基态位涡径向分布对浅水涡旋系统动力稳定性的影响分析          下载免费PDF全文

刘爽  钟玮  刘宇迪 《地球物理学报》2018,61(6):2207-2219

本文基于正压浅水模型，分析基态位涡（Potential Vorticity：PV）结构对热带气旋（Tropical Cyclone：TC）类涡旋系统稳定性及其波动特征的影响.通过引入基态PV结构参数：宽度δ（眼墙内外边界涡度发生陡变的半径长度之比）和中空度γ（眼心相对涡度与内核区域平均相对涡度之比），设计具有相同基流最大切向风速和最大风速半径的170组不同基态PV环结构的敏感性试验，并讨论了不同基态PV结构下涡旋系统最不稳定波数（the most unstable wavenumber：MUWN）和系统最不稳定模态（the most unstable mode of System：MUMS）的特征频率及其不稳定增长率的大小.结果指出：当PV环较宽，系统表现为低波数最不稳定，相应的MUMS为低频波且增长率小；当PV环较窄，系统表现为高波数不稳定，且PV环越实最不稳定波数越高；当PV环窄且空时，MUMS均为中高频波动，且不稳定增长率随PV环的宽度变窄和中空度变空而明显增大.分析典型PV结构下系统演变特征可知，当PV环较宽，MUMS表现为具有平衡约束的低频波动的线性不稳定特征；当PV环趋向窄且空时，MUMS的平衡性约束趋向弱化，同时不稳定增长表现为明显的指数型增长.进一步讨论系统内部非对称结构的形成和传播机制发现，对于弱不稳定的PV环来说，低波数波最不稳定的特征波动具有典型涡旋Rossby波特征；而对于强不稳定的PV环来说，高波数不稳定的特征波动混合波性质明显.  相似文献   

Tropical cyclones and multiscale climate variability: The active western North Pacific Typhoon season of 2018     

Wu  Liang  Zhang  Hongjie  Feng  Tao  Tang  Yulian 《中国科学:地球科学(英文版)》2020,63(1):1-11

The 2018 typhoon season in the western North Pacific(WNP) was highly active, with 26 named tropical cyclones(TCs) from June to November, which exceeded the climatological mean(22) and was the second busiest season over the past twenty years. More TCs formed in the eastern region of the WNP and the northern region of the South China Sea(SCS). More TCs took the northeast quadrant in the WNP, recurving from northwestward to northward and causing heavy damages in China's Mainland(69.73 billion yuan) in 2018. Multiscale climate variability is conducive to an active season via an enhanced monsoon trough and a weakened subtropical high in the WNP. The large-scale backgrounds in 2018 showed a favorable environment for TCs established by a developing central Pacific(CP) El Ni?o and positive Pacific meridional mode(PMM)episode on interannual timescales. The tropical central Pacific(TCP) SST forcing exhibits primary control on TCs in the WNP and large-scale circulations, which are insensitive to the PMM. During CP El Ni?o years, anomalous convection associated with the TCP warming leads to significantly increased anomalous cyclonic circulation in the WNP because of a Gill-type Rossby wave response. As a result, the weakened subtropical high and enhanced monsoon trough shift eastward and northward, which favor TC genesis and development. Although such increased TC activity in 2018 might be slightly suppressed by interdecadal climate variability, it was mostly attributed to the favorable interannual background. In addition, high-frequency climate signals,such as intraseasonal oscillations(ISOs) and synoptic-scale disturbances(SSDs), interacted with the enhanced monsoon trough and strongly modulated regional TC genesis and development in 2018.  相似文献   

