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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 mainland.Many studies have pointed out the significant contribution of southerly anomalies to the transport and accumulation of pollutants in the BTH region.However,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 topic.By 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 RFs.The 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 RF.We then classify the RFs into north and south types by a demarcation line of 32°N.Both 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 HPEs.With occurrences of the RF,low-level winds are observed to accelerate,and the ageostrophic wind components contribute mainly to this acceleration.During 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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Atmospheric eddy anomalies associated with the wintertime North Pacific subtropical front strength and their influences on the seasonal-mean atmosphere

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Science China Earth Sciences 2016年第10期59卷 2022-2036页

作者： WANG LiYing HU HaiBo YANG XunQun REN XueJuan cma-nju joint laboratory for climate prediction studies Instituted for Climate and Global Change Research School of Atmospheric Science Nanjing University

This study investigates transient eddy activity anomalies in the mid-latitude upper troposphere associated with intensity variability of the wintertime North Pacific subtropical front. Our results show that the meridional gradient of air temperature and baroclinic instability in the mid-latitude atmosphere become stronger as the subtropical front intensifies, and the mid-latitude westerly jet accelerates with barotropic structure. We further divide the mid-latitude atmospheric eddy activities into high-(2–7 days) and low-frequency(10–90 days) eddy activities according to their life periods. We find that, when the oceanic subtropical front intensifies, the high-frequency atmospheric eddy activity in the mid-latitudes strengthens while the low-frequency eddy activity weakens. The stronger high-frequency eddy activity tends to moderate the air temperature gradient and baroclinicity in the mid-latitudes. High-frequency eddy anomalies accelerate the westerly jet on the northern side and downstream of the westerly jet, and enhance the jet with equivalent barotropic structure. In contrast, the weaker low-frequency eddy activity has a negative contribution to zonal wind speed tendency and attenuates the zonal homogenization of the jet. The anomalous thermodynamic forcing of the low-frequency eddy activity helps maintain the meridional gradient of air temperature in the mid-troposphere.

关键词：涡旋活动大气温度活动异常北太平洋副热带冬季中纬度地区平均

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Diagnosing SST Error Growth during ENSO Developing Phase in the BCC_CSM1.1(m) prediction System

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Advances in Atmospheric Sciences 2022年第3期39卷 427-442页

作者： Ben TIAN Hong-Li REN Laboratory for Climate Studies&CMA-NJU Joint Laboratory for Climate Prediction Studies National Climate CenterChina Meteorological AdministrationBeijing 100081China State Key laboratory of Severe Weather Institute of Tibetan Plateau&Polar MeteorologyChinese Academy of Meteorological SciencesBeijing 100081China Department of Atmospheric Science School of Environmental StudiesChina University of GeoscienceWuhan 430074China

In this study, the predictability of the El Nino-South Oscillation(ENSO) in an operational prediction model from the perspective of initial errors is diagnosed using the seasonal hindcasts of the Beijing climate Center System Model,BCC;SM1.1(m). Forecast skills during the different ENSO phases are analyzed and it is shown that the ENSO forecasts appear to be more challenging during the developing phase, compared to the decay phase. During ENSO development, the SST prediction errors are significantly negative and cover a large area in the central and eastern tropical Pacific, thus limiting the model skill in predicting the intensity of El Nino. The large-scale SST errors, at their early stage, are generated gradually in terms of negative anomalies in the subsurface ocean temperature over the central-western equatorial Pacific,featuring an error evolutionary process similar to that of El Nino decay and the transition to the La Nina growth phase.Meanwhile, for short lead-time ENSO predictions, the initial wind errors begin to play an increasing role, particularly in linking with the subsurface heat content errors in the central-western Pacific. By comparing the multiple samples of initial fields in the model, it is clearly found that poor SST predictions of the Nino-3.4 region are largely due to contributions of the initial errors in certain specific locations in the tropical Pacific. This demonstrates that those sensitive areas for initial fields in ENSO prediction are fairly consistent in both previous ideal experiments and our operational predictions,indicating the need for targeted observations to further improve operational forecasts of ENSO.

