【作者】 舒建川；

【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， 2012， 博士

【摘要】 平流层对流层物质交换与传输直接影响到大气中痕量成分的空间分布并进一步通过化学—辐射—动力过程的相互耦合影响平流层和对流层内的能量收支和环流特征。深入研究平流层对流层物质交换与传输对理解平流层对流层相互耦合和相互作用,更加全面的认识平流层对对流层天气气候的影响具有重要的意义。本文利用全球气候-化学模式,结合再分析资料与卫星观测资料研究了平流层对流层物质在全球尺度上的交换与传输特征,探讨了气候变化对平流层对流层之间物质交换的影响,并进一步对比分析了中低纬以及高纬度区域平流层内化学物质传输特征以及相关的大气过程,得到以下主要结论：一、大气示踪物质从平流层向对流层的传输在中纬度和高纬度地区具有不同的特征。北半球中纬度地区的下传速度高于南半球,而南半球极地地区的下传要比北半球极地地区快。从全球平均来看,大气示踪物质从平流层向对流层的传输速率在北半球冬季最快,在8月至10月期间最弱。由平流层顶附近释放的大气年龄示踪物质计算所得的对流层大气平均年龄(TM大气年龄)最大值为13年,远大于由对流层释放的大气示踪物质得出的平流层大气平均年龄(SM大气年龄),这表明由对流层向平流层的物质传输速度要快于平流层向对流层的传输。南半球对流层的TM大气年龄要大于北半球的值,这揭示了北半球中高纬度的平流层物质传输到地面的速度要比南半球中高纬度要更快。二、敏感性数值试验的分析诊断表明海温升高会加快对流层示踪物质向平流层的上传速度。由海温变化导致的平流层大气平均年龄(SM大气年龄)的变化远小于海温和温室气体共同变化导致的SM大气年龄变化。海温升高会减慢平流层内大气示踪物向下的传输,导致对流层大气平均年龄(TM大气年龄)在平流层内增加。海温增加的幅度越大,平流层内的TM大气年龄越大,对流层内的TM大气年龄越小。海温增加导致的TM大气年龄变化幅度要大于相应的SM大气年龄变化幅度,然而,不同幅度海温和温室气体增加导致的平流层内TM大气年龄的变化要小于平流层内SM大气年龄的变化。当海温和温室气体增加到2100年的条件时,热带上涌提高了约15%。三、本文进一步诊断分析了平流层长寿命大气成分CH4和N20在中低纬度平流层内呈现双峰结构的机制及其与平流层准两年振荡(QBO)和半年振荡(SAO)的联系。分析发现1993和1995年四月附近出现的双峰结构与当年SAO第一周期中较强的西风有关,而数值模拟结果表明重力波活动对SAO西风的发展以及强度有很大的贡献。分析还发现CH4和N20双峰结构中较低的赤道地区槽并不一定伴随着较高的北半球副热带地区的峰。事实上,双峰结构北半球的峰是与副热带的上升相关的,而这主要受SAO. QBO、以及年度振荡(annual oscillation (AO)谐波分量的调节。此外,模拟结果显示赤道地区甲烷的化学反应率有明显的准半年变化周期,最小值发生在SAO西风盛行的时候。然而,最大的甲烷化学损耗异常的发生位置低于双峰结构槽的高度,这表明甲烷的双峰结构槽主要受平流和涡动传输的影响。四、论文最后利用大气化学气候模式模拟分析了平流层准两年振荡(QBO)以及平流层极地爆发性增温的最后增温事件(stratospheric final warming (SFW))对极地平流层内臭氧分布和化学传输的影响。分析表明北半球中纬度的平流层臭氧柱总量在QBO西风位相下较低,这主要是由QBO西风位相伴随的副热带次级上升环流导致的。此外,北极地区的平流层臭氧柱总量在QBO西风位相下的值比东风位相下的值低大约12DU。进一步的分析发现,在QBO西风位相下北极冬季平流层臭氧的累积消耗量要比QBO东风位相下的要大,北极下平流层较大的臭氧消耗与QBO西风位相下的较低温度导致的异相化学反应加快有关,而在上平流层较大的臭氧损耗则由QBO西风位相下温度偏高导致臭氧消耗气相化学反应加快所致。统计分析还发现,上平流层10hPa左右北半球中纬度甲烷浓度异常与高纬度甲烷浓度异常的相关系数为0.55,而在南半球的相关系数只有0.22。此外,诊断分析表明QBO对北极SFW爆发日期没有显著的影响。如果SFW提前爆发,北极地区甲烷的浓度在SFW爆发前后差别较大。SFW提前爆发后,北极地区甲烷浓度明显升高,臭氧柱总量持续增加,直到爆发后2-3天极地平流层的臭氧柱总量达到最大,然后开始减少。如果SFW推迟爆发,SFW爆发前后甲烷的浓度差别较小,北极平流层臭氧柱总量在SFW爆发前就开始减少。更多还原

