Improvement of Mid-Latitude Atmospheric Predictions Using Coherent Tropical Convective Phenomena

当前一代数值天气预报模式对中纬度变化的描述非常好；然而，由于需要对对流进行参数化，在描述热带变化方面仍然存在重大问题。通过全球大气遥相关，热带地区可以显著影响中纬度地区。因此，有理由期待对热带地区长时间尺度相关现象的描述的改进可能有利于中纬度预报。这是因为这种变异性具有较大的空间尺度和较长的去相关时间。它可以对高纬度地区产生重大而持久的影响，从而影响长期天气预报。近年来，高质量热带资料的提供表明，在许多数值天气预报和气候模式中，对这种相干变化的描述并不令人满意。因此，有充分的理由乐观地认为，对热带相干现象的更好模拟可能会导致中纬度预报的改善。在这些考虑的推动下，将开发一个热带对流更重要方面的随机模式。该模式将能够很好地再现大部分观测到的对流在波数和频率空间上的频谱特征，以及与相干热带变率有关的水平和垂直空间结构。随机模式将嵌入(干)原始方程模式，并将使用理论集合方法和检查对历史预测技能的影响来探索对中纬度预测的影响。这些可预测性结果将与使用传统对流方案的原始方程模式进行比较。理论研究将解决以下问题：1.哪些偏远地区的可预报性受各种热带相关影响最大？为什么？2.大气中导致可预报性变化的主要动力机制是什么？实际预报研究将解决以下问题：1.在热带相关变率有更好表现的不同地区，我们可以预期预报技能有多大的提高？2.应如何集中精力改善对流表现，以从提高预报技能中获得最大回报？这项工作的更广泛影响具有教育性和可操作性：纽约大学库兰特研究所的研究生将接受有关可预测性研究的重要方面的培训。其次，这项工作将为业务天气预报模型师提供具体信息，说明应处理对流行为的哪些特征，以便在预报技能方面取得显着进展。

The depiction of mid-latitude variability in the present generation of numerical weather prediction models is very good; there remain, however, significant problems in the depiction of tropical variability due to the need to parameterize convection. Through global atmospheric teleconnections, the tropics can significantly influence the mid-latitudes. It is reasonable, therefore, to expect that improvements in the depiction of long time-scale coherent phenomena within the tropics may benefit mid-latitude predictions. This follows because such variability has large spatial scales and long decorrelation times. It can induce a significant and long lasting influence on the higher latitudes and thus can affect long-range weather forecasts. In recent years, the availability of high quality tropical data has revealed that the depiction of such coherent variability is less than satisfactory in many numerical weather prediction and climate models. There are thus strong grounds for optimism that better simulation of tropical coherent phenomena may lead to improved mid-latitude forecasts. Motivated by these considerations, a stochastic model of the more important aspects of tropical convection will be developed. This model will be capable of reproducing well most of the important observed spectral features of convection in wave-number and frequency space and the horizontal and vertical spatial structures associated with coherent tropical variability. The stochastic model will be embedded within a (dry) primitive equation model, and the influence on mid-latitude predictions will be explored using a theoretical ensemble approach and by examining the influence on historical forecast skill. These predictability results will be compared with a primitive equation model that uses a conventional convection scheme. The theoretical study will address the following questions: 1. Which remote regions predictability are most strongly influenced by various tropical coherencies and why? 2. What is the principal dynamical mechanism in the atmosphere for causing shifts in predictability? The practical forecast study will address the following questions 1. How much gain in forecast skill might we expect in various regions with a better representation of tropical coherent variability? 2. How should effort be concentrated in improving convection representation to obtain the greatest payoff in increased prediction skill? Broader impacts of this work are educational and operational: Graduate students at the Courant Institute of New York University will be trained in important aspects of predictability research. Secondly this work will provide concrete information to operational weather prediction modelers as to what features of convective behavior should be addressed in order to obtain significant gains in forecast skill.