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| 1 | Meteorological mechanism for a large-scale persistent severe ozone pollution event over eastern China in 2017显示文摘An intensive and persistent regional ozone pollution event occurred over eastern China from 25 June to 5 July 2017.73 out of 96 selected cities,most located in the Beijing-TianjinHebei and the surrounding area(BTHS),suffered severe ozone pollution.A north-south contrast ozone distribution,with higher ozone(199±33μg/m3)in the BTHS and lower ozone(118±25μg/m^3)in the Yangtze River Delta(YRD),was found to be dominated by the position of the West Pacific Subtropical High(WPSH)and mid-high latitude wave activities.In the BTHS,the positive anomalies of geopotential height at 500 hPa and temperature at the surface indicated favorable meteorological conditions for local ozone formation.Prevailing northwesterly winds in the mid-high troposphere and warm advection induced by weak southerly winds in the low troposphere resulted in low-moderate relative humidity(RH),less total cloud cover(TGC),strong solar radiation and high temperatures.Moreover,southerly winds prevailing over the BTHS aggravated the pollution due to regional transportation of O3 and its precursors.On one hand,the deep sinking motion and inversion layer suppressed the dispersion of pollutants.On the other hand,O3-rich air in the upper layer was maintained at night due to temperature inversion,which facilitated O3 vertical transport to the surface in the next-day morning due to elevated convection.Generally,temperature,UV radiation,and RH showed good correlations with O3 in the BTHS,with rates of 8.51(μg/m^3)/℃(within the temperature range of 20-38℃),59.54(μg/m^3)/(MJ/m^2)and-1.93(μg/m^3)/%,respectively. | Jia Mao Lili Wang Chuhan Lu Jingda Liu Mingge Li Guiqian Tang Dongsheng Ji Nan Zhang Yuesi Wang | 2020 | Journal of Environmental Sciences2020，32，6： | 18 |
| 2 | A Modified Algorithm for Identifying and Tracking Extratropical Cyclones显示文摘In this study, a modified identification and tracking algorithm for extratropical cyclones is developed. This identification scheme is based on triangular-mesh contouring techniques combined with a connected-component labeling method in order to detect the outer boundaries and spatial domain characteristics of individual cyclones. A new tracking method allowing for the identification of cyclone merging and splitting events, as well as short-lived windstorms, is developed to reduce the uncertainty in the tracking of extratropical cyclones. I also show that this method excludes the tracks of open systems that would have been unnecessarily detected using conventional NCP methods. The climatological features of the distribution of cyclone frequencies are substantially larger over the traditional storm track regions compared to those seen in previous studies. Interestingly, a significant increase in the cyclone density in the Arctic occurs during all four seasons(up to 19%in summer) compared to that seen with a latitude–longitude gridded mesh analysis. I develop two new regional intensity indices(depth and vorticity) based on the cyclonic domain to better quantify the cyclonic activity in the Arctic region, and find that the interannual variabilities in these two indices are highly consistent. The results of this analysis may shed light on high-latitude cyclonic behavior studies via the newly detected 2D cyclone atlas derived from this cyclonic-domain-based algorithm. | Chuhan LU | 2017 | Advances in Atmospheric Sciences2017，34，7： | 10 |
| 3 | Multi-scale Cyclone Activity in the Changjiang River–Huaihe River Valleys during Spring and Its Relationship with Rainfall Anomalies显示文摘Based on the recognition framework of the outermost closed contours of cyclones, an automated identification algorithm capable of identifying the multi-scale cyclones that occur during spring in the Changjiang River–Huaihe River valleys(CHV)were developed. We studied the characteristics of the multi-scale cyclone activity that affects CHV and its relationship with rainfall during spring since 1979. The results indicated that the automated identification algorithm for cyclones proposed in this paper could intuitively identify multi-scale cyclones that affect CHV. The algorithm allows for effectively describing the shape and coverage area of the closed contours around the periphery of cyclones. We found that, compared to the meso- and sub-synoptic scale cyclone