Steady Response of a Ventilated Thermocline to Enhanced Ekman Pumping     

Atsushi Kubokawa  Shang-Ping Xie 《Journal of Oceanography》2002,58(4):565-575

The steady response of the ventilated thermocline to an increase in Ekman pumping is investigated, focusing on the effect of the mixed layer depth distribution on the subsurface density anomaly. We consider only the subtropical gyre, and the mixed layer is assumed to be deep in the northwest and shallow elsewhere with a narrow transition zone separating the deep and shallow mixed layer regions. At the intersection of this narrow transition zone and the outcrop line, low potential vorticity fluid is subducted into and ventilates the thermocline. In such a situation, an enhancement of the Ekman pumping confined to the northern subtropical gyre leads to pronounced subsurface cold anomalies in the southern subtropics, which is free of anomalous forcing. These density anomalies are much greater than those that occur when either the mixed layer depth is zonally uniform or the Ekman pumping is enhanced in the whole subtropical gyre. They are caused by anomalous changes in the trajectory of the low potential vorticity fluid in response to anomalous Sverdrup flow. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

地震活动时序谱的涨落统计特征与地震活跃期   总被引：1，自引：0，他引：1  

涂鹏  韩渭宾 《四川地震》1997,(4):22-29

为寻求地震活动演化的统计判据，本文采用多项式拟合法展示地震时序谱之涨落谱，以分维函数法判断最小邻间距（NNS）分布的Poisson性，然后采用MKS无参量法判别涨落谱之统计稳定性，确定NNS分布的转变区，具体研讨了四川、云南若干震区地震活动时序谱的涨落统计分布，发现地震活跃期到来时NNS分布表现出非Poisson化的特征。进一步通过改变和调节时序数据样本集之震级下限，并逐段前推进行统计计算的方式进一步验证结果的可靠性，客观地确定了这些震区地震活动时序涨落谱统计特征的转变期，使根据该统计法判断地震活跃期的方法论渐趋完善。  相似文献   

Meeting future food demand with current agricultural resources     

《Global Environmental Change》2016

Meeting the food needs of the growing and increasingly affluent human population with the planet’s limited resources is a major challenge of our time. Seen as the preferred approach to global food security issues, ‘sustainable intensification’ is the enhancement of crop yields while minimizing environmental impacts and preserving the ability of future generations to use the land. It is still unclear to what extent sustainable intensification would allow humanity to meet its demand for food commodities. Here we use the footprints for water, nitrogen, carbon and land to quantitatively evaluate resource demands and greenhouse gas (GHG) emissions of future agriculture and investigate whether an increase in these environmental burdens of food production can be avoided under a variety of dietary scenarios. We calculate average footprints of the current diet and find that animal products account for 43–87% of an individual’s environmental burden – compared to 18% of caloric intake and 39% of protein intake. Interestingly, we find that projected improvements in production efficiency would be insufficient to meet future food demand without also increasing the total environmental burden of food production. Transitioning to less impactful diets would in many cases allow production efficiency to keep pace with growth in human demand while minimizing the food system’s environmental burden. This study provides a useful approach for evaluating the attainability of sustainable targets and for better integrating food security and environmental impacts.  相似文献   

海洋上层暖水在热带气旋迅速增强中的作用:基于台风威马逊(1409)的个例研究   总被引：5，自引：1，他引：4  

孙佳  左军成  凌征  闫运伟 《海洋学报(英文版)》2016,35(3):63-68

在登陆海南岛之前,台风威马逊在南海北部从热带风暴级别迅速增强成为超强台风。观测数据的分析结果显示,海洋上层的异常暖水在威马逊的迅速增强过程中扮演了重要的角色。威马逊期间,南海北部的海表面温度相比于气候态海表面温度暖很多。这部分异常暖水为威马逊提供了更多的能量,从而导致了威马逊的迅速增强。数值模拟结果进一步证明,南海北部的暖水在台风威马逊的迅速增强过程中起重要作用。如果没有这团异常暖水的影响,威马逊只增强25 hPa,仅为有暖水影响条件下增强程度的58.1%。  相似文献   

CAUSAL ANALYSIS AND NUMERICAL MODELING OF THE INSHORE INTENSIFICATION OF SUPER TYPHOON “HATO”     

于鑫  郑腾飞  万齐林  肖辉  刘显通  王婷 《热带气象学报(英文版)》2019,25(3):293-303

This paper comprehensively analyzes the characteristics and cause of the inshore intensification of super typhoon "Hato", the 13 th super typhoon in 2017. The aspects of typhoon structure, evolution of large-scale circulation and physical quantity field are analyzed using observation data from the Guangdong Automatic Station, Shenzhen Doppler Radar data, NCEP 1°×1° reanalysis data, NCEP 0.25°×0.25° sea surface temperature(SST) data, etc.Additionally, in order to investigate the influence of SST change on the intensity of "Hato", the WRF model and ECMWF 0.125°×0.125° reanalysis data are combined to conduct 3 sensitivity tests on"Hato". The results show that the favorable conditions for inshore intensification of "Hato"included the strengthening and westward extension of the subtropical high, continuous increase of low level moisture transport, an anomalous warm SST area north of 20°N in the South China Sea, an extreme divergence value in the northern South China Sea exceeding 6 ×10-5 s-1, and vertical environmental wind shear between 1.1 m/s-4.8 m/s. The intensity of"Hato"was very sensitive to changes in SST. When the SST rose or dropped by 2℃, the minimum central pressure of the typhoon changed by about 13 hPa or 11 hPa,respectively. SST indirectly influenced the intensity of the typhoon through affecting latent heat transport and sensible heat transport.  相似文献   

