On the Response of the Climate System to Solar Forcing

The climate response to changes in radiative forcing depends crucially on climate feedback processes, with the consequence that solar and greenhouse gas forcing have both similar response patterns in the troposphere. This circumstance complicates significantly the attribution of the causes of climate change. Additionally, the climate system displays a high level of unforced intrinsic variability, and significant variations in the climate of many parts of the world are due to internal processes. Such internal modes contribute significantly to the variability of climate system on various time scales, and thus compete with external forcing in explaining the origin of past climate extremes. This highlights the need for independent observations of solar forcing including long-term consistent observational records of the total and spectrally resolved solar irradiance. The stratospheric response to solar forcing is different from its response to greenhouse gas forcing, thus suggesting that stratospheric observations could offer the best target for the identification of the specific influence of solar forcing on climate.     

Climate Variability on Venus and Titan

Venus and Titan are both slowly-rotating, approximately Earth-sized bodies with cloudy, dynamic atmospheres. Each has a complex climate system, even less well understood than the terrestrial equivalent, and the processes that appear to maintain the climate near the surface on both bodies have interesting similarities and differences with each other and with the Earth. By considering these factors and their possible evolution with the aid of elementary climate models, some interesting, albeit tentative, conclusions can be reached concerning the stability of climate on Earth-like planets, and the likely nature of past and future climate change.     

Solar Forcing of Climate. 2: Evidence from the Past

The nature of the climatic response to solar forcing and its geographical coherence is reviewed. This information is of direct relevance for evaluating solar forcing mechanisms and validating climate models. Interpretation of Sun-climate relationships is hampered by difficulties in (1) translating proxy records into quantitative climate parameters (2) obtaining accurate age assessments (3) elucidating spatial patterns and relationships (4) separating solar forcing from other forcing mechanisms (5) lacking physical understanding of the solar forcing mechanisms. This often limits assessment of past solar forcing of climate to identification of correlations between environmental change and solar variability. The noisy character and often insufficient temporal resolution of proxy records often exclude the detection of high frequency decadal and bi-decadal cycles. However, on multi-decadal and longer time scales, notably the ∼90 years Gleisberg, and ∼200 years Suess cycles in the ¹⁰Be and ¹⁴C proxy records of solar activity are also well presented in the environmental proxy records. The additional ∼1500 years Bond cycle may result from interference between centennial-band solar cycles. Proxy evidence for Sun-climate relations is hardly present for Africa, South America and the marine realm; probably more due to a lack of information than a lack of response to solar forcing. At low latitudes, equatorward movement of the ITCZ (upward component of the Hadley cell) occurs upon a decrease in solar activity, explaining humidity changes for (1) Mesoamerica and adjacent North and South American regions and (2) East Africa and the Indian and Chinese Monsoon systems. At middle latitudes equatorward movement of the zonal circulation during solar minima probably (co-)induces wet and cool episodes in Western Europe, and Terra del Fuego as well as humidity changes in Southern Africa, Australia, New Zealand and the Mediterranean. The polar regions seem to expand during solar minima which, at least for the northern hemisphere is evident in southward extension of the Atlantic ice cover. The forcing-induced migration of climate regimes implies that solar forcing induces a non linear response at a given location. This complicates the assessment of Sun-climate relations and calls for nonlinear analysis of multiple long and high resolution records at regional scale. Unfortunately nonlinear Sun-climate analysis is still a largely barren field, despite the fact that major global climate configurations (e.g. the ENSO and AO) follow nonlinear dynamics. The strength of solar forcing relative to other forcings (e.g. volcanism, ocean circulation patterns, tides, and geomagnetism) is another source of dynamic responses. Notably the climatic effects of tides and geomagnetism are hitherto largely enigmatic. Few but well-dated studies suggest almost instantaneous, climatic deteriorations in response to rapid decreases in solar activity. Such early responses put severe limits to the solar forcing mechanisms and the extent of this phenomenon should be a key issue for future Sun-climate studies.     

Regional Response of the Climate System to Solar Forcing: The Role of the Ocean

A coupled climate model is used to explore the regional response of the climate system to solar forcing, with emphasis on the role of the ocean. It is shown that both the transient and the equilibrium response of surface temperature to changes in total solar irradiation is smaller over ocean than over land because of the ocean’s large heat capacity and the feedback involving evaporation. Furthermore, the advection of temperature anomalies and changes in ocean currents have an impact on the timing and the geographical distribution of the response. Nevertheless, at regional scales, the response to the forcing is embedded within the large internal variability of the system making the detection and analysis of the forced response difficult. Furthermore, this forced response could imply both changes in the mean state of the system as well as in its variability.     