activities, the synoptic-scale cyclone activity showed more intimate correlation with the overall activity intensity of multi-scale CHV cyclones during spring. However, the frequency of occurrence of sub-synoptic scale cyclones was the highest, and their effect on changes in CHV cyclone activity could not be ignored. Based on the area of impact and the depth of the cyclones, the sub-synoptic scale, synoptic scale and comprehensive cyclone intensity indices were further defined, which showed a positive correlation with rainfall in CHV during spring. Additionally, the comprehensive cyclone intensity index was a good indicator of strong rainfall events. | Yujing QIN Chuhan LU Liping LI | 2017 | Advances in Atmospheric Sciences2017，34，2： | 10 |
| 4 | On the interannual variation in spring atmospheric inter-hemispheric oscillation linked to synchronous climate in China显示文摘Based on NCEP/NCAR monthly mean reanalysis data and surface observations of Chinese stations, inter-hemispheric oscillations (IHO) of spring atmospheric mass on an interannual basis in conjunction with the linkage to the synchronous climate over China are studied. Results suggest that the spring IHO exhibits a significant seesaw pattern for air mass at bi-hemispheric mid-high latitudes, with a consistent vertical circulation structure. The EOF decomposition of zonally mean surface pressures without signals of Arctic Oscillation (AO) and Antarctic Oscillation (AAO) indicates that the EOF1 IHO feature is remarkable, with the corresponding time coeficients correlated with the spring IHO index (IIHO) at 0.93; the spring IHO bears a close relation to the synchronous climate in China, showing the surface pressure, temperature and relative humidity over the country to be in good correlation with IIHO; the spring duststorms in Qinghai, Gansu, Shaanxi and Inner Mongolia have bearing on IHO. Positive-phase IIHO promotes the strengthening of the Siberian high, during which zonal winds between 60°E and 150°W show a longitudinal teleconnection structure extending from the Arctic to Antarctica, leading to positive westerly wind anomalies over Asia, affecting the spring climate of China. | Chuhan Lu Zhaoyong Guan | 2009 | Progress in Natural Science:Materials International2009，19，9： | 8 |
| 5 | The seasonal cycle of interhemispheric oscillations in mass field of the global atmosphere显示文摘Using the daily and monthly data of surface air pressure, meridional wind, radiation and water vapor from NCEP/NCAR reanalysis for the period of 1979―2006, we have examined the seasonal variations of the interhemispheric oscillations (IHO) in mass field of the global atmosphere. Our results have demonstrated that IHO as observed in surface air pressure field shows the distinct seasonal cycle. This seasonal cycle has an interhemispheric seesaw structure with comparable annual ranges of surface air pressure in the Southern and Northern Hemispheres. Mass of water vapor changes out-of-phase between the Southern and Northern Hemispheres, showing clearly a seasonal cycle with its annual range almost equivalent to annual range of the IHO seasonal cycle. Amazingly, the cross-equatorial flow is found to be induced by annual changes in water vapor mass as a response of the atmosphere to seasonal cycle of forcing from hemispheric net surface short- and long-wave radiations. The IHO seasonality exhibits its larger variations in magnitude in mid-latitudes other than in other regions of the globe. Additionally, our results also show that the global air mass is redistributed seasonally not only between the Northern and Southern Hemispheres but also between land and sea. This land-sea air mass redis- tribution induces a zonal pattern of surface air pressure in the Northern Hemisphere but the meridional pattern in the Southern Hemisphere. | LU ChuHan GUAN ZhaoYong MEI ShiLong QIN YuJing | 2008 | Chinese Science Bulletin2008，53，20： | 8 |
