利用RegCM4.0模拟5-8月青藏高原异常加热的下游效应

Simulation of the Effect of Qinghai-Xizang Plateau Anomalous Heating on the Downstream Flow from May to August by RegCM4.0

利用区域气候模式,通过在青藏高原范围设置三种不同强度的大气异常加热率,讨论了5-8月青藏高原加热异常对同期大气环流的影响。研究结果表明:(1)5月份,以4 K·d-1的速率加热高原大气12天后,500 hPa位势高度异常在鄂霍次克海附近为正值区、中国东北及堪察加半岛以南为负值区,出现了疑似波列结构,但200 hPa呈西正东负的二极分布。6月份这种波列结构更加明显,200 hPa形成了完整的类Okhotsk-Japan(OKJ)波列型。(2)在其他月份未出现类似的波列结构。7月,蒙古至鄂霍次克海及日本以东一带地区200 hPa和500 hPa的负位势高度异常连成一片;8月,日本以东地区转为正值中心、鄂霍次克海附近仍维持负异常。(3)随着异常加热的增强,沿6月波列传播路径上的各点的位势高度异常振幅基本成比例增加。(4)射线追踪分析结果显示,5、6月份的波射线路径分布类似,模拟路径位于纬向波数为3和4对应的射线轨迹之间。

The effect of the Qinghai-Xizang Plateau anomalous heating on the downstream atmospheric circula- tion is explored from May to August by using the Regional Climate Model Version 4. 0, and a series of numeri- cal experiments are performed with three different kinds of anomalous heating rates over the plateau for each month. The results are： （ 1 ） After 12 days when the atmosphere over the plateau is heated with the rate of 4 K. d-1 in May, the geopotential height anomaly on 500 hPa is positive near the Okhotsk Sea and negative in Northeast China and to the south of the Kamchatka Peninsula, forming a suspected wave train; however, it turns to be a di- pole pattern on 200 hPa, with positive in the west and negative in the east. When it comes to June, the construc- tion of this wave train becomes more evident, with a complete wave like the Okhotsk-Japan （OK J） pattern ap- pearing on 200 hPa, which includes a positive anomaly over the plateau, a negative anomaly to the south of Lake Baikal, a positive anomaly around the Okhotsk Sea and a negative anomaly to the east of Japan. The nega- tive geopotential height anomaly on 500 hPa over the plateau indicates the baroclinic effect of this anomalous heating. （2） There are no similar wave structures on both 200 hPa and 500 hPa during other months. In July, the geopotential height anomaly is always negative from Mongolia to the Okhotsk Sea and to the east of Japan on both 200 hPa and 500 hPa. In August, the geopotential height anomaly turns to be positive offthe east coast of Ja- pan, and the negative anomaly near the Okhotsk Sea remains to be unchanged. （3） Sensitivity experiments of dif- ferent anomalous heating rates show that, with the strengthening of anomalous heating over the plateau, the geo- potential height anomalies tend to be almost proportionally increased at each point along the wave track on 200 hPa in June. （4） In addition, the analysis of ray tracing shows that the ray paths in May are similar to those in June, and the simulation routte lies between the ray paths with zonal wavenumber 3 and 4, nearer to the one with zonal wavenumber 4. However, in July and August, the ray paths with three different kinds of zonal wavenum- ber are close to each other, which are very different from those in May and June.