关键词： ENSO prediction initial errors error evolution SST

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Skillful prediction of winter Arctic Oscillation from previous summer in a linear empirical model

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Science China Earth Sciences 2021年第1期64卷 27-36页

作者： Hong-Li REN Yu NIE State Key laboratory of Severe Weather Chinese Academy of Meteorological SciencesBeijing 100081China Laboratory for Climate Studies&CMA-NJU Joint Laboratory for Climate Prediction Studies National Climate CenterChina Meteorological AdministrationBeijing 100081China Department of Atmospheric Science School of Environmental StudiesChina University of GeoscienceWuhan 430074China

The winter Arctic Oscillation(WAO),as a primary atmospheric variability mode in the Northern Hemisphere,plays a key role in influencing mid-high-latitude climate variations.However,current dynamical seasonal forecasting systems have limited skills in predicting WAO with lead time longer than two months.In this study,we design a linear empirical model using two effective precursors from anomalies of the Arctic sea ice concentration(SIC)and the tropical sea surface temperature(SST)initiated in preceding late summer(August)which are both significantly correlated with WAO in recent four decades.This model can provide a skillful prediction of WAO at about half-year lead started from previous summer and perform much better than the dynamical models.Such a significantly prolonged lead time is owed to the stable precursor signals extracted from the SIC and SST anomalies over specific areas,which can persist from previous August and be further enhanced through autumn months.Validation results show that this model can produce a 20-year independent-validated prediction skill of 0.45 for 1999–2018 and a 39-year cross-validated skill of 0.67 for 1980–2018,providing a potentially effective tool for earlier predictions of winter climate variations at mid-high latitudes.

关键词： Arctic Oscillation(AO) Winter AO prediction Sea ice concentration Sea surface temperature Linear empirical model

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The linkage between two ENSO types/modes and the interdecadal changes of ENSO around the year 2000

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Atmospheric and Oceanic Science Letters 2017年第2期10卷 168-174页

作者： WANG Run REN Hong-Li Chinese Academy of Meteorological Sciences Beijing China laboratory for climate studies & cma-nju joint laboratory for climate prediction studies National Climate Center China Meteorological Administration Beijing China

厄尔尼诺和南方涛动(ENSO)在2000年前后发生了明显的年代际变化。与1980-99年相比,2000年以后ENSO的振幅减弱,主周期缩短,中太平洋(CP)型ENSO的发生频率升高,且没有典型的东太平洋(EP)型ENSO出现。本文将两种类型ENSO与两个ENSO模态联... 详细信息

厄尔尼诺和南方涛动(ENSO)在2000年前后发生了明显的年代际变化。与1980-99年相比,2000年以后ENSO的振幅减弱,主周期缩短,中太平洋(CP)型ENSO的发生频率升高,且没有典型的东太平洋(EP)型ENSO出现。本文将两种类型ENSO与两个ENSO模态联系起来,发现ENSO在2000年前后的年代变化实质上是两个ENSO模态的相对活跃性发生了改变:与EP型ENSO相联系的准四年模态在2000年之后活跃性明显降低,与CP型ENSO相联系的准两年模态依然活跃,并成为热带太平洋地区的主模态。分析表明,热带太平洋地区气候平均态的改变可能是这次ENSO年代际变化的主要原因。

关键词：年代际变化东太平洋型ENSO 中太平洋型ENSO 准四年模态准两年模态

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Mechanism of Regional Subseasonal Precipitation in the Strongest and Weakest East Asian Summer Monsoon Subseasonal Variation Years

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Journal of Ocean University of China 2022年第6期21卷 1411-1427页

作者： HU Haibo DENG Yuheng FANG Jiabei WANG Rongrong cma-nju joint laboratory for climate prediction studies Instituted for Climate and Global Change ResearchSchool of Atmospheric ScienceNanjing UniversityNanjing 210093China Key laboratory of Meteorological Disaster of Ministry of Education Nanjing University of Information Science and TechnologyNanjing 210044China

Using the National Center for Environment prediction climate Forecast System Reanalysis coupled dataset during 1979–2010,we selected four subseasonal indexes from the 16 East Asian Summer Monsoon(EASM)indexes to characterize the subseasonal variability of the entire EASM system.The strongest(1996)and weakest(1998)years of the subseasonal variation were revealed based on these subseasonal EASM indexes.Furthermore,three rainfall concentration areas were defined in East Asia,and these areas were dissected by the atmospheric midlatitude jet stream axis and the position of the Western North Pacific Subtropical High(WNPSH).Then,the subseasonal effects of the WNPSH,the South Asian High(SAH),the Mongolian Cyclone(MC),and the Boreal Summer Intraseasonal Oscillation(BSISO)on each rainfall concentration area were studied in the strongest and weakest subseasonal variation years of the EASM.During the summer of 1998,the WNPSH and the SAH were stable in the more southern region,which not only blocked the northward progression of the BSISO but also caused the MC to advance southward.Therefore,the summer of 1998 was the weakest subseasonal variability of the EASM,but with significant subseasonal precipitation episodes in the northern and central rainfall areas.However,in 1996,the BSISO repeatedly spread northward in the south rainfall area because of the weak intensities and northern positions of the WNPSH and the SAH,which caused significant subseasonal precipitation episodes.In addition,MC was blocked to the north of approximately 42°N with a weak subseasonal rainfall.

