Doublet craters on Venus

Of the impact craters on Earth larger than 20 km in diameter, 10-15% (3 out of 28) are doublets, having been formed by the simultaneous impact of two well-separated projectiles. The most likely scenario for their formation is the impact of well-separated binary asteroids. If a population of binary asteroids is capable of striking the Earth, it should also be able to hit the other terrestrial planets as well. Venus is a promising planet to search for doublet craters because its surface is young, erosion is nearly nonexistent, and its crater population is significantly larger than the Earth's. After a detailed investigation of single craters separated by less than 150 km and “multiple” craters having diameters greater than 10 km, we found that the proportion of doublet craters on Venus is at most 2.2%, significantly smaller than Earth's, although several nearly incontrovertible doublets were recognized. We believe this apparent deficit relative to the Earth's doublet population is a consequence of atmospheric screening of small projectiles on Venus rather than a real difference in the population of impacting bodies. We also examined “splotches,” circular radar reflectance features in the Magellan data. Projectiles that are too small to form craters probably formed these features. After a careful study of these patterns, we believe that the proportion of doublet splotches on Venus (14%) is comparable to the proportion of doublet craters found on Earth (10-15%). Thus, given the uncertainties of interpretation and the statistics of small numbers, it appears that the doublet crater population on Venus is consistent with that of the Earth.     

O3浓度增加对冬小麦影响的试验研究

利用OTC 1型开顶式气室对冬小麦进行不同O3 浓度处理的试验研究。结果表明 ,O3 浓度增加 ,冬小麦发育期表现为开花前期有所延迟 ,开花后期的各发育期明显提前 ,生育期缩短 ,植株矮化 ,干物质累积量明显下降。无论是长时期通气处理还是阶段性通气处理 ,产量均明显降低     

Impacts of climate change on the hydrological cycle over France and associated uncertainties

This study deals with the evolution of the hydrological cycle over France during the 21st century. A large multi-member, multi-scenario, and multi-model ensemble of climate projections is downscaled with a new statistical method to drive a physically-based hydrological model with recent improvements. For a business-as-usual scenario, annual precipitation changes generally remain small, except over southern France, where decreases close to 20% are projected. Annual streamflows roughly decrease by 10% (±20%) on the Seine, by 20% (±20%) on the Loire, by 20% (±15%) on the Rhone and by 40% (±15%) on the Garonne. Attenuation measures, as implied by the other scenarios analyzed, lead to less severe changes. However, even with a scenario generally compatible with a limitation of global warming to two degrees, some notable impacts may still occur, with for example a decrease in summer river flows close to 25% for the Garonne.     

SRES A2 情景下中国区域性高温热浪事件变化特征

随全球变暖,应对高温热浪事件是未来现代化城市面临的难题之一。本文利用全球模式-HadAM3p提供的3组不同边界场和初始场驱动区域气候模式系统PRECIS的输出结果,模拟未来情景下中国区域性高温热浪事件发生频率、强度及持续时间的变化趋势。结果表明：全球PRECIS对基准时段（1961-1990年）的高温热浪事件的发生的频率、强度和持续时间及对应的大气环流特征具有较强的模拟能力。相对于基准时段,未来情景下未来时段（2071-2100年）中国各地区的高温热浪的强度增加,发生频率增幅超过了100 %,且持续时间增加30 %以上。此外,观测资料和模拟结果均表明武汉和哈尔滨地区的高温热浪与500 hPa高度场的正距平密切相关。而未来情景下,武汉和哈尔滨地区500 hPa高度场的正距平呈增加趋势,表明这些地区未来可能面临危害更严重的高温热浪事件。     

From impacts assessment to adaptation priorities: the shaping of adaptation policy

Abstract

Under the United Nations Framework Convention on Climate Change (UNFCCC), adaptation has recently gained importance, yet adaptation is much less developed than mitigation as a policy response. Adaptation research has been used to help answer to related but distinct questions. (1) To what extent can adaptation reduce impacts of climate change? (2) What adaptation policies are needed, and how can they best be developed, applied and funded? For the first question, the emphasis is on the aggregate value of adaptation so that this may be used to estimate net impacts. An important purpose is to compare net impacts with the costs of mitigation. In the second question, the emphasis is on the design and prioritisation of adaptation policies and measures. While both types of research are conducted in a policy context, they differ in their character, application, and purpose. The impacts/mitigation research is orientated towards the physical and biological science of impacts and adaptation, while research on the ways and means of adaptation is focussed on the social and economic determinants of vulnerability in a development context. The main purpose of this paper is to demonstrate how the national adaptation studies carried under the UNFCCC are broadening the paradigm, from the impacts/mitigation to vulnerability/adaptation. For this to occur, new policy research is needed. While the broad new directions of both research and policy can now be discerned, there remain a number of outstanding issues to be considered.     

