Dynamics of Low Frequency Phenomena

对海洋-大气耦合系统大尺度低频现象的动力学研究侧重于时间尺度从周到年不等的行星尺度运动。本研究的四个主要领域是：(1)低纬度海洋-大气耦合系统的年循环：越来越多的证据表明，年循环在海洋-大气耦合系统的较长周期年际变率中起着不可或缺的作用。年循环本身是相互作用的、大振幅的非对称（季风）和对称（沃克）分量的复杂组合。如果这些组件的相位不一致，那么可能会出现某些类型的交互。因此，将结合诊断和建模技术来研究这些组件的交互结构。(2)赤道波在非均匀流动中的传播：早期的研究表明，赤道瞬变受到基本流的纬向和纵向结构的显著改变。基流的符号和纬向切变倾向于决定瞬态模式的赤道圈闭程度和侧向伸展（发散）程度，而纵向拉伸变形决定了瞬态模式在纵向上的圈闭程度。本研究将在以往研究的基础上进行扩展，明确地包括热带大气中发现的强垂直切变。这项研究还将利用目前可用的更完整的ECMWF 31级全球操作模型。（三）半球间和温带-热带相互作用：有大量证据表明，温带模态影响热带地区，甚至通过赤道西风道区延伸到另一个半球。该领域的进一步理论研究将使用等熵面上的保守位涡作为区域赤道传播详尽诊断研究的基本工具。一项初步研究似乎确定了在纬度相互作用中可能具有相当相关性的新现象和无法解释的过程。（四）超长赤道异常的快速发展：热带暴和浪涌：对热带的普遍看法是大尺度场弱且变化缓慢，只有小尺度对流扰动才会快速发展。然而，新的分析提出了相反的观点，这些分析表明，快速发展似乎发生在最大的尺度上，数千公里，特别是在热带印度洋和太平洋的暖池地区。将进行一项综合诊断和模拟活动，目的是了解这些热带爆发及其在海洋-大气耦合相互作用中的作用。这四个领域的研究将首先进行详细的诊断研究，这些研究将用于提出假设。然后，这些假设将通过一系列理论数值模型的实验来检验。这种方法在过去的研究中被证明是非常成功的。这项研究很重要，因为它着重于了解海洋-大气耦合系统在数周至数年时间尺度上的行为。这种理解是确定耦合系统在数月至数年的时间尺度上是否可预测的关键，这是TOGA（热带海洋全球大气）计划的具体科学目标之一，该计划旨在研究气候现象的预测。

The research into the dynamics of large-scale, low frequency phenomena of the coupled ocean-atmosphere system has an emphasis on planetary scale motions with time scales ranging from weeks to years. The four main areas of this research are: (I) The annual cycle of the low-latitude coupled ocean-atmosphere system: Mounting evidence indicates that the annual cycle plays an integral role in the longer period, interannual variability of the coupled ocean-atmosphere system. The annual cycle itself is a complicated combination of interactive, large amplitude asymmetric (monsoon) and symmetric (Walker) components. If these components are out-of-phase, as appears to be the case, then certain types of interaction may be expected. Therefore, the interactive structure of these components will be investigated with a combination of diagnostic and modeling techniques. (II) Equatorial Wave Propagation in Inhomogeneous Flows: Earlier studies indicate that equatorial transients are significantly modified by the latitudinal and longitudinal structure of the basic flow. Both the sign and latitudinal shear of the basic flow tend to determine the degree of equatorial trapping and lateral extension (emanation) of the transients while the longitudinal stretching deformation determines the degree to which transient modes are trapped longitudinally. This research will be expanded from the past studies by explicitly including the strong vertical shear found in the tropical atmosphere. This research will also take advantage of the more complete ECMWF 31-level global operational model now available. (III) Interhemispheric and Extratropical-tropical Interaction: Abundant evidence exists to show that extratropical modes influence the tropical regions or even extend to the other hemisphere through the equatorial westerly duct regions. Further theoretical studies in this area will use conservative potential vorticity on an isentropic surface (IPV) as a basic tool in an exhaustive diagnostic investigation of regional equatorial propagation. A pilot study appears to identify new phenomena and unexplained processes which may have considerable relevance in latitudinal interactions. (IV) Rapid Development of Ultra-long Equatorial Anomalies: Tropical Bursts and Surges: A common view of the tropics is that the large scale fields are weak and slowly varying and that only small scale convective disturbances have rapid development. However, a contrary view is suggested by new analyses which show that rapid development appears to occur on the largest scales, thousands of kilometers, especially in the warm pool regions of the tropical Indian and Pacific oceans. A combined diagnostic and modeling activity, aimed at understanding these tropical bursts and their role in the coupled ocean-atmosphere interactions, will be undertaken. Research in each of these four areas will proceed first with detailed diagnostic studies which will be used to pose hypotheses. Then the hypotheses will be tested by experimentation with a hierarchy of theoretical numerical models. This approach has proven to be very successful in past research. This research is important because it focuses on understanding the behavior of the coupled ocean-atmosphere system on time scales of weeks to years. This understanding is key to determining whether the coupled system is predictable on time scales of months to years, one of the specific scientific goals of the TOGA (Tropical Ocean Global Atmosphere) Program which is aimed at studying the prediction of climate phenomena.