华东登陆热带气旋降水不同分布的对比分析

利用CMORPH降水资料，将热带气旋（TC）登陆后的降水分为路径左侧降水（L型）和右侧降水（R型）两类，并针对登陆华东地区TC的 L型和R型降水的大气环流场、环境水平风垂直切变以及台风环流内的动热力条件进行对比分析，结果表明:2005～2014年间登陆华东地区的20例TC中包括12例L型和8例R型。总体来看，大气环流因子对于登陆华东TC降水分布起主要作用。L型降水TC高层南亚高压主要呈纬向带状分布，在登陆过程中路径左侧维持偏东风高空辐散气流，中层西风槽偏东，西太平洋副热带高压（简称副高）偏南，环境水平风垂直切变指向西南。R型降水TC高层南亚高压断裂，呈经向分布。TC路径左侧风场较均匀，右侧东南风高空辐散气流明显。副高的位置偏北呈块状，同时环境水平风垂直切变指向东北，有利于路径右侧降水。台风环流内，低层冷暖平流输送以及水汽辐合与降水落区也有较好对应关系。L型TC低层暖平流的输送使TC西南象限低层增暖，大气稳定度降低。同时水汽辐合区也主要位于西南象限，有利于TC路径左侧降水。而R型TC副高位置偏北可将南侧的东南暖湿气流向台风环流更西部输送，东北象限维持暖平流，有利于路径右侧降水发生。     

Tropical cyclone structure in the South China Sea based on high-resolution reanalysis data and comparison with that of ‘bogus’ vortices

Based on high-resolution reanalysis data of the European Centre for Medium-Range Weather Forecasts, several samples of tropical cyclones (TCs), including tropical storms, severe tropical storms, and typhoons, in the South China Sea (SCS), were selected for composite analysis. The structures of these three types of vortices and their differences with ‘bogus’ vortices were investigated. Results showed that TCs in the SCS have characteristics that are distinctly different from vortices formed by the bogussing scheme used at Guangzhou Institute of Tropical and Marine Meteorology, such as no anticyclone in higher layers, strong convergence concentrated at the bottom of the troposphere, and strong divergence happening in higher layers instead of at 400 hPa. These differences provide clues for constructing a more realistic structure for TCs in the SCS. It was also found that the three types of vortices have some structural features in common. The area with high wind speed is fan-shaped in the north around the TC center, the maximum vorticity appears at 925 hPa, the strongest convergence appears at 1000 hPa, and strong divergence is located from 150 to 100 hPa. On the contrary, significant differences between them were revealed. The warm cores in tropical storms, severe tropical storms, and typhoons are located at 600–400 hPa, 400−300 hPa, and 400−250 hPa, respectively. Among the three types of TCs, the bogus vortex of tropical storms has the largest errors in structure and suffers the largest errors in track forecasts. However, typhoons have the largest errors in the forecast of intensity. This may be related to the great impacts of ocean on TC intensity.     

Tropical cyclone potential hazard in Southeast China and its linkage with the East Asian westerly jet

A new synthesized index for estimating the hazard of both accumulated strong winds and heavy rainfall from a tropical cyclone (TC) is presented and applied to represent TC potential hazard over Southeast China. Its relationship with the East Asian westerly jet in the upper troposphere is also investigated. The results show that the new TC potential hazard index (PHI) is good at reflecting individual TC hazard and has significantly higher correlation with economic losses. Seasonal variation of TC-PHI shows that the largest TC-PHI on average occurs in July-August, the months when most TCs make landfall over mainland China. The spatial distribution of PHI at site shows that high PHI associated with major landfall TCs occurs along the southeast coast of China. An East Asian westerly jet index (EAWJI), which represents the meridional migration of the westerly jet, is defined based on two regions where significant correlations exist between TC landfall frequency and zonal wind at 200 hPa. Further analyses show that an anomalous easterly steering flow occurred above the tracks of TCs, and favored TCs making landfall along the southeast coast of China, leading to an increase in the landfall TC when the EAWJ was located north of its average latitude. Meanwhile, anomalous easterly wind shear and positive anomaly in low-level relative vorticity along TCs landfall-track favored TC development. In addition, anomalous water vapor transport from westerly wind in the South China Sea resulted in more condensational heating and an enhanced monsoon trough, leading to the maintenance of TC intensity for a longer time. All of these environmental factors increase the TC potential hazard in Southeast China. Furthermore, the EAWJ may affect tropical circulation by exciting meridional propagation of transient eddies. During a low EAWJI phase in July-August, anomalous transient eddy vorticity flux at 200 hPa propagates southward over the exit region of the EAWJ, resulting in eddy vorticity flux convergence and the weakening in the zonal westerly flow to the south of the EAWJ exit region, producing a favorable upper-level circulation for a TC making landfall.     

