太阳活动驱动气候变化SGC机制的数理研究

十年至百年时间尺度的气候变化与人类社会关系密切。来自现代气候学和古气候学大量统计分析表明，太阳活动和这一时间尺度的气候变化有很好的相关性。据此，不少学者指出太阳活动强度周期性的变化驱动了这一时间尺度的气候变化。然而对这一观点一直存在众多反对意见。一部分认为，来自于统计研究的结果还不足以证明太阳活动是十年～百年时间尺度气候变化的动力源，因为地球气候系统内部海－气交换的周期性变化也能产生类似周期的气候变化。另一部分认为，由于至今没有较为令人信服的机制能够解释太阳活动对气候变化的影响，因此不能断定就是太阳活动驱动了气候变化。研究太阳活动驱动气候变化的机制已成为目前太阳活动与气候变化间关系研究领域最为迫切有待解决的问题。 目前，在太阳活动和气候变化联系机制研究领域主要存在着三类理论：1）太阳总辐射影响机制：该机制认为，太阳活动强度的变化引起了太阳总辐射量的周期性变化，从而导致了地球气候变化；2）太阳紫外辐射变化影响机制：该机制认为，太阳活动周期中占太阳总辐射9％的太阳短波辐射的变化量占太阳总辐射变化量的32％，短波辐射变化将直接影响地球中层大气热平衡和动力状态，中层大气的变化以行星波的形式传递到低层大气，从而影响地球气候；3）空间天气影响机制：该机制认为太阳活动造成空间环境中的各种高能粒子通量发生相应的变化（如银河宇宙射线、太阳宇宙射线、相对论电子等），高能粒子通量影响低空大气中的云量，云量变化改变了气候系统能量平衡，从而驱动气候变化。70年代以来，欧美利用卫星平台对太阳总辐射进行了观测。目前的结果表明，在一个太阳活动周期内太阳总辐射的变化仅有0.1％。根据目前的气候理论如此小的辐射能量变化还不足以引起显著的气候变化。对于紫外辐射变化影响机制，虽然观测到的短波辐射变化足以引起中层大气的热状态和动力状态的变化，但目前对中低层大气的联系机制还缺乏长时间的观测数据支持。20世纪60年代以来，在空间物理学家的努力下，发展了空间天气影响机制（这里简称空间天气机制）。空间天气机制目前主要形成两大次级理论，1）离子诱导成核机制（IMN机制）；2）空间天气－全球电路－静电云微物理机制（SGC机制）。离子诱导成核机制认为银河宇宙射线通量的变化能够通过离子诱导成核过程影响云层中云滴的粒子谱，导致全球的云量变化。然而随着对银河宇宙射线通量变化和全球云量间关系研究的深入人们发现，银河宇宙射线通量的变化不但仅与低层云云量有较好的相关性，而且呈现较强的纬度分异。这些都无法运用离子诱导成核理论来进行解释。空间天气－全球电路－静电云微物理机制（SGC机制），是通过对天际尺度空间天气变化与气象要素间的统计研究而建立起来。在这一时间尺度上，海气作用等因素被排除，太阳活动成为引起天气要素变化唯一的影响因子。该机制不但能有效地解释银河宇宙射线、太阳宇宙射线和相对论电子等引起的低空大气变化，而且更能解释低层大气响应的纬度分异性。同时该机制还有机地将离子诱导成核理论融入。因此，该机制可能是当前最接近太阳活动与气候变化间联系真是面目的理论。然而，该理论目前仅仅完成了理论框架体系，对静电云微物理过程进行了初步探讨，还需进行大量的定量研究。本文主要在该机制的理论框架体系下，初步尝试了定量化研究，主要建立与该机制有关的三个物理模型：1）全球电路模型；2）准静止状态下层云中电荷分布模型；3）较为完善的静电云微物理模型。 1． 全球电路模型 本文的全球电路模型，运用更为精确的银河宇宙射线成因电荷分布模型和放射性成因电荷分布模型模拟全球低空大气电荷分布，并引入了太阳活动对电荷产率的影响，同时采用了更为准确的全球地面高程数据和地表气溶胶数据，并首次引入平流层火山成因的超细气溶胶层，探讨它对全球电路的影响。通过模拟结果表明： 1） 本全球电路模型输出结果与实测数据有较好的对应，能够反映全球电路的基本特征，以及太阳活动对全球电路的影响。 