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1.
采用Cloudsat/CPR云雷达,FY2C/TBB亮温,Aura/MLS大气成分等卫星遥感资料,结合ECMWF气象分析资料和HYSPLIT4轨迹模式,研究了2009年6月一次东亚切断低压的暖区深对流和异常副热带锋面的结构和演变.分析表明,由于低压切断前的旧槽背景,在低涡的近成熟期,内部冷、暖锋降水偏弱,边沿的高空副热带锋面异常发展到对流层底部,低空西南暖湿水汽在副热带锋前聚集,形成千公里长的暖区深对流降水带.随着该锋面的快速东移,副热带锋区进入原暖区雨带,锋区热力间接次级环流的强上升支,加强了锋下冷侧(原暖湿区)的深对流,但该锋面阻挡了来自暖侧的水汽补充,降水结束.该异常副热带锋区还发生了强烈的平流层-对流层相互交换,在高空急流出口区的下方,平流层1.5PVU等位涡线向下入侵可达5.5km(约500hPa)处,锋下向上的深对流注入可达10km,在入侵-注入混合区,臭氧和水汽的散点图上出现了二者浓度双高和双低的特殊气团. 相似文献
2.
副热带急流对中国南部地区对流层中上层臭氧浓度的影响程度及地理范围目前还研究较少,且缺乏综合使用常规气象资料及卫星资料来判识对流层中上层臭氧浓度增高的方法.本文利用NCEP再分析与最终分析资料、日本GMS-5地球静止卫星水汽云图资料,以2001年3月27~29日中国南部的临安、昆明、香港臭氧探测个例为基础,结合1996年3月29日香港与2001年4月13日临安对流层中上层高浓度臭氧分布个例对副热带急流对中国南部对流层中上层臭氧浓度的影响进行了详细分析,提出根据气象要素场判识春季中国南部对流层中上层臭氧浓度增高的充分条件为根据卫星水汽图像上的暗区、高空急流入口区的左侧辐合区、高空锋区、对流层中上层≥1 PVU的向下伸展的舌状高位涡区来综合判断.本文的分析结果表明,本文个例中对流层中上层高浓度臭氧来自平流层;香港对流层中上层低浓度臭氧来自热带海洋地区.不仅臭氧垂直廓线的多个极小与极大值表明臭氧垂直分布的多尺度变化特征,而且对流层中上层PV分布以及卫星水汽图像分析也表明大气中的多尺度运动对臭氧垂直分布特征有显著影响.本文的结果表明与副热带高空急流相联系的平流层空气侵入不仅发生在中国大陆的较高纬度地区,较低纬度的昆明与香港地区也有平流层空气侵入导致对流层中上层臭氧浓度升高. 相似文献
3.
对流性重力波对中层大气环境有显著影响.重力波活动及重力波源的地理和季节性变化等信息是理解和模拟重力波效应的基础.卫星高光谱红外大气垂直探测器AIRS的4μm和15μm波段可用于识别30~40km高度范围和41km高度附近的重力波,其11μm通道可同步观测对流层深对流.观测个例表明,海面和陆面上空的平流层扰动影响范围均可达1000km,不同高度的扰动强度分布也存在差异.基于2007年6月至8月的AIRS观测资料,分析了东亚区域的对流层深对流活动和平流层的重力波,得到了深对流和重力波发生频率的水平分布.统计结果表明,东亚区域夏季夜间的深对流活动明显少于白天,但AIRS观测到的平流层重力波发生频率和扰动强度均显著大于白天,揭示了夜间对流层深对流诱发的平流层重力波在强度、范围等方面可能与白天存在显著差异.进一步对比分析表明,AIRS观测的平流层扰动高值区与深对流高值区明显不同.平流层重力波与对流层深对流之间的相关分析表明,在36°N以南的区域,41km高度上AIRS观测的重力波中,深对流云诱发的重力波的比例约为30%~100%.在10°N至36°N区间,90%的深对流均可诱发平流层重力波.分析得到的30~40km高度区间和41km高度附近的重力波水平分布对比表明,后一高度上的扰动强度明显大于前一高度,且前一高度在东南亚区域存在强扰动中心而在后一高度则没有.最后,给出了AIRS观测的几种典型形态的东亚区域平流层波动,表明了该区域平流层环境波动形态的复杂性和多样性. 相似文献
4.
