热带平流层准两年振荡对热带对流层顶和深对流活动的影响

Effects of Quasi-biennual Oscillation on Tropical Tropopause and Deep Convective Activities

利用NCEP/NCAR再分析资料通过合成分析的方法研究了热带平流层准两年振荡(QBO)影响热带对流层顶及深对流活动的基本特征及可能的物理机制。研究发现,QBO对对流层顶和大气射出长波辐射(OLR)的影响存在明显的季节和空间上的差异。QBO对对流层顶和OLR的影响在冬、秋季最大,春、夏季相对较弱。与QBO造成的对流层顶高度和温度异常所不同是,QBO造成的OLR异常并没有呈现出一样的沿热带的带状分布特征,OLR异常沿赤道区域有正有负。另外,QBO对OLR的影响主要在热带对流活跃区域,尤其是在印度尼西亚和西太平洋区域,QBO东风位相下的对流活动要强于QBO西风位相下的对流活动。QBO造成的OLR异常和对流层顶异常在水平分布上有显著的差异,表明QBO对对流层顶的影响主要是与QBO风切变的异常有关,QBO影响热带深对流活动进而影响对流层顶温度的作用是次要的。进一步研究QBO影响对流活动可能的机制发现,QBO造成的浮力频率异常和对流层有效位能(CAPE)异常与OLR异常在水平分布上有较一致的变化,说明QBO不仅通过调节对流层顶高度和温度影响热带的深对流活动,还可以通过调节对流层的静力稳定度、CAPE来影响热带地区深对流活动。

Using NCEP reanalysis data and composite method,the effects of the Quasi-Biennual Oscillation（ QBO） on tropical tropopause and deep convection were analyzed and the possible mechanisms were investigated.The analysis indicates that the effects of the QBO on tropical tropopause and Out going Longwave Radiation（ OLR）have significant seasonal and spatial variations. The effects of the QBO on tropical tropopause and OLR are most significant in winter and autumn while relatively insignificant in spring and summer. The tropical tropopause height and temperature anomalies associated with the QBO exhibit a belted distribution in the tropics while the OLR anomalies have both positive and negative anomalies along the equator. The effect of the QBO on OLR is most significant within the convection active regions within the tropics. In Indonesia and tropical western pacific regions,in particular,the convective activities are stronger during the QBO east phase than that during the QBO west phase. The difference of the horizontal distribution between the QBO-induced tropical tropopause height anomalies and OLR anomalies implies that the effect of the QBO on tropical tropopause is mainly due to the downward propagation of zonal wind shear anomalies induced by the QBO and the indirect QBO effect on tropopause via modulating tropical convective activities is a secondary factor. Further analysis of the possible mechanisms responsible for the effect of the QBO on OLR reveals that the buoyancy frequency anomalies and Convective Potential Energy（ CAPE） anomalies associated with the QBO are spatially in accordance with the QBO-induced OLR anomalies,suggesting that the QBO can affect tropical convective activities not only via modulating the tropical tropopause,but also through modulating the static stability and the CAPE in the tropical troposphere.