A new model of meteoric calcium in the mesosphere and lower thermosphere
A new model of meteoric calcium in the mesosphere and lower thermosphere
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DOI：
10.5194/acp-18-14799-2018
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发表时间：
2018-10
影响因子：
6.3
通讯作者：
J. Plane;W. Feng;J. C. Gómez Martín;M. Gerding;S. Raizada
中科院分区：
文献类型：
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作者：
J. Plane;W. Feng;J. C. Gómez Martín;M. Gerding;S. Raizada
抽象的。流星烧蚀在中层和低热层（MLT）中产生金属原子层。 30 多年来人们就知道，尽管这些元素在球粒陨石中的元素丰度几乎相同，但与 Na 相比，Ca 原子层的贫化程度却高出 2 个数量级以上。相比之下，Ca+离子丰度减少了不到10倍。为了解释这些观察结果，过去十年测量的Ca物种中性和离子-分子反应动力学的大型数据库被纳入整个大气群落气候模型（WACCM）。 Ca 和 Na 的新流星输入函数是使用化学烧蚀模型导出的，该模型已使用流星烧蚀模拟器进行了实验测试，表明 Ca 的烧蚀效率比 Na 低近 1 个数量级。与激光雷达观测结果相比，WACCM-Ca 令人满意地模拟了季节性 Ca 层，但往往高估了火箭质谱和激光雷达进行的 Ca+ 测量。一个关键发现是 CaOH 和 CaCO3 是非常稳定的储存物种，因为它们参与与 O2 和 O 的基本上封闭的反应循环。这一点已通过 CaOH 的实验得到证明，并且在本研究中使用电子结构和统计速率理论对 CaCO3 进行了证明。因此，大部分中性钙被锁定在这些储存库中，通过聚合成流星烟雾颗粒而迅速损失，这解释了钙的极度消耗。
Abstract. Meteoric ablation produces layers of metal atoms in the mesosphere and lower thermosphere (MLT). It has been known for more than 30 years that the Ca atom layer is depleted by over 2 orders of magnitude compared with Na, despite these elements having nearly the same elemental abundance in chondritic meteorites. In contrast, the Ca+ ion abundance is depleted by less than a factor of 10. To explain these observations, a large database of neutral and ion–molecule reaction kinetics of Ca species, measured over the past decade, was incorporated into the Whole Atmosphere Community Climate Model (WACCM). A new meteoric input function for Ca and Na, derived using a chemical ablation model that has been tested experimentally with a Meteoric Ablation Simulator, shows that Ca ablates almost 1 order of magnitude less efficiently than Na. WACCM-Ca simulates the seasonal Ca layer satisfactorily when compared with lidar observations, but tends to overestimate Ca+ measurements made by rocket mass spectrometry and lidar. A key finding is that CaOH and CaCO3 are very stable reservoir species because they are involved in essentially closed reaction cycles with O2 and O. This has been demonstrated experimentally for CaOH, and in this study for CaCO3 using electronic structure and statistical rate theory. Most of the neutral Ca is therefore locked in these reservoirs, enabling rapid loss through polymerization into meteoric smoke particles, and this explains the extreme depletion of Ca.