The impacts of global warming on farmers in Brazil and India

How big a threat is global warming to climate-sensitive and economically important sectors such as agriculture in developing countries? How well will farmers be able to adapt to the threats of global warming? This paper attempts to shed light on these two important questions. A cross-sectional analysis is employed to estimate the climate sensitivity of agriculture in Brazil and India. Using panel data from both countries, the study measures how net farm income or property values vary with climate, and consequently, how farmers in India and Brazil react and adapt to climate. The estimated relationships are then used to predict the consequence of alternative climate scenarios. Global warming by the end of the next century could cause annual damages in Brazil between 1% and 39% and between 4% and 26% in India, although some of this effect may be potentially offset by carbon fertilization. These estimates do not factor into account climate-induced extreme weather events.     

不同对流参数化方案试验中凝结加热的特征及对暴雨中尺度模拟结果的影响

使用20 km分辨率的MM5模式,分别选用KUO,GRELL,KAIN-FRITSCH和BETTS-MILLER(以下简称KU,GR,KF和BM)等4种不同对流参数化方案,对1996年8月3~4日石家庄特大暴雨过程作数值模拟试验,分析比较了4个不同试验中网格尺度(显式方案)和次网格尺度(对流参数化方案)凝结加热的水平、垂直分布和时变特征;研究探讨了凝结加热分布及差异对暴雨中尺度模拟结果的可能影响。分析显示,暴雨过程中,4个不同对流参数化方案试验所得到的次网格尺度凝结加热基本都呈单峰特征、加热峰值在对流层中层,但加热层厚度和强度在不同试验间存在差别;4个试验的网格尺度凝结加热的垂直范围表现出较好的一致性,加热重心位于对流层低层,但加热强度仍有所不同;GR和KF及BM试验的总凝结加热率的垂直分布特征主要受其网格尺度凝结加热率特征的影响、加热重心在对流层低层,而KU试验的总凝结加热率的垂直分布特征由其次网格尺度凝结加热率特征所决定、加热重心在对流层中层。研究表明,尽管4个试验在暴雨期间总凝结加热的垂直分布差异并不显著,但对暴雨中尺度模拟的影响却不能忽视。凝结加热的分布特征及演变直接影响与暴雨发生发展密切关联的物理量场的中尺度结构和演变;凝结加热对暴雨中尺度的影响具有连锁性,由加热差异波及局部环流细致结构和强度及其变化的差异,进而影响暴雨发生发展的细致特征。在20 km或更高一些分辨率的条件下,对于描述温带/中纬度暴雨的发展和结构,选用KF方案得到的模拟结果可能更具物理合理性;而KU方案模拟结果容易出现格点气柱的水汽和温度被过量调整的不合理情况。要得到一个可信的中尺度模拟结果,对降水模拟结果进行细化特征的验证、特别是随时间演变特征的验证分析是非常重要的,因为降水的细致演变特征与凝结加热及与之相联系的物理量场的中尺度演变特征密切关联。     

1961-2009年辽河流域气候变化特征及其对水资源的影响

辽河流域是我国七大流域之一,长期以来一直存在水资源严重不足的问题。采用1961-2009年辽河流域境内水文、气象观测数据,研究气象、水文要素历史变化特征,并采用同期和滞后相关分析,建立气象要素与水文要素的最优相关关系。结果表明：辽河流域气候变暖明显,增温幅度远高于全球和中国的同期增温幅度;辽河流域降水量增减趋势不明显,总体上为略减少趋势,但存在明显的少-多-少-多-少5个阶段性变化。辽河流域蒸发量为略减少趋势,春季、夏季是蒸发量较大季节;辽河流域近50年来径流量为减少趋势,经历了偏多-偏少-偏多-偏少4个阶段的变化,最近的1996-2009年经历了年径流量最少阶段,平均年径流量仅为16.2亿 m³,只达到多年平均径流量的58 %、径流量最多年代的32 %。7月、8月是流量最为集中的月份,2个月流量就占到全年的50.24 %,超过全年的一半;辽河流域降水量与径流量有较好的相关关系。在年尺度,径流量与铁岭、法库等周边地区相关系数基本达到0.6左右;在日尺度,日降水量与降水发生后第二日流量相关程度最好,在所有等级上两者相关系数均在0.7以上,在日降水量大于等于25 mm等级上,相关系数最高可达到0.85。