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321.
Statistical and dynamical assessment of vegetation feedbacks on climate over the boreal forest 总被引:1,自引:1,他引:0
Vegetation feedbacks over Asiatic Russia are assessed through a combined statistical and dynamical approach in a fully coupled
atmosphere–ocean–land model, FOAM-LPJ. The dynamical assessment is comprised of initial value ensemble experiments in which
the forest cover fraction is initially reduced over Asiatic Russia, replaced by grass cover, and then the climatic response
is determined. The statistical feedback approach, adopted from previous studies of ocean–atmosphere interactions, is applied
to compute the feedback of forest cover on subsequent temperature and precipitation in the control simulation. Both methodologies
indicate a year-round positive feedback on temperature and precipitation, strongest in spring and moderately substantial in
summer. Reduced boreal forest cover enhances the surface albedo, leading to an extended snow season, lower air temperatures,
increased atmospheric stability, and enhanced low cloud cover. Changes in the hydrological cycle include diminished transpiration
and moisture recycling, supporting a reduction in precipitation. The close agreement in sign and magnitude between the statistical
and dynamical feedback assessments testifies to the reliability of the statistical approach. An additional statistical analysis
of monthly vegetation feedbacks over Asiatic Russia reveals a robust positive feedback on air temperature of similar quantitative
strength in two coupled models, FOAM-LPJ and CAM3–CLM3, and the observational record.
CCR Contribution # 931. 相似文献
322.
Highly restricted gene flow between disjunct populations of the skunk clownfish (Amphiprion akallopisos) in the Indian Ocean
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The skunk clownfish (Amphiprion akallopisos) has a disjunct distribution, occurring in the Eastern Indian Ocean (EIO) and the Western Indian Ocean (WIO), separated by several thousands of kilometres. Information on connectivity of marine species is very important for the correct spacing of marine protected areas, a powerful instrument for the protection of coral reefs. The population genetic structure of A. akallopisos was analysed in order to investigate connectivity amongst populations and to explain the disjunct distribution of the species. A fragment of the mitochondrial control region was used to investigate the genetic population structure. Fin clips were collected from 263 individuals at 14 sites in the WIO and three sites in the EIO. The obtained DNA sequences were used to calculate genetic diversity, evaluate demographic history and to construct a haplotype network. An analysis of molecular variance (AMOVA) was conducted to evaluate the significance of the observed genetic population structure. None of the identified 69 haplotypes was shared between the WIO and EIO. Haplotype as well as nucleotide diversity was considerably higher in the EIO than in the WIO. Significant genetic population structure was revealed by an AMOVA with an overall φst‐value of 0.28 (P < 0.001) in the Indian Ocean. The overall AMOVA (φst = ?0.00652) was not significant in the EIO, but was significant in the WIO (φst = 0.016; P < 0.01). Demographic analysis indicated population expansion in the EIO and WIO. Population genetic analysis revealed highly restricted gene flow between the EIO and WIO. Genetic diversity was much higher in the EIO than in the WIO, suggesting that the EIO is the geographical origin of the species. Given the large distance between the disjunct populations and the short pelagic larval duration, long‐distance dispersal is rather unlikely. A stepping stone model involving islands in the Central Indian Ocean is a more likely scenario for colonization of the WIO. 相似文献
323.
一个简单的印-太海气耦合模式 总被引:1,自引:0,他引:1
本文基于一层半海洋模式和SVD(Singular Value Decomposition)大气模式构建了一个简单的海气耦合模式, 引入热通量的作用, 分析ENSO影响热带印度洋地区的动力学和热力学耦合过程。其中, 使用统计大气模式, 由给定的SST(Sea Surface Temperature)异常得到风应力异常, 进而驱动海洋环流反馈给SST, 完成海气的动力耦合; 使用块体经验公式由SST异常和风场异常计算热通量异常, 直接作用于SST, 实现海气的热力学耦合。动力耦合实验揭示, 太平洋第一EOF(Empirical Orthogonal Functions) 模态与观测基本吻合。并且模拟Ni?o 3指数存在两年左右的谱峰周期。这说明, 海气动力学耦合是ENSO生成的主要因素。热力耦合的加入是为了考察ENSO影响热带印度洋的热力学效应。同时考虑动力和热力耦合的实验结果表明, 热带太平洋暖异常中心更加接近观测值, 热带印度洋出现海盆尺度海温正异常。这意味着热带太平洋的ENSO信号通过海气界面的热量交换实现对热带印度洋地区的遥强迫, 导致印度洋海盆尺度增暖。 相似文献
324.
