Kilometer-scale simulations of trade-wind cumulus capture processes of mesoscale organization
Kilometer-scale simulations of trade-wind cumulus capture processes of mesoscale organization
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中尺度组织信风积云捕获过程的公里级模拟
DOI：
10.1002/essoar.10511907.1
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发表时间：
2022
期刊：
影响因子：
--
通讯作者：
Saffin L
中科院分区：
文献类型：
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作者：
Saffin L
EUREC4A（阐明云和环流耦合在气候中的作用）的国际实地活动收集了观测结果，以更好地了解信风积云、其组织和更大尺度之间的联系，这是气候预测中不确定性的一个重要来源。最近的一项大涡模拟（LES）研究表明，在EUREC4A（2020年2月2日）期间发生的云转变，其中小的浅云发展成为具有疏散层的较大云，这是由于中尺度垂直速度的动力反馈产生的中尺度组织增加造成的。我们发现，尽管分辨率要低得多，但使用英国气象局统一模型的大尺度模拟再现了中尺度组织的增加及其产生过程。模拟发展中尺度组织强，早于LES，更符合卫星观测。敏感性试验与较短的旋转时间，以减少初始组织，仍然有相同的时间发展和敏感性试验与冷池抑制显示只有一个小的影响中尺度组织。这些结果表明，大尺度环流，与垂直速度和水分辐合的增加，是推动中尺度组织的增加，而不是在云的发展达到的阈值。中尺度组织和云对分辨率很敏感，这会影响净辐射的变化，云与观测结果仍然有很大的差异。因此，虽然大尺度模拟有助于了解中尺度组织过程和与大尺度的联系，包括对气候变化的反应，但模拟仍将受到辐射收支方面的重大误差和不确定性的影响。
The international field campaign for EUREC4A (Elucidating the role of clouds and circulation coupling in climate) gathered observations to better understand the links between trade-wind cumulus clouds, their organization, and larger scales, a large source of uncertainty in climate projections. A recent large-eddy simulation (LES) study showed a cloud transition that occurred during EUREC4A (2nd February 2020), where small shallow clouds developed into larger clouds with detrainment layers, was caused by an increase in mesoscale organization generated by a dynamical feedback in mesoscale vertical velocities. We show that kilometer-scale simulations with the Met Office Unified Model reproduce this increase in mesoscale organization and the process generating it, despite being much lower resolution. The simulations develop mesoscale organization stronger and earlier than the LES, more consistent with satellite observations. Sensitivity tests with a shorter spin-up time, to reduce initial organization, still have the same timing of development and sensitivity tests with cold pools suppressed show only a small effect on mesoscale organization. These results suggest that large-scale circulation, associated with an increased vertical velocity and moisture convergence, is driving the increase in mesoscale organization, as opposed to a threshold reached in cloud development. Mesoscale organization and clouds are sensitive to resolution, which affects changes in net radiation, and clouds still have substantial differences to observations. Therefore, while kilometer-scale simulations can be useful for understanding processes of mesoscale organization and links with large scales, including responses to climate change, simulations will still suffer from significant errors and uncertainties in radiative budgets.