Modulation of hydroxyl variability by ENSO in the absence of external forcing.
Modulation of hydroxyl variability by ENSO in the absence of external forcing.
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DOI：
10.1073/pnas.1807532115
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发表时间：
2018-09-04
影响因子：
11.1
通讯作者：
Cohen RC
中科院分区：
文献类型：
--
作者：
Turner AJ;Fung I;Naik V;Horowitz LW;Cohen RC
羟基自由基（OH）是对流层化学的核心，但目前的测量不足以评估它对大气甲烷逐年变化的影响。我们在全球化学-气候耦合模型中使用6,000 y控制模拟来研究OH的自然变率。我们发现，自然的氢氧根变率可以产生（非强迫的）甲烷趋势，与过去几十年观测到的甲烷变化一样大。此外，我们发现OH和La Niña之间存在联系。虽然我们不能直接测量年度全球平均OH，但我们可以利用我们对La Niña的了解来提高我们对OH的理解。反过来，这可能会提高我们对近期甲烷趋势的理解。羟基自由基（OH）是对流层中的主要氧化剂，其波动对甲烷收支的影响近年来一直存在争议，但对OH的测量不足以表征与甲烷相关的全球年际波动。在这里，我们使用一个化学-气候模型对工业化前条件进行6000 y的控制模拟，以量化OH的自然变化和控制这种变化的内部反馈。我们发现，即使在没有外部强迫的情况下，十年来最大OH变化为3.8 0.8%，这在2007-2017年近期甲烷增长的背景下是很大的。我们表明，氢氧根的变化不是一个白噪声过程。小波分析表明，氢氧根变化具有与El Niño-Southern振荡（ENSO）相同的周期性。我们发现氢氧根变率的内在调制，这表明氢氧根可能在未来几十年里表现出快速变化或不变化的时期，这完全是由于内部气候动力学（而不是外部强迫）。经验正交函数分析进一步表明，ENSO是OH变率的主要模式，OH的调制主要通过闪电发生。La Niña与热带太平洋对流的增加有关，这增加了模拟闪电的发生，并允许更多的OH产生。了解OH和ENSO之间的这种联系可以提高对流层氧化能力的可预测性，并有助于阐明当前和历史甲烷趋势的原因。
The hydroxyl radical (OH) is central to tropospheric chemistry, but current measurements are insufficient to assess its effects on year-to-year changes in atmospheric methane. We use a 6,000-y control simulation in a global coupled chemistry-climate model to study the natural variability of OH. We find that natural OH variability can produce (unforced) methane trends as large as the observed changes in methane over the last few decades. Additionally, we find a link between OH and La Niña. While we cannot directly measure annual global mean OH, we can use what we know about La Niña to improve our understanding of OH. This may, in turn, improve our understanding of recent methane trends. The hydroxyl radical (OH) is the primary oxidant in the troposphere, and the impact of its fluctuations on the methane budget has been disputed in recent years, however measurements of OH are insufficient to characterize global interannual fluctuations relevant for methane. Here, we use a 6,000-y control simulation of preindustrial conditions with a chemistry-climate model to quantify the natural variability in OH and internal feedbacks governing that variability. We find that, even in the absence of external forcing, maximum OH changes are 3.8 0.8% over a decade, which is large in the context of the recent methane growth from 2007–2017. We show that the OH variability is not a white-noise process. A wavelet analysis indicates that OH variability exhibits significant feedbacks with the same periodicity as the El Niño–Southern Oscillation (ENSO). We find intrinsically generated modulation of the OH variability, suggesting that OH may show periods of rapid or no change in future decades that are solely due to the internal climate dynamics (as opposed to external forcings). An empirical orthogonal function analysis further indicates that ENSO is the dominant mode of OH variability, with the modulation of OH occurring primarily through lightning . La Niña is associated with an increase in convection in the Tropical Pacific, which increases the simulated occurrence of lightning and allows for more OH production. Understanding this link between OH and ENSO may improve the predictability of the oxidative capacity of the troposphere and assist in elucidating the causes of current and historical trends in methane.
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