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A Survey of Statistical Relationships between Tropical Cyclone Genesis and Convectively Coupled Equatorial Rossby Waves

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Advances in Atmospheric Sciences 2022年第5期39卷 747-762页

作者： Shuguang WANG Juan FANG Xiaodong tanG zhe-min tan Key Laboratory of Mesoscale Severe Weather(MOE) School of Atmospheric SciencesNanjing UniversityNanjing 210093China

Convectively coupled equatorial Rossby waves(ERW)modulate tropical cyclone activities over tropical *** study presents a survey of the statistical relationship between intraseasonal ERWs and tropical cyclone genesis(TCG)over major global TC basins using four-decade-long outgoing longwave radiation(OLR)and TC best-track *** ERWs are identified from the OLR anomalies using an empirical orthogonal function(EOF)analysis method without imposing equatorial *** find that westward-propagating ERWs are most significant in four tropical ocean basins over the summer hemisphere and that ERWs exhibit similar northeast-southwest(southeast-northwest)tilted phase lines in the northern(southern)hemisphere,with an appreciable poleward advance of wave energy in most TC *** EOF-based ERW indices quantitatively show that ERWs significantly modulate TC *** convectively active(suppressed)phases of ERWs coincide with increased(reduced)TCG *** TCG modulation by ERWs achieves the maximum where the ERWs propagate through the climatological TCG *** a result,the total number of TCG occurrences in the TC basins varies significantly according to the ERW *** ERW-TCG relationship is significant over the northwestern Pacific Ocean,northeastern Pacific Ocean,and the northern Indian Ocean during the northern summer *** the southern summer season,the ERW-TCG relationship is significant over the southern Indian Ocean,Indonesian-Australia basin,and the southwestern Pacific ***,ERW activities are weak in the main TC development region of the Atlantic Ocean;and the impact on Atlantic TCG appears to be insignificant.

关键词： tropical cyclone genesis equatorial Rossby waves statistical analysis

The importance of data assimilation components for initial conditions and subsequent error growth

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Science China Earth Sciences 2024年第1期67卷 105-116页

作者： Zhongrui WANG Haohao SUN Lili LEI zhe-min tan Yi ZHANG Key Laboratory of Mesoscale Severe Weather Ministry of Educationand School of Atmospheric SciencesNanjing UniversityNanjing 210023China Frontiers Science Center for Critical Earth Material Cycling Nanjing UniversityNanjing 210023China

Despite a specific data assimilation method,data assimilation(DA)in general can be decomposed into components of the prior information,observation forward operator that is given by the observation type,observation error covariances,and background error *** a classic Lorenz model,the influences of the DA components on the initial conditions(ICs)and subsequent forecasts are systematically investigated,which could provide a theoretical basis for the design of DA for different scales of *** forecast errors undergo three typical stages:a slow growth stage from 0 h to 5 d,a fast growth stage from 5 d to around 15 d with significantly different error growth rates for ensemble and deterministic forecasts,and a saturation stage after 15 *** strategies that provide more accurate ICs can improve the *** assimilation is superior to offline assimilation,and a flow-dependent background error covariance matrix(Pf)provides better analyses than a static background error covariance matrix(B)for instantaneous observations and frequent time-averaged observations;but the opposite is true for infrequent time-averaged observations,since cycling simulation cannot construct informative priors when the model lacks predictive skills and the flow-dependent Pf cannot effectively extract information from low-informative observations as the static *** observations contain more information than time-averaged observations,thus the former is preferred,especially for infrequent observing ***,ensemble forecasts have advantages over deterministic forecasts,and the advantages are enlarged with less informative observations and lower predictive-skill model priors.

关键词： Data assimilation Atmospheric predictability Background error covariances Ensemble forecasts

Typhoon Track,Intensity,and Structure:From Theory to Prediction

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Advances in Atmospheric Sciences 2022年第11期39卷 1789-1799页

作者： zhe-min tan Lili LEI Yuqing WANG Yinglong XU Yi ZHANG Key Laboratory of Mesoscale Severe Weather Ministry of Educationand School of Atmospheric SciencesNanjing UniversityNanjing 210063China International Pacific Research Center and Department of Atmospheric SciencesSchool of Ocean and Earth Science and TechnologyUniversity of Hawaii at ManoaHonoluluHawaii 96822USA National Meteorological Center of CMA Beijing 100081China

To improve understanding of essential aspects that influence forecasting of tropical cyclones(TCs),the National Key Research and Development Program,ministry of Science and Technology of the People's Republic of China conducted a five-year project titled“Key Dynamic and Thermodynamic Processes and Prediction for the Evolution of Typhoon Intensity and Structure”(KPPT).Through this project,new understandings of TC intensification,including outer rainbanddriven secondary eyewall formation and the roles of boundary layer dynamics and vertical wind shear,and improvements to TC data assimilation with integrated algorithms and adaptive localizations are *** promote a breakthrough in TC intensity and structure forecasting,a new paradigm for TC evolution dynamics(i.e.,the correlations,interactions,and error propagation among the triangle of TC track,intensity,and structure)is proposed;and an era of dynamic-constrained,big-data driven,and strongly coupled data assimilation at the subkilometer scale and seamless prediction is expected.

