Pacific Ocean Forcing and Atmospheric Variability Are the Dominant Causes of Spatially Widespread Droughts in the Contiguous United States
Pacific Ocean Forcing and Atmospheric Variability Are the Dominant Causes of Spatially Widespread Droughts in the Contiguous United States
复制标题
DOI：
10.1029/2018jd029219
复制
发表时间：
2019-03
期刊：
影响因子：
--
通讯作者：
Seung H. Baek;J. Smerdon;R. Seager;A. P. Williams;Benjamin I. Cook
中科院分区：
文献类型：
--
作者：
Seung H. Baek;J. Smerdon;R. Seager;A. P. Williams;Benjamin I. Cook
使用1856-2012年观测到的海表温度（SST）强迫的共同体气候模式第3版（CCM 3）的16个成员集合，研究了海洋和大气变率对美国邻近地区空间分布广泛的夏季干旱（以下简称泛美国大陆干旱）的贡献。所采用的SST强迫场是（i）全球性的或仅限于（ii）热带太平洋或（iii）热带大西洋，以隔离这两个海洋区域对泛美国干旱的影响。模式结果表明，泛CONUS干旱的SST强迫几乎完全来自热带太平洋，因为拉尼娜条件建立了从北方太平洋到北美东部的大气高压，热带大西洋的贡献很小。值得注意的是，在所有三种模式配置中，内部大气变率对泛CONUS干旱发生的影响与海洋强迫一样多或更多，并且可以通过建立一个以美国西部山区为中心的主导高压来单独导致泛CONUS干旱。社区大气模式版本5（CAM 5）也有类似的结果。模式结果与观测记录进行了比较，这支持了模式推断的拉尼娜和内部大气变率对泛CONUS干旱的贡献。虽然在观测记录中可能存在与温暖的大西洋SST的额外关联，但由于观测到的泛美国干旱数量有限，这种关联是模糊的。因此，这种不确定性有可能使观测结果受到20世纪取样的限制，与模式集合中太平洋强迫的主导地位并不矛盾。
The contributions of oceanic and atmospheric variability to spatially widespread summer droughts in the contiguous United States (hereafter, pan‐CONUS droughts) are investigated using 16‐member ensembles of the Community Climate Model version 3 (CCM3) forced with observed sea surface temperatures (SSTs) from 1856–2012. The employed SST forcing fields are either (i) global or restricted to the (ii) tropical Pacific or (iii) tropical Atlantic to isolate the impacts of these two ocean regions on pan‐CONUS droughts. Model results show that SST forcing of pan‐CONUS droughts originates almost entirely from the tropical Pacific because of atmospheric highs from the northern Pacific to eastern North America established by La Niña conditions, with little contribution from the tropical Atlantic. Notably, in all three model configurations, internal atmospheric variability influences pan‐CONUS drought occurrence by as much or more than the ocean forcing and can alone cause pan‐CONUS droughts by establishing a dominant high centered over the U.S. montane west. Similar results are found for the Community Atmosphere Model version 5 (CAM5). Model results are compared to the observational record, which supports model‐inferred contributions to pan‐CONUS droughts from La Niñas and internal atmospheric variability. While there may be an additional association with warm Atlantic SSTs in the observational record, this association is ambiguous due to the limited number of observed pan‐CONUS droughts. The ambiguity thus opens the possibility that the observational results are limited by sampling over the twentieth century and not at odds with the suggested dominance of Pacific Ocean forcing in the model ensembles.