastwest like *** profiles exhibit convex to double-concave shapes with upstream-propagating tectonic knickpoints that separate upstream and downstream reaches,indicating different phases of river *** spatial distribution of ksn shows high values along with low concavity values at the eastern part of the study area,reflecting disequilibrium conditions that are likely responding to a high uplift *** integral distribution shows a variation in drainage divide migration between the eastern and western parts of the study *** study suggests that the rivers in the Siwalik Hills are undergoing active incision likely related to the ongoing uplift and active deformation associated with the Himalayan *** above findings can bring fresh perspectives to comprehend the neotectonic deformation and lateral variability along the Siwalik Hills landscapes within the Himalaya.

关键词： Longitudinal river profiles Siwalik Hills Nepalese Himalaya Active Tectonics

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Optimized Vertical Layers for the Hybrid Terrain-Following Coordinate Minimizing Numerical Errors in a 2D Rising Bubble Experiment near Steep Terrain

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Journal of Meteorological Research 2023年第6期37卷 896-907页

作者： Hao YANG Yiyuan LI Bin WANG State Key Laboratory of Numerical Modeling for atmospheric sciences and Geophysical Fluid Dynamics Institute of Atmospheric PhysicsChinese Academy of SciencesBeijing100029China College of earth and Planetary sciences University of Chinese Academy of SciencesBeijing100049China

The basic terrain-following(BTF)coordinate simplifies the lower boundary conditions of a numerical model but leads to numerical error and instability on steep *** terrain-following(HTF)coordinates with smooth slopes of vertical layers(slopeVL)generally overcome this ***,the HTF coordinate becomes very desirable for atmospheric and oceanic numerical ***,improper vertical layering in HTF coordinates may also increase the incidence of *** for the slopeVL of an HTF coordinate,this study further optimizes the HTF coordinate focusing on the thickness of vertical layers(thickVL).Four HTF coordinates(HTF1–HTF4)with similar slopeVL but different vertical transition methods of thickVL are designed,and the relationship between thickVL and numerical errors in each coordinate is compared in the classic idealized thermal convection[two-dimensional(2D)rising bubble]experiment over steep *** errors of potential temperatureθand vertical velocity w are reduced most,by approximately 70%and 40%,respectively,in the HTF1 coordinate,with a monotonic increase in thickVL according to the increasing height;however,the errors ofθincreased in all the other HTF coordinates,with nonmonotonic ***,analyses of the errors of vertical pressure gradient force(VPGF)show that due to the interpolation errors of thickVL,the inflection points in the vertical transition of thickVL induce the initial VPGF errors;therefore,the HTF1 coordinate with a monotonic increase in thickVL has the smallest errors among all the *** importantly,the temporal evolution of VPGF errors manifests top-type VPGF errors that propagate upward gradually during the time *** the HTF1 and HTF4 coordinates with a monotonic increase in thickVL near the top of the terrain can suppress this *** optimized HTF coordinate(i.e.,HTF1)can be a reference for designing a vertical thickVL in a numerical model.

关键词： hybrid terrain-following coordinate thickness of vertical layer numerical error pressure gradient force two-dimensional(2D)rising bubble experiment steep terrain

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Monsoon Break over the South China Sea during Summer: Statistical Features and Associated atmospheric Anomalies

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Advances in atmospheric sciences 2023年第10期40卷 1749-1765页

作者： Minghao BI Ke XU Riyu LU State Key Laboratory of Numerical Modeling for atmospheric sciences and Geophysical Fluid Dynamics Institute of Atmospheric PhysicsChinese Academy of SciencesBeijing 100029China College of earth and Planetary sciences University of Chinese Academy of SciencesBeijing 100049China

This study identifies break events of the South China Sea(SCS)summer monsoon(SCSSM)based on 42 years of data from 1979 to 2020,and investigates their statistical characteristics and associated atmospheric anomalies.A total of 214 break events are identified by examining the convection evolution during each monsoon *** is found that most events occur between June and September and show a roughly even ***-lived events(3–7 days)are more frequent,accounting for about two thirds of total events,with the residual one third for long-lived events(8–24 days).The SCSSM break is featured by drastic variations in various atmospheric ***,the convection and precipitation change from anomalous enhancement in adjoining periods to a substantial suppression during the break,with the differences being more than 60 W m−2 for outgoing longwave radiation(OLR)and 10 mm d−1 for *** convection/precipitation suppression is accompanied by an anomalous anticyclone in the lower troposphere,corresponding to a remarkable westward retreat of the monsoon trough from the Philippine Sea to the Indochina Peninsula,which reduces the transportation of water vapor into the ***,the pseudo-equivalent potential temperature()declines sharply,mainly attributable to the local specific humidity reduction caused by downward dry ***,it is found that the suppressed convection and anomalous anticyclone responsible for the monsoon break form near the equatorial western Pacific and then propagate northwestward to the SCS.

