Modeling of the atmospheric transport of the cosmogenic radionuclides ¹⁰Be and ⁷Be using the ECHAM5-HAM general circulation model
Modeling of the atmospheric transport of the cosmogenic radionuclides ¹⁰Be and ⁷Be using the ECHAM5-HAM general circulation model
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使用 ECHAM5-HAM 大气环流模型对宇宙放射性核素 1⁰Be 和 ⁷Be 的大气传输进行建模
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发表时间：
2007
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通讯作者：
U. Heikkilä
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作者：
U. Heikkilä
从冰芯等自然档案中获取的宇宙生成放射性核素数据是重建过去太阳活动和地磁场强度以及研究过去气候变化的极好工具。然而，为了正确地解释数据，必须将这些不同的信号分离开来。宇宙产生的放射性核素的产生速率的物理特性是已知的，它是太阳和地磁活动的函数，但是它们从大气到自然档案的传输还没有得到很好的理解。本文的主要目的是填补这一空白，提高我们对宇宙起源放射性核素Be和Be的大气输运的认识。这是利用新的观测资料和ECHAM5-HAM环流模式进行的模拟实验得出的。该模型是一个包含气溶胶物理和化学的三维大气环流模型。本文介绍了在瑞士高海拔（Jungfraujoch, 3580 m）和低海拔（d<s:1> bendorf, 440 m）测得的新的Be和Be降水数据。这些数据用于研究Be/Be比值的高度依赖性，Be/Be比值是空气年龄的代表，对平流层空气进入对流层的入侵很敏感。两站的Be/Be比值比较显示出不同的季节依赖性，表明高海拔站少女峰测得的Be/Be比值受平流层空气的影响比低海拔站<s:1>本多夫测得的Be/Be比值更大。下一步，通过比较模拟和观测到的全球表面空气浓度和Be沉积通量，对模型进行验证。结果表明，观测数据与模式结果吻合较好。另一个模式实验模拟了蒙德极小期（公元1645-1715年）的Be浓度和沉积通量，这是一个太阳活动低和气候较冷的时期。与当前模拟的比较表明，Be通量的主要信号是太阳活动减弱引起的产量增加。气象引起的波动就不那么重要了。然而，在极地地区，由于铍沉积非常低，这些波动相对较大。最后，模拟了太阳活动引起的产量变化对Be沉积的影响，特别是在极地地区。结果与格陵兰冰芯项目（GRIP）在格陵兰峰顶测量的高分辨率（季节性）Be浓度进行了比较。模拟的Be浓度与测量的Be浓度非常吻合。在测量和模拟的浓度中也观察到一个明显的趋势，与太阳活动的趋势平行。这证实了测得的极地冰中Be浓度主要反映了生产变化，例如由太阳活动和地磁场强度引起的变化。当地气象的影响明显较小。
Cosmogenic radionuclide data retrieved from natural archives, such as ice cores, are excellent tools to use for reconstruction of past solar activity and geomagnetic field intensity, and to study past climate changes. To interpret the data correctly, however, it is essential to separate these different signals. The physics of the production rate of the cosmogenic radionuclides as a function of solar and geomagnetic activity is known, but their transport from the atmosphere into natural archives is not well understood. The main goal of this thesis is to fill this gap and to improve our understanding of the atmospheric transport of the cosmogenic radionuclides Be and Be. This was made using new observational data and performing modeling experiments with the ECHAM5–HAM general circulation model. This model is a three–dimensional atmospheric circulation model that includes aerosol physics and chemistry. New Be and Be data measured in precipitation at a high (Jungfraujoch, 3580 m) and a low (Dübendorf, 440 m) altitude stations in Switzerland are presented. These data are used to study the altitudinal dependence of the Be/Be ratio, which is a proxy for the age of air and is sensitive to intrusions of stratospheric air into the troposphere. The comparison of the Be/Be ratio between the two stations shows a different seasonal dependence indicating that the Be/Be ratio measured at the high altitude station Jungfraujoch is more influenced by the stratospheric air than the ratio in Dübendorf. In the next step, the model was validated by comparing modeled and observed surface air concentrations and deposition fluxes of Be worldwide. The results showed good agreement between observational data and model results. Another model experiment was performed to simulate the Be concentrations and deposition fluxes during the Maunder Minimum (1645–1715 AD), a period characterized by low solar activity and a cooler climate. Comparison with a present day simulation shows that the dominant signal in the Be flux is the production increase caused by the lower solar activity. The fluctuations caused by meteorology are less important. Nevertheless, in polar regions these fluctuations are relatively large because of the very low Be deposition. In the last step, the influence of the solar activity induced production changes on the Be deposition was modeled especially in polar regions. The results were compared with high resolution (seasonal) Be concentrations measured at Summit, Greenland within the Greenland Ice Core Project (GRIP). Excellent agreement between the modeled and measured Be concentrations was obtained. Also a clear trend was observed in both the measured and modeled concentrations, parallel with the trend in the solar activity. This confirms that the measured Be concentrations in polar ice reflect mainly production changes, such as those caused by solar activity and geomagnetic field intensity. The effect of local meteorology is significantly smaller.