Transforming agricultural land use through marginal gains in the food system     

《Global Environmental Change》2019

There is an increasing need for transformational changes in the global food system to deliver healthy nutritional outcomes for a growing population while simultaneously ensuring environmental sustainability. However, such changes are subject to political and public constraints that usually allow only gradual, incremental changes to occur. Drawing inspiration from the British cycling team’s concept of marginal gains, we show how transformation might be reconciled with incremental changes. We demonstrate that a set of marginal food system changes acting to increase production efficiency, to reduce losses or to adjust diets could collectively reduce the agricultural land required globally for food production by 21%, or over a third given higher adoption rates. The results show that while all categories of action are important, changes in consumer choices in Europe, North America and Oceania and in the supply-chain in Africa and West and Central Asia have the greatest potential to reduce the land footprint of the food system.  相似文献   

南印度洋热带气旋快速增强事件气候特征及其年际变率     

汪浩  王静  郑佳喻 《热带海洋学报》2022,41(1):94-105

利用美国联合台风预警中心的热带气旋最佳路径数据集、美国国家海洋和大气管理局的扩展重构海表温度数据、全球海洋数据同化系统的温度、盐度数据及美国国家环境预报中心/国家大气研究中心的再分析资料, 分析了1981—2019年南印度洋热带气旋快速增强事件的气候特征和年际变率。结果表明, 南印度洋热带气旋快速增强事件产生频率呈现单峰分布, 主要产生在每年的12月至次年4月。南印度洋热带气旋增强事件的产生位置呈带状分布, 其中3个高值中心分别位于马达加斯加岛东北海域、南印度洋中部海域和澳大利亚西北海域, 这主要是由于热带气旋热潜和垂直风切变两个大尺度环境变量决定的。年际变率方面, 厄尔尼诺-南方涛动对南印度洋热带气旋增强事件产生频率的调制作用是不对称的, 厄尔尼诺年与拉尼娜年南印度洋热带气旋快速增强事件均减少, 但使其减少的物理机制不同。厄尔尼诺年, 热带气旋快速增强事件减少主要是较高的垂直风切变造成的; 拉尼娜年, 热带气旋快速增强事件减少主要是由于热带气旋热潜的降低, 而海表温度、垂直风切变和相对湿度也存在一定贡献。  相似文献   

Influence of friction on the motion of quasigeostrophic vortices     

Boris Moro 《地球物理与天体物理流体动力学》2013,107(3-4):209-225

Abstract

Who show through numerical experiments that friction may enhance westward motion of vortices on the beta-plane and establish a relation betwen the dissipation coefficients and westward aceleration. This suggests an explanation fot the dunamics of westward intensification.  相似文献   

震源系统小震调制比（r＿m）和异常面积（Sr＿m）起伏加剧的时空特征与强震的中、短期预报     

秦保燕  张晓东  王裕仓  郭星全 《地震工程学报》1994,(3)

本文对强震前震源系统的调制比ｒ＿ｍ和调制比异常面积Ｓｒ＿ｍ随时间变化的起伏加剧现象进行回顾性研究，得到下列研究结果：（１）强震前近源区以及中强震前近源区大多出现调制比ｒ＿ｍ的起伏加剧，并大多在起伏频次达三次时有大震或中强震发生。（２）大多数中、强地震前ｒ＿ｍ异常面积Ｓｒ＿ｍ围绕震源区呈现由小至大、由大至小的过程，因此引入最小异常面积Ｓｒ＿（ｍｉｎ）和最大异常面积Ｓｒ＿（ｍａｘ）之比γ作为中、短期预报指标，根据统计得到异常指标［γ］如下式某些震例在震前出现异常面积Ｓｒ＿ｍ起伏的加剧过程，初步认为是震源区周围调整单元调整能力较差导致的结果。（３）ｒ＿ｍ、Ｓｒ＿ｍ起伏加剧开始时间与震级有关，震级愈大，起伏加剧出现愈早。根据半年步长逐月滑动得到的ｒ＿ｍ－Ｔ图，起伏加剧开始至发震的时间与震级Ｍ的统计，得到如下关系（Ｔ以月计）Ｍ＝４．２９＋０．１１Ｔ（４）强震前场区异常一般呈现随机异常型、波动型和衰减型三种。若场区某统计区出现ｒ＿ｍ的三次起伏加剧时，说明该统计区未来有强震发生。（５）由自治系统和非自治系统原理初步解释了震前震源区周围调整区调制比ｒ＿ｍ及调制比异常面积Ｓｒ＿ｍ起伏现象的周期特征。  相似文献   

气压场巨涨落与非线性地震系统状态的突变和临震预报研究（上）     

赵洪声  张世杰  蔡静观 《高原地震》1994,(3)

本研究以非线性孕震系统在爆发前夕的外敏性为物理基础，对大气扰动下的岩体失稳突变问题进行了初步的探讨，给出了气─－地耦合的一般表示，并连续分析了云南近３５年来大气压力场演化与场内近百次５级以上地震（内含１９次６级，４次７级）的基本关系，系统地证明了绝大部分强震都是在其上覆大气涨落加剧及与邻区气压梯度增大时突然爆发的，这种自然共性的揭示，既是对理论的认证，也丰富了短临地震预报的科学依据。  相似文献