In this study we present a diagnostic model for the large-scale tropical circulation (vertical motion) based on the moist static energy equation for first baroclinic mode anomalies (MSEB model). The aim of this model is to provide a basis for conceptual understanding of the drivers of the large-scale tropical circulation changes or variations as they are observed or simulated in Coupled Model Inter-comparison Project (CMIP) models. The MSEB model is based on previous studies relating vertical motion in the tropics to the driving forces of the tropospheric column heating rate, advection of moisture and heat, and the moist stability of the air columns scaled by the first baroclinic mode. We apply and evaluate the skill of this model on the basis of observations (reanalysis) and CMIP model simulations of the large-scale tropical vertical motion. The model is capable of diagnosing the large-scale pattern of vertical motion of the mean state, annual cycle, interannual variability, model-to-model variations and in warmer climates of climate change scenarios; it has spatial correlations of 0.6–0.8 and nearly unbiased amplitudes for the whole tropics (30° S–30° N). The skills are generally better over oceans at large scales and worse over land regions. For the interannual variation of zonally anomalous and zonal mean circulation in tropical Pacific region, it has temporal correlations ~ 0.8. The model also tends to have an upward motion bias at higher latitudes, but still has good correlations in temporal and spatial variations even at the higher latitudes. It is further illustrated how the MSEB model sensitivities can be used to determine the mechanisms in the models that are responsible for the mean state, seasonal cycle and interannual variability such as El Nino. The model clearly illustrates that the seasonal cycle in the circulation is driven by the incoming solar radiation and that the El Nino shift in the Walker circulation results mainly from the sea-surface temperature changes. Overall, the model provides a powerful diagnostic tool to understand tropical circulation change on larger and longer (> month) time scales.

在这项研究中，我们基于第一斜压模式异常的湿静能量方程（MSEB 模型）提出了一个大规模热带环流（垂直运动）的诊断模型。该模型的目的是为在耦合模型比对项目 (CMIP) 模型中观察或模拟的大规模热带环流变化或变化的驱动因素提供概念性理解的基础。MSEB 模型基于先前的研究，这些研究将热带的垂直运动与对流层柱加热速率、湿气和热量的平流以及由第一斜压模式缩放的气柱的湿稳定性的驱动力相关联。我们在对大规模热带垂直运动的观测（再分析）和 CMIP 模型模拟的基础上应用和评估该模型的技能。该模式能够诊断气候变化情景中平均状态、年周期、年际变率、模式间变化和较暖气候的大尺度垂直运动模式；它具有 0.6-0.8 的空间相关性，并且在整个热带地区（30° S-30° N）具有几乎无偏的振幅。这些技能通常在大范围的海洋上更好，而在陆地区域上则更差。对于热带太平洋地区纬向异常和纬向平均环流的年际变化，其时间相关性为~0.8。该模型在高纬度地区也趋于向上运动偏差，但即使在高纬度地区，时空变化也具有良好的相关性。进一步说明了如何使用 MSEB 模型敏感性来确定模型中负责平均状态、季节周期和年际变化（如厄尔尼诺现象）的机制。该模型清楚地表明，环流中的季节性周期是由入射的太阳辐射驱动的，沃克环流中的厄尔尼诺现象主要是由海面温度变化引起的。总体而言，该模型提供了一种强大的诊断工具，可以了解更大和更长（> 月）时间尺度上的热带环流变化。该模型清楚地表明，环流中的季节性周期是由入射的太阳辐射驱动的，沃克环流中的厄尔尼诺现象主要是由海面温度变化引起的。总体而言，该模型提供了一种强大的诊断工具，可以了解更大和更长（> 月）时间尺度上的热带环流变化。该模型清楚地表明，环流中的季节性周期是由入射的太阳辐射驱动的，沃克环流中的厄尔尼诺现象主要是由海面温度变化引起的。总体而言，该模型提供了一种强大的诊断工具，可以了解更大和更长（> 月）时间尺度上的热带环流变化。