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.

北半球夏季季内振荡 (BSISO) 系统在印度洋上空的向北传播对亚洲夏季风和包括台风在内的极端天气事件产生了显着影响，但许多气候模型未能很好地模拟 BSISO 的北移。在这里，我们建议修改后的参数化可以通过增强气候模型中平均垂直风切变和平均水分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。我们假设气候模型中的BSISO模拟效果不佳可能是由于过于频繁的深层对流导致边界层（BL）中没有大量水分的缘故。为了表示它们，修改后的参数化包括 (a) BL 深度相关对流触发器，(b) 浅对流方案中的底部重扩散，(c) 相对湿度相关的对流夹带率，以及 (d) 降低对流云水向雨水的转化率。修改后的参数化通过增强对流层上层的东风异常增加了北印度洋上的垂直切变，导致正正压涡度异常。增强的正涡度在 BSISO 对流中心北部产生边界层水分辐合和正对流不稳定，诱发下一次对流，从而改善 BSISO 向北传播。随着边界层水分向上输送的增加，修改后的参数化还改善了对流层低层平均水分平流的经向梯度。通过修改参数化增加的海气相互作用往往会加强 BSISO 向北运动的信号。结果表明，修改后的参数化在不同类型的对流参数化中都能正常工作。讨论了将我们的假设应用于其他气候模型以改善BSISO向北传播的可能性。