| 6 | An unusual high ozone event over the North and Northeast China during the record-breaking summer in 2018显示文摘Under the background of global warming,the summer temperature of the North and Northeast China(NNEC)has significantly increased since 2017,which was accompanied by the aggravated ozone(O_(3))pollution.In 2018,the NNEC experienced a record-breaking summer of the past 40 years.Influenced by the abnormal high temperatures,a regional ozone event occurred on 2-3 August,over 63%of 79 selected cities in the NNEC were exposed to O_(3)pollution,and the maximum value of MDA8 O_(3)reached 268μg/m 3.Observations indicated that ozone concentrations agree well with the maximum temperature at 2 meters(MT2M)over NNEC with a correlation coefficient of 0.69.During the pollution episode,strong downdraft in the local high(35°N-42.5°N,112.5°E-132.5°E;LH)over the NNEC created the favourable meteorological conditions for O_(3)formation.By analyzing the horizontal wind and wave activity fluxes(WAFs)at 200 h Pa,we found that the LH formation was resulted from the Rossby wave propagation from upstream along the mid-latitude Asian jet.The split polar vortex intrusion further strengthened the amplitude of the Rossby wave and reinforced the LH.Moreover,a secondary circulation between Typhoon Jongdari and the LH contributed to the enhanced LH with strong subsidence.On the other hand,the stratospheric intrusions under the deep subsidence also contributed to the enhanced surface O_(3).In this study,the deep-seated meteorological dynamical mechanisms contributing to the abnormal high temperatures were investigated,which can lead to a better understanding of the regional O_(3)pollution over NNEC under the global-warming background. | Chuhan Lu Jia Mao Lili Wang Zhaoyong Guan Guangna Zhao Mingge Li | 2021 | Journal of Environmental Sciences2021，33，6： | 7 |
| 7 | Detecting the Relationship Between Summer Rainfall Anomalies in Eastern China and the SSTA in the Global Domain with a New Significance Test Method显示文摘It is suggested that the multiple samples in a correlation map or a set of correlation maps should be examined with significance tests as per the Bernoulli probability model. Therefore, both the contemporaneous and lag correlations of summertime precipitation R in any one of the three regions of Northern China (NC), the Changjiang-Huaihe River Valley (CHRV), and Southern China (SC) with the SSTA in the global domain have been tested in the present article, using our significance test method and the method proposed by Livezey and Chen (1983) respectively. Our results demonstrate that the contemporaneous correlations of summer R in CHRV with the SSTA are larger than those in NC. Significant correlations of SSTA with CHRV R are found to be in some warm SST regions in the tropics, whereas those of SSTA with NC R, which are opposite in sign as compared to the SSTA-CHRV R correlations, are found to be in some regions where the mean SSTs are low. In comparison with the patterns of the contemporaneous correlations, the 1 to 12 month lag correlations between NC R and SSTA, and those between CHRV summer R and SSTA show similar patterns, including the magnitudes and signs, and the spatial distributions of the coefficients. However, the summer rainfall in SC is not well correlated with the SSTA, no matter how long the lag interval is. The results derived from the observations have set up a relationship frame connecting the precipitation anomalies in NC, CHRV, and SC with the SSTA in the global domain, which is critically useful for our understanding and predicting the climate variabilities in different parts of China. Both NC and CHRV summer R are connected with El Nio events, showing a ‘––’pattern in an El Nio year and a ‘+ +’ pattern in the subsequent year. | LU Chuhan GUAN Zhaoyong WANG Panxing DUAN Mingken | 2009 | Journal of Ocean University of China2009，8，1： | 4 |
| 8 | Interhemispheric atmospheric mass oscillation and its relation to interannual variations of the Asian monsoon in boreal summer显示文摘Using NCEP/NCAR reanalysis and precipitation records of Chinese stations, we have investigated the relationship of interhemispheric oscillation of air mass (IHO) with global lower-level circulation and monsoon anomalies in boreal summer. Our results show that the summer IHO explains a greater portion of variance in the abnormal distribution of atmospheric mass over 30°S-60°N as well as the Antarctic. The IHO strongly correlates to the variations of sea level pressure (SLP) in these regions. It is shown that IHO has some influences on both atmospheric mass transports and water vapor fluxes over 30°S-60°N in association with three anomalous cyclonic circulations over land areas of the eastern hemisphere, which is in close relation to the changes in summer monsoon intensity in eastern Asia and western Africa. Composites of summer rainfall anomalies in China for high and low IHO-index years indicate that the eastern Asian summer monsoon is more intense, with positive