Megadroughts in the Indian monsoon region and southwest North America and a mechanism for associated multidecadal Pacific sea surface temperature anomalies
Megadroughts in the Indian monsoon region and southwest North America and a mechanism for associated multidecadal Pacific sea surface temperature anomalies
复制标题
DOI：
10.1175/jcli3675.1
复制
发表时间：
2006-05-01
影响因子：
4.9
通讯作者：
Hu, Aixue
中科院分区：
文献类型：
--
作者：
Meehl, Gerald A.;Hu, Aixue
本文分析了一个全球耦合气候模式（并行气候模式）的1360年控制运行。它模拟了美国西南部和印度季风区的“特大干旱”。特大干旱代表与印度洋和太平洋几十年SST变化的主导模式有关的自然发生的几十年降水变化的极端事件。因此，要深入了解特大干旱的发生，就需要了解产生这种多年代SST变率的机制。对模式变率的分析表明，该机制涉及大气-海洋和热带-中纬度相互作用，其中一个关键因素是太平洋北纬20度和南纬25度附近的风强迫海洋Rossby波，其过境时间确定了十年时间尺度。在西边界，Rossby波反射到赤道太平洋，影响温跃层深度。产生的反馈。包括表面温度。风和副热带环流的强度，产生海温异常和相关的降水和对流加热异常。这些异常与大气Rossby波以及由此产生的中纬度北太平洋和南太平洋异常大气环流型有关。对流表面风应力异常向赤道方向延伸到热带地区，并有助于迫使海洋罗斯贝波接近北纬20度和南纬25度。虽然各种ENSO过程有一些共同的要素，但这种年代际机制在物理上是不同的，主要是由于20 ° N和25 ° S附近的地面风应力异常补充了东部边界的波浪反射，迫使海洋Rossby波提供了年代际时间尺度。这些风场异常与中纬度大气环流异常密切相关，中纬度大气环流异常是几十年SST和热带对流加热异常遥相关的产物。它们本身与美国西南部和南亚与特大干旱有关的降水异常有关。
A 1360-yr control run from a global coupled climate model (the Parallel Climate Model) is analyzed. it simulates "megadroughts" in the southwestern United States and Indian monsoon regions. The megadroughts represent extreme events of naturally occurring multidecadal precipitation variations linked to the dominant pattern of multidecadal SST variability in the Indian and Pacific Oceans. Gaining insight into the occurrence of megadroughts thus requires an understanding of the mechanism that is producing this multidecadal SST variability. Analysis of the model variability shows that the mechanism involves atmosphere-ocean and tropical-midlatitude interactions, with a crucial element being wind-forced ocean Rossby waves near 20 degrees N and 25 degrees S in the Pacific whose transit times set the decadal time scale. At the western boundary, the Rossby waves reflect into the equatorial Pacific to affect thermocline depth. The resulting feedbacks. involving surface temperature. winds, and the strength of the subtropical cells, produce SST anomalies and associated precipitation and convective heating anomalies. These anomalies are associated with atmospheric Rossby waves and resulting anomalous atmospheric circulation patterns in the midlatitude North and South Pacific. Consequent surface wind stress anomalies extend equatorward into the Tropics and help force ocean Rossby waves near 20 degrees N and 25 degrees S. and so on. Though there are some common elements with various ENSO processes, this decadal mechanism is physically distinct mainly because the surface wind stress anomalies near 20 degrees N and 25 degrees S supplement the wave reflections at the eastern boundary to force the ocean Rossby waves that provide the decadal time scale. These wind anomalies are closely tied to the anomalous midlatitude atmospheric circulation that is a product of teleconnections from the multidecadal SST and tropical convective heating anomalies. themselves linked to precipitation anomalies in the southwestern United States and south Asia associated with megadroughts.