Aspects of Deep Ocean Mixing

The turbulent motions responsible for ocean mixing occur on scales much smaller than those resolved in numerical simulations of oceanic flows. Great progress has been made in understanding the sources of energy for mixing, the mechanisms, and the rates. On the other hand, we still do not have adequate answers to first order questions such as the extent to which the thermohaline circulation of the ocean, and hence the earth's climate, is sensitive to the present mixing rates in the ocean interior. Internal waves, generated by either wind or flow over topography, appear to be the principle cause of mixing. Mean and eddy flows over topography generate internal lee waves, while tidal flows over topography generate internal tides. The relative importance of these different internal wave sources is unknown. There are also great uncertainties about the spatial and temporal variation of mixing. Calculations of internal tide generation are becoming increasingly robust, but we do not know enough about the subsequent behavior of internal tides and their eventual breakdown into turbulence. It does seem, however, that most internal tide energy flux is radiated away from generation sites as low modes that propagate over basin scales. The mechanisms of wave-wave interaction and topographic scattering both act to transfer wave energy from low modes to smaller dissipative scales. This revised version was published online in August 2006 with corrections to the Cover Date.     

Ocean Waves: Half-a-Century of Discovery

While the nature of most ocean waves has long been known and their basic physics understood since the nineteenth century, intense study of ocean waves during the second half of the twentieth century has taken the subject from the realm of mathematical exercises to that of practical engineering. Modern understanding of the generation, propagation and interactions of ocean waves with each other and with oceanic features has advanced to a quantitative level offering predictive capacity. This paper presents a brief qualitative review of advances in knowledge of sound waves, wind waves, tsunamis, tides, internal waves and long-period vorticity waves. The review is aimed at non-specialists who may benefit from an overview of the current state of the subject and access to a bibliography of general-interest references. This revised version was published online in August 2006 with corrections to the Cover Date.     

On the tidal variation of the geopotential

In this paper analytical expressions are derived for the temporal variations ofJ ₂ andJ ₂₂ due to the tides of the solid Earth, taking into account only the deformation of the mantle, and employing a procedure already used by the authors in their Hamiltonian theory of the Earth's rotation, which obtain the necessary parameters in a direct way by integration of those provided by a selected model of Earth interior.Numerical tables giving the periodic variation of coefficients are given, as well as a new prediction for UT1. For J ₂ and J ₂₂ the amplitudes reach such a magnitude that both two variations should not be ignored in studies involving the analysis of highly precise satellite tracking data. Moreover, the possibility of improving our knowledge of the value of those harmonic coefficients in only a more exact digit appears as to be strongly dependent on the limitations in the theoretical modeling of the variations of the inertia tensor due to solid tides.     

The green revolution and poverty: a theoretical and empirical examination of the relation between technology and society

The paper deals with the effects of the green revolution (GR) technology on poverty both conceptually and empirically. It provides a brief overview of the GR debate and then presents a `slice' of this debate in detail - in particular, Lipton's and others' views on the supposed positive and negative benefits of the GR for the poor. The paper then provides a provocative critique of this literature for its underlying neo-Malthusianism of a specific type, for ignoring class issues in the analysis of the GR-poverty relation, and for treating this relation as a necessary relation. It subsequently presents an alternative statement on the GR-poverty issue, arguing that it is class relations that set limit within which population and technology work and affect poverty and that the GR-poverty relation is a contingent one, rather than necessary. In the light of the paper's criticisms and the alternative view it provides, a statistical analysis of the relation between the GR and the population factor on the one hand and poverty level and poverty reduction on the other in India is performed. This analysis is generally consistent with the paper's critique of the Liptonian framework.     

Analysis and comparison of the tidal gravity observations obtained with LCR-ET20 spring gravimeter

Introduction The tidal variation signals of the solid Earth recorded with the modern measuring techniques can be used to provide effectively the means to cognize the Earths motion, deformation and structure character, especially to monitor the material motion in the Earths interior. In the recent 20 years, the distribution character of the global gravity field has made great progress since the continuous and deep theoretical studies in geophysics and geodesy domains. The successful manufactur…     

吉林省发展绿色食品的农业生态环境优势分析

发展绿色食品生产是吉林省实施“生态省”建设工程的主导产业之一，本文按照绿色食品产地环境质量标准要求，客观评价了吉林省发展绿色食品的产地环境条件，得出吉林省具有发展绿色食品生产的显著农业生态环境优势。基于吉林省良好的农业生态环境质量，结合区域自然条件和资源优势，将全省分为东部山区、中部松辽平原区、西部松嫩平原区和大、中城市郊区四种区域类型，并分别提出了其发展绿色食品生产的宏观策略。     

变参考慢度Born近似傅氏偏移

针对常规Born近似傅氏偏移方法对于剧烈横向变速介质不能精确成像的状况而提出了变参考慢度Born近似傅氏偏移，理论上解决了任意速度变化地质模型的偏移成像问题。此外，为进一步提高复杂地层的成像精度和波场延拓算子的稳定性，对散射波场的计算公式作了改进。将改进的方法运用于盐丘模型的正演和偏移试验，并与常规Born近似偏移方法相比较，可明显看出变参考慢度Born近似傅氏偏移方法在效果上要优于后者，其处理速度横向变化的能力大大增强。     

确定精密重力仪相位滞后方法的研究

从系统辨识的原理出发,给出了确定精密重力仪相位滞后的一种方法,即记录精密重力仪在阶跃信号作用下的输出数据,利用这些数据对仪器的传递函数进行辨识,从而确定重力仪对各潮汐波产生的相位滞后角度.用这种方法对ET-21地潮重力仪进行了相位滞后的确定,并给出这台仪器对15个主要潮汐波的相位滞后角度.