关键词： South China Sea summer monsoon monsoon break atmospheric circulation convection

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Assessment of the regional source contributions to PM_(2.5) mass concentration in Beijing

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atmospheric and Oceanic Science Letters 2018年第2期11卷 143-149页

作者： HAN Xiao ZHANG Mei-Gen State Key Laboratory of atmospheric Boundary Layer physics and atmospheric Chemistry Institute of Atmospheric Physics Chinese Academy of Sciences College of earth Science University of Chinese Academy of Sciences

A source apportionment tool,ISAM （Integrated Source Apportionment Method）,coupled with a regional air quality modeling system,RAMS-CMAQ （Regional atmospheric Modeling System and Community Multiscale Air Quality）,was applied to simulate the major aerosol components （sulfate,nitrate,ammonium,black carbon,organic carbon,dust,and sea salt） and investigate the impact of local and regional sources on the PM2.5 （particulate matter with an aerodynamic diameter less than 2.5 μm） mass concentration over the North China Plain （NCP） in July *** simulation results indicated that the high mass burden of PM2.5 mainly appeared in the south part of Hebei and west part of *** PM2.5 particles emitted from Beijing and Tianjin were just concentrated in the local area,but Hebei and Shandong were the dominant source over the *** on Beijing,the local contribution was just 20%-30% due to the emissions control strategies executed in recent years in *** pollutants derived from Hebei and Shandong were major contributors,providing more than 25% and 10% to the PM2.5 mass concentration in Beijing,***,the surrounding regions showed larger contributions against the pollution *** contribution percentage from Hebei and Shandong increased in both cases when the air quality became ***,it is suggested that comprehensive control strategies should be implemented based on coordinated control of emissions at the regional scale in Beijing,especially during pollution periods.

关键词： Emissions control PM2.5 source apportionmentmodel CMAQ

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Different Impacts of Intraseasonal Oscillations on Precipitation in Southeast China between Early and Late Summers

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Advances in atmospheric sciences 2022年第11期39卷 1885-1896页

作者： Junqi LIU Riyu LU State Key Laboratory of Numerical Modeling for atmospheric sciences and Geophysical Fluid Dynamics Institute of Atmospheric PhysicsChinese Academy of SciencesBeijing 100029China College of earth and Planetary sciences University of Chinese Academy of SciencesBeijing 100029China

This study investigates the influences of boreal summer intraseasonal oscillation(BSISO), which originates from the equatorial Indian Ocean and prevails over the Indo-Pacific region, on precipitation over Southeast China, including South China and Yangtze River Valley. The results indicate that the BSISO-related precipitation anomalies are remarkably different between early summer(May–June) and late summer(July–August). The BSISO-related precipitation anomalies tend to appear more northward in late summer in comparison with early summer. Accordingly, the BSISO is significantly related to precipitation anomalies over South China during many phases in early summer but related to very weak anomalies during all the phases in late summer. Such northward shifts of precipitation anomalies from early summer to late summer are clearest during phases 4 and 7, when the lower-tropospheric anticyclonic and cyclonic circulation anomalies dominate over the subtropical western North Pacific, respectively. Finally, we explain the differences between early and late summers through the seasonal northward migration of climatological equivalent potential temperature gradient, which is located in the South China during early summer but migrates northward to the YRV during late summer.