关键词： East Asian Summer Monsoon Subseasonal Western North Pacific Subtropical High Mongolian Cyclone Boreal Summer Intraseasonal Oscillation

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Upper-Ocean Dynamical Features and prediction of the Super El Nino in 2015/16:A Comparison with the Cases in 1982/83 and 1997/98

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Journal of Meteorological Research 2017年第2期31卷 278-294页

作者： Hong-Li REN Run WANG Panmao ZHAI Yihui DING Bo LU laboratory for climate studies National Climate CenterChina Meteorological AdministrationBeijing 100081 Chinese Academy of Meteorological Sciences Beijing 100081 cma-nju joint laboratory for climate prediction studies School of Atmospheric SciencesNanjing UniversityNanjing 210023

The 2015/16 super El Ni？o event has been widely recognized as comparable to the 1982/83 and 1997/98 El Ni？o events.This study examines the main features of upper-ocean dynamics in this new super event,contrasts them to those in the two historical super events,and quantitatively compares the major oceanic dynamical feedbacks based on a mixed-layer heat budget analysis of the tropical Pacific.During the early stage,this new event is characterized by an eastward propagation of SST anomalies and a weak warm-pool El Ni？o;whereas during its mature phase,it is characterized by a weak westward propagation and a westward-shifted SST anomaly center,mainly due to the strong easterly wind and cold upwelling anomalies in the far eastern Pacific,as well as the westward anomalies of equatorial zonal current and subsurface ocean temperature.The heat budget analysis shows that the thermocline feedback is the most crucial process inducing the SST anomaly growth and phase transition of all the super events,and particularly for this new event,the zonal advective feedback also exerts an important impact on the formation of the strong warming and westward-shifted pattern of SST anomalies.During this event,several westerly wind burst events occur,and oceanic Kelvin waves propagate eastwards before being maintained over eastern Pacific in the mature stage.Meanwhile,there is no evidence for westward propagation of the off-equatorial oceanic Rossby waves though the discharging process of equatorial heat during the development and mature stages.The second generation El Ni？o prediction system of the Beijing climate Center produced reasonable event real-time operational prediction during 2014–16,wherein the statistical prediction model that considers the preceding oceanic precursors plays an important role in the multi-method ensemble prediction of this super.

关键词： El Ni?o–Southern Oscillation super El Ni?o event ocean dynamics feedback prediction

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Improvement of Soil Moisture Simulation in Eurasia by the Beijing climate Center climate System Model from CMIP5 to CMIP6

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Advances in Atmospheric Sciences 2021年第2期38卷 237-252页

作者： Yinghan SANG Hong-Li REN Xueli SHI Xiaofeng XU Haishan CHEN School of Atmospheric Sciences Nanjing University of Information Science&TechnologyNanjing 210044China State Key laboratory of Severe Weather Chinese Academy of Meteorological SciencesBeijing 100081China Laboratory for Climate Studies&CMA-NJU Joint Laboratory for Climate Prediction Studies National Climate CenterChina Meteorological AdministrationBeijing 100081China China Meteorological Administration Beijing 100081China