热带东印度洋SST对气候变暖和变冷的响应     

徐杉  罗义勇 《海洋学报(英文版)》2019,38(5):76-85

The response of the eastern tropical Indian Ocean(ETIO) to heat fluxes of equal amplitude but opposite sign is investigated using the Community Earth System Model(CESM). A significant positive asymmetry in sea surface temperature(SST) is found over the ETIO—the warming responses to the positive forcing exceeds the cooling to the negative forcing. A mixed layer heat budget analysis is carried out to identify the mechanisms responsible for the SST asymmetry. Results show that it is mainly ascribed to the ocean dynamical processes, including vertical advections and diffusion. The net surface heat flux, on the contrary, works to reduce the asymmetry through its shortwave radiation and latent heat flux components. The former is due to the nonlinear relationship between SST and cloud, while the latter is resulted mainly from Newtonian damping and air-sea stability effects. Changes in the SST skewness are also evaluated, with more enhanced negative SST skewness over the ETIO found for the cooling than heating scenarios due to the asymmetric thermocline-SST feedback.  相似文献   

再探温跃层有孔虫B/Ca与温度和[CO₃^2-]的依赖性及其在24 ka以来热带西太平洋次表层碳酸盐系统重建中的应用     

郭景腾  李铁刚  熊志方  仇晓华  常凤鸣 《海洋学报(英文版)》2019,38(9):71-86

The B/Ca ratio of planktonic foraminifer shells has been used as a proxy for reconstructing past ocean carbonate chemistry. However, recent studies have revealed significant uncertainties associated with this proxy, such as whether seawater temperature or [ CO_3~(2-)] is the dominant control on the partition coefficient(K_D) of planktonic foraminiferal B/Ca. To address these uncertainties and thus improve our understanding of the planktonic foraminiferal B/Ca proxy, we analysed B/Ca ratios in the tests of Neogloboquadrina dutertrei(300–355 μm) and Pulleniatina obliquiloculata(355–400 μm) in surface sediment samples from the tropical western Pacific and South China Sea. The relationship between these B/Ca ratios and bottom water calcite saturation states(Δ[ CO_3~(2-)]) is weak, thus suggesting only a small dissolution effect on the B/Ca of the two species. The correlation coefficients(R~2) between the B/Ca ratios of N. dutertrei and P. obliquiloculata and environmental parameters(e.g., temperature, salinity, phosphate, DIC and ALK) in the tropical western Pacific and South China Sea are not high enough to justify using B/Ca ratios as a palaeoenvironmental proxy in the study areas. The significant correlation between K_D values of N. dutertrei and P. obliquiloculata and carbonate system parameters(e.g.,[ CO_3~(2-)], DIC, ALK, pH and [ HCO_3~-]) in the study area reflect chemical links between the K_D denominator and these variables. Based on our surface sediment calibration, an empirical relationship between the K_D of N.dutertrei and temperature is proposed in the tropical western Pacific. We also generated a record of B/Ca ratios in N. dutertrei(300–355 μm) from Core MD06-3052 in the tropical western Pacific over the past 24 ka to evaluate the application of the revised B/Ca proxy method. Based on the reconstructed empirical relationship for B/Ca and subsurface seawater ALK, we estimated subsurface seawater carbonate system parameters in the tropical western Pacific since 24 ka. In general, the estimated subsurface seawater pH and [ CO_3~(2-)] show an increase with time, and the record of subsurface seawater pCO_2 shows a decrease with time, in the tropical western Pacific over the past 24 ka. The consistent trends in subsurface seawater pCO_2 and opal flux during deglaciation may imply that the reported increase in subsurface water pCO_2 in the study area was promoted by enhanced upwelling in the Southern Ocean.  相似文献   

Tropical precipitation anomalies and d‐excess evolution during El Niño 2014‐16          下载免费PDF全文

Ricardo Sánchez‐Murillo  Ana M. Durán‐Quesada  Christian Birkel  Germain Esquivel‐Hernández  Jan Boll 《水文研究》2017,31(4):956-967

