热带加热异常影响冬季平流层极涡强度的数值模拟

本文利用大气环流模式SAMIL/LASG,通过选择两种对流参数化方案,研究了热带加热异常对热带外平流层模拟的影响。结果表明,因不同对流参数化方案引起的热带对流加热状况的差异,可显著影响模式对北半球冬季平流层极涡强度的模拟偏差。与采用Manabe对流参数化方案相比,采用Tiedtke参数化方案可以显著改善对平流层极涡强度的模拟,使平流层极涡“过强”及极区“过冷”的模拟偏差得到明显改善。研究其中的影响过程发现,由于Manabe方案最大凝结潜热加热高度过低,在对流层中低层;而Tiedtke方案的最大凝结潜热加热位置在对流层中上层,因而Tiedtke(Manabe)方案时热带大气温度在对流层中上层较为偏暖(偏冷),在平流层低层较为偏冷(偏暖)。自秋季开始,与热带对流层高层温度的暖偏差相联系,热带外对流层高层以及热带平流层低层出现伴随的温度冷偏差;与之对应,平流层中纬度从秋季开始也出现持续的温度暖偏差。另外,随着秋冬季节平流层行星波活动的出现,Tiedtke方案时热带外地区行星波1波的强度也明显强于Manabe方案,使得秋冬季节涡动引起的向极热通量在Tiedtke方案时明显偏强,从而造成了冬季平流层极区温度偏暖、极涡强度偏弱。

Numerical Simulations of the Impacts of Tropical Convective Heating on the Intensity of the Northern Winter Stratospheric Polar Vortex

By applying two different convective parameterization schemes, the AGCM SAMIL/LASG was used to investigate the impacts of tropical convective heating on simulated extratropical stratospheric circulation. The results show that different choices of convective parameterization schemes can markedly influence the simulation of boreal winter stratospheric polar vortex intensity. Comparison of the results from SAMIL with the Manabe convective parameterization scheme showed that the simulation of the northern winter stratospheric polar vortex from SAMIL with Tiedtke scheme was effectively improved, particularly the known “cold bias” in the polar region. Because the maximum convective heating rate in the tropics lies in the upper troposphere in the Tiedtke scheme but in the lower troposphere in the Manabe scheme, the simulated temperature from SAMIL-Tiedtke was found to be warmer (cooler) in the tropical upper (lower) troposphere than that from SAMIL-Manabe. Considering the differences between SAMIL-Tiedtke and SAMIL-Manabe, there are marked warmer temperature anomalies in the tropical upper troposphere, which are coupled with marked cooler anomalies in the tropical lower stratosphere. In autumn, cooler temperature anomalies prevail in the midlatitude upper troposphere, which in turn are coupled with warmer temperature anomalies in the midlatitude stratosphere. In addition, the amplitude of planetary wavenumber-1 during autumn-winter in SAMIL-Tiedtke is also stronger than in SAMIL-Manabe. The stronger planetary wavenumber-1 and the warmer midlatitude stratosphere induce a stronger poleward eddy heat flux into the polar region and result in a weaker and warmer stratospheric polar vortex.