Evolution of the Double‐ITCZ Bias Through CESM2 Development
Evolution of the Double‐ITCZ Bias Through CESM2 Development
复制标题
通过 CESM2 开发实现双 ITCZ 偏差的演变
DOI：
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发表时间：
2019
影响因子：
6.8
通讯作者：
R. Neale
中科院分区：
文献类型：
--
作者：
M. Woelfle;C. Bretherton;C. Hannay;R. Neale
共同体地球系统模式第2版（CESM 2）模拟的东太平洋热带辐合带（ITCZ）的结构与其以前的版本CESM第1版相比有很大的改进。作为CESM 2开发过程的一部分，对中间模型版本的检查表明，与更广泛的热带平均值相比，ITCZ的改善与东南太平洋海面温度（SST）相对温暖度的降低密切相关。在CESM2的早期版本中，该区域的冷却SST增强了纬向SST和表面气压梯度，并减少了北半球春季出现的向南SST梯度。东南太平洋SST的改善归因于东南部低云覆盖的增加和相关的短波云强迫。使用固定SST模拟的敏感性试验表明，在两个中间模型版本，119和125之间的云量增加，驱动的去除依赖的自动转换和吸积率云水方差，以及去除二次凝结计划。这两种变化都减少了暖云中的毛毛雨率，增加了层积云到交换积云过渡区的云寿命和云分数。东南太平洋短波云强迫和ITCZ气候学的改善持续通过云微物理参数化的后续变化。尽管东太平洋ITCZ有所改善，但全球平均ITCZ位置和太平洋冷舌偏置强度在整个发展模拟中没有表现出系统的改善。
The structure of the east Pacific Intertropical Convergence Zone (ITCZ) as simulated in the Community Earth System Model version 2 (CESM2) is greatly improved as compared to its previous version, CESM version 1. Examination of intermediate model versions created as part of the development process for CESM2 shows the improvement in the ITCZ is well correlated with a reduction in the relative warmth of southeast Pacific sea surface temperatures (SSTs) as compared to the broader tropical mean. Cooling SST in this region enhances the zonal SST and surface pressure gradients and reduces the anomalously southward SST gradient present in boreal spring in early version of CESM2. The improvements in southeast Pacific SST are attributed to increases in low cloud cover and the associated shortwave cloud forcing over the southeast. Sensitivity tests using fixed SST simulations demonstrate the increase in cloud cover between two intermediate model versions, 119 and 125, to be driven by removal of the dependence of autoconversion and accretion rates on cloud water variance as well as the removal of a secondary condensation scheme. Both of these changes reduce drizzle rates in warm clouds increasing cloud lifetime and cloud fraction in the stratocumulus to trade cumulus transition region. The improvements in southeast Pacific shortwave cloud forcing and ITCZ climatology persist through subsequent changes to the cloud microphysics parameterizations. Despite improvements in the east Pacific ITCZ, the global mean ITCZ position and Pacific cold tongue bias strength do not exhibit a systematic improvement across the development simulations.
影响因子：
4.6
作者：
Hawcroft, Matt;Haywood, Jim M.;Stephens, Graeme
通讯作者：
Stephens, Graeme