青藏高原为亚洲季风区的典型代表区域,研究其水汽进入平流层的过程和机理对认识全球气候和大气环境变化具有一定的现实意义. 本文基于中尺度气象模式(WRF)的模拟输出结果(2006年8月20日至8月26)驱动拉格朗日大气输送模式FLEXPART,通过追踪并解析气块的三维轨迹以及温度、湿度等相关物理量的相关变化特征,初步分析了夏季青藏高原地区近地层-对流层-平流层的水汽输送特征. 研究结果表明,源于高原地区近地层的水汽在进入平流层的过程中受南亚高压影响下的大尺度环流和中小尺度对流的共同影响.首先,在对流抬升作用下,气块在短时间内(24 h)可抬升到9~12 km的高度,然后在南亚高压闭合环流影响下,相当部分气块在反气旋的东南侧穿越对流层顶进入平流层中,并继续向低纬热带平流层输送,进而参与全球对流层-平流层的水汽循环过程. 在对流抬升高度上气块位置位于高原的西北侧,然而气块拉格朗日温度最小值主要分布于高原南侧,两个位置上气块的平均位温差值可达15~35 K,这种显著的温度差异将导致气块进入平流层时"脱水". 比较而言,夏季青藏高原地区近地层水汽进入平流层的多寡主要和大尺度汽流的垂直输送有关,而深对流的作用相对较弱. 相似文献
5.
《中国科学:地球科学》2017,(3)
基于诊断和数值模拟,研究了夏季青藏高原和伊朗高原热力强迫的相互作用,其对亚洲副热带季风区水汽通量辐合的贡献及对欧亚大陆上空高对流层顶和平流层低层冷中心形成的影响.结果表明两大高原感热加热存在相互影响和反馈,伊朗高原感热加热减少青藏高原的表面加热,而青藏高原的感热加热则增加伊朗高原的表面加热;形成了观测到的伊朗高原感热加热-青藏高原感热加热和凝结潜热释放-大气垂直环流之间的准平衡耦合系统(TIPS),影响大气环流.青藏高原上的感热-潜热相互反馈在这个TIPS耦合系统中起主要作用.两大高原感热加热对其他地区的影响有相互加强也有相互抵消;青藏高原感热加热引发的对亚洲副热带季风区水汽通量辐合贡献率为伊朗高原感热影响的2倍以上;伊朗高原和青藏高原的感热加热共同作用对亚洲副热带季风区的水汽辐合作出最主要的贡献.TIPS的加热作用使对流层温度升高,并抬升了其上空的对流层顶,造成了那里平流层下层温度偏低;与欧亚大陆大尺度热力强迫共同作用,形成了对流层上层的暖性但在平流层下层为冷性的强大的反气旋环流南亚高压,从而影响区域和全球的天气气候. 相似文献
6.
利用三维非静力中尺度数值模式MM5模拟了干湿大气条件中纬度典型斜压波及其锋面系统的生成与演变过程, 重点讨论地表拖曳对干、湿大气中地面锋结构、锋生过程的影响作用. 研究结果表明, 在干大气中, 地表拖曳力对地面锋锋生具有双向作用, 一方面是锋消作用, 主要体现在地表拖曳力减慢地面锋锋生、地面斜压波系统发展; 另一方面, 地表拖曳力导致强的非地转流形成, 从而延长了冷锋锋生过程维持时间, 有利于冷锋强度增大. 同时地表拖曳力可以造成边界层内锋面近乎垂直于地面, 导致锋前垂直运动增强, 这些结果进一步推广了谈哲敏和伍荣生的理论结果. 在湿大气中, 地表拖曳过程对锋面雨带分布有重要的影响作用, 地表拖曳力可减缓对流上 升, 从而导致地表能量的耗散减缓. 当大气低层湿度较小时, 对流不是很强, 地表拖曳力可减缓地表水汽、能量的迅速耗散, 且在锋后边界层中产生摩擦辐合上升区, 这些上升区可逐渐东移到冷锋前, 补偿了锋前上升带的强度, 有利于冷锋降水的维持. 当大气低层湿度场很强时, 对流发展比较旺盛, 此时地表拖曳对低层水汽与能量的束缚作用相对较弱, 相应地表拖曳对锋面及其降水系统影响较小. 相似文献
7.
