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Convectively coupled Kelvin and easterly waves in a regional climate simulation of the tropics

机译：热带区域气候模拟中的对流开尔文波和东风波

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This study evaluates the performance of a regional climate model in simulating two types of synoptic tropical weather disturbances: convectively-coupled Kelvin and easterly waves. Interest in these two wave modes stems from their potential predictability out to several weeks in advance, as well as a strong observed linkage between easterly waves and tropical cyclogenesis. The model is a recent version of the weather research and forecast (WRF) system with 36-km horizontal grid spacing and convection parameterized using a scheme that accounts for key con-vective triggering and inhibition processes. The domain spans the entire tropical belt between 45°S and 45°N with periodic boundary conditions in the east-west direction, and conditions at the meridional/lower boundaries specified based on observations. The simulation covers 6 years from 2000 to 2005, which is long enough to establish a statistical depiction of the waves through space-time spectral filtering of rainfall data, together with simple lagged-linear regression. Results show that both the horizontal phase speeds and three-dimensional structures of the waves are qualitatively well captured by the model in comparison to observations. However, significant biases in wave activity are seen, with generally overactive easterlyrnwaves and underactive Kelvin waves. Evidence is presented to suggest that these biases in wave activity (which are also correlated with biases in time-mean rainfall, as well as biases in the model's tropical cyclone climatology) stem in part from convection in the model coupling too strongly to rotational circulation anomalies. Nevertheless, the model is seen to do a reasonable job at capturing the genesis of tropical cyclones from easterly waves, with evidence for both wave accumulation and critical layer processes being importantly involved.
机译：这项研究评估了区域气候模型在模拟两种类型的天气性热带天气扰动方面的性能：对流耦合的开尔文波和东风波。对这两种波动模式的兴趣源于它们潜在的可预测性（提前几周），以及观察到的东风和热带气旋作用之间的强烈联系。该模型是天气研究和预报（WRF）系统的最新版本，具有36公里的水平网格间距和对流，参数化使用对流关键触发和抑制过程进行解释的方案进行了参数化。该区域跨越整个热带带，介于45°S和45°N之间，具有东西向的周期性边界条件，并且根据观测结果指定了子午/下边界的条件。从2000年到2005年，模拟历时6年，时间足够长，可以通过对降雨数据进行时空频谱滤波以及简单的滞后线性回归来建立波浪的统计描述。结果表明，与观测值相比，该模型在质量上都很好地捕获了波浪的水平相位速度和三维结构。但是，在波浪活动中出现了明显的偏差，通常是东风活动过度的东风浪和开尔文活动不足的浪潮。证据表明，波浪活动的这些偏差（也与时间平均降雨的偏差以及模型热带气旋气候的偏差有关）部分是由于模型中的对流与旋转环流异常的耦合太强。然而，该模型被认为在捕捉东风浪中热带气旋的成因方面做得很合理，同时也很重要地证明了海浪聚集和关键层过程的证据。

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