precipitation anomaly centers in northern and northeastern parts of China, as opposed to the negative center over the mid-lower reaches of the Yangtze River (MLRYR) in stronger IHO years. In weak IHO years, a feeble summer monsoon appears in eastern Asia, leading to positive center of precipitation anomalies displaced into the MLRYR. Furthermore, a teleconnection in wind fields between the western African and eastern Asian monsoon regions was observed in the middle and higher troposphere in the scenario of IHO. The anomalous cyclonic (anticyclonic) circulations along the path of this Africa-East Asia teleconnection were found to be just over the diabatic heating (cooling) centers, suggesting that diabatic forcings are responsible for the formation of this Africa-East Asia teleconnection. | LU ChuHan, GUAN ZhaoYong & CAI JiaXi Key Laboratory of Meteorological Disaster of Ministry of Education and College of Atmospheric Sciences, Nanjing University of Information Science & Technology, Nanjing 210044, China | 2010 | Science China Earth Sciences2010，53，9： | 4 |
| 9 | An Objective Identification Method for Wintertime Cold Fronts in Eurasia显示文摘The present study identifies wintertime cold fronts in Eurasia from gridded datasets using a new objective two-step identification scheme.The simple and classic conception of a front is adopted,where a cold front is identified as the warm boundary of the frontal zone with a suitable horizontal temperature gradient and cold advection.We combine the traditional thermal front parameter with temperature advection to first identify the cold frontal zone,and then its eastern and southern boundaries are objectively plotted as a cold front in Eurasia.By comparing different cold front identification methods,the results from this two-step cold front identification method and subjective analysis are more consistent,and the positions of the cold front identified with our method are more reasonable.This objective technique is also applied to a nationwide cold wave event over China.Results show that the horizontal extent and movement of the cold front are in good agreement with the related circulation and the associated cold weather.The proposed method and results in this study may shed light on the rapid identification of cold fronts in operational weather analysis and facilitate further research on the long-term activity characteristics of continental cold fronts. | Mengru FENG Yujing QIN Chuhan LU | 2021 | Advances in Atmospheric Sciences2021，38，10： | 1 |
| 10 | On the Interrelation between Spring Bihemispheric Circulations at Middle and High Latitudes显示文摘Bihemispheric atmospheric interaction and teleconnection allow us to deepen our understanding of large-scale climate and weather variability. This study uses 1979-2017 spring NCEP reanalysis to show that there is interrelation between bihemispheric circulations at the extratropics. This is regarded as a significant negative correlation between the Antarctic and the Arctic regional surface air pressure anomalies, which is induced by interhemispheric oscillation (IHO) of the atmospheric mass. The spatial pattern of IHO is characterized by antiphase extratropical airmass anomalies and geopotential height anomalies from the troposphere to stratosphere between the Southern and Northern Hemisphere. IHO is closely related to stronger bihemispheric low-frequency signals such as Antarctic Oscillation and Arctic Oscillation, thereby demonstrating that IHO can be interpreted as a tie in linking these two dominant extratropical circulations of both hemispheres. IHO is associated with a strong meridional teleconnection in zonal winds from the middle-high troposphere to the lower stratosphere, with the wind anomalies in the form of alternate positive-negative wavy bands extending from the Antarctic to Arctic region, which act as a possible approach to interactions between the bihemispheric atmospheric mass. It is argued that IHO-related omega angular momentum anomalies led by the extratropical atmosphere cause the meridional teleconnection of relative angular momenta, thereby giving rise to the zonal wind anomalies. The modeling of GFDL and UKMO as components of the CMIP5 project have been verified, achieving the related IHO structure shown in the present paper. | Chuhan LU Zhaoyong GUAN | 2019 | Advances in Atmospheric Sciences2019，36，12： | 1 |