关键词： intraseasonal oscillation precipitation Southeast China

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Enhanced Cooling Efficiency of Urban Trees on Hotter Summer Days in 70 Cities of China

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Advances in atmospheric sciences 2024年第11期41卷 2259-2275页

作者： Limei YANG Jun GE Yipeng CAO Yu LIU Xing LUO Shiyao WANG Weidong GUO School of atmospheric sciences Nanjing UniversityNanjing 210023China Joint International Research Laboratory of atmospheric and earth System sciences Nanjing UniversityNanjing 210023China Frontiers Science Center for Critical earth Material Cycling Nanjing UniversityNanjing 210023China

Increasing the urban tree cover percentage(TCP) is widely recognized as an efficient way to mitigate the urban heat island effect. The cooling efficiency of urban trees can be either enhanced or attenuated on hotter days, depending on the physiological response of urban trees to rising ambient temperature. However, the response of urban trees' cooling efficiency to rising urban temperature remains poorly quantified for China's cities. In this study, we quantify the response of urban trees' cooling efficiency to rising urban temperature at noontime [~1330 LT(local time), LT=UTC+8] in 17summers(June, July, and August) from 2003–19 in 70 economically developed cities of China based on satellite observations. The results show that urban trees have stronger cooling efficiency with increasing temperature, suggesting additional cooling benefits provided by urban trees on hotter days. The enhanced cooling efficiency values of urban trees range from 0.002 to 0.055℃ %-1 per 1℃ increase in temperature across the selected cities, with larger values for the lowTCP-level cities. The response is also regulated by background temperature and precipitation, as the additional cooling benefit tends to be larger in warmer and wetter cities at the same TCP level. The positive response of urban trees' cooling efficiency to rising urban temperature is explained mainly by the stronger evapotranspiration of urban trees on hotter *** results have important implications for alleviating urban heat risk by utilizing urban trees, particularly considering that extreme hot days are becoming more frequent in cities under global warming.

关键词： urban trees cooling efficiency China's cities evapotranspiration summer hot days

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Essence of Inviscid Shear Instability： a Point View of Vortex Dynamics

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Chinese Physics Letters 2008年第4期25卷 1343-1346页

作者：孙亮 School of earth and Space sciences University of Science and Technology of China Hefei 230026 LASG Institute of Atmospheric Physics Chinese Academy of Sciences Beijing 100029

The essence of shear instability is reviewed both mathematically and physically, which extends the instability theory of a sheet vortex from the viewpoint of vortex dynamics. For this, the Kelvin-Arnol＇d theorem is retrieved in linear context, i.e., the stable flow minimizes the kinetic energy associated with vorticity. Then the mechanism of shear instability is explored by combining the mechanisms of both Kelvin Helmholtz instability （K-H instability） and resonance of waves. The waves, which have the same phase speed with the concentrated vortex, have interactions with the vortex to trigger the instability. The physical explanation of shear instability is also sketched by extending Batchelor＇s theory. These results should lead to a more comprehensive understanding on shear instabilities.

关键词： FLOW

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Optical Properties of Cirrus Transition Zones over China Detected by CALIOP

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Journal of Meteorological Research 2017年第3期31卷 576-585页

作者： Hongke CAI Yunfei FU Quanliang CHEN Xiao FENG Xin TIE Ranting TAO Kepiao XU School of atmospheric Science Chengdu University of Information Technology/Plateau Atmospheric and Environment Laboratory of Sichuan Province School of earth and Space sciences University of Science and Technology of China

A transition zone near cirrus lateral boundaries can be detected by CALIOP （cloud-aerosol lidar with orthogonal polarization）. In the present study, for such transition zones over China, a number of optical properties, such as the backscatter coefficient and depolarization ratio, showed transitional characteristics between cirrus and clear sky. The stepped horizontal profile showed sharp changes in particle number and morphology between cirrus clouds and clear sky. The color ratio, however, was unable to show cirrus transition features because of the low signal-to-noise ratio. Typical ice particles presented a color ratio of 0.55-1.25 and a depolarization ratio of greater than 0.12, which were significantly higher than those of clear sky. Therefore, optical properties in transition took the form of stepwise hori- zontal profiles. The proportion of typical-featured particles also demonstrated a stepped horizontal profile similar to the optical characteristics, but the relationship between the proportion and the optical characteristics was not uniform in the cirrus clouds, transition zone, and clear sky. Therefore, the optical changes in the transition zone were caused by not only the change in particle concentration, but also the change in the particles themselves. The probability dens- ity distribution of the transition-zone widths showed a positive skewness distribution, and transition zones with widths of 3-5 km occurred most frequently. Overall, transition-zone width decreased with increasing temperature and increased with increasing vertical and horizontal wind speeds. This trend demonstrated independence with the direc- tion of the vertical and horizontal winds. These observations implied that the transitional features were caused by ma- terial exchange, such as entrainment and turbulent transport, near the cirrus lateral boundaries, and by the phase trans- formation of particles, such as sublimation.