A STATISTICAL ANALYSIS ON THE DIFFERENT FEATURES OF TC EXTRATROPICAL TRANSITION OVER LAND AND OCEAN

The extratropical transitions(ETs)of tropical cyclones(TCs)over China and the ocean east to 150°E are investigated by the use of best-track data and JRA-25 reanalysis spanning 1979-2008.The ET events occurring north of 25°N and in the warm season(from May to October)are extracted from the reanalysis to emphasize the interaction between TC and midlatitude circulation.Statistical analysis shows that 18.5%of the warm-season TCs go through land ETs north of 25°N in the western North Pacific.And 20.5%of the ET events occur over the ocean east of 150°E.Most(62.2%)ET TCs over China gradually die out after ET,but more(70.7%)ocean ET cases have post-ET reintensification.The evolutions in cyclone phase space and the composite fields for land and ocean ETs,as well as the ET cases with and without post-ET reintensification,are further analyzed.It is found that most TCs with ET over China and those without post-ET reintensification evolve along the typical ET phase path as follows:emergence of thermal asymmetry→losing upper-level warm core→losing lower-level cold core→evolving as extratropical cyclone.The TCs undergoing ETs over ocean and those with post-ET reintensification form a high-level cold core before the ET onset.The TCs with land ET have long distance between the landing TC and a high-level trough.That makes the TC maintain more tropical features and isolates the TC flow from the upstream and downstream jets of the midlatitude trough.The structure of circulation leads to weak development of baroclinicity in land ET.On the contrary,shorter distance between ocean TC and high-level trough makes the high-level trough absorb the TC absolutely.Under that baroclinicity-favorable environment,strong cold advection makes the TC lose its high-level warm core before ET onset.The composite fields confirm that the TC with ocean ET has stronger baroclinic features.Generally,the TC at land ET onset is located to the south of the ridge of the subtropical high,which tends to prevent the TCs from interacting with midlatitude circulation.But for the ocean ET,the situation is just the opposite.Similar analyses are also carried out for the TCs with and without post-ET reintensification over both land and ocean east of 150°E.The results further prove that the TC with stronger baroclinic characteristics,especially in the circumstance favorable to its interaction with high-level midlatitude systems,has more opportunity to reintensify as an extratropical cyclone after ET.     

AN ANALYSIS ON INTERDECADAL VARIATIONS OF TROPICAL CYCLONE PRECIPITATION IN GUANGDONG PROVINCE OF CHINA

The interdecadal variations of tropical cyclones(TCs) and their precipitation over Guangdong Province are investigated using the observational data of TCs and precipitation from 26 observational stations in the province from 1951 to 2005.The results show that the TCs precipitation shows an oscillation with a peak value of about 25 years,with both the numbers of the Guangdong-influencing TCs and TCs formed in the western North Pacific oscillating with a peak value of about 23 years.The correlations are highly positive between the interdecadal variation of TC precipitation over the province and these numbers.The interdecadal variation of TC precipitation in the province shows significant negative correlations with the interdecadal variation of annual mean SST in some parts of the western North Pacific and the interdecadal variation of annual mean 500 hPa geopotential heights in some parts of the middle and high latitudes over the North Pacific.In general,there are high mean SSTs on the equator from central to eastern Pacific,low mean SSTs in the middle and high latitudes over the North Pacific and a main strong East Asian trough over the North Pacific in the period of less TC precipitation as compared with the period of more TC precipitation over the province.     

