A model-model and data-model comparison for the early Eocene hydrological cycle
A model-model and data-model comparison for the early Eocene hydrological cycle
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DOI：
10.5194/cp-12-455-2016
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发表时间：
2016-01-01
影响因子：
4.3
通讯作者：
Pancost, Richard D.
中科院分区：
文献类型：
--
作者：
Carmichael, Matthew J.;Lunt, Daniel J.;Pancost, Richard D.
最近，一系列替代观测为地球水文循环如何应对始新世早期气候变化提供了限制。然而，代理数据与大气环流模式(GCM)模拟的水文学的比较有限，模型间的变异性仍然没有得到很好的表征。在这项工作中，我们在扩展的EoMIP集合(始新世建模对比项目；Lant等人，2012)中对GCM得到的降水和P-E分布进行了相互比较，其中包括以前发表的使用五个边界条件、模式结构和与降水相关的参数化方案不同的GCM进行的早期始新世模拟。我们表明，相对于工业化前条件，所有始新世模拟都模拟了一个强化的水文循环，表现为全球降水和蒸发率的增加。这主要是由于大气中的古二氧化碳升高，导致温度升高，尽管古地理和冰盖差异的影响在某些模型中也很重要。对于给定的二氧化碳水平，全球平均降雨率在不同模型之间差异很大，主要是由于模拟的地面气温不同造成的。降水率对温度的全球敏感度(dp/dt)相似的模式对给定的温度变化显示了不同的区域降水响应。对模式选择特别敏感的地区包括南太平洋、热带非洲和周特提斯地区，这些地区可能是未来代理获取的目标。从始新世早期和中期从树叶化石获得的降水估计与GCM输出的比较表明，GCM通常低估了高纬度的降雨率，尽管不能排除代理可能存在的季节性偏差。通过二氧化碳升高或通过改变约束较差的模型参数值来使这些地区变暖的模型，在模拟与地质数据的匹配方面最成功。现在需要来自低纬度地区的进一步数据和对始新世早期二氧化碳的更好限制来区分这些模型模拟，因为古降水估计有很大的误差。考虑到模拟的降水分布在总体内的明显差异，我们的结果表明，古水文数据提供了一种独立的手段来评估温暖气候的模式技能。
A range of proxy observations have recently provided constraints on how Earth's hydrological cycle responded to early Eocene climatic changes. However, comparisons of proxy data to general circulation model (GCM) simulated hydrology are limited and inter-model variability remains poorly characterised. In this work, we undertake an intercomparison of GCM-derived precipitation and P-E distributions within the extended EoMIP ensemble ( Eocene Modelling Intercomparison Project; Lunt et al., 2012), which includes previously published early Eocene simulations performed using five GCMs differing in boundary conditions, model structure, and precipitation-relevant parameterisation schemes.We show that an intensified hydrological cycle, manifested in enhanced global precipitation and evaporation rates, is simulated for all Eocene simulations relative to the preindustrial conditions. This is primarily due to elevated atmospheric paleo-CO2, resulting in elevated temperatures, although the effects of differences in paleogeography and ice sheets are also important in some models. For a given CO2 level, globally averaged precipitation rates vary widely between models, largely arising from different simulated surface air temperatures. Models with a similar global sensitivity of precipitation rate to temperature (dP/dT) display different regional precipitation responses for a given temperature change. Regions that are particularly sensitive to model choice include the South Pacific, tropical Africa, and the Peri-Tethys, which may represent targets for future proxy acquisition.A comparison of early and middle Eocene leaf-fossilderived precipitation estimates with the GCM output illustrates that GCMs generally underestimate precipitation rates at high latitudes, although a possible seasonal bias of the proxies cannot be excluded. Models which warm these regions, either via elevated CO2 or by varying poorly constrained model parameter values, are most successful in simulating a match with geologic data. Further data from low-latitude regions and better constraints on early Eocene CO2 are now required to discriminate between these model simulations given the large error bars on paleoprecipitation estimates. Given the clear differences between simulated precipitation distributions within the ensemble, our results suggest that paleohydrological data offer an independent means by which to evaluate model skill for warm climates.