325.
林雪原 《武汉大学学报(信息科学版)》2012,37(3):274-277
研究了可用于多传感器组合导航系统的两级分布式最优融合算法,以理论的形式证明了在有、无信息反馈的情况下最终的融合结果是等价的与最优的。仿真结果在验证上述理论的情况下,也说明了来自融合中心的反馈信息可明显提高子滤波的滤波性能。 相似文献
326.
Summer Persistence Barrier of Sea Surface Temperature Anomalies in the Central Western North Pacific
The persistence barrier of sea surface temperature anomalies(SSTAs) in the North Pacific was investigated and compared with the ENSO spring persistence barrier.The results show that SSTAs in the central western North Pacific(CWNP) have a persistence barrier in summer:the persistence of SSTAs in the CWNP shows a significant decline in summer regardless of the starting month.Mechanisms of the summer persistence barrier in the CWNP are different from those of the spring persistence barrier of SSTAs in the central and eastern equatorial Pacific.The phase locking of SSTAs to the annual cycle does not explain the CWNP summer persistence barrier.Remote ENSO forcing has little linear influence on the CWNP summer persistence barrier,compared with local upper-ocean process and atmospheric forcing in the North Pacific.Starting in wintertime,SSTAs extend down to the deep winter mixed layer then become sequestered beneath the shallow summer mixed layer,which is decoupled from the surface layer.Thus,wintertime SSTAs do not persist through the following summer.Starting in summertime,persistence of summer SSTAs until autumn can be explained by the atmospheric forcing through a positive SSTAs-cloud/radiation feedback mechanism because the shallow summertime mixed layer is decoupled from the temperature anomalies at depth,then the following autumn-winter-spring,SSTAs persist.Thus,summer SSTAs in the CWNP have a long persistence,showing a significant decline in the following summer.In this way,SSTAs in the CWNP show a persistence barrier in summer regardless of the starting month. 相似文献
327.
328.
基于LaSalle不变定理和Lyapunov方法,针对混沌系统同步问题提出了一种改进的自适应反馈方法。与一般线性反馈系统不同,这种方法能自动调整更新规则的可变反馈变量。在该自适应更新规则的控制下,反馈强度可自动调整到新的自适应规则,从而使响应系统的状态全局同步于驱动系统的状态。Chen氏混沌系统和Lu氏混沌系统说明了所设计的自适应反馈方法的有效性。 相似文献
329.
Along with the economic development,large tunnels need to be constructed in many high mountains or complex structure regions,and the design and construction of detailed tunnel exploration become particularly important.Transient electromagnetic method (TEM) uses a non-grounded loop or an electrode to send a primary electromagnetic pulse into the ground,and observes spatial and temporal distribution of secondary electromagnetic field,which is widely applied in mineral resource exploration,engineering geology,etc.The application of TEM in the tunnel construction of Kaiyuan Temple is researched in this study.The smoke loop inversion is adopted for inverting the transient electromagnetic data.The drilling data and high density resistivity method data are combined for comparison.The obtained inversion result greatly coincides with the actual conditions.Therefore,the geophysical prospecting basis can be provided for the division of stratum,delineation of geologi-cal structure,and design and construction of tunnel pavement.By virtue of TEM,drilling data and high density resistivity method,the tunnel construction of Kaiyuan Temple has obtained satisfactory results. 相似文献
330.