The last 2014‐16 El Niño event was among the three strongest episodes on record. El Niño considerably changes annual and seasonal precipitation across the tropics. Here, we present a unique stable isotope data set of daily precipitation collected in Costa Rica prior to, during, and after El Niño 2014‐16, in combination with Lagrangian moisture source and precipitation anomaly diagnostics. δ²H composition ranged from ‐129.4 to +18.1 (‰) while δ¹⁸O ranged from ‐17.3 to +1.0 (‰). No significant difference was observed among δ¹⁸O (P=0.186) and δ²H (P=0.664) mean annual compositions. However, mean annual d‐excess showed a significant decreasing trend (from +13.3 to +8.7 ‰) (P<0.001) with values ranging from +26.6 to ‐13.9 ‰ prior to and during the El Niño evolution. The latter decrease in d‐excess can be partly explained by an enhanced moisture flux convergence across the southeastern Caribbean Sea coupled with moisture transport from northern South America by means of an increased Caribbean Low Level Jet regime. During 2014‐15, precipitation deficit across the Pacific domain averaged 46% resulting in a very severe drought; while a 94% precipitation surplus was observed in the Caribbean domain. Understanding these regional moisture transport mechanisms during a strong El Niño event may contribute to a) better understanding of precipitation anomalies in the tropics and b) re‐evaluate past stable isotope interpretations of ENSO events in paleoclimatic archives within the Central America region.  相似文献   

Glacial flood pulse effects on benthic fauna in equatorial high‐Andean streams          下载免费PDF全文

Sophie Cauvy‐Fraunié  Patricio Andino  Rodrigo Espinosa  Roger Calvez  Fabien Anthelme  Dean Jacobsen  Olivier Dangles 《水文研究》2014,28(6):3008-3017

Equatorial glacier‐fed streams present unique hydraulic patterns when compared to glacier‐fed observed in temperate regions as the main variability in discharge occurs on a daily basis. To assess how benthic fauna respond to these specific hydraulic conditions, we investigated the relationships between flow regime, hydraulic conditions (boundary Reynolds number, Re*), and macroinvertebrate communities (taxon richness and abundance) in a tropical glacier‐fed stream located in the high Ecuadorian Andes (> 4000 m). Both physical and biotic variables were measured under four discharge conditions (base‐flow and glacial flood pulses of various intensities), at 30 random points, in two sites whose hydraulic conditions were representative to those found in other streams of the study catchment. While daily glacial flood pulses significantly increased hydraulic stress in the benthic habitats (appearance of Re* > 2000), low stress areas still persisted even during extreme flood events (Re* < 500). In contrast to previous research in temperate glacier‐fed streams, taxon richness and abundance were not significantly affected by changes in hydraulic conditions induced by daily glacial flood pulses. However, we found that a few rare taxa, in particular rare ones, preferentially occurred in highly stressed hydraulic habitats. Monte‐Carlo simulations of benthic communities under glacial flood reduction scenarios predicted that taxon richness would be significantly reduced by the loss of high hydraulic stress habitats following glacier shrinking. This pioneer study on the relationship between hydraulic conditions and benthic diversity in an equatorial glacial stream evidenced unknown effects of climate change on singular yet endangered aquatic systems. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

南海-西北太平洋季风槽中热带气旋群发的研究Ⅱ.影响机制研究          下载免费PDF全文

高建芸  吕心艳  张秀芝  江志红 《海洋学报》2011,33(3):28-37

应用1979-2005年西北太平洋热带气旋(TC)资料和OLR,NCEP/DOE AMIP-Ⅱ再分析逐日资料,探讨南海-西北太平洋季风槽中TC(简称MTTC)群发的可能机理,得到以下几点结论:(1)5～10月季风槽强度及形态与索马里越赤道气流的强弱、副高的位置以及南半球澳洲冬季风的强弱密切相关,不同区域季风槽强度增强都...  相似文献   

A primary study of the correlation between the net air-sea heat flux and the interannual variation of western North Pacific tropical cyclone track and intensity   总被引：3，自引：0，他引：3  