A comprehensive classification of anomalous circulation patterns responsible for persistent precipitation extremes in South China

Based on observational precipitation at 63 stations in South China and NCEP NCAR reanalysis data during 1951 2010,a cluster analysis is performed to classify large-scale circulation patterns responsible for persistent precipitation extremes(PPEs) that are independent of the influence of tropical cyclones(TCs).Conceptual schematics depicting configurations among planetary-scale systems at different levels are established for each type.The PPEs free from TCs account for 38.6%of total events,and they tend to occur during April August and October,with the highest frequency observed in June.Corresponding circulation patterns during June August can be mainly categorized into two types,i.e.,summer-Ⅰ type and summer-Ⅱtype.In summer-Ⅰ type,the South Asian high takes the form of a zonal-belt type.The axis of upstream westerly jets is northwest-oriented.At the middle level,the westerly jets at midlatitudes extend zonally.Along the southern edge of the westerly jet,synoptic eddies steer cold air to penetrate southward;the Bay of Bengal(BOB) trough is located to the north;a shallow trough resides over coastal areas of western South China;and an intensified western Pacific subtropical high(WPSH) extends westward.The anomalous moisture is mainly contributed by horizontal advection via southwesterlies around 20°N and southeasterlies from the southern flange of the WPSH.Moisture convergence maximizes in coastal regions of eastern South China,which is the very place recording extreme precipitation.In summer-Ⅱ type,the South Asian high behaves as a western-center type.The BOB trough is much deeper,accompanied by a cyclone to its north;and a lower-level trough appears in northwestern parts of South China.Different to summer-Ⅰ type,moisture transport via southwesterlies is mostly responsible for the anomalous moisture in this type.The moisture convergence zones cover Guangdong,Guangxi,and Hainan,matching well with the areas of flooding.It is these set combinations among different systems at different levels that trigger PPEs in South China.     

华北冷季一次大范围雷暴与暴雪共存天气过程分析

利用常规气象资料、多普勒雷达及NCEP客观分析资料,对2013年3月12日华北出现的一次比较罕见的大范围雷暴和暴雪共存天气过程进行了诊断分析。结果表明：本次大范围的雷暴为发生在低层冷空气堆之上的高架雷暴。虽然雷暴区中低层水汽通量辐合较弱,但中高层θe平流差造成中层出现条件不稳定,在850 hPa切变线前部西南风中辐合配合冷平流以及切变线的先后触发下,不稳定能量得以释放,这是河北中部发生大范围雷暴的主要原因。暴雪区中层较强的水汽通量辐合及辐合层厚度爆发性增长、700 hPa槽区以及槽前西南气流和偏西气流的强辐合是造成北部暴雪天气的重要原因。此外,中低层正的差动涡度平流较散度场对暴雪及雷暴区的动力作用的反映更明显。     

STATISTICAL ANALYSIS AND NUMERICAL SIMULATION OF POYANG LAKE'S INFLUENCE ON TROPICAL CYCLONES

Based on the Tropical Cyclone(TC briefly thereafter)Yearbook 1980-2009,this paper first analyzes the number and intensity change of the TCs which passed directly over or by the side of Poyang Lake(the distance of TC center is less than 1°longitude or 1°latitude from the Lake)among all the landfalling TCs in China during the past 30 years.Two cases are examined in detail in this paper.One is severe typhoon Rananim with a speed of 3.26 m/s and a change of 1 hPa in intensity when it was passing the Lake.The other is super typhoon Saomai with a faster moving speed of 6.50 m/s and a larger change in intensity of 6 hPa.Through numerical simulation experiments,this paper analyzes how the change of underlying surface from water to land contributes to the differences in intensity,speed and mesoscale convection of the two TCs when they passed the Lake.Results show that the moisture and dynamic condition above the Lake were favorable for the maintenance of the intensity when Rananim was passing through Poyang Lake,despite the moisture supply from the ocean was cut off.As a result,there was strong convection around the lake which led to a rainfall spinning counter-clockwise as it was affected by the TC movement.However,little impact was seen in the Saomai case.These results indicate that for the TCs coming ashore on Poyang Lake with a slow speed,the large water body is conducive to the sustaining of the intensity and strengthening of the convection around the TC center and the subsequent heavy rainfall.On the contrary,a fast-moving TC is less likely to be influenced by the underlying surface in terms of intensity and speed.     