2） 受太阳活动的影响，大气电阻发生明显的变化，各地大气电阻值的变化与当地的地磁纬度密切相关，即太阳活动对全球电路的影响具有很强的纬度效应，在火山活动平静期高低纬度全球电路对太阳活动的响应存在着10％～25％的差异。 3） 火山活动高峰期，高纬度中高平流层中的硫酸在离子诱导成核机制的作用下形成超细气溶胶层，由于该超细气溶胶层的存在造成全球电路对太阳活动响应的纬度效应进一步增大。在火山活动高峰期高低纬度大气柱电阻对太阳活动响应的差异可达45～85％。这造成在太阳活动强度变化过程中高纬度和低纬度地区大气补偿电流出现相反的变化。 2． 准静止状态下层云中电荷分布模型 目前通过飞机平台对非对流云系中电荷分布的观测还刚刚起步（以往的观测均来自对通过山顶观测站云层的观测，观测误差较大；以飞机为平台，穿越云层进行观测，精度较高），而对层云中电荷分布的定量模拟更是鲜见。本文尝试建立了这一模型，结果表明： 1） 本模型的计算结果得到在标准状态下云层上下边界层中云滴带电量为50～100e（e为基本带电单位），这与Beard（2004）进行的野外观测结果对应良好。云层电荷主要集中在云边界层中，在云顶层富集正气溶胶、带正电云滴，在云滴富集负气溶胶与带负电云滴。云滴和气溶胶上吸附的电荷量受大气补偿电流、云滴和气溶胶粒度、云滴和气溶胶浓度、云层高度影响显著。 2） 太阳活动引起的大气补偿电流的变化能造成低层云边界层中云滴带电量发生显著的变化，而对高层云的影响较小。结合静电云微物理过程低层云中得电荷分布将对低层云的理化特性产生较大影响，从而引起天气、气候变化。 3． 静电云微物理模型 Tinsley（2000，2001）的静电云微物理过程模型计算结果表明，带电云滴和气溶胶（包括成冰核、云凝结核），在长程斥力和短程吸引力（无论云滴带电状态如何）的作用下，碰撞过程均会发生相应变化。本文在Tinsley（2000，2001）静电微物理模型的基础上，在模型中引入小颗粒的惯性参量和云滴的重位移参量，采用新的流态模型，将参与碰撞的小颗粒的粒径范围拓展到0.1～10μm。在此基础上，运用导电面方法讨论静电云微物理过程，和原有映射电荷方法结果进行了对比。结果表明： 1） 在考虑了云滴或粒子上所带电荷在另一方上产生的映射电荷的情况下，在低层云中带电云滴与0.1～3.0μm粒径的带电粒子间的碰撞效率与不带电条件下所得的碰撞效率差异明显，随粒子所带电量的增长，碰撞效率逐步增加。而在高层大气中由于梯度力的作用控制了碰撞过程，因此静电力对碰撞过程的影响较小。粒径大于3.0μm的粒子，随着粒子质量的增加碰撞过程将受粒子自身惯性主导，静电力对这一范围内云滴－粒子的碰撞没有影响。 2） 在受静电力主导的粒子粒径范围内，随粒子密度的增大，粒子质量增加，粒子的碰撞效率随粒子的密度增大而减小。 3） 映射电荷方法和导电面方法的差异仅在“Greenfield Gap”区域表现的较为显著。在“Greenfield Gap”区域导电面方法获得的粒子碰撞效率显著高于映射电荷方法所得值。随云滴与小颗粒粒径比增大两种方法所得结果的差异逐步减小。 通过以上三个模型的模拟得到以下推论：1）与高层云相比较低层云更易受到太阳活动引起的空间环境变化的影响。而且低空大气对太阳活动的响应具有纬度效应。这与Svensmark等（2000），Kniveton等（2004）统计研究结果吻合。2）火山活动增强了全球电路对太阳活动响应的纬度差异。3）太阳活动－空间环境变化－全球电路－云静电物理过程能使太阳活动成为“小冰期”主要驱动力，太阳活动的强弱变化控制了小冰期的起止。随着太阳活动减弱，极地降雪、云量和赤道雷暴系统产生的总上升电流构成的正反馈系统加速了“小冰期”的变冷过程。对于更长时间尺度的“Milankovich”周期，受太阳常数和太阳辐射全球分布的变化，总上升电流发生相应的调制，通过SGC机制对气候产生一定影响。

