【作者】 冼桃；

【导师】 傅云飞；

【作者基本信息】 中国科学技术大学 ， 空间物理， 2014， 博士

【摘要】 在深对流活动中,有一部分对流能穿透对流层顶,这类对流称为穿透性对流,它对上对流层/下平流层(upper troposphere and lower stratosphere,简称UTLS)区域的能量、水汽以及痕量气体的收支起重要的调节作用,而UTLS区域内的辐射平衡也是全球能量平衡的一个重要组成部分。随着卫星观测资料的广泛应用,人们对深对流活动有了一定认识,特别是首部星载测雨雷达的升空,深对流及穿透性对流的内部结构也为人们所了解。然而由于缺乏准确的对流层顶资料,深对流是否穿透对流层顶?穿透性对流对UTLS区域产生什么影响?我们对这些的认识仍然不足。本论文利用多卫星平台多仪器观测资料、探空资料,结合再分析资料,研究了全球对流层顶诸参量的变化特征,率先建立了逐月全球对流层顶诸参量的时空变化数据集。依据逐月对流层顶诸参量的数据集,确定了准确的对流层顶信息,结合星载测雨雷达探测的对流活动,系统地研究了热带副热带地区穿透性对流活动特征及其对UTLS区域温湿结构的影响。论文还就西北太平洋台风活动产生的深对流和穿透性对流对UTLS区域臭氧分布的变化进行了研究,揭示了该地区台风活动对UTLS臭氧变化的影响程度。本论文取得的主要结论如下：(1)揭示了全球热力对流层顶气候特征资料分析结果表明,热力学对流层顶高度在热带地区超过16.5km,在副热带地区出现显著的梯度区,在极区则小于9km,这是地球大气热力平均状态。但是,深对流和穿透性对流活动会造成局地对流层顶高度的扰动,资料分析表明这种扰动小于1km,也表明了大尺度气团的稳定性。对流层顶附近的静力稳定度在对流层顶之上0至1km和1至3km附近,分别出现两个最大值,其中0至1km的最大值位于赤道附近,而1至3km的最大值出现在南北半球10°-15°纬度带内；就季节而言,北半球冬春季节对流层顶以上静力稳定度的最大值位于非洲中部、热带西太平洋和热带东太平洋,而在副热带其静力稳定度明显变小。不同资料对流层顶差异的分析表明,COSMIC与IGRA差异较小,两者对流层顶高度差异0.02±0.54km,气压差异1.61±15.44hPa,温度差异-0.06±2.25K,位温差异-0.52±5.59K；差异的区域特征表明在印度次大陆差异较为明显,这与该地区探空数据质量可信度较低有关。而COSMIC与NCEP对流层顶差异较大：北半球冬季高度-0.20±0.57km,夏季高度-0.16±0.90km;其中NCEP对流层顶在热带明显偏低约2km,而在南半球明显偏高达到2km。研究表明全球多对流层顶事件发生与急流关系密切,急流附近对流层顶厚度可达6km;在北半球冬春季节,东太平洋和大西洋西部由于急流减弱引起对流层Rossby波破碎频发,从而导致这两地区多对流层顶发生频次下降。安第斯山脉地区多对流层顶几乎没有显现季节变化特征,这里全年都可观测到多对流层事件。研究结果还发现,多对流层顶事件发生时,对流层顶之间几乎都伴随着低稳定度的出现。(2)揭示了热带副热带穿透性对流特征研究结果表明热带副热带穿透性对流降水发生频次为0.005～0.05%,且具有较大的区域差异及显著的季节变化特征；陆面穿透性对流频次及强度均高于海面；穿透性对流活动在ITCZ、亚洲夏季风区、非洲中部及亚马逊地区最为活跃。穿透性对流的平均雨顶高度为14～18.5km。论文定义了穿透性对流雨团的等效半径和穿透尺度。研究结果发现95%以上的穿透性对流的等效半径为2.5km,穿透尺度小于4.5km。与洋面相比,陆面穿透性对流雨团的等效半径更大；亚洲夏季风穿透性对流发展深厚,并且雨团水平尺度更宽,因此穿透性对流的等效半径和穿透尺度均大。论文还就穿透性对流的物质输送进行了初步的分析,结果表明亚洲季风区穿透性对流在平流层与对流层交换通量过程中的贡献显著。(3)揭示了深对流及穿透性对流活动对UTLS区域温湿结构的影响程度研究表明陆面、季风区和洋面的深对流及穿透性对流的降水结构存在明显的差异,如陆面这类对流的降水更剧烈、雨团中存在更强的雷达回波(更大的降水率)、雨顶更高等；而洋面的降水强度最弱、雨顶高度也最低；季风区深对流和穿透性对流的降水强度比洋面的大；深对流及穿透性对流的潜热垂直结构也表现了类似区域性特征,其中穿透性对流的区域性差异更为突出。研究还表明大气温度垂直结构与深对流垂直结构存在一定的关系,深对流云体内出现暖异常(与潜热加热有关),深对流云顶附近出现冷异常(与气团绝热上升冷却有关),而在深对流云顶之上存在暖异常,这个暖异常与高层空气绝热下沉增温有关。对于穿透性对流情况,上述现象更为明显。深对流和穿透性对流均造成对流层整层显著的加湿,其中最明显的加湿作用发生在陆面,这里的水汽混合比增加程度可超过40%；在季风区稍弱,而洋面最弱。与此同时,深对流和穿透性对流还造成云顶附近气层脱水,其中深对流的脱水效应比穿透性对流的大。(4)揭示了西北太平洋台风中对流活动对UTLS区域臭氧的影响个例研究发现,台风可造成200hPa以上臭氧柱浓度下降超过-4DU,且臭氧垂直廓线也有明显的亏损,可达-12%或更多。强台风阶段臭氧亏损程度还明显增强,亏损的水平和垂直范围也显著增大。西北太平洋台风雨带中穿透性对流雨团加权平均等效半径为4.0km,加权穿透尺度0.49km。西北太平洋台风可造成台风中心附近10°之内200～50hPa臭氧柱浓度(简称OCUTLS)显著亏损,亏损程度达-5DU,相应的变化百分比为-5%。其中台风云墙内(距离台风中心0.5°-3°环带区)强对流造成显著的OCUTLS负异常。较以往的研究结果,论文率先给出了基于准确对流层顶高度的穿透性对流活动的空间特征尺度,并揭示了穿透性对流活动的垂直结构特征及其相应的温度和湿度垂直结构特征,以及上述特征的区域性差异,增进了我们对穿透性对流活动的认知,并为模式模拟提供了准确的观测事实依据。更多还原

【Abstract】 Deep convection penetrating the tropopause, also known as penetrating convection, plays a crucial role in controlling the budget of energy, water vapor, as well as other trace constituents of the tropical upper troposphere and lower stratosphere (UTLS). In order to understand these important impacts, a number of ways to observe the distribution and frequency of penetrating convection from spaceborne platforms have been proposed. The launch of Tropical Rainfall Measuring Mission (TRMM) Precipitation Radar (PR) provides a new opportunity to study the vertical structure and the intensity of tropical convection. However, since the previous studies do not use the accurate tropopause data, TRMM PR and Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) radio occultation (RO) observations are first combined to understand the characteristics of deep and penetrating convection over tropics and subtropics in this thesis. Meanwhile, we aim to better quantify the deep convective temperature and water vapor signals in the UTLS using multiple datasets. In addition, the contribution of typhoons to ozone variation in the UTLS over the western North Pacific is also estimated. The major findings are presented as follows.(1) Characteristics of Global thermal tropopauseClimatological tropopause height reaches its maximum16.5km over tropics and sharply decreases in subtropics, settling to values of9km at the poles. Meanwhile, the static stability over tropopause shows a unique horizontally and vertically variation, with maxima located0-1km and1-3km above the tropopause. The lower maximum is centered at the equator; the upper maximum has its largest magnitude at10°-15°latitude in both hemispheres. It can be found that static stability maxima are significant over Central Africa, West Pacific and East Pacific between December and May. Moreover, static stability minima occur over the subtropics. The fluctuations of tropopause caused by convective clouds are limited within1km. The results reveal that tropopause over tropics and subtropics is modified by both the convective activity and processes in the UTLS, rather than the convective activity.The mean deviations between COSMIC and IGRA tropopause parameters are (0.02±0.54) km for height,(1.61±15.44) hPa for pressure,(-0.06±2.25) K for temperature and (-0.52±5.59) K for potential temperature. Comparisons of tropopause height between COSMIC and NCEP are (0.20±0.57) km and (-0.16±0.90) km during December-January-February and June-July-August, respectively. NCEP tropopause is2-km higher over the tropics and2-km lower over subtropics.Multiple tropopause events have a strong tendency to follow the subtropical jet and are presented over Andes throughout the year. Thickness of Multiple tropopause events is6km at subtropical jet. During December-May, there is a decrease in multiple tropopause frequency over the eastern Pacific and western Atlantic, which is regions of Rossby wave breaking triggered by jet weakening. Multiple tropopause is accompanied by a low static stability between tropopauses.(2) Characteristics of Penetrating ConvectionIt is found that0.005～0.05%of the total PR pixel numbers can penetrate the tropopause.Penetrating Convection shows regional variability and seasonal variations. Penetrating convection is more frequent over land than over ocean. The highest frequency of penetrating convection is found over ITCZ, Asian Summer Monsoon, Central Africa and Amazon. The average rain top of penetrating convection ranges from14to18.5km.Results also show