2003年渭河流域5次致洪暴雨过程的水汽场诊断分析

利用实况高空探测和地面观测资料、NCEP/NCAR再分析资料, 从水汽输送、水汽收支以及水汽含量等方面着手, 对2003年发生在渭河流域的5次致洪暴雨过程进行了对比分析, 结果表明:强降水发生时, 降水区700 hPa上的比湿值均不低于7 g/kg; 在垂直结构上, 强降水地区低层水汽含量在降水前6~12 h出现峰值, 强降水出现在高层比湿的峰值附近; 致洪暴雨过程的水汽通道与西太平洋副热带高压的位置有着明显的相关性; 渭河流域南边界是水汽的主要输入方, 主要的水汽输送层在850~700 hPa, 西边界是水汽的主要输出方。     

Short timescale air-sea coupling in the tropical deep convective regime

Summary The relationship between surface rainfall rate and sea-surface temperature (SST) over tropical cloudy areas is revisited, and associated air-sea interaction processes are investigated based on hourly grid simulation data over cloudy areas from a two-dimensional coupled ocean-cloud resolving atmosphere model. A cloud-weighted data analysis shows that surface evaporation flux decreases with increasing SST and is one order of magnitude smaller than the residual between moisture convergence and condensation, playing a negligible role in moisture budget. Moisture convergence determines the surface rainfall rate by determining vapor condensation and deposition rates. Ocean mixed-layer thermal budget shows that the atmospheric surface flux is a major process responsible for SST variation while thermal advection and thermal entrainment play a secondary role. The results indicate that atmospheric impacts on the ocean are important whereas oceanic impacts on the atmosphere are not, in the tropical air-sea system, on short timescales. Thus, the relationship between surface rainfall rate and SST over tropical cloudy areas is not physically important. Further estimates indicate that the surface evaporation flux and residual between moisture convergence and condensation could have the same order of magnitude in daily-mean moisture budget.     

浙江2011-01—20强降雪过程降雪带南压成因的诊断分析

利用自动站、Micaps、雷达风廓线等资料和6h间隔的NCEP1°×1°再分析资料,对浙江2011年1月20日强降雪过程中降雪带南压的成因进行了诊断分析。结果表明：高空槽、中低县切变配合近地面的冷空气渗透影响是强降雪发生的有利天气尺度背景;强降雪发生在低空西南急流左侧水汽通量散度的辐合区内,且低空西南急流的南压领先于降...     

Favorable versus unfavorable synoptic backgrounds for indirect precipitation events ahead of tropical cyclones approaching the Korean Peninsula: A comparison of two cases

This study identifies favorable synoptic backgrounds for indirect precipitation events over the Korean Peninsula that occur well in advance of tropical cyclone (TC) landfall. Two TCs, i.e., Rammasun (2002) and Maemi (2003) that made landfall and produced heavy rainfall over the Peninsula are compared. Although both had a remarkably similar accumulated rainfall pattern over the peninsula, the temporal evolutions of hourly rainfall were different. Only Maemi had an indirect precipitation event in conjunction with a midlatitude trough to its north. The confluent flows at middle-to-upper levels were strengthened due to the increased pressure gradient between the midlatitude trough and the subtropical high, and the warm advection by the confluent flows also became stronger near the confluent zone. By contrast, Rammasun encountered the subtropical ridge while moving northward, which results in slow recurvature and reduction of the thermal gradient over the peninsula. The highly baroclinic synoptic backgrounds in the Maemi case lead to the midlevel frontogenesis. Budget analyses using the three-dimensional frontogenesis equation revealed that the horizontal deformation forcing had a primary role in generating the front. The front was associated with a thermally direct circulation that contributed to strong ascent and indirect precipitation over the peninsula well in advance of the landfall of Maemi. Moreover, the indirect precipitation could intensify due to the abundant low-level moisture supply to the frontal zone by the southerly wind on the east side of the TC.     

Impact of Mid- and Upper-Level Dry Air on Tropical Cyclone Genesis and Intensification: A Modeling Study of Durian (2001)

The impact of mid- and upper-level dry air, represented by low relative humidity (RH) values, on the genesis of tropical cyclone (TC) Durian (2001) in the South China Sea was investigated by a series of numerical experiments using the Weather Research and Forecasting model. The mid-level RH was lowered in different regions relative to TC Durian (2001)'s genesis location. Results suggest that the location of dry air was important to Durian (2001)'s genesis and intensification. The rapid development of the TC was accompanied by sustained near-saturated mid- and upper-level air, whereas low humidity decelerated its development. Water vapor budget analysis showed that moisture at mid and upper levels was mainly supplied by the vertical convergence of moisture flux and the divergence terms, and consumed by the condensation process. The horizontal convergence of moisture flux term supplied moisture in the air moistening process but consumed moisture in the air drying process. With a dryer mid- and upper-level environment, convective and stratiform precipitation were both inhibited. The upward mass fluxes and the diabatic heating rates associated with these two precipitation types were also suppressed. Generally, convection played the dominant role, since the impact of the stratiform process on vertical mass transportation and diabatic heating was much weaker. The vorticity budget showed that the negative vorticity convergence term, which was closely related to the inhibited convection, caused the vorticity to decrease above the lower troposphere in a dryer environment. The negative vorticity tendency is suggested to slow down the vertical coherence and the development rate of TCs.     