【Abstract】 The stratosphere troposphere exchange (STE) and tracer transport directly influence the spatial distribution of atmospheric constitutes, and further impact on the atmospheric energy budget and circulation via the chemistry—radiation—dynamic interactions. Detailed investigations on the STE and tracer transport are important for understanding the stratosphere-troposphere coupling and the effect of stratospheric processes on the tropospheric weather and climate. Using a climate-chemistry model, reanalysis data and satellite measurements, the character of global spatial scale exchange and transport between stratosphere and troposphere are analysed and the effect of climate changes on the STE is investiaged in this thesis. In addition, the charateristics of tracer transport in the polar stratosphere are compared with those in the low-middle latitude stratosphere. The main conclusions are summarized as following:1. There are significant hemispheric differences in tracer transport properties at midlatitudes and high latitudes. The downward tracer transport in the northern midlatitude stratosphere is faster than at southern midlatitudes, whereas the descent is stronger in the southern polar region than in the north. On the global average, the fastest stratosphere-to-troposphere transport occurs in northern winter, while from August to October the downward transport from stratosphere is weakest. The maximum troposphere mean (TM) age-of-air derived from an age tracer released in the upper stratosphere can reach13years and is much larger than the maximum stratosphere mean (SM) age-of-air derived from the age tracer released from the troposphere, suggesting that tracer transport from the troposphere to stratosphere is more rapid than from the stratosphere to troposphere. The TM age-of-air in the Southern Hemisphere is older than in the Northern Hemisphere, indicating that the age tracer in the northern midlatitudes and high latitudes is transported down to the surface faster than in the southern midlatitude and high latitude.2. In the stratosphere, increased SSTs tend to accelerate upward transport because of enhanced upwelling from the troposphere. Changes in the SM age-of-air caused by uniform increases in SSTs are much smaller than those caused by the combined changes in SSTs and GHG values. Increased SSTs tends to slow the downward transport in the stratosphere and cause increases in the TM age-of-air. The larger SST increases give rise to a larger TM age-of-air in the stratosphere and a smaller TM age-of-air in the troposphere. Changes in the TM age-of-air caused by increased SSTs are larger in magnitude than corresponding changes in the SM age-of-air. However, the differences between increases in TM age-of-air in the stratosphere because of different SST and GHG increases are smaller than the differences between decreases in the SM age-of-air in the stratosphere caused by different SST and GHG increases. When both SST and GHG values are increased to the2100conditions, the tropical upwelling is enhanced by15%compared to the present-day conditions.3. The mechanisms for the occurrence of the double peak in the long-lived stratospheric tracers, i.e., CH4and N2O, and its connection with the stratospheric semiannual oscillation (SAO) and quasi-biennial oscillation (QBO) are investigated to explain the interannual variations in the stratopause double peak in CH4and N2O. It is found that douple peak distributions in HALOE CH4mixing ratio in April1993and1995are associated with the prominent first cycle of the SAO westerlies, which cause local vertical downwelling in the upper equatorial stratosphere. The sensitivity simulations of the Whole Atmosphere Community Climate Model version3(WACCM3) verified that gravity waves have a large contribution to the development and strength of the SAO westerlies. In addition, the deeper equatorial trough of the double peak is unlikely to always be accompanied by the more prominent Northern Hemispheric lobe. In fact, the Northern Hemispheric lobe of the double peak is attributed to subtropical upwelling, which is mainly affected by the SAO, QBO, and annual oscillation harmonics. The modeled equatorial chemical destruction of CH4shows a semiannual variation, with the minimum occurring when the first and second cycles of SAO westerlies are prevalent. However, the altitude of greatest chemical destruction is below the trough of the double peak, which is dominated by the advection and eddy transport.4. Based on model simulations, the effect of QBO and stratospheric final warming (SFW) on polar ozone and chemical constituents transport are analyzed. Due to the subtropical secondary upwelling induced by the QBO westerlies, the partial column ozone in the northern middle latitude stratosphere is relatively low. The patial column ozone in the northern polar stratosphere during westly QBO phase is about12DU lower than that during eastly QBO phase. The accumulated ozone depletion in the northern polar winter upper and lower stratosphere is larger during westly QBO phase than that during eastly QBO phase. The stronger ozone depletion in the northern polar lower stratosphere is likely associated with the lower temperature, which can lead to more polar stratospheric cloud (PSC) and heterogeneous ozone depletion in the lower polar stratosphere. In the northern polar upper stratosphere, where the temperature is warm enough so that the few PSC shaped, the higher temperature induced by the adiabatic heating from strengthened northern polar vortex descending motion results in more rapid gas-phase ozone reduction reactions. The statistical analysis reveals that the correlation coefficient between midlatitude and high latitude CH4anomalies at10hPa is0.55in the northern hemisphere stratosphere, while it is0.22in the southern hemisphere stratosphere. The simulated results show that the QBO has little impact on the onset date of the stratospheric final warming date. For early SFW events composites, the northern polar CH4mixing ratios in northern polar stratosphere show abrupt increases during the evolution time of SFW. After early SFW events occurred, CH4mixing ratios in the northern polar stratosphere are obviously enhanced. The partial column ozone in the northern polar stratosphere TCO increases continuously until days2-3after the early SFW events onset, and then decreases. For late SFW events with a later onset date, CH4mixing ratios in the northern polar stratosphere show a less significant variation during the evolution time of SFW events, and the partial column ozone in the northern polar stratosphere decreases before the onset of late SFW events.更多还原