that penetrating convection clouds are frequently observed within an equivalent radius of2.5km. The vertical distributions show that most of penetrating convective clouds overshoot less than4.5km above the tropopause. The regional statistics indicate that the penetrating convective clouds are wider and taller in the Asian monsoon region.The relationship between stratosphere-troposphere flux and the horizontal extents of penetrating convective clouds is demonstrated to be strong in the Asian monsoon region and weak in the other region of tropics and extratropics. Therefore, penetrating convection of Asian monsoon region may play a significant role in the stratosphere-troposphere exchange.(3) The role of deep convection on temperature and water vapor in the UTLSThere is an evident regional difference in deep convective structures. Deep convection is strongest over land and is weakest over ocean, with monsoonal convection intermediate between them. Latent heat profiles shows similar characteristic. Major regional difference on convective structure are related to updraft and microphysics. Temperature anomaly profile reveals a wave like response to deep convection:warming middle tropopause and upper half of the UTLS and cooling the lower UTLS. The most pronounced temperature signal appears for temperature profiles in proximity to penetrating convection.Both deep and penetrating convection can hydrate the troposphere. The most significant hydration can be found over land (water vapor mixing ration increase more than40%), less over monsoon region, and least over ocean. Meanwhile, deep and penetrating convection can dehydrate the environment near cloud top. Deep convection shows a stronger dehydration.(4) Impact of typhoon on the ozone variations in the UTLS over the northwest PacificDuring the passage of Typhoon Hai-Tang in2005over the northwest Pacific, low values of ozone column and ozone mixing ratio above200hPa are observed right above the typhoon’s track, a result due to the strong upward propagation of air associated with overshooting convection in typhoon. A comparative analysis of different stages of Hai-Tang suggests that in the region where typhoon has higher intensity the troposphere-to-stratosphere transport is enhanced.The statistic analysis for typhoon over the northwest Pacific during2004-2012suggests that0.18%of the convective pixel numbers reach the tropopause, with a weighted averaged equivalent radius and penetrating depth of4.0km and0.49km, respectively. Typhoons cause ozone column between200hPa and50hPa (OCUTLS) decrease significantly within10°radius, with-5DU (about-5%of the local OCTULS). The strongest decrease appears within0.5°-3°radius of the typhoon center.This thesis reveal the deep convection penetrating the accurate tropopause. In addition, we exhibit precipitation, temperature and water vapor structures of penetrating convection in the UTLS and offer new guidance for categorization of convection over land, monsoon and ocean for modeling studies.更多还原