The global distribution of sources of atmospheric decadal variability and mechanisms over the tropical Pacific and southern North America
The global distribution of sources of atmospheric decadal variability and mechanisms over the tropical Pacific and southern North America
复制标题
热带太平洋和北美南部大气年代际变率来源和机制的全球分布
DOI：
--
复制
发表时间：
1999
期刊：
影响因子：
--
通讯作者：
F. Zwiers
中科院分区：
文献类型：
--
作者：
D. Rowell;F. Zwiers
摘要了解自然大气年代际变率是气候研究的一个重要组成部分，在这里，我们探讨了其竞争源之间的平衡的地理和季节多样性。 数据提供了一个合奏的几十年大气环流模式实验，强迫观测到的海表温度（SST），并对观测进行了验证。首先，研究了大气内部变率的性质。通过评估其光谱特性，我们驳斥了这样的想法，即内部模式可能会持续或振荡多年的时间尺度上，无论是通过纯粹的内部机制的大气，或通过耦合到陆地表面，相反，他们表现为一个白色噪声过程。其次，更重要的是，海洋强迫的作用，相对于内部的变化，是通过扩展的“方差分析”技术的频率域。还讨论了显著性检验和置信区间。在热带地区，大气年代际变率通常由海洋强迫控制，尽管在某些地区，这种控制程度低于年际时间尺度。在某些季节，在一些热带以外的地区也发现了中度的海洋影响。对观测到的平均海平面气压（MSLP）数据的验证表明，这些影响中的许多是现实的，虽然也发现了一些模型误差。在其他中高纬度地区，局地模拟的年代际变率主要是随机过程，即混沌天气系统的综合效应。第三，我们专注于在两个特定的地区（在那里的模式表现良好）的年代际变率的机制。在热带太平洋，SST对年代际MSLP的相对影响具有很强的季节性，在9月至11月（SON）达到峰值。这是解释注意到，模型大气响应SST在SON比它在其他季节更远一点，在这里它拿起相对更多的十年动力从海洋（西太平洋被较少占主导地位的ENSO时间尺度），导致大气的“信噪比”在SON的十年时间尺度增强。在北美洲南部，强SST的影响被发现在夏季和秋季，导致近几十年来的上升趋势的MSLP。我们认为这是由加勒比海（在一定程度上，热带东北太平洋夏季）的年代际SST变化引起的，这会导致这些地区的异常对流加热，因此更广泛的MSLP响应。
Abstract Understanding natural atmospheric decadal variability is an important element of climate research, and here we investigate the geographic and seasonal diversity in the balance between its competing sources. Data are provided by an ensemble of multi-decadal atmospheric general circulation model experiments, forced by observed sea surface temperatures (SSTs), and verified against observations. First, the nature of internal atmospheric variability is studied. By assessing its spectral character, we refute the idea that internal modes may persist or oscillate on multi-annual time-scales, either through mechanisms purely internal to the atmosphere, or via coupling to the land surface; instead, they behave as a white noise process. Second, and more importantly, the role of oceanic forcing, relative to internal variability, is investigated by extending the ‘analysis of variance’ technique to the frequency domain. Significance testing and confidence intervals are also discussed. In the tropics, atmospheric decadal variability is usually dominated by oceanic forcing, although for some regions less so than at interannual time-scales. A moderate oceanic impact is also found for some extratropical regions in some seasons. Verification against observed mean sea-level pressure (MSLP) data suggests that many of these influences are realistic, although some model errors are also revealed. In other mid- and high-latitude regions, local simulated decadal variability is dominated by random processes, i.e. the integrated effects of chaotic weather systems. Third, we focus on the mechanisms of decadal variability in two specific regions (where the model is well behaved). Over the tropical Pacific, the relative impact of SSTs on decadal MSLP is strongly seasonal such that it peaks in September to November (SON). This is explained by noting that the model atmosphere is responsive to SSTs a little farther west in SON than it is in other seasons, and here it picks up relatively more decadal power from the ocean (the western Pacific being less dominated by ENSO time-scales), causing atmospheric ‘signal-to-noise ratios’ to be enhanced at decadal timescales in SON. Over southern North America, a strong SST impact is found in summer and autumn, resulting in an upward trend of MSLP over recent decades. We suggest this is caused by decadal SST variability in the Caribbean (and to some extent the tropical northeast Pacific in summer), which induces anomalous convective heating over these regions and hence the wider MSLP response.