| 11 | Detection of the synoptic southeastward-extending Siberian cold high during 1978-2017显示文摘为了更好地研究西伯利亚地区反气旋与冷空气活动,东亚地区气温变化之间的关联,本文提出一种基于Mask R-CNN的反气旋识别方法,能够较为准确地刻画反气旋形态特征变化.使用该方法能够识别对中国冬季气温具有较大影响的东南延伸型西伯利亚冷高压(SEESCH),这种冷高压是冬季出现在西伯利亚地区的主要天气系统之一(45.7%).SEESCH携带的冷空气与下游地区温度变化呈显著负相关,52%的SEESCH伴随着华北华东地区冷空气聚集,对区域降温有显著影响.这些结果为研究SEESCH与极端寒冷事件之间的联系提供线索. | Yumin Zhang Chuhan Lu | 2022 | Atmospheric and Oceanic Science Letters2022，15，3： | 0 |
| 12 | Analysis on mechanisms of anomalous variations of tropopause pressure over the Tibetan Plateau during summer in Northern Hemisphere显示文摘Using the monthly mean data from NCEP-NCAR reanalysis,through building tropopause pressure index,we investigated the mechanisms of anomalous variations of tropopause pressure over the Tibetan Plateau during summer in Northern Hemisphere.For comparative analysis we selected representative years of 1992 and 1998 to study,and they were respectively the highest and the lowest year of tropopause pressure anomaly over the Tibetan Plateau.The results are summarized as follows:(1) Over the Tibetan Plateau,the variations of tropopause pressure are well correlated respectively with anomalous temperature and geopotential height in both troposphere and stratosphere.Besides,the anomalous tropopause pressure has also close relation with anomalous surface temperature in the Tibetan Plateau.In 1992,the surface temperature was anomalously low,correspondingly,the tropopause pressure over the Tibetan Plateau was anomalously high;but in 1998,the opposite was the case.(2) Over the Tibetan Plateau,the correlation of tropopause pressure and OLR(Outgoing Longwave Radiation) is found to be positive.Furthermore,by further diagnosing the circulation fields between 850 hPa and 200 hPa levels and the whole troposphere vapour field,we found out that the anomalously high tropopause pressure in 1992 corresponded to the anticyclonic divergence of low level wind fields and the cyclonic convergence of high level wind fields,and coupled with divergence of the whole troposphere vapour fields along with the South Asian High weakened at the same time.While in 1998,the case was opposite to that in 1992.These facts indicated that the anomalous convection resulted in the significant difference of tropopause pressure in 1992 and 1998 over the Tibetan Plateau.(3) The vertically integrated heat budget anomalies were responsible for explaining tropopause pressure anomalies in 1992 and 1998 over the Tibetan Plateau. | BaoLin Zhu ChuHan Lu ZhaoYong Guan Zhi Cheng WenJun Liu | 2012 | Research in Cold and Arid Regions2012，4，2： | 0 |
| 13 | Role of Intraseasonal Oscillation in a Compound Drought and Heat Event over the Middle of the Yangtze River Basin during Midsummer 2018显示文摘In late July 2018, a compound drought and heat event(CDHE) occurred in the middle of the Yangtze River basin(MYRB) and caused great damage to the national economy. The CDHE over the MYRB has been documented to be linked with intraseasonal oscillations(ISOs) from different regions. However, specific roles of different ISOs on the development of the CDHE cannot be separated in the observational analysis. By using partial lateral forcing experiments driven by ISO in the Weather Research and Forecasting(WRF) model, we found that the midlatitude ISO generated by a westerly wave train in the upper troposphere played an important role in this heatwave and drought event in the northern MYRB, causing a regional average temperature rise of 1.65°C and intensification of drought over23.49% of the MYRB area. On the other hand, the ISO associated with the Pacific-Japan(PJ)-like teleconnection wave train in the lower troposphere induced a more pronounced impact on the event, causing an average temperature rise of 2.44°C, intensifying drought over 29.62% of the MYRB area. The MYRB was mainly affected by northward warm advection driven by the westward extension of the western North Pacific subtropical high in the early period of the CDHE development. In the late period, because of the establishment of a deep positive geopotential height field through the troposphere leading to intensive local subsidence, there was a remarkable temperature rise and moisture decrease in the MYRB. The results will facilitate a better understanding of the occurrence of CDHE and provide empirical precursory signals for subseasonal forecast of CDHE. | Chuhan LU Yichen SHEN Yonghua LI Bo XIANG Yujing QIN | 2022 | Journal of Meteorological Research2022，36，4： | 0 |
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