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51.
本文采用中国地区基于卫星观测的植被光合有效辐射资料(FPAR)和月平均气候数据(1982-2000年)来分析中国区域陆面植被与气温、降水的反馈作用.通过计算和分析超前滞后相关系数和反馈系数发现:春、夏季FPAR超前气温一个月相关系数在全国大部分地区为负值,反映出植被生长旺盛,可以降低局地气温.春、秋两季气温与FPAR的同期相关系数较大.夏季降水超前FPAR一个月的正相关性反映出夏季降水对于植被生长存在促进作用.在中国长江流域以南区域,植被对于气温的反馈系数为一致正值,可达0.5 ℃(0.1FPAR)-1;在30°N以北区域显示出一致的负反馈,可达-0.42 ℃(0.1FPAR)-1.FPAR对降水全年反馈系数全国区域平均可达-2.12 cm month-1(0.1FPAR)-1.不同植被类型、不同季节的植被反馈效应也存在差异.植被反馈系数可以用来验证动态植被模式计算的植被大气反馈作用. 相似文献
52.
This paper presents dynamical modeling and robust control of a Mini Unmanned Underwater Vehicle (MUUV) equipped with a new arrangement of water jet propulsion. The water jet propulsion includes some advantages comparing with a propeller one, such as, reducing the number of required motors, desired number and arrangement of the propulsions, removing adverse torque and cavitation due to propeller rotation and etc. In order to model the proposed MUUV, the gray box method is used in such a way that the dynamical equation of motion is derived analytically by Euler-Lagrangian method, and then the hydrodynamic coefficients (such as added mass and drag coefficients) are derived by performing some tests in a Computational Fluid Dynamic (CFD) software. The dynamical model is used to simulate the MUUV system and also to design the proposed controllers, which are Feedback Linearization Controller (FLC) and Sliding Mode Controller (SMC). In order to investigate and compare the performance of the MUUV and the applied controllers, three types of tests including a desired signal tracking case and two desired path tracking cases are designed. To do so, a method is presented to obtain the desired signals from a desired path under predetermined conditions. Then, an MUUV prototype is designed and constructed in order to investigate the performance of the proposed water jet propulsions and controllers for regulation and tracking desired signal purpose, experimentally. As it is expected, the simulation and experimental results show better performance of the SMC compared to FLC. Furthermore, the experimental results reveal that the water jet propulsion is implementable to practical prototypes and also can be produced in an industrial level. 相似文献
53.
T. J. Raddatz C. H. Reick W. Knorr J. Kattge E. Roeckner R. Schnur K.-G. Schnitzler P. Wetzel J. Jungclaus 《Climate Dynamics》2007,29(6):565-574
Global warming caused by anthropogenic CO2 emissions is expected to reduce the capability of the ocean and the land biosphere to take up carbon. This will enlarge the
fraction of the CO2 emissions remaining in the atmosphere, which in turn will reinforce future climate change. Recent model studies agree in
the existence of such a positive climate–carbon cycle feedback, but the estimates of its amplitude differ by an order of magnitude,
which considerably increases the uncertainty in future climate projections. Therefore we discuss, in how far a particular
process or component of the carbon cycle can be identified, that potentially contributes most to the positive feedback. The
discussion is based on simulations with a carbon cycle model, which is embedded in the atmosphere/ocean general circulation
model ECHAM5/MPI-OM. Two simulations covering the period 1860–2100 are conducted to determine the impact of global warming
on the carbon cycle. Forced by historical and future carbon dioxide emissions (following the scenario A2 of the Intergovernmental
Panel on Climate Change), they reveal a noticeable positive climate–carbon cycle feedback, which is mainly driven by the tropical
land biosphere. The oceans contribute much less to the positive feedback and the temperate/boreal terrestrial biosphere induces
a minor negative feedback. The contrasting behavior of the tropical and temperate/boreal land biosphere is mostly attributed
to opposite trends in their net primary productivity (NPP) under global warming conditions. As these findings depend on the
model employed they are compared with results derived from other climate–carbon cycle models, which participated in the Coupled
Climate–Carbon Cycle Model Intercomparison Project (C4MIP).
相似文献
T. J. RaddatzEmail: |
54.