火山活动对北半球平流层气候异常变化的影响 总被引：8，自引：0，他引：8
文中利用逐次滤波法滤除北半球平流层70 hPa约15~22 km高空大气温度异常变化中太阳活动的影响之后，进一步分析了火山活动的气候效应，分析结果表明，火山活动能引起平流层较大幅度增温，对于北半球70hPa高空气候异常变化的影响超过了总方差的30%；火山活动影响最显著的高度是平流层70 hPa约15~22 km高空，由此高度向上或向下，火山活动的影响都逐渐减小；火山活动引起平流层大气升温的同时还将引起对流层大气降温，其分界线大致位于对流层顶300 hPa附近；强火山爆发如皮纳图博火山爆发、阿贡火山爆发和堪察加北楮缅奴等火山爆发是引起未来两年左右平流层中下层温度异常变化最重要的因素，其方差贡献率超过百分之五十三！；火山喷发高度越高，引起平流层增温效应的层次也越高；北半球大气温度异常变化对南半球火山活动响应的滞后时间比北半球火山活动长. 平流层高空气候异常变化还具有显著的22年变化周期，分析认为是大气温度场对太阳磁场磁性周期22年异常变化的响应，其方差贡献率超过9%. 相似文献
8.
采用ERA-Interim气象分析资料、云顶亮温TBB资料、Cloudsat云雷达资料、降雨量资料等,对2009年6月10日至12日我国东北地区的一次冷涡天气过程进行研究,重现了该冷涡的精细三维结构和演变过程.分析表明冷涡发生前,东北亚地区处于南北双槽结构之间,随后北槽向赤道发展切断后形成东北冷涡.南槽背景的冷涡热力结构特殊,强冷空气集中在涡内西北象限,暖湿空气在东北象限,南部为相对中性空气,该配置导致北部暖锋强盛,西部冷锋仅在发展初期较强,冷涡过程没有经典挪威学派的气旋锢囚锋出现.冷涡发展初期,狭长冷舌快速入侵南下,冷舌前冷锋对流降水较强,冷舌后部左侧还有暖锋降水;冷涡发展后期,冷锋减弱,冷锋上的高层云停止降水,系统内主要为冷涡北部的暖锋雨层云降水;冷涡成熟后,中心辐合加强,有较强的对流性降水. 相似文献
9.
青藏高原和热带西北太平洋大气热源在亚洲地区夏季平流层-对流层水汽交换的年代际变化中的作用 总被引：5，自引：0，他引：5
利用欧洲中期天气预报中心ERA40资料,借助Wei诊断模式研究平流层一对流层水汽交换过程,重点分析亚洲地区夏季平流层．对流层水汽交换的年代际特征,探讨青藏高原和热带西北太平洋大气热源在其变化中的作用．气候学特征表明,北半球夏季“亚洲南部半岛-印度洋-太平洋交汇区”为全球最强的对流层向平流层输送的通道,它能将亚洲季风区丰富的水汽源源不断地输送到平流层,影响平流层水汽的分布和变化．北半球夏季亚洲地区穿越对流层顶水汽交换整体上都具有明显的年代际变化,且在近44a可以分为三段比较稳定的时段：1958～1977年、1978～1992年和1993。2001年．在这三个时段中,孟加拉湾．东亚大陆及南海海域的水汽交换通道作用在逐渐减弱,而西北太平洋地区在水汽交换中扮演着越来越重要的角色．进一步研究发现,青藏高原、热带西北太平洋热源的年代际异常是亚洲地区平流层．对流层水汽交换年代际变化的主要原因．44a来青藏高原和热带西北太平洋的热力作用均发生了重大调整,在年代际尺度上两者的综合作用决定了亚洲夏季风的年代际变异,从而影响平流层．对流层水汽交换的年代际异常．然而不同时段不同地区两者的贡献有所不同,尤其是1992年以后,高原热源影响明显减弱,而热带西北太平洋热源在影响平流层．对流层水汽交换中起主要作用．这些结果对深入认识其他大气成份输送过程和正确评估人类活动（排放）对全球气候的影响也具有重要的指示意义． 相似文献
10.
