Observed Modulation of the Tropical Radiation Budget by Deep Convective Organization and Lower-Tropospheric Stability
Observed Modulation of the Tropical Radiation Budget by Deep Convective Organization and Lower-Tropospheric Stability
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DOI：
10.1029/2019av000155
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发表时间：
2020-09-01
期刊：
影响因子：
8.4
通讯作者：
Emanuel, K. A.
中科院分区：
文献类型：
--
作者：
Bony, S.;Semie, A.;Emanuel, K. A.
这项研究分析了观测到的每月的热带辐射收支的非季节化和去趋势的变化，并建议，低对流层的稳定性和深对流的空间组织的变化都强烈有助于这种变化。卫星观测表明，平均而言，在热带地区，当深对流更加聚集时，自由对流层更加干燥，深对流云覆盖范围较小，向空间发射的热量增加;因此，深对流聚集的增强与热带地区的辐射冷却有关。热带平均低对流层稳定度的增加也与热带地区的辐射冷却相一致，主要是因为它与更多的海洋低云和太阳辐射的反射增强有关，尽管自由对流层干燥也有助于冷却。对流聚合和对流层低层稳定度对辐射收支调制的贡献是互补的，在很大程度上彼此独立，并且同样强大。它们加在一起，占热带辐射收支方差的60%以上。因此，卫星观测结果与模拟研究提出的深对流的空间组织对地球辐射平衡有重大影响的观点是一致的。这强调了了解控制对流组织和对流层低层稳定度变化的因素的重要性，以及随着气候变暖监测其变化的必要性。简明语言概述热带平均辐射平衡的异常决定了热带气候的时间变化。低层大气的稳定性已被证明会影响这种平衡，因为稳定性的增加有利于低空云层的形成和太阳辐射向太空的反射。模拟研究表明，深对流的空间分布，特别是深云聚集的程度，也可能影响湿度和云层覆盖，从而影响地球系统的辐射平衡。然而，在热带尺度上，云团、湿度和辐射收支之间的关系从未被观察到。通过分析卫星观测的长时间序列，我们发现，低层大气稳定度和对流成团的月变化都与热带地区辐射冷却的变化密切相关，它们对辐射收支的调制的贡献是互补的，同样重要。因此，这些观测结果证实了模拟推论，并强调，为了预测我们的气候的未来，有必要确定深对流的稳定性和聚类将如何随着变暖而变化。关键点热带深对流组织的月变化是利用卫星观测研究的。深对流组织的增强与对流层干燥，高层云减少，观测结果表明，对流组织和低层稳定度对热带辐射收支有着同等和互补的调制作用
This study analyzes the observed monthly deseasonalized and detrended variability of the tropical radiation budget and suggests that variations of the lower-tropospheric stability and of the spatial organization of deep convection both strongly contribute to this variability. Satellite observations show that on average over the tropical belt, when deep convection is more aggregated, the free troposphere is drier, the deep convective cloud coverage is less extensive, and the emission of heat to space is increased; an enhanced aggregation of deep convection is thus associated with a radiative cooling of the tropics. An increase of the tropical-mean lower-tropospheric stability is also coincident with a radiative cooling of the tropics, primarily because it is associated with more marine low clouds and an enhanced reflection of solar radiation, although the free-tropospheric drying also contributes to the cooling. The contributions of convective aggregation and lower-tropospheric stability to the modulation of the radiation budget are complementary, largely independent of each other, and equally strong. Together, they account for more than sixty percent of the variance of the tropical radiation budget. Satellite observations are thus consistent with the suggestion from modeling studies that the spatial organization of deep convection substantially influences the radiative balance of the Earth. This emphasizes the importance of understanding the factors that control convective organization and lower-tropospheric stability variations, and the need to monitor their changes as the climate warms.Plain Language Summary Anomalies of the tropically averaged radiative balance determine the time variations of the tropical climate. The stability of the lower atmosphere has been shown to influence this balance because increased stability favors the formation of low-level clouds and the reflection of solar radiation to space. Modeling studies have suggested that the spatial distribution of deep convection, especially the degree of clustering of deep clouds, could also impact humidity and cloud coverage, and thus the radiative balance of the Earth system. However, the relationships between cloud clustering, humidity, and the radiation budget have never been observed at the scale of the tropics. By analyzing long time series of satellite observations, we show that monthly variations of lower-atmospheric stability and convective clustering are both strongly correlated with variations of the radiative cooling of the tropics and that their contributions to the modulation of the radiation budget are complementary and equally important. These observational results thus confirm modeling inferences and emphasize that to predict the future of our climate, it will be necessary to determine how the stability and the clustering of deep convection will change with warming.Key PointsThe monthly variability of deep convective organization in the tropics is investigated using satellite observations An enhanced organization of deep convection is associated with a drier troposphere, fewer high clouds, and a radiative cooling of the tropics Observations suggest equal and complementary modulations of the tropical radiation budget by convective organization and low-level stability