This study provides a comprehensive evaluation of historical surface soil moisture simulation(1979-2012)over Eurasia at annual and seasonal time scales between two medium-resolution versions of the Beijing climate Center climate System Model(BCC-CSM)—one that is currently participating in phase 6 of the Coupled Model Intercomparison Project(CMIP6),i.e.,BCC-CSM2-MR,and the other,BCC-CSM1.1m,which participated in CMIP5.We show that BCC-CSM2-MR is more skillful in reproducing the climate mean states and standard deviations of soil moisture,with pattern correlations increased and biases reduced significantly.BCC-CSM2-MR performs better in capturing the first two primary patterns of soil moisture anomalies,where the period of the corresponding time series is closer to that of reference data.Comparisons show that BCC-CSM2-MR performs at a high level among multiple models of CMIP6 in terms of centered pattern correlation and“amplitude of variation”(relative standard deviation).In general,the centered pattern correlation of BCC-CSM2-MR,ranging from 0.61 to 0.87,is higher than the multi-model mean of CMIP6,and the relative standard deviation is 0.75,which surmounts the overestimations in most of the CMIP6 models.Due to the vital role played by precipitation in land-atmosphere interaction,possible causes of the improvement of soil moisture simulation are further related to precipitation in BCC-CSM2-MR.The results indicate that a better description of the relationship between soil moisture and precipitation and a better reproduction of the climate mean precipitation by the model may result in the improved performance of soil moisture simulation.

关键词： BCC-CSM soil moisture CMIP6 historical simulation Eurasia

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Interdecadal Variations of ENSO around 1999/2000

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Journal of Meteorological Research 2017年第1期31卷 73-81页

作者： Zeng-Zhen HU Arun KUMAR Bohua HUANG Jieshun ZHU Hong-Li REN climate prediction Center NCEP/NWS/NOAA5830 University Research CourtCollege ParkMD 20740USA Department of Atmospheric Oceanic and Earth Sciences and Center for Ocean-Land-Atmosphere StudiesGeorge Mason University4400 University DriveFairfaxVA 22030USA Laboratory for Climate Studies&CMA-NJU Joint Laboratory for Climate Prediction Studies National Climate CenterChina Meteorological AdministrationBeijing 100081China

This paper discusses the interdecadal changes of the climate in the tropical Pacific with a focus on the correspond- ing changes in the characteristics of the E1 Nifio-Southern Oscillation （ENSO）. Compared with 1979-1999, the whole tropical Pacific climate system, including both the ocean and atmosphere, shifted to a lower variability regime after 1999/2000. Meanwhile, the frequency of ENSO became less regular and was closer to a white noise process. The lead time of the equatorial Pacific＇s subsurface ocean heat content in preceding ENSO decreased remarkably, in addition to a reduction in the maximum correlation between them. The weakening of the correlation and the shorten- ing of the lead time pose more challenges for ENSO prediction, and is the likely reason behind the decrease in skill with respect to ENSO prediction after 2000. Coincident with the changes in tropical Pacific climate variability, the mean states of the atmospheric and oceanic components also experienced physically coherent changes. The warm an- omaly of SST in the western Pacific and cold anomaly in the eastern Pacific resulted in an increased zonal SST gradi- ent, linked to an enhancement in surface wind stress and strengthening of the Walker circulation, as well as an in- crease in the slope of the thermocline. These changes were consistent with an increase （a decrease） in precipitation and an enhancement （a suppression） of the deep convection in the western （eastern） equatorial Pacific. Possible con- nections between the mean state and ENSO variability and frequency changes in the tropical Pacific are also dis- cussed.

关键词： ENSO interdecadal variation amplitude suppression frequency change mean state

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Contribution of Atmospheric Rivers to Precipitation and Precipitation Extremes in East Asia:Diagnosis with Moisture Flux Convergence

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Journal of Meteorological Research 2021年第5期35卷 831-843页

作者： Yating XIONG Xuejuan REN cma–nju joint laboratory for climate prediction studies School of Atmospheric SciencesNanjing UniversityNanjing 210023

Atmospheric rivers(ARs),the long and narrow conveyors of intense moisture transport,have a non-negligible impact on hydrometeorological events over the extratropical regions.This study analyzes the climatology and interannual variability of ARs and their quantitative association with precipitation and precipitation extremes over East Asia(EA)during 1979-2019,based on calculations of not only moisture transport but also moisture flux convergence.It is found that the ARs over EA occur frequently in spring and summer,accounting for 25%-40%of seasonal precipitation and 60%-75%of extreme precipitation over EA.Increases in AR frequency are observed over EA during post-El Ni?o summers,meanwhile the AR-related anomalous moisture convergence is found leading to the increase of extreme precipitation.Specifically,increased ARs account for 70%-90%of total precipitation anomalies and up to 90%of extreme precipitation anomalies over the middle-lower reaches of the Yangtze River,and the anomalies of moisture flux convergence are caused mainly by changes in horizontal wind convergence rather than moisture advection during the post-El Ni?o summers.

关键词： atmospheric rivers precipitation extreme events water vapor interannual variability

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