Effects of meridional sea surface temperature changes on stratospheric temperature and circulation

Using a state-of-the-art chemistry-climate model,we analyzed the atmospheric responses to increases in sea surface temperature （SST）.The results showed that increases in SST and the SST meridional gradient could intensify the subtropical westerly jets and significantly weaken the northern polar vortex.In the model runs,global uniform SST increases produced a more significant impact on the southern stratosphere than the northern stratosphere,while SST gradient increases produced a more significant impact on the northern stratosphere.The asymmetric responses of the northern and southern polar stratosphere to SST meridional gradient changes were found to be mainly due to different wave properties and transmissions in the northern and southern atmosphere.Although SST increases may give rise to stronger waves,the results showed that the effect of SST increases on the vertical propagation of tropospheric waves into the stratosphere will vary with height and latitude and be sensitive to SST meridional gradient changes.Both uniform and non-uniform SST increases accelerated the large-scale Brewer-Dobson circulation （BDC）,but the gradient increases of SST between 60°S and 60°N resulted in younger mean age-of-air in the stratosphere and a larger increase in tropical upwelling,with a much higher tropopause than from a global uniform 1.0 K SST increase.     

Automated design of gravity-assist trajectories to Mars and the outer planets

In this paper, a new approach to planetary mission design is described which automates the search for gravity-assist trajectories. This method finds all conic solutions given a range of launch dates, a range of launch energies and a set of target planets. The new design tool is applied to the problems of finding multiple encounter trajectories to the outer planets and Venus gravity-assist trajectories to Mars. The last four-planet grand tour opportunity (until the year 2153) is identified. It requires an Earth launch in 1996 and encounters Jupiter, Uranus, Neptune, and Pluto. Venus gravity-assist trajectories to Mars for the 30 year period 1995–2024 are examined. It is shown that in many cases these trajectories require less launch energy to reach Mars than direct ballistic trajectories.Assistant Professor, School of Aeronautics and AstronauticsGraduate Student, School of Aeronautics and Astronautics     

深对流云向平流层的水汽垂直输送问题研究进展

水汽是一种比CO₂温室效应更强的温室气体,在平流层中为光化学反应提供氢氧自由基,凝结成冰晶后还能为臭氧的消耗提供非均相化学反应界面,从而加速臭氧的消耗,因而对气候有重要影响.深对流云对水汽的垂直输送是平流层水汽的重要来源之一,因此研究深对流云向平流层的水汽输送可以为研究气候变化提供参考.回顾了近年来关于深对流云向平流层的水汽垂直输送问题的研究进展,包括水汽垂直输送到平流层的证据、穿透性深对流云的识别方法、水汽被深对流云垂直输送到平流层的机理以及穿透性深对流云对平流层湿度作用的影响因子4个方面,并进行了小结和展望.     

平流层爆发性增温过程中臭氧的垂直分布特征

利用ECMWF资料分析了平流层爆发性增温 (SSW) 过程中臭氧体积混合比的垂直分布的变化, 结果表明: 平流层爆发性增温过程中臭氧体积混合比增大, 而其极大值大多数形成在增温盛期。同时臭氧体积混合比的高值区在爆发性增温过程中随高度发生一定的变化, 据此对其变化分为两类: (1) 下传型: 在增温初期臭氧体积混合的高值区随高度下传至一定高度, 在增温盛期形成极大值然后随高度抬升到大致增温前的高度。 (2) 增厚型: 在增温过程中臭氧体积混合比的高值区厚度增加, 同时附近区域的臭氧体积混合比也增大, 而且在增温前臭氧体积混合比高值区在高度上没有多大变化, 增温开始后有所抬升。平流层爆发性增温过程中臭氧高值区随高度变化的这两种类型, 是由于平流层爆发性增温期间剩余环流对臭氧输送的结果。臭氧变化的下传型是由于在爆发性增温前剩余环流存在着中纬度向极地的明显输送, 并且伴随着极地强烈的下沉运动, 这就使得中纬度输送来的臭氧向下输送, 因此出现了臭氧高值区的下传; 而臭氧变化的增厚型是由于在爆发性增温期间剩余环流不但有中纬度向极地的输送, 而且在极地附近5 hPa高度处出现了上下两支输送气流, 向上的输送气流使中纬度输送来的臭氧向上输送, 而向下的输送气流使中纬度输送来的臭氧向下输送, 进而使增温期间极地附近的臭氧的高值区增厚。同时分析还表明: 平流层爆发性增温过程中中纬度臭氧体积混合比减少。     