关键词： cirrus transition zone lidar temperature wind speed

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Interannual Influences of the Surface Potential Vorticity Forcing over the Tibetan Plateau on East Asian Summer Rainfall

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Advances in atmospheric sciences 2022年第7期39卷 1050-1061页

作者： Chen SHENG Bian HE Guoxiong WU Yimin LIU Shaoyu ZHANG State Key Laboratory of Numerical Modeling for atmospheric sciences and Geophysical Fluid Dynamics(LASG) Institute of Atmospheric PhysicsChinese Academy of SciencesBeijing 100029China College of earth and Planetary sciences University of Chinese Academy of SciencesBeijing 100049China

The influences of interannual surface potential vorticity forcing over the Tibetan Plateau(TP)on East Asian summer rainfall(EASR)and upper-level circulation are explored in this *** results show that the interannual EASR and associated circulations are closely related to the surface potential vorticity negative uniform leading mode(PVNUM)over the *** the PVNUM is in the positive phase,more rainfall occurs in the Yangtze River valley,South Korea,Japan,and part of northern China,less rainfall occurs in southern China,and vice versa.A possible mechanism by which PVNUM affects EASR is *** air induced by the positive phase of PVNUM could stimulate significant upward motion and a lower-level anomalous cyclone over the *** a result,a dipole heating mode with anomalous cooling over the southwestern TP and anomalous heating over the southeastern TP is *** experiment results regarding this dipole heating mode indicate that anomalous cooling over the southwestern TP leads to local and northeastern Asian negative height anomalies,while anomalous heating over the southeastern TP leads to local positive height *** results greatly resemble the realistic circulation pattern associated with *** analysis indicates that the anomalous water vapor transport associated with this anomalous circulation pattern is responsible for the anomalous ***,changes in surface potential vorticity forcing over the TP can induce changes in EASR.

关键词： surface potential vorticity East Asian summer monsoon rainfall the Tibetan Plateau

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CAS-ESM2.0 Model Datasets for the CMIP6 Ocean Model Intercomparison Project Phase 1 (OMIP1)

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Advances in atmospheric sciences 2021年第2期38卷 307-316页

作者： Xiao DONG Jiangbo JIN Hailong LIU He ZHANG Minghua ZHANG Pengfei LIN Qingcun ZENG Guangqing ZHOU Yongqiang YU Mirong SONG Zhaohui LIN Ruxu LIAN Xin GAO Juanxiong HE Dongling ZHANG Kangjun CHEN International Center for climate and Environment sciences Institute of Atmospheric PhysicsChinese Academy of SciencesBeijing 100029China State Key Laboratory of Numerical Modeling for atmospheric sciences and Geophysical Fluid Dynamics Institute of Atmospheric PhysicsChinese Academy of SciencesBeijing 100029China College of earth and Planetary sciences University of Chinese Academy of SciencesBeijing 100049China Institute of atmospheric Physics Chinese Academy of SciencesBeijing 100029China

As a member of the Chinese modeling groups,the coupled ocean-ice component of the Chinese Academy of sciences’earth System Model,version 2.0(CAS-ESM2.0),is taking part in the Ocean Model Intercomparison Project Phase 1(OMIP1)experiment of phase 6 of the Coupled Model Intercomparison Project(CMIP6).The simulation was conducted,and monthly outputs have been published on the ESGF(earth System Grid Federation)data *** this paper,the experimental dataset is introduced,and the preliminary performances of the ocean model in simulating the global ocean temperature,salinity,sea surface temperature,sea surface salinity,sea surface height,sea ice,and Atlantic Meridional Overturning Circulation(AMOC)are *** results show that the model is at quasi-equilibrium during the integration of 372 years,and performances of the model are reasonable compared with *** dataset is ready to be downloaded and used by the community in related research,e.g.,multi-ocean-sea-ice model performance evaluation and interannual variation in oceans driven by prescribed atmospheric forcing.

关键词： OGCM CMIP6 OMIP1 AMOC ocean temperature/salinity sea ice

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