关键词： typhoons track intensity structure theories predictions

On the relationship between tropical cyclone size and environmental helicity in the South China Sea

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Atmospheric and Oceanic Science Letters 2022年第4期15卷 32-37页

作者： min Li Kekuan Chu Jian-Feng Gu zhe-min tan School of Atmospheric Sciences Nanjing UniversityNanjingChina Key Laboratory of Mesoscale Severe Weather/ministry of Education Nanjing UniversityNanjingChina Department of Meteorology University of ReadingLondonUK

In this study,the impact of environmental factors on tropical cyclone(TC)outer-core size was investigated for both migrating and local TCs in the South China Sea during the period 2001–*** all the thermodynamic and dynamic factors,the low-level environmental helicity showed the strongest positive correlation with TC outer-core *** helicity favors the development and organization of convection in TCs,and the corresponding strong inflow and large angular momentum fluxes into the system is beneficial for the maintenance and enlargement of TC outer-core ***,the asymmetric distribution of helicity may account for the asymmetry of TC outer-core ***,the environmental helicity,as an integrated dynamic factor,can provide an alternative view on TC outer-core size.

关键词： Tropical cyclone Outer-core size Helicity Angular momentum

Evaluation of a Regional Ensemble Data Assimilation System for Typhoon Prediction

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Advances in Atmospheric Sciences 2022年第11期39卷 1816-1832页

作者： Lili LEI Yangjinxi GE zhe-min tan Yi ZHANG Kekuan CHU Xin QIU Qifeng QIAN Key Laboratory of Mesoscale Severe Weather/ministry of Education School of Atmospheric SciencesNanjing UniversityNanjing 210063China National Meteorological Center China Meteorological AdministrationBeijing 100081China

An ensemble Kalman filter(EnKF) combined with the Advanced Research Weather Research and Forecasting model(WRF) is cycled and evaluated for western North Pacific(WNP) typhoons of year 2016. Conventional in situ data, radiance observations, and tropical cyclone(TC) minimum sea level pressure(SLP) are assimilated every 6 h using an 80-member ensemble. For all TC categories, the 6-h ensemble priors from the WRF/EnKF system have an appropriate amount of variance for TC tracks but have insufficient variance for TC intensity. The 6-h ensemble priors from the WRF/EnKF system tend to overestimate the intensity for weak storms but underestimate the intensity for strong storms. The 5-d deterministic forecasts launched from the ensemble mean analyses of WRF/EnKF are compared to the NCEP and ECMWF operational control forecasts. Results show that the WRF/EnKF forecasts generally have larger track errors than the NCEP and ECMWF forecasts for all TC categories because the regional simulation cannot represent the large-scale environment better than the global simulation. The WRF/EnKF forecasts produce smaller intensity errors and biases than the NCEP and ECMWF forecasts for typhoons, but the opposite is true for tropical storms and severe tropical storms. The 5-d ensemble forecasts from the WRF/EnKF system for seven typhoon cases show appropriate variance for TC track and intensity with short forecast lead times but have insufficient spread with long forecast lead times. The WRF/EnKF system provides better ensemble forecasts and higher predictability for TC intensity than the NCEP and ECMWF ensemble forecasts.

关键词： ensemble Kalman filter typhoon prediction ensemble forecast

Variability of microphysical characteristics in the “21·7” Henan extremely heavy rainfall event

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Science China Earth Sciences 2022年第10期65卷 1861-1878页

作者： Gang CHEN Kun ZHAO Yinghui LU Yuanyuan zheNG ming XUE zhe-min tan Xin XU Hao HUANG Haonan CHEN Fen XU Ji YANG Shushi ZHANG Xueqi FAN Key Laboratory of Transportation Meteorology of China Meteorological Administration Nanjing Joint Institute for Atmospheric SciencesNanjing 210041China Key Laboratory for Mesoscale Severe Weather/MOE and School of Atmospheric Science Nanjing UniversityNanjing 210023China State Key Laboratory of Severe Weather and Joint Center for Atmospheric Radar Research of CMA/NJU Chinese Academy of Meteorological SciencesBeijing 100081China Center for Analysis and Prediction of Storms and School of Meteorology University of OklahomaNormanOklahoma 73072USA Colorado State University Fort CollinsCO 80523USA

