Improved boreal summer intraseasonal oscillation simulations over the Indian Ocean by modifying moist parameterizations in climate models
Improved boreal summer intraseasonal oscillation simulations over the Indian Ocean by modifying moist parameterizations in climate models
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DOI：
10.1007/s00382-021-05822-9
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发表时间：
2021-05
期刊：
影响因子：
4.6
通讯作者：
Young‐Min Yang;Jeong-A Cho;J. Moon;Ki-Young Kim;Bin Wang
中科院分区：
文献类型：
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作者：
Young‐Min Yang;Jeong-A Cho;J. Moon;Ki-Young Kim;Bin Wang
印度洋北部夏季季内涛动（BSISO）系统的北向传播对亚洲夏季风和包括台风在内的极端天气事件有重要影响，但许多气候模式对BSISO的北向运动模拟较差。在此，我们认为修正的参数化可以通过增强平均垂直风切变和平均水汽经向梯度下的涡度异常来改善BSISO向北传播和三维动力和热力学结构。我们假设气候模式中的BSISO模拟较差可能是由于过于频繁的深层对流，而边界层（BL）中没有充足的水分。为了表示它们，修改的参数化包括(a) BL深度相关的对流触发，(b)浅对流方案中底部重扩散率，(c)相对湿度相关的对流携带率，以及(d)对流云水转化为雨水的减少率。修正后的参数化通过加强对流层上层的偏东异常增加了北印度洋上空的垂直切变，引起正正压涡度异常。正涡度增强在BSISO对流中心北部产生边界层水汽辐合和正对流不稳定，诱导下一波对流，从而促进了BSISO向北传播。修正后的参数化还改善了对流层下层平均水汽平流的经向梯度，增加了边界层水汽的向上输送。经改进的参数化分析，海气相互作用的增强使BSISO向北移动的信号趋于强化。结果表明，改进的参数化方法适用于不同类型的对流参数化。讨论了我们的假设可以应用于其他气候模式以改善BSISO向北传播的可能性。
Northward propagation of the boreal summer intraseasonal oscillation (BSISO) system over the Indian Ocean significantly affects Asia summer monsoon and extreme weather events including typhoons but many climate models poorly simulate the norward movement of BSISO. Here, we suggest that the modified parameterizations can improve BSISO northward propagation and three-dimensional dynamic and thermodynamic structures by enhancing the vorticity anomalies under the mean vertical wind shear and meridional gradient of mean moisture in the climate models. We hypothesize that poor BSISO simulation in a climate model may result from too frequent deep convections without abundant moisture in the boundary layer (BL). To represent them, the modified parameterizations include (a) a BL depth-dependent convective trigger, (b) a bottom-heavy diffusivity in the shallow convection scheme, (c) Relative humidity-dependent convective entrainment rate, and (d) reduced conversion rate of convective cloud water to rainwater. The modified parameterizations increase vertical shear over the northern Indian Ocean by strengthened easterly anomalies in the upper troposphere, inducing positive barotropic vorticity anomalies. The enhanced positive vorticities generate boundary layer moisture convergence and positive convective instability in the north of the BSISO convection center, inducing next convection and thereby improving northward propagation of the BSISO. The modified parameterizations also improve the meridional gradient of mean-moisture advection in the lower troposphere with increasing upward transport of moisture in the boundary layer. The increased air-sea interaction by modified parameterization tends to intensify the signal of the northward movement of the BSISO. It is shown that the modified parameterizations work properly in different types of convective parameterizations. The possibility that our hypothesis may be applied to other climate models for improvement of the BSISO northward propagation is discussed.