Surface Rainfall Processes during the Genesis Period of Tropical Cyclone Durian(2001)

The rainfall processes during the formation of tropical cyclone(TC) Durian(2001) were investigated quantitatively using the three-dimensional(3 D) WRF-based precipitation equation. The rain rate(PS) decreased slightly as the TC approached to formation, and then increased as Durian began to intensify. The rate of moisture-related processes(QWV) in the equation contributed around 80% to PSbefore TC genesis, and made more contribution during and after TC genesis. The rate of hydrometeor-related processes(QCM) contributed about 20% before TC formation, followed by less contribution during and after TC formation. QWVwere dominated by the 3 D moisture flux advection rate(QWVA), while the surface evaporation rate(QWVE) also played an important role. Just before TC genesis, moisture from QWVAand QWVEhelped the local atmosphere moisten(negative QWVL). QCMwere determined by the 3 D hydrometeor advection rates(QCLAand QCIA) and the local change rates of hydrometeors(QCLLand QCIL). During TC formation, QCMlargely decreased and then reactivated as Durian began to intensify, accompanied by the development of TC cloud. Both the height and the strength of the net latent heating center associated with microphysical processes generally lowered before and during TC genesis, resulting mainly from lessening deposition and condensation. The downward shift of the net latent heating center induced a more bottom-heavy upward mass flux profile, suggesting to promote lower-tropospheric convergence in a shallower layer, vorticity amplification and TC spin-up.     

双TC和梅雨锋共同作用下的一次暴雨过程分析

通过NCEP再分析资料计算各种物理量和应用卫星云图、雷达资料,并用WRF中尺模式做数值模拟,从动力过程、水汽输送过程、中小尺度系统等3个方面对TC和梅雨锋共同作用在浙北产生的一次暴雨过程进行分析。结论如下:(1)动力过程特点:300 hPa急流出口区辐散,中层3支气流汇合形成变形场锋生,产生强烈上升运动。低层TC外围的东南气流输入暖平流和湿位涡,使海上台风倒槽向北传播发展,最终形成气旋。TC高层流出气流对梅雨锋南侧垂直环流的维持有利;(2)水汽主要由两个TC外围的环流输送;(3)卫星云图和雷达回波显示有不同的降水云团合并且有加强的过程。用WRF中尺模式做数值模拟显示:700 hPa中小尺度的切变线或辐合区与强降水回波相对应。过程主要特点是中低层两个TC外围的气流与西风带气流在华东地区汇合,形成变形场锋生,产生强烈的辐合上升。在不同的气流汇合后产生了强急流输送水汽,加强垂直环流和中小尺度的辐合,是强降水产生的主要原因。西南季风经过台风绕流后在合适的环境场下仍有可能到达华东地区,这时往往与中纬度西风带汇合,在这种情况下会加强梅雨降水。     

2019年台风利奇马引发山东特大暴雨成因分析

利用地面观测资料、雷达资料、FY-2G卫星云图资料及欧洲中心细网格资料,对台风利奇马登陆北上引发山东特大暴雨的成因进行分析。发现:利奇马登陆北上过程中,冷空气先后从台风的西部、西南部与南部侵入至台风中心内部,使其暖心结构逐渐减弱,其变性时段发生在10日20:00至11日08:00。山东的特大暴雨主要出现在台风变性前12h至台风变性后6h。变性之前的暴雨主要是由于台风螺旋云带与高空槽尾部云系相叠加造成的,变性之后的暴雨则是由于冷空气侵入致使台风外围云系演变成强对流复合体造成的。变性之前,对流层内800～500hPa风速小,500～250hPa风速大,气层内有暖平流,整层的上升运动,降水以暖区对流降水为主;变性之后800～500hPa风速大,500～250hPa风速小,500hPa至地面是上升运动,以上为下沉运动,降水以斜压锋区附近的对流降水为主。当500hPa至地面气层内出现冷平流时,湿层变薄,降水趋于减弱。特大暴雨区出现在台风中心西北方向,与850hPa假相当位温锋区与水汽通量散度辐合大值区相吻合。     

