Intraseasonal variations in the tropical Western Hemisphere and the generation mechanism of stratospheric Kelvin waves

利用基于球上原始方程的数值模型解决了大气对热带加热响应的四个问题。模型加热作为外部强迫给出。第一个问题是澄清非平稳性在对固定加热的响应中的作用。为此，建立了时间积分和平稳模型。在平稳解不稳定的参数范围内，两种模型的结果在异常场上存在显著差异。也就是说，由时间积分模型得到的时间均值比平稳解具有更大的振幅。此外，从热带热源发出的罗斯比波束经过中纬度地区，再次返回热带地区。因此，即使在远离热源的地区，波幅也会变得很大。接下来，我们研究了热带-温带相互作用在季节内变化中的作用。该机型的加热温度可从60E调至180℃，加热时间可超过40天。当没有热带-温带相互作用时，即中纬度纬向平均气流较弱时，只有在热源中心120E附近，季内变化幅度较大。相反，当中纬度西风带很强时，从热带出发的气流穿过中纬度，返回热带。然后，季节内变化在西半球放大。在同一模式中还研究了大气角动量的变化。研究发现，与季节内变化相关的AAM的来源不在于赤道地区，而在于亚热带地区。赤道地区是明显的源，因为AAM是从亚热带输送到赤道的。还澄清了罗斯比波束在AAM的获取和运输中发挥重要作用。最后，通过数值实验验证了平流层开尔文波是由西半球对流层季节内变化产生的假设。到目前为止，我们还没有得到关于这个假设的肯定结果。少

Four problems about the atmospheric response to tropical heating were tackled using numerical models based on the primitive equations on the sphere. The model heating was given as an external forcing.The first problem is to clarify the role of nonstationarity in the response to stationary heating. For this purpose, time integration and stationary models are constructed. In parameter ranges for which stationary solutions are unstable, results from the both models show a significant difference in anomaly fields. That is, the time mean yielded from the time integration model has larger amplitudes than the stationary solution. Further, Rossby wavetrains radiating from the tropical heat source go through the midlatitude, again returning to the tropics. Thus, wave amplitudes become large even in regions which are far from the heat source.Next, we examine the role of the tropical-extratropical interaction in the intraseasonal variation. Heating in this model moves from 60E to 180ﾟ, having the … More period of 40days. When there is no tropical-extratropical interaction, i.e., the zonal mean flow in midlatitudes is weak, the amplitude of the intraseasonal variation is large only near the heat source centered 120E. In contrast, when the midlatitude westerly is strong, wavetrains starting from the tropics pass through the midlatitude, returning to the tropics. Then, the intraseasonal variation amplifies in the Western Hemisphere.Variations of the atmospheric angular momentum (AAM) are also examined in the same model. It is found that the source of the AAM associated with the intraseasonal variation does not lie in the equatorial region but the subtropics. The equatorial region is the apparent source, since the AAM is transported from the subtropics to the equator. It is also clarified that Rossby wavetrains play an important role in the acquisition and transportation of the AAM.Finally, numerical experiments are performed, in order to examine the hypothesis that stratospheric Kelvin waves are generated from the tropospheric intraseasonal variation in the Western Hemisphere. We have not so far obtained a positive result about this hypothesis. Less