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Impact of the return flow on Heavy Pollution in Winter over the Beijing–Tianjin–Hebei Region

Journal of Meteorological Research 2023年第3期37卷 370-386页

作者： Mei MEI Yihui DING Zunya WANG Chinese Academy of Meteorological Sciences China Meteorological Administration(CMA)Beijing 100081 University of Chinese Academy of Sciences Beijing 100049 Laboratory for Climate Studies/CMA–NJU Joint Laboratory for Climate Prediction Studies National Climate CentreChina Meteorological AdministrationBeijing 100081 National Climate Centre China Meteorological AdministrationBeijing 100081

In North China,the return flow(RF)refers to the airflow at the rear of an inshore high pressure,bringing southerly wind to the Beijing–Tianjin–Hebei(BTH)region when the high pressure pushes deeper from coast into the *** studies have pointed out the significant contribution of southerly anomalies to the transport and accumulation of pollutants in the BTH ***,the relationship between RF and heavy pollution episodes(HPEs)in the BTH region requires more in-depth analysis,and this study will focus on this *** objectively identifying RFs and HPEs based on the ERA5 reanalysis data and observed hourly PM_(2.5)concentration data during 9 winters of 2012–2020,it is found that almost two-thirds of the HPEs in the BTH region coincide with the occurrence of *** northward transport of warm and humid air is stronger in the HPEs under RF conditions,whereas the sinking motion and the decrease in boundary layer height dominate the HPEs without any *** then classify the RFs into north and south types by a demarcation line of 32°*** types of RFs are featured with a zonal circulation pattern,stable atmosphere,and southerly airflow favoring the development of HPEs,but the south type RFs bring warmer and wetter air masses to the BTH region,forming a more stable and thicker inversion layer and causing more severe *** occurrences of the RF,low-level winds are observed to accelerate,and the ageostrophic wind components contribute mainly to this *** the presence of RFs,the kinetic energy generation at the high level decreases,and the weakened downward transport results in weak low-level northerly winds,weak turbulence,and a shallow boundary layer,thus hindering the diffusion of atmospheric pollutants in the BTH region.

关键词： the Beijing-Tianjin-Hebei region return flow heavy pollution episode PM2.5

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A Case Study on the Rapid Rain-to-Snow Transition in Late Spring 2018 over Northern China:Effects of return flows and Topography

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Journal of Meteorological Research 2022年第1期36卷 107-127页

作者： Wenlong ZHANG Xiaopeng CUI Bolong DUAN Bo YU Runxia GUO Haiwen LIU Institute of Urban Meteorology China Meteorological AdministrationBeijing 100089 Key Laboratory of Cloud-Precipitation Physics and Severe Storms Institute of Atmospheric PhysicsChinese Academy of SciencesBeijing 100029 Lanzhou Central Meteorological Observatory Lanzhou 730020 Beijing Weather Forecast Center Beijing 100089 Department of Aviation Meteorology Civil Aviation University of ChinaTianjin 300300 University of Chinese Academy of Sciences Beijing 100049

Phase changes in the precipitation processes of early winter and late spring in midlatitude regions represent challenges when forecasting the timing and magnitude of *** 4 April 2018,a heavy snow process occurred in Beijing and northwestern Hebei Province,becoming the most delayed occurrence of heavy spring snow ever recorded over Beijing in the last 30 *** paper uses observational and numerical simulation data to investigate the causes for the rapid rain-to-snow(RRTS)phase transition during this *** following results are obtained.(1)return flows(RFs),an interesting type of easterly wind,including those at 1000,925,and 800 hPa,played an important role in this heavy snow process and presented a characteristic"sandwich"*** RFs,complex topography,and snow particles that dominated the clouds,were the three key factors for the RRTS transition.(2)The RRTS transition in the plains was directly related to the RF at 925 hPa,which brought about advective cooling initiated approximately 4-6 h before the onset of ***,the RF played a role of diabatic cooling when snow particles began to fall at the onset of precipitation.(3)The RRTS transition in the northern part of the Taihang Mountains was closely related to the relatively high altitude that led to a lower surface temperature owing to the vertical temperature lapse *** immediately before and after the onset of precipitation,the snow particles in clouds entrained the middle-level cold air downward,causing the melting layer(from surface to the 0℃-isotherm level)to become very thin;and thus the snow particles did not have adequate time to melt before falling to the ground.(4)The rapid RRTS over the Yanqing mountainous area in the northwest of Beijing could have involved all the three concurrent mechanisms:the advective cooling of RF,the melting cooling of cloud snow particles,and the high-altitude *** with that in the plain area with less urbanization the duration