夏季区域西风指数对中国西北地区水汽场特征影响的对比分析

利用1970—1997年NCEP／NCAR冉分析月平均资料,设计了区域西风指数。通过分析西北地区夏季的水汽输送通量散度,发现该地区水汽平流引起的水汽输送通量散度项年际变化极小,而风场辐合(辐散)引起的水汽输送通量散度项年际变化却很大,在西北地区区域西风指数较强年份风场辐合比区域西风指数较弱年份强。由此可知．两风年际变化对西北地区的风场辐合(辐散)的影响是我国西北地区水汽场年际变化的主要原因。中国西北地区;区域西风指数;水汽输送通量散度;降水     

Negative relationship between Korea landfalling tropical cyclone activity and Pacific Decadal Oscillation

The present study discovered a strong negative correlation between Korea-landfalling tropical cyclone (TC) frequency and Pacific Decadal Oscillation (PDO) in the summer. Thus, the present study selected years that had the highest PDO index (positive PDO years) and years that had the lowest PDO index (negative PDO years) to analyze a mean difference between the two phases in order to determine the reason for the strong negative correlation between the two variables. In the positive PDO years, TCs were mainly generated in the southeastern part of the western North Pacific, and lower TC passage frequency was found in most regions in the mid-latitude in East Asia. Moreover, a slightly weaker TC intensity than that in the negative PDO years was revealed. In order to determine the cause of the TC activity revealed in the positive PDO years, 850 hPa and 500 hPa stream flows were analyzed first. In the mid-latitude region in East Asia, anomalous huge cyclonic circulations were strengthened, while anomalous anticyclonic circulations were strengthened in the low-latitude region. Accordingly, Korea was being influenced by anomalous northwesterlies, which played a role in blocking TCs from moving northward to Korea. The results of analysis on 850 hPa air temperature, precipitation, 600 hPa relative humidity, and sea surface temperature (SST) showed that negative anomalies were strengthened in the northwest region in the western North Pacific while positive anomalies were strengthened in the southeast region. The atmospheric and oceanic environments were related to frequent occurrences of TCs in the southeast region in the western North Pacific during the positive PDO years. All factors of air temperature, precipitation, 600 hPa relative humidity, and SST revealed negative (positive for vertical wind shear) anomalies near Korea, so that atmospheric and oceanic environments were formed that could rapidly weaken TC intensity, even if the TCs moved northward to Korea in the positive PDO years.     

The UVic earth system climate model: Model description,climatology, and applications to past,present and future climates

Abstract

A new earth system climate model of intermediate complexity has been developed and its climatology compared to observations. The UVic Earth System Climate Model consists of a three‐dimensional ocean general circulation model coupled to a thermodynamic/dynamic sea‐ice model, an energy‐moisture balance atmospheric model with dynamical feedbacks, and a thermomechanical land‐ice model. In order to keep the model computationally efficient a reduced complexity atmosphere model is used. Atmospheric heat and freshwater transports are parametrized through Fickian diffusion, and precipitation is assumed to occur when the relative humidity is greater than 85%. Moisture transport can also be accomplished through advection if desired. Precipitation over land is assumed to return instantaneously to the ocean via one of 33 observed river drainage basins. Ice and snow albedo feedbacks are included in the coupled model by locally increasing the prescribed latitudinal profile of the planetary albedo. The atmospheric model includes a parametrization of water vapour/planetary longwave feedbacks, although the radiative forcing associated with changes in atmospheric CO₂ is prescribed as a modification of the planetary longwave radiative flux. A specified lapse rate is used to reduce the surface temperature over land where there is topography. The model uses prescribed present‐day winds in its climatology, although a dynamical wind feedback is included which exploits a latitudinally‐varying empirical relationship between atmospheric surface temperature and density. The ocean component of the coupled model is based on the Geophysical Fluid Dynamics Laboratory (GFDL) Modular Ocean Model 2.2, with a global resolution of 3.6° (zonal) by 1.8° (meridional) and 19 vertical levels, and includes an option for brine‐rejection parametrization. The sea‐ice component incorporates an elastic‐viscous‐plastic rheology to represent sea‐ice dynamics and various options for the representation of sea‐ice thermodynamics and thickness distribution. The systematic comparison of the coupled model with observations reveals good agreement, especially when moisture transport is accomplished through advection.