In this study, significant rainfall microphysical variability is revealed for the extremely heavy rainfall event over Henan Province in July 2021(the “21·7” Henan EHR event) using a dense network of disdrometers and two polarimetric *** broad distributions of specific drop size distribution(DSD) parameters are identified in heavy rainfall from the disdrometer observations, indicating obvious microphysical variability on the surface. A K-means clustering algorithm is adopted to objectively classify the disdrometer datasets into separate groups, and distinct DSD characteristics are found among these heavy rainfall groups. Combined with the supporting microphysical structures obtained through radar observations, comprehensive microphysical features of the DSD groups are derived. An extreme rainfall group is dominantly formed in the deep convection over the plain regions, where the high number of concentrations and large mean sizes of surface raindrops are underpinned by both active ice-phase processes and efficient warm-rain collision-coalescence processes in the vertical direction. Convection located near orographic regions is characterized by restricted ice-phase processes and high coalescence efficiency of liquid hydrometeors, causing the dominant DSD group to comprise negligible large raindrops. Multiple DSD groups can coexist within certain precipitation episodes at the disdrometer stations, indicating the potential microphysical variability during the passage of convective system on the plain regions.

关键词： The“21·7”Henan EHR event Microphysical characteristics Variability Disdrometer Polarimetric radar

The Roles of Asymmetric Inflow Forcing Induced by Outer Rainbands in Tropical Cyclone Secondary Eyewall Formation

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The Roles of Asymmetric Inflow Forcing Induced by Outer Rain...

Objective satellite methods including AI algorithms reviewed for the tenth International workshop on tropical cyclones(IWTC-10)

第八届全国优秀青年气象科技工作者学术研讨会

作者： XIN QIU zhe-min tan Key Laboratory of Mesoscale Severe Weather/MOE and School of Atmospheric Sciences Nanjing University

This study analyzes the secondary eyewall formation（SEF） process in an idealized cloud-resolving simulation of a tropical cyclone. In particular, the unbalanced boundary layer response to asymmetric inflow forcing induced by outer rainbands（ORBs） is examined in order to understand the mechanisms driving the sustained convection outside the primary eyewall during the early phase of *** enhancement of convection in the SEF region follows the formation and inward contraction of an ORB. The azimuthal distribution of the enhanced convection is highly asymmetric but regular, generally along a half circle starting from the downwind portion of the ORB. It turns out that the descending radial inflow in the middle and downwind portions of the ORB initiates/maintains a strong inflow in the boundary layer. The latter is able to penetrate into the inner-core region, sharpens the gradient of radial velocity, and reinforces convergence. Consequently, warm and moist air is continuously lifted up at the leading edge of the strong inflow to support deep convection. Moreover, the inflow from the ORB creates strong supergradient winds that are ejected outward downwind, thereby enhancing convergence and convection on the other side of the storm. The results provide new insight into the key processes responsible for convection enhancement during the early phase of SEF in three dimensions and suggest the limitations of axisymmetric studies. There are also implications regarding the impact of the asymmetric boundary layer flow under a translating storm on SEF.

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Tropical Cyclone Research and Review 2023年第4期12卷 259-266页

作者： Quoc-Phi Duong Anthony Wimmers Derrick Herndon zhe-min tan Jing-Yi Zhuo John Knaff Ibrahim Al Abdulsalam Takeshi Horinouchi Ryota Miyata Arthur Avenas Laboratoire de l’Atmosphere et des Cyclones(UMR8105 LACy) Universite de La ReunionCNRSMeteo-FranceSaint-DenisFrance Cooperative Institute for Meteorological Satellite Studies University of Wisconsin–MadisonWisconsinUSA Key Laboratory of Mesoscale Severe Weather/ministry of Education Nanjing UniversityNanjingChina School of Atmospheric Sciences Nanjing UniversityNanjingChina NOAA Center for Satellite Applications and Research Fort CollinsCOUSA Center of Excellence for Satellite Applications Oman Faculty of Environmental Earth Science Hokkaido UniversityHokkaidoJapan Faculty of Engineering University of the RyukyusOkinawaJapan IFREMER Universite BrestCNRSIRDLaboratoire d'Oceanographie Physique et SpatialeBrestFrance

Here we explore the latest four years(2019–2022)of using satellite data to objectively analyze tropical cyclones(TC)and issue recommendations for improved *** first discuss new methods of direct retrieval from SAR and geostationary ***,we survey some of the most prominent new techniques in AI and discuss their major capabilities(especially accuracy in nonlinear TC behavior,characterization of model uncertainty and creation of synthetic satellite imagery)and limitations(especially lack of transparency and limited amount of training data).We also identify concerns with biases and unlabeled uncertainties in the Best Track records as being a first-order limitation for further progress in objective *** article concludes with recommendations to improve future objective methods,especially in the area of more accurate and reliable training data sets.

关键词： AI Tropical cyclone Deep learning Satellite imagery analysis

Improving the behavior of the cumulus parameterization for tropical cyclone prediction: Convection trigger

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Improving the behavior of the cumulus parameterization for t...