本文使用欧洲ECMWF（ERA40）再分析资料，通过经验正交函数（Empirical Orthogonal Function，EOF）分解探讨了冬季北太平洋风暴轴的变异特征，使用回归分析得到了与风暴轴空间异常型相关的冬季大气平均流异常、表层海温（Sea Surface Temperature，SST）异常的空间耦合型.研究结果表明，冬季北太平洋风暴轴主要有两种空间异常型，第一种是风暴轴中东部明显北抬（南压），使得整个风暴轴向东北（东南）倾斜，与此同时，在中纬度北太平洋海区，冬季暖（冷）异常的洋面上是异常高压（低压），海气系统在垂直向表现为一种暖脊（冷槽）配置，在对流层中高层是太平洋-北美（Pacific North American，PNA）型负（正）位相.第二种是风暴轴整体性加强（减弱）并偏北（南），此时，黑潮区海温异常偏暖（冷），低层阿留申低压和高空的西风急流略偏北（南），对流层中高层表现为西太平洋（Western Pacific，WP）型负（正）位相.风暴轴EOF分解的时间系数与阿留申低压指数、PNA指数、WP指数，以及与尼诺3区（NINO3）指数、黑潮海温指数间显著的相关性再次证实了在北太平洋中纬度地区存在着SST异常、风暴轴异常和大气平均流异常三者间的空间耦合型. 相似文献
11.
本文根据季节转换前后副高脊面附近经向温度梯度变号的本质，利用相关分析和合成分析等方法研究了季节转换年际变化与外部影响因子的联系. 结果表明，冬春季青藏高原热状况和ENSO（El Nio/Southern Oscillation，厄尔尼诺/南方涛动）是决定亚洲季风区季节转换年际变化的主要因素. 当冬、春季海温呈现El Nio异常时，Walker环流减弱，于是西太平洋暖池区对流活动受到抑制，而赤道东太平洋对流活动加强则强迫赤道印度洋地区产生绝热下沉运动，使得印度洋地区大气偏暖，结果增大了南北向温度梯度，季节转换往往偏晚. 反之，季节转换偏早. 初春高原上空对流层中高层的气温异常对于判断季节转换迟早有很好的指示意义. 相似文献
12.
Pluriannual series of Meteosat-2 water vapor (WV) images are used to build average maps of decadal and monthly brightness temperatures in the 6.3 μm channel. This processing is applied to all the 3-hourly scenes, clear or cloudy, for July 1983 to July 1987. The ISCCP cloudiness analyses confirm that the warmest spots in the monthly WV images correspond to scenes either clear or covered with low clouds, whereas the coldest areas correspond to scenes where cloud tops above 440 hPa frequently occur. The WV statistics are then used to characterize seasonal and interannual variations of both the ITCZ (InterTropical Convergence Zone) and the warm (dry) areas, corresponding to subtropical subsidence. Thanks mainly to the seasonal variations, relationships between the variations in the ITCZ and in dry subtropical areas can be studied. It is shown that, for the Meteosat sector, a wetter subtropical high troposphere is associated with an enhanced activity of the ITCZ, and vice versa. For this area where the north-south assymetry is large, the negative water vapor feedback previously proposed seems not to occur. 相似文献
13.
