Development and evaluation of a system of proxy data assimilation for paleoclimate reconstruction
Development and evaluation of a system of proxy data assimilation for paleoclimate reconstruction
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DOI：
10.5194/cp-13-379-2017
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发表时间：
2016-11
影响因子：
4.3
通讯作者：
A. Okazaki;K. Yoshimura
中科院分区：
文献类型：
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作者：
A. Okazaki;K. Yoshimura
抽象的。数据同化（DA）已成功地应用于古气候学领域，重建过去的气候。然而，从替代数据重建的数据已被同化，而不是实际的替代值。这妨碍了充分利用代理服务器中记录的信息。本研究探讨了替代DA的古气候重建的可行性。同位素替代物（冰芯、珊瑚和树木年轮纤维素中的δ 18 O）被同化到模型中：同位素启用的大气环流模型（GCM）和前向替代模型，使用离线数据同化。首先，我们研究了使用观测系统模拟实验（OSSE）的可行性。分析表明，与第一次猜测相比，在同位素比值的再现性的代理，以及温度和降水场，只有同位素信息被同化的显着改善。在低纬度地区，温度和降水的重建技术特别高。这是因为同位素代用指标受低纬度温度和/或降水的强烈影响，而这些温度和/或降水又受到厄尔尼诺-南方涛动（ENSO）在年际时间尺度上的调制。随后，用真实的代理数据进行代理DA。与OSSE相比，重建技能降低。特别是，减少是显着的印度洋，东太平洋和大西洋的代理模型的再现性较低。通过逐步改变实验设计，技能下降被认为是由于大气和代理模型和/或观测质量的歪曲。虽然替代数据的改进还有很多工作要做，但结果充分表明替代数据重建过去气候是可行的。
Abstract. Data assimilation (DA) has been successfully applied in the field of paleoclimatology to reconstruct past climate. However, data reconstructed from proxies have been assimilated, as opposed to the actual proxy values. This prevented full utilization of the information recorded in the proxies. This study examined the feasibility of proxy DA for paleoclimate reconstruction. Isotopic proxies (δ18O in ice cores, corals, and tree-ring cellulose) were assimilated into models: an isotope-enabled general circulation model (GCM) and forward proxy models, using offline data assimilation. First, we examined the feasibility using an observation system simulation experiment (OSSE). The analysis showed a significant improvement compared with the first guess in the reproducibility of isotope ratios in the proxies, as well as the temperature and precipitation fields, when only the isotopic information was assimilated. The reconstruction skill for temperature and precipitation was especially high at low latitudes. This is due to the fact that isotopic proxies are strongly influenced by temperature and/or precipitation at low latitudes, which, in turn, are modulated by the El Nino–Southern Oscillation (ENSO) on interannual timescales. Subsequently, the proxy DA was conducted with real proxy data. The reconstruction skill was decreased compared to the OSSE. In particular, the decrease was significant over the Indian Ocean, eastern Pacific, and the Atlantic Ocean where the reproducibility of the proxy model was lower. By changing the experimental design in a stepwise manner, the decreased skill was suggested to be attributable to the misrepresentation of the atmospheric and proxy models and/or the quality of the observations. Although there remains a lot to improve proxy DA, the result adequately showed that proxy DA is feasible enough to reconstruct past climate.