Non-clinical outcomes of antiretroviral therapy for HIV/AIDS in developing countries: a systematic literature review

The impacts of antiretroviral therapy on quality of life, mental health, labor productivity, and economic wellbeing for people living with HIV/AIDS in developing countries are only beginning to be measured. We conducted a systematic literature review to analyze the effect of antiretroviral therapy (ART) on these non-clinical indicators in developing countries and assess the state of research on these topics. Both qualitative and quantitative studies were included, as were peer-reviewed articles, gray literature, and conference abstracts and presentations. Findings are reported from 12 full-length articles, 7 abstracts, and 1 presentation (representing 16 studies). Compared to HIV-positive patients not yet on treatment, patients on ART reported significant improvements in physical, emotional and mental health and daily function. Work performance improved and absenteeism decreased, with the most dramatic changes occurring in the first three months of treatment and then leveling off. Little research has been done on the impact of ART on household wellbeing, with modest changes in child and family wellbeing within households where adults are receiving ART reported so far. Studies from developing countries have not yet assessed non-clinical outcomes of therapy beyond the first year; therefore, longitudinal outcomes are still unknown. As ART roll out extends throughout high HIV prevalence, low-resource countries and is sustained over years and decades, both positive and adverse non-clinical outcomes need to be empirically measured and qualitatively explored in order to support patient adherence and maximize treatment benefits.

Improving the use of asset-building financial services by Latino immigrants in Langley Park, Maryland

Gemstone Team ANSWER Poverty (Assessing the Need for Services Which Effectively Reduce Poverty)

Is there a decline in marine phytoplankton?

Phytoplankton account for approximately 50% of global primary production, form the trophic base of nearly all marine ecosystems, are fundamental in trophic energy transfer and have key roles in climate regulation, carbon sequestration and oxygen production. Boyce et al.1 compiled a chlorophyll index by combining in situ chlorophyll and Secchi disk depth measurements that spanned a more than 100-year time period and showed a decrease in marine phytoplankton biomass of approximately 1% of the global median per year over the past century. Eight decades of data on phytoplankton biomass collected in the North Atlantic by the Continuous Plankton Recorder (CPR) survey2, however, show an increase in an index of chlorophyll (Phytoplankton Colour Index) in both the Northeast and Northwest Atlantic basins3, 4, 5, 6, 7 (Fig. 1), and other long-term time series, including the Hawaii Ocean Time-series (HOT)8, the Bermuda Atlantic Time Series (BATS)8 and the California Cooperative Oceanic Fisheries Investigations (CalCOFI)9 also indicate increased phytoplankton biomass over the last 20–50 years. These findings, which were not discussed by Boyce et al.1, are not in accordance with their conclusions and illustrate the importance of using consistent observations when estimating long-term trends.

An Absence of Ghosts: cultural and theatrical translation in the British Reception of The Mysteries-Yiimimangaliso

Mark Dornford-May’s widely-acclaimed adaptation of the medieval English Chester “mystery” plays, The Mysteries-Yiimimangaliso, reveal the extent to which theatrical translation, if it is to be intelligible to audiences, risks trading in cultural stereotypes belonging to both source and target cultures. As a South African production of a medieval English theatrical tradition which subsequently plays to an English audience, The Mysteries-Yiimimangaliso enacts a number of disorientating forms of cultural translation. Rather than facilitating the transmission of challenging literary and dramatic traditions, The Mysteries-Yiimimangaliso reveals the extent to which translation, as a politically correct - and thus politically anaemic - act, can become an end in itself in a globalised Anglophone theatrical culture.