Global warming simulations conducted using the model to explore the role of moisture advection reveal a climate sensitivity of 3.0°C for a doubling of CO₂, in line with other more comprehensive coupled models. Moisture advection, together with the wind feedback, leads to a transient simulation in which the meridional overturning in the North Atlantic initially weakens, but is eventually re‐established to its initial strength once the radiative forcing is held fixed, as found in many coupled atmosphere General Circulation Models (GCMs). This is in contrast to experiments in which moisture transport is accomplished through diffusion whereby the overturning is reestablished to a strength that is greater than its initial condition.

When applied to the climate of the Last Glacial Maximum (LGM), the model obtains tropical cooling (30°N‐30°S), relative to the present, of about 2.1°C over the ocean and 3.6°C over the land. These are generally cooler than CLIMAP estimates, but not as cool as some other reconstructions. This moderate cooling is consistent with alkenone reconstructions and a low to medium climate sensitivity to perturbations in radiative forcing. An amplification of the cooling occurs in the North Atlantic due to the weakening of North Atlantic Deep Water formation. Concurrent with this weakening is a shallowing of, and a more northward penetration of, Antarctic Bottom Water.

Climate models are usually evaluated by spinning them up under perpetual present‐day forcing and comparing the model results with present‐day observations. Implicit in this approach is the assumption that the present‐day observations are in equilibrium with the present‐day radiative forcing. The comparison of a long transient integration (starting at 6 KBP), forced by changing radiative forcing (solar, CO₂, orbital), with an equilibrium integration reveals substantial differences. Relative to the climatology from the present‐day equilibrium integration, the global mean surface air and sea surface temperatures (SSTs) are 0.74°C and 0.55°C colder, respectively. Deep ocean temperatures are substantially cooler and southern hemisphere sea‐ice cover is 22% greater, although the North Atlantic conveyor remains remarkably stable in all cases. The differences are due to the long timescale memory of the deep ocean to climatic conditions which prevailed throughout the late Holocene. It is also demonstrated that a global warming simulation that starts from an equilibrium present‐day climate (cold start) underestimates the global temperature increase at 2100 by 13% when compared to a transient simulation, under historical solar, CO₂ and orbital forcing, that is also extended out to 2100. This is larger (13% compared to 9.8%) than the difference from an analogous transient experiment which does not include historical changes in solar forcing. These results suggest that those groups that do not account for solar forcing changes over the twentieth century may slightly underestimate (～3% in our model) the projected warming by the year 2100.     

Characteristics and Diagnosis of the Landfalling Tropical Cyclones in the Guangdong-Hong Kong-Macao Greater Bay Area of China During 1981-2018

This paper applies statistical and synthetic analysis methods to study the characteristics of the three types of tropical cyclone (TC) that landed in the Guangdong-Hong Kong-Macao Greater Bay Area (GBA) from 1981 to 2018 and the reasons for the differences of TC-induced wind and precipitation. The results show that there are interdecadal changes in the frequency and intensity of the landfalling TCs in the GBA, with decreased frequency but increased intensity in the 2010s. The TCs that landed in the west of the Pearl River Estuary (PRE) have the most frequency and the strongest intensity during landing, which bring the strongest winds; the TCs that landed in the PRE have the least frequency and the shortest duration after landing, which cause the strongest precipitation; the TCs that landed in the east of the PRE have the relatively longest duration on the land. This study shows that near the center of the TCs that landed in the PRE, there is a weak anomalous cyclonic shear compared with the ones that landed in the west of the PRE. Compared with the TCs that landed in the east of the PRE, it is a confluence area of anomalous north wind and anomalous southwest wind, with better water vapor convergence and dynamic rising conditions, which is conducive to the formation of heavy precipitation. Compared with the TCs that landed in the PRE and in its east, there is a closed positive anomalous center of pressure gradient in the northwest center of the TCs that landed in its west, resulting in higher wind speeds in the west of the PRE. The characteristics of the three types of TCs in the GBA are highly related to TC-induced damage. In the future, the GBA needs to focus on preventing TCs landing in its west. Zhuhai, Jiangmen and Huizhou are key cities to guard against TCs. The results of this study provide foundations for effective management and reduction of TC disaster risks in the future construction of the GBA.