Rainfall From Resolved Rather Than Parameterized Processes Better Represents the Present-Day and Climate Change Response of Moderate Rates in the Community Atmosphere Model
Rainfall From Resolved Rather Than Parameterized Processes Better Represents the Present-Day and Climate Change Response of Moderate Rates in the Community Atmosphere Model
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DOI：
10.1002/2017ms001188
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发表时间：
2018-04-01
影响因子：
6.8
通讯作者：
Timmermans, Ben W.
中科院分区：
文献类型：
--
作者：
Kooperman, Gabriel J.;Pritchard, Michael S.;Timmermans, Ben W.
全球气候模型中所使用的对流参数化的不足，常常导致模拟的降雨强度分布呈现失真的情况（即，弱降雨率产生的降雨量过多）。虽然随着社区大气模型的水平分辨率提高到接近25千米，人们发现高百分位降雨强度有令人鼓舞的改善，但我们表明，产生大部分累积降雨量的中等降雨率并没有相应的改善。利用一个旨在强调降水强度和累积降雨量之间联系（不仅仅是频率分布）的统计框架，我们发现，即使分辨率提高，CAM也无法真实地模拟中等降雨率，也无法捕捉它们在气候变化下的增强情况。然而，通过分离对总降雨量的参数化对流贡献和大尺度可分辨贡献，我们发现，尽管存在参数化对流的问题，CAM的大尺度降雨率的强度、地理模式以及对气候变化的响应与观测结果（热带降雨测量任务3B42）、超参数化以及理论预期更为一致。提高CAM的水平分辨率确实改善了总降雨强度的呈现，但这不是由于大尺度降雨率强度的变化，大尺度降雨率对水平分辨率令人惊讶地不敏感。相反，改善是通过大尺度成分对累积降雨总量的相对贡献增加而实现的。对对流时间尺度和夹卷率的敏感性分析证实了这些参数在可能开发尺度感知参数化过程中的重要性，但也揭示了降水频率和总量相互交织所带来的未被认识到的权衡。
Deficiencies in the parameterizations of convection used in global climate models often lead to a distorted representation of the simulated rainfall intensity distribution (i.e., too much rainfall from weak rain rates). While encouraging improvements in high percentile rainfall intensity have been found as the horizontal resolution of the Community Atmosphere Model is increased to similar to 25 km, we demonstrate no corresponding improvement in the moderate rain rates that generate the majority of accumulated rainfall. Using a statistical framework designed to emphasize links between precipitation intensity and accumulated rainfall beyond just the frequency distribution, we show that CAM cannot realistically simulate moderate rain rates, and cannot capture their intensification with climate change, even as resolution is increased. However, by separating the parameterized convective and large-scale resolved contributions to total rainfall, we find that the intensity, geographic pattern, and climate change response of CAM's large-scale rain rates are more consistent with observations (TRMM 3B42), superparameterization, and theoretical expectations, despite issues with parameterized convection. Increasing CAM's horizontal resolution does improve the representation of total rainfall intensity, but not due to changes in the intensity of large-scale rain rates, which are surprisingly insensitive to horizontal resolution. Rather, improvements occur through an increase in the relative contribution of the large-scale component to the total amount of accumulated rainfall. Analysis of sensitivities to convective timescale and entrainment rate confirm the importance of these parameters in the possible development of scale-aware parameterizations, but also reveal unrecognized trade-offs from the entanglement of precipitation frequency and total amount.