Louise Nuijens Kerry Emanuel Hirohiko Masunaga Tristan L’Ecuyer 《Surveys in Geophysics》2017,38(6):1257-1282
Space-borne observations reveal that 20–40% of marine convective clouds below the freezing level produce rain. In this paper we speculate what the prevalence of warm rain might imply for convection and large-scale circulations over tropical oceans. We present results using a two-column radiative–convective model of hydrostatic, nonlinear flow on a non-rotating sphere, with parameterized convection and radiation, and review ongoing efforts in high-resolution modeling and observations of warm rain. The model experiments investigate the response of convection and circulation to sea surface temperature (SST) gradients between the columns and to changes in a parameter that controls the conversion of cloud condensate to rain. Convection over the cold ocean collapses to a shallow mode with tops near 850 hPa, but a congestus mode with tops near 600 hPa can develop at small SST differences when warm rain formation is more efficient. Here, interactive radiation and the response of the circulation are crucial: along with congestus a deeper moist layer develops, which leads to less low-level radiative cooling, a smaller buoyancy gradient between the columns, and therefore a weaker circulation and less subsidence over the cold ocean. The congestus mode is accompanied with more surface precipitation in the subsiding column and less surface precipitation in the deep convecting column. For the shallow mode over colder oceans, circulations also weaken with more efficient warm rain formation, but only marginally. Here, more warm rain reduces convective tops and the boundary layer depth—similar to Large-Eddy Simulation (LES) studies—which reduces the integrated buoyancy gradient. Elucidating the impact of warm rain can benefit from large-domain high-resolution simulations and observations. Parameterizations of warm rain may be constrained through collocated cloud and rain profiling from ground, and concurrent changes in convection and rain in subsiding and convecting branches of circulations may be revealed from a collocation of space-borne sensors, including the Global Precipitation Measurement (GPM) and upcoming Aeolus missions. 相似文献
14.
Paquita Zuidema Giuseppe Torri Caroline Muller Arunchandra Chandra 《Surveys in Geophysics》2017,38(6):1283-1305
Pools of air cooled by partial rain evaporation span up to several hundreds of kilometers in nature and typically last less than 1 day, ultimately losing their identity to the large-scale flow. These fundamentally differ in character from the radiatively-driven dry pools defining convective aggregation. Advancement in remote sensing and in computer capabilities has promoted exploration of how precipitation-induced cold pool processes modify the convective spectrum and life cycle. This contribution surveys current understanding of such cold pools over the tropical and subtropical oceans. In shallow convection with low rain rates, the cold pools moisten, preserving the near-surface equivalent potential temperature or increasing it if the surface moisture fluxes cannot ventilate beyond the new surface layer; both conditions indicate downdraft origin air from within the boundary layer. When rain rates exceed \(\sim\) 2 mm h\(^{-1}\), convective-scale downdrafts can bring down drier air of lower equivalent potential temperature from above the boundary layer. The resulting density currents facilitate the lifting of locally thermodynamically favorable air and can impose an arc-shaped mesoscale cloud organization. This organization allows clouds capable of reaching 4–5 km within otherwise dry environments. These are more commonly observed in the northern hemisphere trade wind regime, where the flow to the intertropical convergence zone is unimpeded by the equator. Their near-surface air properties share much with those shown from cold pools sampled in the equatorial Indian Ocean. Cold pools are most effective at influencing the mesoscale organization when the atmosphere is moist in the lower free troposphere and dry above, suggesting an optimal range of water vapor paths. Outstanding questions on the relationship between cold pools, their accompanying moisture distribution and cloud cover are detailed further. Near-surface water vapor rings are documented in one model inside but near the cold pool edge; these are not consistent with observations, but do improve with smaller horizontal grid spacings. 相似文献
15.
