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ANALYSIS OF INDICES FOR severe CONVECTIVE weather UNDER THE INFLUENCE OF TROPICAL CYCLONES IN JIANGSU

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Journal of Tropical Meteorology 2014年第4期20卷 368-375页

作者：杨程宋金杰王元曾明剑 Key laboratory of Mesoscale severe weather /MOE and School of Atmospheric SciencesNanjing University Jiangsu Institute of Meteorological Sciences

By statistical research on the occurrence pattern of severe convective weather in Jiangsu province under the influence of tropical cyclones within a 10-year period(from 2001 to 2010),this paper discovers that among different severe convective weather,the occurrence frequency of short-range heavy precipitation is the highest,thunderstorms and gales come in second,and general thunderstorms rarely happen,while hailstorms and tornadoes never *** statistical results also showed that within the research period there are 21 tropical cyclones(TCs) affecting the Jiangsu area and most of them are in the stage of weakening to tropical ***,through studying indices for relevant cases of severe convection,it is discovered that their thresholds are lower than that of previous research,which indicated that convective instability and energy accumulation can easily lead to severe convective weather eventually due to the influence of TCs.

关键词： tropical cyclones severe convection statistics

Synoptic Pattern and severe weather Associated with the Wide Convection over Southeast China During the Summer Monsoon Period

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Journal of Meteorological Research 2015年第1期29卷 41-58页

作者：汪会罗亚丽张人禾 State Key laboratory of severe weather Chinese Academy of Meteorological Sciences Key laboratory for Cloud Physics and weather Modification of China Meteorological Administration Chinese Academy of Meteorological Sciences Collaborative Innovation Center on Forecast and Evaluation of Meteorological Disasters Nanjing University of Information Science & Technology

Based on the Tropical Rainfall Measuring Mission（TRMM） precipitation radar observations, wide convection（WC） is defined as contiguous convective echoes over 40 d BZ, accompanied with a near surface rainfall area exceeding 1000 km^2. In Southeast China, the maximal occurrence frequency of WC takes place over the flat land region in the central plain of East China during the summer monsoon period of 1998–2010. When WC occurs in this region, the 500-h Pa atmospheric fields are categorized into three patterns by using an objective classification method, i.e., the deep-trough-control（DTr） pattern, the subtropical-highmaintenance（STH） pattern, and the typhoon-effect（Typh） pattern, which respectively accounts for 20.8%,52.8%, and 26.4% of the total WC occurrences. The DTr pattern starts to emerge the earliest（16–31 May）and occurs the most often in the second half of June; the STH pattern has a significant occurrence peak in the first half of July; the Typh pattern occurs mostly in July and *** all WC occurrences in this region are associated with thunderstorms, due to large convective available potential energy and abundant moisture. Among the three synoptic patterns, the DTr pattern features the driest and coldest air in the region, leading to the least occurrences of short-duration heavy rainfall. Strong winds occur the most often under the DTr pattern, probably owing to the largest difference in air humidity between the mid and low troposphere. Hail at the surface is rare for all occurrences of WC,which is probably related to the humid environmental air under all weather patterns and the high（〉 5 km）freezing level under the STH pattern.

关键词： Tropical Rainfall Measuring Mission (TRMM) wide convection central plain of East China synoptic condition severe weather

Numerical Study on the Initiation of the severe Convective weather in Chongqing on 6 May 2010

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Acta meteorologica Sinica 2013年第3期27卷 364-378页

作者：孙一昕方娟 Key laboratory of Mesoscale severe weather/Ministry of Education and School of Atmospheric SciencesNanjing University Tianjin Air Traffic Management Sub-Bureau Civil Aviation Administration of China

As a follow-up of a previously published article on the synoptic background of the development of the severe convective weather that happened in Chongqing on 6 May 2010, this study further examines the initiation of the severe convective weather via a better high-resolution simulation with the weather Research and Forecasting （WRF） model. It is found that the cold front approaching Chongqing from the northwest played a critical role in the initiation of the severe convective weather. As the cold front approached Chongqing, the low-to-mid level updrafts ahead of the front acted to increase the atmospheric lapse rate via the stretching effect, which in combination with the low-level diabatic heating induced by the sensible heat fluxes and infrared radiation emitted from the ground surface led to the continuous decrease of the low-level static stability and the increase of the convective available potential energy （CAPE） in Chongqing area. This provided necessary unstable energy for the development of deep moist convection. Furthermore, along with the reaching of a nearly east-west-oriented mesoscale convergence line from the southeast of Chongqing, the outflow right above the cold front began to interact with that above the mesoscale convergence line and induced distinct convergence at the altitude of approximately 1-2 km in the triangular area sandwiched by the cold front and the mesoscale convergence line. It is found that the updrafts associated with this convergence provided lifting necessary for the initiation of the severe convection. The sensitivity experiment without the terrain west of Chongqing indicates that the local topography did not play an important role in the initiation of this severe convective weather.