纬向平均的风向改变指数与季节转换

通过定义一个能客观定量描述大气环流四维时空变化的风向改变指数WI,用以研究大气环流的时空演变规律和季节转换。在对纬向平均的WI做了经验正交函数(EOF)分析后,得到了其前四个模态。第一模态揭示的是全年平均的WI空间分布的基态。第二模态反映的是WI场的偏差中呈现准调和变化的部分,热带、副热带、温寒带季风区在该模态中均有明显体现。第三模态反映的是WI场的偏差中呈现非调和变化的部分,该部分揭示了因南北半球海陆分布的差异和因大气、海洋流体的非线性效应,其所造成的从春到秋与从秋到春的季节变化的不对称性以及平流层的二月突变现象。第四模态反映的是全球各层盛行风反向区域从春到夏的北进和从夏到秋南撤的现象。     

Aerosol optical depths at Mohal-Kullu in the northwestern Indian Himalayan high altitude station during ICARB

First time observations of spectral aerosol optical depths (AODs) at Mohal (31.9°N, 77.11°E; altitude 1154 m amsl) in the Kullu valley, located in the northwestern Indian Himalayan region, have been carried out during Integrated Campaign for Aerosols, gases and Radiation Budget (ICARB), as a part of the Indian Space Research Organisation-Geosphere Biosphere Program (ISRO-GBP). AODs at six wavelengths are obtained using Microtops-II Sunphotometer and Ozonometer. The monthly mean values of AOD at 500 nm are found to be 0.27 ± 0.04 and 0.24 ± 0.02 during March and April, 2006 respectively. However, their monthly mean values are 0.33 ± 0.04 at 380 nm and 0.20 ± 0.03 nm at 870 nm during March 2006 and 0.31 ± 0.3 at 380 nm and 0.17 ± 0.2 at 870 nm during April 2006, showing a gradual decrease in AOD with wavelength. The Ångstrom wavelength exponent ‘α’ had a mean value of 0.72 ± 0.05, implying reduced dominance of fine particles. Further, the afternoon AOD values are higher as compared to forenoon values by ～ 33.0% during March and by ～ 9.0% during April 2006 and are attributed to the pollutant lifted up from the valley by the evolving boundary layer. Besides the long-range transportation of aerosol particles by airmass from the Great Sahara and the Thar Desert regions to the observing site, the high values of AODs have also been influenced by biomass burning and frequent incidents of forest fire at local levels.     

历史名人轨迹的空间可视化与分析

历史名人的行为轨迹反映了当时的历史文化背景,通过历史名人行为轨迹的空间化和可视化,可以对历史社会状态进行探索和分析。对历史名人的社交关系网络进行可视化研究,有利于剖析当时的政治背景与人物关系。目前,基于GIS的空间人文社会科学深层次分析方法和工具还很少,根据地理位置对历史人物的社交网络进行分时段的研究也很少。本文以玄奘和欧阳修为例,探索了基于WebGIS的历史人物轨迹空间可视化分析方法,基于核密度估计与标准差椭圆的空间分析方法,分析历史名人轨迹点的空间分布特征,统计迁徙指数、首都距、家乡距、成长地距以分析基于距离的轨迹点移动特点;分时段构建了历史名人的空间社交网络,并结合历史背景、名人事迹、名人作品和空间化结果进行了综合分析。分析结果表明： ① 历史名人的迁移轨迹与当时的历史人口迁移趋势基本是一致的,受社会变动影响较大;② 历史名人在事业上升期有更大的社交网络圈,而在人生没落阶段社交网络圈减小。本文对历史名人轨迹的空间可视化与分析方法进行了探索,可以为空间人文社会科学相关领域的分析研究提供参考。     