Numerical Analysis of Groundwater Ridging Processes Considering Water‐Air Flow in a Hillslope 
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下载免费PDF全文 In this study, a water‐air two‐phase flow model was employed to investigate the formation, extension, and dissipation of groundwater ridging induced by recharge events in a hypothetical hillslope‐riparian zone, considering interactions between the liquid and gas phases in soil voids. The simulation results show that, after a rain begins, the groundwater table near the stream is elevated instantaneously and significantly, thereby generating a pressure gradient driving water toward both the stream (the discharge of groundwater to the stream) and upslope (the extension of groundwater ridging into upslope). Meanwhile, the airflow upslope triggered by the advancing wetting front moves downward gradually. Therefore, the extension of groundwater ridging into upslope and the downward airflow interact within a certain region. After the rain stops, groundwater ridging near the stream declines quickly while the airflow in the lower part of upslope is still moving into the hillslope. Thus, the airflow upslope mitigates the dissipation of groundwater ridging. Additionally, the development of groundwater ridging under different conditions, including rain intensity, intrinsic permeability, capillary fringe height, and initial groundwater table, was analyzed. Changes in intrinsic permeability affect the magnitude of groundwater ridging near the stream, as well as the downward speed of airflow, thereby generating highly complex responses. The capillary fringe is not a controlling factor but an influence factor on the formation of groundwater ridging, which is mainly related to the antecedent moisture. It was demonstrated that groundwater ridging also occurs where an unsaturated zone occurs above the capillary fringe with a subsurface lateral flow. 相似文献
16.
《Advances in water resources》2005,28(11):1254-1266
A detailed model was formulated to describe the non-isothermal transport of water in the unsaturated soil zone. The model consists of the coupled equations of mass conservation for the liquid phase, gas phase and water vapor and the energy conservation equation. The water transport mechanisms considered are convection in the liquid phase, and convection, diffusion and dispersion of vapor in the gas phase. The boundary conditions at the soil–atmosphere interface include dynamical mass flux and energy flux that accounts for radiation transport. Comparison of numerical simulations results with published experimental data demonstrated that the present model is able to describe water and energy transport dynamics, including situations of low and moderate soil moisture contents. Analysis of field studies on soil drying suggests that that dispersion flux of the water vapor near the soil surface, which is seldom considered in soil drying models, can make a significant contribution to the total water flux. 相似文献
17.
The Crust-Mantle Structure in Zhangbei-Shangyi Earthquake Area 总被引：4，自引：0，他引：4
Zhu Zhiping Zhang Jianshi Zhang Xiankang Zhang Chengke Liu Mingqing and Nie WenyingResearch Center of Exploration Geophysics CSB Zhengzhou China 《中国地震研究》1999,(4)
The seismic data obtained from the wide angle reflection and refraction profiles that pass through Zhangjiakou area of Hebei Province were interpreted. Some conclusions drawn from the result are as follows: (1) The nearly EW-trending Zhangbei-Chongli crustal fault zone and WNW-trending Zhangjiakou-Bohai Sea deep crustal fault zone meet in the Zhangbei earthquake (Ms = 6.2) area; (2) At the intersection, the two deep crustal fault zones that stretch to the Moho and the discontinuities of interfaces within the crust form the path for large area basalt eruption in Hannuoba; (3) In the earthquake area, the local velocity reversal in the middle-upper crust and abnormal low velocity zone in the lower crust imply that the magmatic activity there is still fairly violent; and (4) The recent activity of Zhangjiakou-Bohai Sea deep crustal fault zone may be the main cause of the Zhangbei earthquake. 相似文献
18.