关键词： midlatitude heavy snow return flow phase transition Bohai Sea cold pool complex terrain numerical simulation

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COMPUTATION OF return flowS DUE TO NAVIGATION TRAFFICS IN RESTRICTED WATERWAYS

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International Journal of Sediment Research 2006年第4期21卷 249-260页

作者： B. S. MAZUMDER S. K. DAS S. N. DAS Indian Statistical Institute Kolkata-700 108 IndiaProf. International Institute of Information Technology Pune India Prof. Assis. Res. Officer Central Water and Power Research Station Pune-411 024 India

The paper deals with the development of an empirical model to compute the return flow due to the movement of navigation traffics in restricted waterway when the speed of the navigation traffic is under sub-critical range. The velocity profile of the return flow is modelled, where the functional dependence with respect to ambient flow, principal dimensions of the vessel, wetted cross-sectional area of the river, width and average depth of the river, and the lateral distance of the vessel from the bank are implicitly considered. This model has been validated with the observed data collected from the four specific sites, such as Kampsville, Apple River Island, Goose Island and Clarks Ferry of Illinois River during barge-tow movement. The present model shows significant improvement of return flow prediction in comparison to earlier empirical results. This model has also the ability to determine the locus of zero velocity point.

关键词： return flow Navigation traffic Empirical model Restricted waterway Barge-tow Zero velocity point Froude number

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Toroidal component of velocity for geodesic acoustic modes in the edge plasmas of the J-TEXT tokamak

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Plasma Science and Technology 2021年第10期23卷 112-119页

作者：谢耀禹赵开君陈志鹏董家齐 Kimitaka ITOH 陈忠勇石跃江丁永华程钧严龙文刘海程芝峰杨州军王能超王璐许健强梁云峰 J-TEXT Team School of Nuclear Science and Engineering East China University of TechnologyNanchang 330013People’s Republic of China International Joint Research Laboratory of Magnetic Confinement Fusion and Plasma Physics State Key Laboratory of Advanced Electromagnetic Engineering and TechnologySchool of Electrical and Electronic EngineeringHuazhong University of Science and TechnologyWuhan 430074People's Republic of China Southwestern Institute of Physics Chengdu 610041People's Republic of China Institute of Science and Technology Research Chubu UniversityKasuga 816-8580Japan Research Center for Plasma Turbulence Kyushu UniversityKyushu UniversityChubu UniversityAichi 487-8501Japan National Institute for Fusion Science Toki 509-5292Japan ENN Science and Technology Development Co. Ltdand Hebei Key Laboratory of Compact FusionLangfang 065001People's Republic of China Institute of Fusion Science School of Physical Science and TechnologySouthwest Jiaotong UniversityChengdu 610031People's Republic of China

The toroidal component of the velocity for geodesic acoustic modes(GAMs)is first *** Langmuir probe arrays set up near the top tokamak of the J-TEXT were utilized for this study.A significant peak at the GAM frequency is observed in Mach number *** toroidal velocity for the GAMs is estimated as 10–100 ms-1 and increases with the poloidal *** ratio of toroidal component to the poloidal one of the velocity is mainly located in the interval between 0.3 and *** higher safety factors q,the ratio almost does not change with decreasing the safety factor,whereas it goes up sharply at low *** coherencies between poloidal electric fields and Mach number fluctuations in turbulence frequency bands are also evaluated,and are higher than those between radial electric fields and Mach number fluctuations.

关键词： zonal flow geodesic acoustic mode tokamak return flow Mach number

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