一次华南双雨带暴雨中的位涡演变与雨带间的相互作用

利用实况资料和WRF中尺度数值模式对2008年6月12日18时—14日00时的华南双雨带暴雨过程进行了数值模拟与诊断分析。结果表明:随着锋面的南压,在锋面的西南方向(广西沿海)生成一低涡,该低涡作为位涡源在中高层表现稳定,分别为锋面雨带(北雨带)与暖区雨带(南雨带)提供正位涡。南雨带对北雨带的作用主要体现在中层(112~114°E附近),南雨带中有位涡的大值向北输送,其输送过程导致两条雨带在该处相连,而在115°E以东的南雨带则无明显的输送过程。同时,北部高空槽中也有大值位涡向北雨带输送,以维持北雨带。研究还发现,本次过程中暖区暴雨与锋面暴雨雨带的结构差异明显,锋面雨带的结构与传统雨带的结构比较一致;有利于暖区暴雨降水的形势主要表现在中高层。RIP轨迹模式的结果也表明,质点在运动过程中位涡的输送源是位于广西沿海的低涡,可见该位涡源对双雨带形成有重要的作用。     

Changes and continuity of wood-pastures in the lowland landscape in Czechia

The term wood-pastures is usually applied to areas with trees or other woody vegetation, scattered through a mainly grazed grassland area, and reflects one of the oldest land use types in Europe, which plays important ecological, agricultural and socio-cultural roles. However, a rapid decline in their area due to changes in land use and a lack of tree regeneration has recently been observed all over Europe, which has led to the necessity of a deeper understanding of their behaviour in relation to different factors via a detailed analysis of the history of the changes in their distribution over space and time. Despite the recent increase in the number of related studies, information on historic patterns of wood-pastures in many European locations, such as Czechia, remains incomplete. The goal of this study is to assess the habitat continuity of current wood-pastures and to analyse the land-use/land-cover changes of historical and current wood-pastures in lowlands and warm landscapes of hills and basins of Czechia. To achieve this, nine sites covering a total area of 98.6 km² were studied in Czechia. The situation on three time horizons (1820–1840s, the early 1950s and today) was analysed. The results have shown that almost all wood-pastures from the 1st half of the 19th century have now been lost and most of the currently existing ones were formed from the 1950s till today. Most wood-pastures, which were lost by the 1950s, were turned into open habitats, such as arable lands, and the ones lost from 1950 were turned into forest. New wood-pastures are mostly formed from open habitats, often in former military areas.     

When does economic development promote mitigation and why?

Is economic development compatible with mitigation? On the one hand, development should promote effective climate policy by enhancing states’ capacities for mitigation. On the other hand, economic growth creates more demand for production, thereby inhibiting emissions reduction. These arguments are often reconciled in the environmental Kuznets curve (EKC) thesis. According to this approach, development initially increases emissions in poor economies, but begins to lower emissions after a country has attained a certain level of development.

The aim of this article is to determine empirically whether the EKC hypothesis seems plausible in light of emissions trends over the birth and implementation of the Kyoto Protocol. Drawing on data from the World Bank World Development Indicators and World Resources Institute Climate Data Explorer, it conducts a large-N investigation of the emissions behaviour of 120 countries from 1990 to 2012. While several quantitative studies have found that economic factors influence emissions activity, this article goes beyond existing research by employing a more sophisticated – multilevel – research design to determine whether economic development: (a) continues to be a significant driver once country-level clustering is accounted for and (b) has different effects on different countries. The results of this article indicate that, even after we account for country-level clustering and hold constant the other main putative drivers of emissions activity, economic development tends to inhibit emissions reduction. They also provide strong evidence that emissions trends resemble the EKC, with development significantly constraining emissions reduction in the South and promoting it in the North.

POLICY RELEVANCE

This article contributes to the understanding of the (changing) role of economic development in shaping emissions activity. It demonstrates the need for a contextualized, country-specific approach for evaluating the effectiveness of economic development in promoting emissions reduction and uncovers new evidence in support of the EKC hypothesis.