【作者】 谢飞；

【导师】 田文寿；

【作者基本信息】 兰州大学 ， 大气物理与环境， 2011， 博士

【摘要】 相比于对流层天气系统研究,平流层大气过程的研究比较薄弱。近些年来,随着观测手段的不断提高和中层大气模式的发展,平流层大气过程的研究开始受到越来越多的关注。本论文从平流层研究一些前沿科学问题入手,利用大气环流模式、大气化学-气候模式,结合卫星观测资料、欧洲中心(ECMWF)和NCEP再分析资料研究了气候变化背景下平流层对流层物质交换(STE)的变化特征,分析了STE的变化对平流层水汽浓度及空间分布的影响,并在此基础上进一步探讨了平流层水汽变化以及未来温室气体排放对平流层臭氧的影响。所得的主要结论如下：(1)利用大气环流模式,通过一系列的数值试验研究了臭氧变化对STE的潜在影响,同时对比分析了臭氧和二氧化碳浓度以及海温(SST)变化对STE影响的相对重要性。研究发现,全球臭氧减少15%会使平流层温度降低,最大可达-2.4K,热带上升流会增加7.2%；全球臭氧增15%,会导致平流层温度增加2.1K,同时使热带上升流减少约4%。100hPa以下的臭氧无论是增加还是减少15%,对STE的影响都不是很显著；然而,在70hPa-200hPa区域臭氧增加15%产生的辐射效应与全球臭氧增加15%产生的辐射效应对STE的影响差别不大,这说明对流层上层和平流层下层的臭氧增加是造成热带上升流变化的主要原因。当SST随温室气体增加而增加时,会对STE产生非常显著的影响：热带上升流显著增加,增加幅度达20.4%；但是,如果不考虑温室气体增加引起的海温变化,二氧化碳浓度加倍的辐射效应对STE的影响还不及全球臭氧增加15%产生的影响。(2)利用大气环流模式,通过一系列的数值试验研究了臭氧变化对平流层水汽变化的影响,探讨了臭氧变化影响平流层水汽的主要机制,同时对比分析了大气中二氧化碳浓度加倍产生的辐射效应对平流层水汽变化的影响。研究表明,全球臭氧减少15%会导致更高更冷的对流层顶,因此从对流层进入平流层的水汽会减少。全球臭氧浓度增加15%可使更多水汽从对流层进入平流层,因为其产生的效应使对流层顶变得更低更暖。二氧化碳浓度加倍和海温增加的综合效果,会导致一个更高更暖的对流层顶,同时平流层的水汽也会显著增加。若只考虑二氧化碳浓度加倍的大气辐射效应,其对对流层顶和平流层水汽造成的影响都不显著。(3)利用ECMWF/NCEP再分析资料、AURA MLS、UARS HALOE卫星观测资料以及厄尔尼诺海洋指数(ONI),研究了厄尔尼诺事件和拉尼娜事件对平流层水汽变化的影响。总体来说,厄尔尼诺事件增加了平流层低层的水汽却减少了平流层中层的水汽,拉尼娜活动会使赤道附近(5°S-5°N平均)的平流层低层变得更干燥,但总体上会使热带平流层(25°S-25°N平均)内的水汽增加。拉尼娜活动造成的这种使热带平流层低层变湿的效应,主要是由拉尼娜活动使南半球热带平流层低层区域的热带上升流显著增加所致。厄尔尼诺活动对北半球赤道以外区域热带上升流的作用比对南半球赤道以外区域热带上升流的作用要更强,而ENSO活动的净效应(厄尔尼诺活动与拉尼娜活动产生的效应之和)对南半球平流层水汽的影响要比对北半球平流层水汽的影响更强。(4)利用一个耦合的大气化学-气候模式研究了甲烷排放的增加对平流层水汽变化的影响。结果表明,当甲烷的地表排放量在2000年排放量基础上增加50%时,平流层水汽平均增加了约0.8ppmv。其中,12%的平流层水汽增加来自于甲烷增加对对流层顶的辐射加热作用,而剩余的88%基本上是甲烷化学氧化导致的。南半球平流层甲烷转化为水汽的效率比北半球要高。在北半球平流层中一摩尔甲烷分子大概可以转化为1.63摩尔水汽分子,而在南半球一摩尔甲烷分子大概可以转为1.82摩尔水汽分子。(5)利用一个耦合的大气-化学气候模式,研究了甲烷地表排放的增加对大气中臭氧浓度的影响。结果表明,当甲烷的地表排放量在2000年排放量基础上增加50%时,会使全球中低纬度地区以及北半球高纬度地区的臭氧柱总量增加3%左右,但会使南半球高纬度地区臭氧柱总量增加近8%。在南半球和北半球低纬度地区,臭氧增加主要是由甲烷增加的直接效应所致(这里,我们称甲烷产生的水汽对臭氧的影响为间接效应,甲烷自身对臭氧的影响为直接效应),而在北半球中纬度地区,甲烷增加引起的平流层水汽增加导致的辐射和化学作用(间接效应)对平流层臭氧也有不可忽视的影响。在北极,间接效应甚至超过了直接效应对臭氧的影响。值得特别注意的是,当甲烷的地表排放增加50%时,南极地区春季臭氧柱总量最大增加幅度可达到20%。南极春季臭氧的这种显著增加主要是由甲烷增加引起的化学效应所致,其次是动力传输的作用,而辐射效应的贡献很小。更多还原