WU Liang  WEN Zhiping  HUANG Ronghui 《海洋学报(英文版)》2011,30(6):27-35

A singular value decomposition (SVD) analysis is carried out to reveal the relationship between the interannual variation of track and intensity of the western North Pacific tropical cyclones (WNPTCs) in the tropical cyclone (TC) active season (July-November) and the global net air-sea heat flux (Q net ) in the preceding season (April-June). For this purpose, a tropical cyclone track and intensity function (TIF) is defined by a combination of accumulated cyclone energy (ACE) index and a cyclone track densit...  相似文献   

Rare earth elements in suspended and bottom sediments of the Mandovi estuary, central west coast of India: Influence of mining     

R. ShynuV. Purnachandra Rao  Pratima M. KessarkarT.G. Rao 《Estuarine, Coastal and Shelf Science》2011,94(4):355-368

Rare earth elements (REEs) in the suspended particulate matter (SPM) of the Mandovi estuary indicated that the mean total-REEs (∑REE) and light REE to heavy REE ratios are lower than that of the average suspended sediment in World Rivers and Post-Archean average Australian shale. High ∑REE were associated with high SPM/low salinity and also with high SPM/high salinity. Although the ∑REE broadly agree with SPM levels at each station, their seasonal distributions along transect are different. SPM increased seaward in the estuary both during the monsoon and pre-monsoon, but consistently low at all stations during the post-monsoon. The mean ∑REE decreased marginally seaward and was <25% at sea-end station than at river-end station. Spatial variations in ∑REE are maximum (64%) during the pre-monsoon. Strong to moderate correlation of ∑REE with Al, Fe and Mn in all seasons indicates adsorption and co-precipitation of REEs with aluminosilicate phases and Fe, Mn-oxyhydroxides. The ratio of mean ∑REE in sediment/SPM is low during the monsoon (1.27), followed by pre-monsoon (1.5) and post-monsoon (1.62). The middle REE- and heavy REE-enriched patterns with positive Ce and Eu anomalies are characteristic at every station and season, both in SPM and sediment. They also exhibit tetrad effect with distinct third and fourth tetrads. Fe-Mn ore dust is the most dominant source for REEs. However, the seasonal changes in the supply of detrital silicates, Fe-Mn ore dust and particulates resuspended from bottom sediments diluted the overall effect of salinity on fractionation and distribution of REEs in the estuary.  相似文献   

0908号台风“莫拉克”异常路径及其对台湾海峡两岸强降水的影响     

刘爱鸣  高珊 《台湾海峡》2011,30(2):151-157

应用常规资料,结合雷达、卫星云图和其他观测资料,分析了0908号台风＂莫拉克＂异常路径及其对台湾海峡两岸强降水的影响.结果表明：（1）500 hPa欧亚中高纬度为两槽一脊的形势和东北区域大范围的正变高使副热带高压加强西伸,以及0909号热带气旋＂艾涛＂前身低压阻挡了副热带高压南落的共同作用,使＂莫拉克＂台风前期向偏西方向移动.（2）高空冷涡提供了有利于热带低压维持和发展的动力条件,热带低压的维持又对＂莫拉克＂的移动造成影响.（3）冷空气持续南下造成副热带高压减弱,并且在＂莫拉克＂台风北侧形成稳定低能区;高空冷涡引起其北侧中高层高度下降和东风引导气流减弱;在弱环流和多热带气旋的环境场下,以及热带风暴＂天鹅＂（0907号）、＂艾涛＂对＂莫拉克＂台风的反方向作用力等因素的综合作用,是＂莫拉克＂台风在台湾海峡移速异常缓慢的原因.（4）＂莫拉克＂台风在台湾海峡滞留时间长,其北侧强偏东风和南侧强西南风带来充沛的水汽,及迎风坡辐合抬升所产生的中小尺度系统是造成闽北、浙南和台湾岛南部强降水持续时间长、累计雨量大的重要原因.  相似文献