【作者】 刘玮；

【导师】 田文寿；

【作者基本信息】 兰州大学 ， 大气物理学与大气环境， 2014， 硕士

【摘要】 本文利用NCEP/NCAR和ERA-Interim再分析资料以及MLS卫星资料,并结合WACCM气候模式探讨了平流层准两年振荡(QBO)对热带对流层顶及深对流活动、残余环流和平流层水汽的影响,得到以下结论：1.QBO引起的对流层顶变化沿赤道呈现带状分布。在热带地区,QBO东风位相下的对流层顶高度(温度)较西风位相下的高(低),而在热带外地区,西风位相下的对流层顶高度(温度)较东风位相下的高(低)。QBO对对流层顶高度的影响存在明显的季节和空间上的差异。QBO对大气上界射出长波辐射(OLR)的影响也存在明显的季节和空间上的差异,其影响在冬、秋季最大,春、夏季相对较小。QBO对OLR的影响在印度尼西亚和西太平洋区域最为显著,在该区域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,而此区域QBO东风位相时对流层顶比QBO西风位相下对流顶高。这从一个侧面反映出QBO可以通过影响热带对流活动进一步影响该区域的对流层顶高度和温度。但是与QBO造成的对流层顶高度异常所不同是,QBO造成的OLR异常并没有呈现出与对流层顶高度异常一样的沿热带的带状分布特征。这说明QBO对对流层顶的影响主要是与QBO引起的风切变异常有关,QBO通过影响热带深对流活动进而影响对流层顶的作用是次要的。进一步的研究发现,QBO造成的浮力频率异常和对流有效位能(CAPE)异常与OLR异常在水平分布上有较一致的变化,说明QBO可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。2.QBO引起的残余环流垂直速度(w*)异常在50-70hPa和10-30hPa存在两个极值中心,并且符号相反。在平流层低层(50-70hPa), QBO西风(东风)位相下残余环流减弱(加强),而在平流层中层(10-30hPa)存在一个更强的相反的残余环流异常,在QBO西风(东风)位相下残余环流加强(减弱)。另外,QBO引起的残余环流异常存在明显的季节变化。冬半球的异常明显大于夏半球。QBO引起的w*、纬向风切变以及温度异常在垂直方向上都存在两极结构和季节差异,其中冬、秋季节的异常较大。QBO的净效果使得平流层低层的残余环流在各个季节都有所减弱,而在平流层中层,QBO对残余环流影响较小。进一步分析QBO对全球穿越对流层顶物质通量的影响发现,在四个季节,QBO西风位相下热带向上穿越对流层顶的物质通量均减少,而东风位相下热带向上穿越对流层顶的物质通量均增加。其中,在秋季和冬季,QBO西风位相下热带向上穿越对流层顶的物质通量减少的幅度较为显著,而夏季和冬季,QBO东风位相下热带向上穿越对流层顶穿过对流层顶物质通量增加幅度较为显著。3.QBO主要通过调节深对流活动、平流层低层温度及残余环流进而调节上对流层下平流层(UTLS)水汽的变化。在对流层上层(100-200hPa), QBO主要通过影响深对流活动进而影响热带水汽的变化,并且这种影响很显著。除夏季外,其余季节QBO不同位相下OLR的分布与上对流层水汽异常的分布均有很好的对应。在平流层低层(50-100hPa), QBO主要通过影响平流层低层的温度和残余环流来影响水汽的变化。冬、秋季节在平流层低层,QBO西风位相下热带区域的对流层顶温度较高,有利于水汽的进入。同时在该区域,QBO引起的异常下沉的残余环流,也有利于水汽向下平流层的输送,另一方面,下沉放热造成的平流层低层加热更有利于水汽进入。反之,QBO东风位相下热带区域的对流层顶温度较低,不利于水汽的进入。同时,QBO引起的异常上升的残余环流,将平流层底的低值水汽向上输送,使平流层低层水汽值更低,另一方面,绝热上升造成的平流层低层降温更不利于水汽进入。在平流层中层(10-30hPa), QBO主要是通过影响残余环流、温度以及与温度有关的化学过程影响该层水汽。冬、秋、夏季平流层中层,QBO主要通过影响温度和残余环流来影响北半球热带和赤道的水汽分布,而南半球水汽的分布更多地受残余环流的影响,因此导致QBO不同位相下南北半球水汽异常分布不同。在该层春季水汽异常相较于其他季节的水汽异常要小。进一步分析QBO的净效应对水汽的影响,我们发现QBO的净效应在上对流层下平流层(UTLS)区域是增湿的效果,其中QBO的净效应对冬季UTLS区域的增湿效果最为显著,在春季最弱。在50-160hPa, QBO对水汽净的影响的季节差异较大,而在10-50hPa其季节差异较小。更多还原