关键词： convection initiation cold front mesoscale convergence line topography

The Effect of Surface Friction on the Development of Tropical Cyclones

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Advances in Atmospheric Sciences 2009年第6期26卷 1146-1156页

作者：方娟汤剑平伍荣生 Key laboratory of Mesoscale severe weather Nanjing University

When tropical cyclones （hereafter referred as TCs） are over the ocean, surface friction plays a dual role in the development of TCs. Prom the viewpoint of water vapor supply, frictional convergence and Ekman pumping provide a source of moisture for organized cumulus convection and is propitious to the spin-up of TCs. On the other hand, surface friction leads to a dissipation of kinetic energy that impedes the intensification of TCs. Which role is dominant in the developing stage of TCs is a controversial issue. In the present work, the influence of surface friction on the growth of TCs is re-examined in detail by conducting two sets of numerical experiments initialized with different cyclonic disturbances. Results indicate that, because of the inherent complexities of TCs, the impact of surface friction on the evolution of TCs can not be simply boiled down to being positive or negative. In the case that a TC starts from a low-level vortex with a warm core, surface friction and the resultant vertical motion makes an important contribution to the convection in the early developing stage of the TC by accelerating the build-up of convective available potential energy （CAPE） and ensuring moisture supply and the lifting of air parcels. This effect is so prominent that it dominates the friction-induced dissipation and makes surface friction a facilitative factor in the spin-up of the TC. However, for a TC formed from a mesoscale convective vortex （MCV） spawned in a long-lasting mesoscale convective system （MCS）, the initial fields, and especially the low-level humidity and cold core, enable the prerequisites of convection （i.e., conditional instability, moisture, and lifting）, to be easily achieved even without the help of boundary-layer pumping induced by surface friction. Accordingly, the reliance of the development of TCs on surface friction is not as heavy as that derived from a lowlevel vortex. The positive effect of surface friction on the development of TCs realized

关键词： surface friction tropical cyclone boundary-layer pumping convective available potential energy

Shearing Wind Helicity and Thermal Wind Helicity

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Advances in Atmospheric Sciences 2006年第4期23卷 504-512页

作者：韩瑛伍荣生方娟 The Key laboratory of Mesoscale severe weather Nanjing University

Helicity is defined as H ： V ω, where V and ω are the velocity and vorticity vectors, respectively. Many works have pointed out that the larger the helicity is, the longer the life cycle of the weather system is. However, the direct relationship of the helicity to the evolution of the weather system is not quite clear. In this paper, the concept of helicity is generalized as shearing wind helicity （SWH）. Dynamically, it is found that the average SWH is directly related to the increase of the average cyclonic rotation of the weather system. Physically, it is also pointed out that the SWH, as a matter of fact, is the sum of the torsion terms and the divergence term in the vorticity equation. Thermal wind helicity （TWH）, as a derivative of SWH, is also discussed here because it links the temperature field and the vertical wind field. These two quantities may be effective for diagnosing a weather system. This paper applies these two quantities in cylindrical coordinates to study the development of Hurricane Andrew to validate their practical use. Through analyzing the hurricane, it is found that TWH can well describe the characteristics of the hurricane such as the strong convection and release of latent heat. SWH is not only a good quantity for diagnosing the weather system, but also an effective one for diagnosing the development of the hurricane.

关键词： helicity shearing wind helicity thermal wind helicity hurricane SWH TWH

Nonlinearity and Finite-Time Instability in a T21L3 Quasigeostrophic Model

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Acta meteorologica Sinica 2011年第4期25卷 419-429页

作者：姜智娜王东海 State Key laboratory of severe weather Chinese Academy of Meteorological Sciences

In this paper, a nonlinear optimization method is used to explore the finite-time instability of the atmospheric circulation with a three-level quasigeostrophic model under the framework of the conditional nonlinear optimal perturbation （CNOP）. As a natural generalization of linear singular vector （SV）, CNOP is defined as an initial perturbation that makes the cost function the maximum at a prescribed forecast time under certain physical constraint conditions. Special attentions are paid to the different structures and energy evolutions of the optimal perturbations. The results show that the most instable region of the global atmospheric circulation lies in the midlatitude Eurasian continent. More specially, SV and CNOP in the total energy norm with an optimization time of 2 days both present localness： they are mainly located in the midlatitude Asian continent and its east coast. With extension of the optimization time, SVs are more upstream and less localized in the zonal direction, and CNOPs differ essentially from SVs with broader zonal and meridional coverages; as a result, CNOPs acquire larger kinetic and available potential energy amplifications than SVs in the nonlinear model at the corresponding optimization time. For the climatological wintertime flow, it is seen that the baroclinic terms remain small over the entire time evolution, and the energy production comes essentially from the eddy kinetic energy, which is induced by the horizontal shear of the basic flow. In addition, the effects of SVs and CNOPs on the Eurasian atmospheric circulation are explored. The results show that the weather systems over the Eurasian continent in the perturbed fields by CNOPs are stronger than those by SVs at the optimization time. This reveals that the CNOP method is better in evaluating the instability of the atmospheric circulation while the SV method underestimates the possibility of extreme weather events.