Wind-induced subduction at the South Atlantic subtropical front 总被引：1，自引：1，他引：0
Paulo H. R. Calil 《Ocean Dynamics》2017,67(10):1351-1365
The South Atlantic Subtropical Front, associated with the eastward-flowing South Atlantic Current, separates the colder, nutrient-rich waters of the subpolar gyre from the warmer, nutrient-poor waters of the subtropical gyre. Perturbations to the quasi-geostrophic, eastward flow generate meanders and filaments which induce cross-frontal exchange of water properties. Down-front winds transport denser waters from the South over warm waters from the North, inducing convective instability and subduction. Such processes occur over spatial scales of the order of 1 km and thus require high horizontal spatial resolution. In this modeling study, a high-resolution (4 km) regional grid is embedded in a basin-wide configuration (12 km) of the South Atlantic Ocean in order to test the importance of submesoscale processes in water mass subduction along the subtropical front. Stronger and more numerous eddies obtained in the high-resolution run yield more intense zonal jets along the frontal zone. Such stronger jets are more susceptible to instabilities, frontogenesis, and the generation of submesoscale meanders and filaments with \(\mathcal {O}(1)\) Rossby number. As a consequence, vertical velocities larger than 100 md 1 are obtained in the high-resolution run, one order of magnitude larger than in the low-resolution run. Wind-driven subduction occurs along the frontal region, associated with negative Ertel potential vorticity in the surface layer. Such processes are not observed in the low-resolution run. A passive tracer experiment shows that waters with density characteristics similar to subtropical mode waters are preferentially subducted along the frontal region. The wind-driven buoyancy flux is shown to be much larger than thermal or haline fluxes during the wintertime, which highlights the importance of the frictional component in extracting PV from the surface ocean and inducing subduction, a process that has been overlooked in subtropical mode water formation in the region. 相似文献
19.
Alberto R. Piola Osmar O. Möller Jr. Raúl A. Guerrero Edmo J.D. Campos 《Continental Shelf Research》2008
Hydrographic data collected during surveys carried out in austral winter 2003 and summer 2004 are used to analyze the distributions of temperature (T) and salinity (S) over the continental shelf and slope of eastern South America between 27°S and 39°S. The water mass structure and the characteristics of the transition between subantarctic and subtropical shelf water (STSW), referred to as the subtropical shelf front (STSF), as revealed by the vertical structure of temperature and salinity are discussed. During both surveys, the front intensifies downward and extends southwestward from the near coastal zone at 33°S to the shelf break at 36°S. In austral winter subantarctic shelf water (SASW), derived from the northern Patagonia shelf, forms a vertically coherent cold wedge of low salinity waters that locally separate the outer shelf STSW from the fresher inner shelf Plata Plume Water (PPW) derived from the Río de la Plata. Winter T–S diagrams and cross-shelf T and S distributions indicate that mixtures of PPW and tropical water only occur beyond the northernmost extent of pure SASW, and form STSW and an inverted thermocline characteristic of this region. In summer 2004, dilution of Tropical water (TW) occurs at two distinct levels: a warm near surface layer, associated to PPW–TW mixtures, similar to but significantly warmer than winter STSW, and a colder (T∼16 °C) salinity minimum layer at 40–50 m depth, created by SASW–STSW mixtures across the STSF. In winter, the salinity distribution controls the density structure creating a cross-shore density gradient, which prevents isopycnal mixing across the STSF. Temperature stratification in summer induces a sharp pycnocline providing cross-shelf isopycnal connections across the STSF. Cooling and freshening of the upper layer observed at stations collected along the western edge of the Brazil Current suggest offshore export of shelf waters. Low T and S filaments, evident along the shelf break in the winter data, suggest that submesoscale eddies may enhance the property exchange across the shelf break. These observations suggest that as the subsurface shelf waters converge at the STSF, they flow southward along the front and are expelled offshore, primarily along the front axis. 相似文献
20.
Data from several coincident satellite sensors are analyzed to determine the dependence of cloud and precipitation characteristics of tropical regions on the variance in the water vapor field. Increased vapor variance is associated with decreased high cloud fraction and an enhancement of low-level radiative cooling in dry regions of the domain. The result is found across a range of sea surface temperatures and rain rates. This suggests the possibility of an enhanced low-level circulation feeding the moist convecting areas when vapor variance is large. These findings are consistent with idealized models of self-aggregation, in which the aggregation of convection is maintained by a combination of low-level radiative cooling in dry regions and mid-to-upper-level radiative warming in cloudy regions. 相似文献