【Abstract】 Compared to researches on tropospheric weather and climate, the studies of stratospheric processes are relatively fewer. In recent years, with the improvement of space exploration technology and development of numerical models for the middle atmosphere, more and more attentions have been paid on stratospheric processes. Focused on some hot topics of the stratosphere research, a comprehensive study on stratosphere troposphere exchange (STE) and its effect on stratospheric water vapor is carried using a general circulation model and a state-of-art chemistry-climate model outputs data, satellite observations, European Center for Medium range Weather Forecasting (ECMWF) 40 years reanalysis data and National Centers for Environmental Prediction (NCEP) reanalysis-2 data. The effects of stratospheric water vapor changes and greenhouse gases (GHGs) emissions changes on stratospheric ozone are also analysed. The main conclusions are as following:(1) The potential radiative impact of ozone changes on stratosphere-troposphere exchange (STE) is investigated by a series of general circulation model (GCM) simulations. The impact of an arbitrary 15% O3 change on temperature and cross-tropopause mass flux is compared to the corresponding effect of CO2 doubling. Our analysis shows that a 15% global O3 decrease can cause a maximum cooling of 2.4 K in the stratosphere and-7.2% increase in the tropical upwelling. A global 15% O3 increase gives rise to-2.1 K stratospheric warming and-4% decrease in the tropical upwelling. The effect of a±15% change in O3 below 100 hPa is relatively small. However, the effect of a 15% O3 increase between 200-70 hPa is similar to that of a 15% O3 increase through the whole model domain, suggesting that ozone increases in the UTLS dominate the impact on temperature and tropical upwelling. Sea-surface temperature (SST) changes associated with increasing atmospheric GHGs have a profound impact on the STE. Without corresponding SST changes, the radiative effects of the CO2 doubling on the STE are less significant than a global 15% O3 increase. When the SST changes are considered in the doubled CO2 experiment, the tropical upwelling is significantly increased (by 20.4%).(2) The potential radiative impacts of ozone changes on tropopause, which directly influence stratospheric water vapor, are investigated by a series of general climate model (GCM) simulations. The impacts of an arbitrary 15% O3 change on the tropopause and stratospheric water vapor are compared to the corresponding effects from a doubling of atmospheric CO2. Our analysis shows that a 15% global O3 decrease can results in a higher tropical tropopause and lower tropopause temperatures, and hence less stratospheric water vapor and smaller amplitude of the so-called tape recorder signal. A global 15% O3 increase gives rise to more water vapor entering the stratosphere due to a lower tropopause and higher tropopause temperatures. When the SST changes are considered in the doubled CO2 experiment, the stratospheric water vapor is significantly increased with a much higher, but warmer, tropopause. Without corresponding SST changes, the radiative effects of the CO2 doubling on the stratospheric water vapor are less significant.(3) Using the ECMWF/NCEP reanalysis data, satellite observations from AURA MLS and UARS HALOE, and Oceanic Nino Index (ONI) data, the effects of El Nin-o and La Nin-a events on the stratospheric water vapor changes are investigated. Overall, El Nin-o events tend to moisten the lower stratosphere but dry the middle stratosphere. La Nin-a events are likely to dry the lower stratosphere over a narrow band of tropics (5°S-5°N) but have a moistening effect on the whole stratosphere when averaged over a broader region of tropics between 25°S-25°N. The moistening effect of La Nin-a events mainly occurs in lower stratosphere in the southern hemisphere tropics where a significant 20% increase in the tropical upwelling is caused by La Nin-a events. El Nin-o events have a more significant effect on the tropical upwelling in the northern hemisphere extratropics than in southern hemisphere extratropics. The net effect of ENSO activities on the lower stratospheric water vapor is stronger in the southern hemisphere tropics than in the northern hemisphere tropics.(4) Using a state-of-the-art, fully coupled chemistry climate model-Whole Atmosphere Community Climate Model 3 (WACCM3), the impact of increasing surface emissions of methane (CH4) on stratospheric water vapor is investigated. Relative to 2000 surface emissions of GHGs, a 50% increase in CH4 surface emissions causes an average increase of 0.8 ppmv water vapor in the stratosphere. The radative effect of increased CH4 on the tropopause contributes 12% to the stratospheric water vapor increases, and the chemical process explains the rest of 88%. The oxidation of CH4 into water vapor is more efficient in the southern hemisphere than in the northern hemisphere. In the northern hemisphere:1 mol CH4 molecule→1.63 mol H2O molecule; in the southern hemisphere:1 mol CH4 molecule→1.82 mol H2O molecule.(5) Using a state-of-the-art, fully coupled chemistry climate model WACCM3, the impact of increasing surface emissions of methane (CH4) on ozone is investigated. Relative to the 2000 surface emissions of GHGs, a 50% increase in the CH4 emission would lead to an overall increase of total column ozone (TCO) by-3% at the lower-mid latitudes as well as at the northern high latitudes, and a maximum increase of -8% at the southern high latitudes. In the northern hemisphere mid-high latitudes, the direct and indirect impacts of CH4 increases tend to increase TCO (Here, the indirect impact referes to the impact of water vapor increases caused by oxidation of CH4. The direct impact referes to the impact of increased CH4 on ozone by itself). However, in the northern hemisphere lower latitudes and the whole southern hemisphere the TCO increases are mostly due to the direct impact. It is worth to note that a 50% increase in CH4 surface emission is capable of causing a significant increase of TCO over Antarctic in southern Spring, with a maximum growth rate of up to-20%. It is found that the significant TCO increase is mainly caused by the chemical effect and the dynamical effect plays a second role. The radiative effect of CH4 increases on the stratospheric ozone increase is small.更多还原