关键词： nonlinearity finite-time instability barotropic baroclinic

Comparison of the effects of soil moisture and El Nino on summer precipitation in eastern China

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Science China Earth Sciences 2020年第2期63卷 267-278页

作者： Juan ZHOU Zhiyan ZUO Xinyao RONG State Key laboratory of severe weather Chinese Academy of Meteorological Sciences

The effects of spring soil moisture over the vast region from the lower and middle reaches of the Yangtze River valley to North China(YRNC) and El Ni?o on the East Asian summer monsoon(EASM) and precipitation in eastern China, as well as the relevant mechanisms, are investigated using the modified atmospheric model ECHAM5 coupled with the Common Land Model. These models are the atmospheric and land components of the climate system model developed at the Chinese Academy of Meteorological Sciences(CAMS-CSM). The simulations show that both soil moisture anomalies in eastern China and El Ni?o sea surface temperature(SST) anomalies have significant influences on the EASM, with the effect of soil moisture being slightly greater than that of the El Ni?o. However, the impacts of soil moisture on EASM and rainfall in eastern China are markedly different from those of the El Ni?o. Wetter(drier) soil over the YRNC corresponds to less(more) precipitation over northern and southeastern China, and more(less) precipitation over the Yangtze River basin and northeastern China, as well as a strengthened(weakened) and westward-shifted(eastward-shifted) West Pacific Subtropical High and a deepened(shallower) East Asian trough, representing a weakened(strengthened) EASM pattern. During El Ni?o developing summers, an anomalous anticyclone extends from northeastern to northern China, and an anomalous cyclone occupies the middle and lower reaches of the Yangtze River and southern China. Concurrently, the West Pacific Subtropical High is anomalously weaker than normal. As a result,rainfall anomalously increases over the lower reaches of the Yangtze River and southern China, and decreases over northern and northeastern China. In El Ni?o decaying summers, there is an anomalous cyclone over northeastern China and an anomalous anticyclone over southern China. The convergence of southerly airflow and northerly winds leads to enhanced rainfall around northern China and the middle reaches of the Y

关键词： Soil moisture El Nino East Asian summer monsoon Precipitation Numerical simulation

A Simple Method of Calculating the Optimal Step Size in 4DVAR Technique

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Advances in Atmospheric Sciences 2000年第3期17卷 433-444页

作者：王云峰伍荣生王元潘益农 laboratory of Mesoscale severe weather Nanjing University 210093 Nanjing

In four—dimensional variational data assimilation (4DVAR) technology, how to calculate the optimal step size is always a very important and indeed difficult task. It is directly related to the computational efficiency. In this research, a new method is proposed to calculate the optimal step size more effectively. Both nonlinear one—dimensional advection equation and two—dimensional inertial wave equation are used to test and compare the influence of different methods of the optimal step size calculations on the iteration steps, as well as the simulation results of 4DVAR processes. It is in evidence that the different methods have different influences. The calculating method is very important to determining whether the iteration is convergent or not and whether the convergence rate is large or small. If the calculating method of optimal step size is properly determined as demonstrated in this paper, then it can greatly enlarge the convergence rate and further greatly decrease the iteration steps. This research is meaningful since it not only makes an important improvement on 4DVAR theory, but also has useful practical application in improving the computational efficiency and saving the computational time. Key words 4DVAR - Optimal step size - Iterative convergence rate This work was supported by the National Natural Science Foundation under grants: 49735180 and 49675259, the “973 Project? CHERES(G 1998040907), the Project of Natural Science Foundation of Jiangsu Province(BK99020), and the Project Sponsored by the Scientific Research Foundation for the Returned Overseas Chinese Scholars.

关键词： 4DVAR Optimal step size Iterative convergence rate

Kinematic Features of a Bow Echo in Southern China Observed with Doppler Radar

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Advances in Atmospheric Sciences 2013年第6期30卷 1535-1548页

作者：彭新东张人禾王红艳 State Key laboratory of severe weather Chinese Academy of Meteorological Sciences

A bow echo is a type of mesoscale convective phenomenon that often induces extreme weather and appears with strong reflectivity on radar images. A strong bow echo that developed from a supercell was observed over Foshan City in southern China on 17 April 2011. The intense gusty winds and showers caused huge losses of property and severely affected human lives. This paper presents an analysis of this strong meso- n-scale convective system based on Doppler radar observations. The isolated bow echo exhibited a horizontal scale of about 80 km in terms of reflectivity above 40 dBZ, and a life span of 8 hours. The system originated from the merging of a couple of weakly organized cells in a shear line, and developed into an arch shape as it moved through the shear zone. Sufficient surface moisture supply ensured the convective instability and development of the bow echo. The low-altitude winds retrieved from single Doppler radar observations showed an obvious rear-inflow jet along the notch area. Different from the conventional definition, no book- end anticyclone was observed throughout the life cycle. Very strong slantwise updrafts and downdrafts were recognizable from the retrieved winds, even though the spatial scale of the bow echo was small. Strong winds and induced damage on the surface are considered to have been caused by the mid-level rear-inflow jet and intense convective downdrafts.

关键词： bow echo kinematic features Doppler radar wind retrieval