Sr-Nd-Pb Isotope Evidence for Ice-Sheet Presence on Southern Greenland During the Last Interglacial

To ascertain the response of the southern Greenland Ice Sheet (GIS) to a boreal summer climate warmer than at present, we explored whether southern Greenland was deglaciated during the Last Interglacial (LIG), using the Sr-Nd-Pb isotope ratios of silt-sized sediment discharged from southern Greenland. Our isotope data indicate that no single southern Greenland geologic terrane was completely deglaciated during the LIG, similar to the Holocene. Differences in sediment sources during the LIG relative to the early Holocene denote, however, greater southern GIS retreat during the LIG. These results allow the evaluation of a suite of GIS models and are consistent with a GIS contribution of 1.6 to 2.2 meters to the =4-meter LIG sea-level highstand, requiring a significant sea-level contribution from the Antarctic Ice Sheet.

The Palisades is a key reference site for the middle Pleistocene of eastern Beringia: New evidence from paleomagnetics and regional tephrostratigraphy

The Palisades, in central Alaska, is one of the most prominent exposures of Quaternary sediments on the Yukon River. Perennially-frozen silt and sand at the Palisades are presently thought to preserve paleoenvironmental records from the Holocene to ~Marine Isotope Stage (MIS) 8 and, beneath a major unconformity, the earliest Pleistocene (~2 Ma). We present new paleomagnetic and tephrochronologic constraints that substantially revise the age of the sediments at the Palisades. We describe 15 new tephra beds, including five beds below the prominent PAL tephra that correlate to known tephra with independent age control from other sites in eastern Beringia. These five known tephra include Chester Bluff tephra, which is present in east-central Alaska and the Yukon, and the newly named Alyeska Pipeline and Taylor Highway tephra from central Alaska; all are constrained to the middle Pleistocene. Paleomagnetic transects from the base of the bluff to the MIS 5e forest bed yield normal polarity, with the exception of a brief reversal event between Old Crow tephra (124 ± 10 ka) and the MIS 5e forest bed that is likely the first documentation of the Blake paleomagnetic event in Alaskan loess. The detailed tephrostratigraphy and paleomagnetic data collectively suggest that most of the sedimentary record at the Palisades is middle Pleistocene in age. The Palisades thus preserves a rare record of late to middle Pleistocene paleoenvironments with multiple regionally distributed tephra beds. © 2013 Elsevier Ltd.

Anniversaries

The hundredth anniversary of the outbreak of the First World War is only the first of a large number of major European historical anniversaries that will occur in the coming four years. Other twentieth-century anniversaries include that of the Russian Revolution and the Easter Uprising; notable corollaries from earlier centuries include the Battle of Bannockburn, the Hanoverian succession, the Battle of Waterloo and, perhaps most significant of all, the five hundredth anniversary of the Lutheran Reformation. Rather than commission special issues or other features to tie in to individual anniversaries centred on or relevant to German history in a manner which repeats unthinkingly the conventions of scholarly and popular culture, the editors elected to reflect more fundamentally on what might be at stake in major anniversaries for professional scholars of history. In anticipation of the major wave of scholarly and popular publications, commemorative activities and memory conflicts that each of these will generate, and in order to reflect upon the dynamics of German history, memory and commemoration in a more overtly comparative context, the editors invited a number of scholars working on different national histories to reflect on the possibilities and potential pitfalls such anniversaries offer to historians who tie their work in to such moments. They are Jörg Arnold (Nottingham), Thomas A. Brady (Berkeley), Fearghal McGarry (Queen’s University, Belfast), Tim Grady (Chester) and Dan Healey (St Antony’s College, Oxford). The questions were posed by the editors.