On the discrepancy of HCl processing in the core of the wintertime polar vortices
On the discrepancy of HCl processing in the core of the wintertime polar vortices
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DOI：
10.5194/acp-18-8647-2018
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发表时间：
2018-06-20
影响因子：
6.3
通讯作者：
Madronich, Sasha
中科院分区：
文献类型：
--
作者：
Grooss, Jens-Uwe;Mueller, Rolf;Madronich, Sasha
在臭氧空洞被发现30多年后，人们相信人们对其形成过程有了非常详细的了解。目前最先进的模型可以再现春季极地平流层中观测到的化学成分，特别是关于卤素催化的臭氧损失的量化。然而，我们在这里报告了在氯活化开始的较少研究期间的模拟和观察之间的差异。在南极，这段时间是在5月到7月之间，模型模拟大大高估了极地夜间极地涡旋内部的关键化学物种之一HCl。在北极也观察到了这种氯化氢的差异。这种差异在不同的模式中存在着不同程度的差异，这里我们讨论了三个独立的模式，即平流层化学拉格朗日模式(CLAMS)和欧拉模式SD-WACCM(全大气社区气候模式的指定动力学版本)和TOMCAT/SlimCat。在拉格朗日化学输运模型中，南极极涡核心中的HCl在6月至8月期间保持不变，而观测表明在这段时间内，HCl持续下降。文中还给出了欧拉模型SD-WACCM和TOMCAT/SlimCat的较小差异。欧拉模式输送方案中的数值扩散被认为是模式间差异的可能原因。虽然缺失的过程尚未被识别，但我们根据差异的特征考察了不同的假设。由于差异的温度相关性，极地平流层云(PSC)粒子(主要由H2O和HNO3组成)对HCl的吸收被低估了，无法解释这一现象。此外，颗粒HNO3的直接光解不能解决这种差异，因为它还会导致冬末氯化学的变化，而这些变化是没有观察到的。星系宇宙射线引起的电离提供了一个额外的NOx和Hox源，只能解释大约20%的差异。然而，模型模拟表明，假设通过一些与太阳高度无关的其他过程来分解颗粒HNO3，例如涉及星系宇宙射线，可能是解决HCl差异的一种可能机制。由于这里报告的差异发生在氯活化期的开始，那里的臭氧损失率很小，所以在南极冬季和春季期间，对整个臭氧层柱损失的影响只有2%左右。
More than 3 decades after the discovery of the ozone hole, the processes involved in its formation are believed to be understood in great detail. Current state-of the-art models can reproduce the observed chemical composition in the springtime polar stratosphere, especially regarding the quantification of halogen-catalysed ozone loss. However, we report here on a discrepancy between simulations and observations during the less-well-studied period of the onset of chlorine activation. During this period, which in the Antarctic is between May and July, model simulations significantly overestimate HCl, one of the key chemical species, inside the polar vortex during polar night. This HCl discrepancy is also observed in the Arctic. The discrepancy exists in different models to varying extents; here, we discuss three independent ones, the Chemical Lagrangian Model of the Stratosphere (CLaMS) as well as the Eulerian models SD-WACCM (the specified dynamics version of the Whole Atmosphere Community Climate Model) and TOMCAT/SLIMCAT. The HCl discrepancy points to some unknown process in the formulation of stratospheric chemistry that is currently not represented in the models.We characterise the HCl discrepancy in space and time for the Lagrangian chemistry-transport model CLaMS, in which HCl in the polar vortex core stays about constant from June to August in the Antarctic, while the observations indicate a continuous HCl decrease over this period. The somewhat smaller discrepancies in the Eulerian models SD-WACCM and TOMCAT/SLIMCAT are also presented. Numerical diffusion in the transport scheme of the Eulerian models is identified to be a likely cause for the inter-model differences. Although the missing process has not yet been identified, we investigate different hypotheses on the basis of the characteristics of the discrepancy. An underestimated HCl uptake into the polar stratospheric cloud (PSC) particles that consist mainly of H2O and HNO3 cannot explain it due to the temperature correlation of the discrepancy. Also, a direct photolysis of particulate HNO3 does not resolve the discrepancy since it would also cause changes in chlorine chemistry in late winter which are not observed. The ionisation caused by galactic cosmic rays provides an additional NOx and HOx source that can explain only about 20% of the discrepancy. However, the model simulations show that a hypothetical decomposition of particulate HNO3 by some other process not dependent on the solar elevation, e.g. involving galactic cosmic rays, may be a possible mechanism to resolve the HCl discrepancy. Since the discrepancy reported here occurs during the beginning of the chlorine activation period, where the ozone loss rates are small, there is only a minor impact of about 2% on the overall ozone column loss over the course of Antarctic winter and spring.