【Abstract】 Using NCEP/NCAR, ERA-Interim reanalysis data and satellite observation data from AURA MLS combined with WACCM climate model, the effects of the quasi-biennial oscillation (QBO) on tropical tropopause, deep convection, Brewer-Dobson circulation and water vapor in stratosphere are analyzed,the main conclusions as following:1.The tropical tropopause anomalies associated with the QBO exhibit a belted distribution along the equator. In the tropics, the tropopause height (temperature) anomalies are higher (lower) during QBO east phase than that during west phase, while in the extra-tropics, the tropopause height (temperature) anomalies are higher (lower) during QBO west phase than that during east phase. The effects of QBO on tropical tropopause have significant seasonal and spatial variations. The effects of QBO on OLR also have significant seasonal and spatial variations. The effects are most significant in winter and autumn while relatively insignificant in spring and summer. And 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. Compared tropical tropopause anomalies associated with the QBO with OLR anomalies in this area, we can claim that QBO can indirectly influence tropopause via modulating tropical convective activities. But 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. This 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 research 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. It suggests that the QBO can affect tropical convective activities through modulating the static stability and the CAPE in the tropical troposphere.2. The Brewer-Dobson circulation vertical velocity (w*) anomalies associated with QBO have two maxima located at50-70hPa and10-30hPa and these two maxima have opposite sign. In the lower stratosphere (50-70hPa), the Brewer-Dobson circulation become stronger (weaker) during the QBO west (east) phase. At the middle stratosphere (10-30hPa), the Brewer-Dobson circulation is stronger (weaker) during QBO the west (east) phase. Moreover, the effects of QBO on the Brewer-Dobson circulation have significant seasonal variations. Vertical velocity anomalies in the winter hemisphere are more stronger than that in the summer hemisphere. The QBO-induced Brewer-Dobson circulation vertical velocity anomalies (w*’), zonal wind shear anomalies and temperature anomalies all exhibit significant two maxima structure and seasonal variations in the vertical direction with stronger anomalies in winter and autumn. The net effect of QBO on the lower stratospheric Brewer-Dobson circulation is weaker in all seasons, while at the middle stratosphere, this effect become smaller. Further analysis of the effect of QBO on the cross-tropopause mass flux reveals that the tropical upward mass flux increases during the QBO east phase while the downward mass flux decrease during the QBO west phase in all seasons. In autumn and winter, the tropical upward mass flux decreases significantly during the QBO west phase. While in summer and winter, the tropical upward cross tropopause mass flux increases significantly during the QBO east phase.3. The effects of the QBO on water vapor in the upper troposphere and lower stratosphere (UTLS) are mainly though modulating tropical deep convective activities, lower stratospheric temperature and Brewer-Dobson circulation. The effect of QBO on the tropical upper troposphere (100-200hPa) is mainly via modulating tropical deep convective activities and this effect is significant. The horizontal distributions of the QBO-induced OLR anomalies and tropical upper tropospheric water vapor anomalies are in accordance with each other in all seasons except for summer. The effect of QBO on the tropical lower stratospheric (50-100hPa) water vapor is mainly via modulating the lower stratospheric temperature and Brewer-Dobson circulation. In winter and autumn, as the tropical tropopause temperature is higher during the QBO west phase, more water vapor of tropospheric origin could enter into the stratosphere. Meanwhile, in the lower stratosphere, QBO-induced anomalous downwelling tends to transport water vapor in upper stratosphere into lower stratosphere. Conversely, the lower tropical tropopause temperature during the QBO east phase leads to less water vapor getting into the stratosphere and QBO-induced anomalous upwelling transport the water vapor in the lower stratosphere upward. The effect of QBO on the tropical middle stratosphere (10-30hPa) is mainly via modulating lower stratospheric Brewer-Dobson circulation, temperature and the chemical process associated with the lower stratospheric temperatures. In winter, autumn and summer, the effect of QBO on water vapor in the north hemisphere and equator is mainly via modulating Brewer-Dobson circulation and temperature while water vapor anomalies in the south hemisphere is mainly influenced by Brewer-Dobson circulation anomalies. Therefore, the distributions of QBO-induce water vapor anomalies in the north hemisphere and south hemisphere are different during different QBO phase. Moreover, the water vapor in spring is much smaller than in other season. Further analysis of the net effect of QBO on water vapor shows that the net effect of QBO is moistening the upper troposphere and lower stratosphere (UTLS). In winter the moistening effect is most significant and in spring this effect is relatively insignificant. At50-160hPa,the effects of the QBO on water vapor have significant seasonal variations. But at10-50hPa this seasonal variations is insignificant.更多还原