The Role of Dynamics in Solar Forcing

This paper reviews the solar influence on climate through stratospheric dynamical processes. There are two possible processes, both being a consequence of the wave-mean flow interaction in the upper stratosphere. One involves changes in the vertical propagation of planetary waves and the resultant tropospheric circulation change in the extratropics of the winter hemisphere. The other involves change in the global meridional circulation in the stratosphere and associated convective activity change in the tropics. These processes have been discussed on an 11-year solar cycle, but they are also applicable for centennial-scale solar influence on climate.     

The Response of the Middle Atmosphere to Solar Cycle Forcing in the Hamburg Model of the Neutral and Ionized Atmosphere

This paper studies the response of the middle atmosphere to the 11-year solar cycle. The study is based on numerical simulations with the Hamburg Model of the Neutral and Ionized Atmosphere (HAMMONIA), a chemistry climate model that resolves the atmosphere from the Earth’s surface up to about 250 km. Results presented here are obtained in two multi-year time-slice runs for solar maximum and minimum conditions, respectively. The magnitude of the simulated annual and zonal mean stratospheric response in temperature and ozone corresponds well to observations. The dynamical model response is studied for northern hemisphere winter. Here, the zonal mean wind change differs substantially from observations. The statistical significance of the model’s dynamical response is, however, poor for most regions of the atmosphere. Finally, we discuss several issues that render the evaluation of model results with available analyses of observational data of the stratosphere and mesosphere difficult. This includes the possibility that the atmospheric response to solar variability may depend strongly on longitude.     

The Climate Response to the Astronomical Forcing

Links between climate and Earth’s orbit have been proposed for about 160 years. Two decisive advances towards an astronomical theory of palæoclimates were Milankovitch’s theory of insolation (1941) and independent findings, in 1976, of a double precession frequency peak in marine sediment data and from celestial mechanics calculations. The present chapter reviews three essential elements of any astronomical theory of climate: (1) to calculate the orbital elements, (2) to infer insolation changes from climatic precession, obliquity and eccentricity, and (3) to estimate the impact of these variations on climate. The Louvain-la-Neuve climate-ice sheet model has been an important instrument for confirming the relevance of Milankovitch’s theory, but it also evidences the critical role played by greenhouse gases during periods of low eccentricity. It is recognised today that climatic interactions at the global scale were involved in the processes of glacial inception and deglaciation. Three examples are given, related to the responses of the carbon cycle, hydrological cycle, and the terrestrial biosphere, respectively. The chapter concludes on an outlook on future research directions on this topic.     

Solar Influence on Earth's Climate

An increasing number of studies indicate that variations in solar activity have had a significant influence on Earth's climate. However, the mechanisms responsible for a solar influence are still not known. One possibility is that atmospheric transparency is influenced by changing cloud properties via cosmic ray ionisation (the latter being modulated by solar activity). Support for this idea is found from satellite observations of cloud cover. Such data have revealed a striking correlation between the intensity of galactic cosmic rays (GCR) and low liquid clouds (<3.2 km). GCR are responsible for nearly all ionisation in the atmosphere below 35 km. One mechanism could involve ion-induced formation of aerosol particles (diameter range, 0.001–1.0 μm) that can act as cloud condensation nuclei (CCN). A systematic variation in the properties of CCN will affect the cloud droplet distribution and thereby influence the radiative properties of clouds. If the GCR-Cloud link is confirmed variations in galactic cosmic ray flux, caused by changes in solar activity and the space environment, could influence Earth's radiation budget. This revised version was published online in August 2006 with corrections to the Cover Date.     

Aerosol Effects on Clouds and Climate

Aerosols affect the climate system by changing cloud characteristics in many ways. They act as cloud condensation and ice nuclei, they may inhibit freezing and they could have an influence on the hydrological cycle. While the cloud albedo enhancement (Twomey effect) of warm clouds received most attention so far and traditionally is the only indirect aerosol forcing considered in transient climate simulations, here I discuss the multitude of effects.     

What do Cosmogenic Isotopes Tell us About Past Solar Forcing of Climate?

In paleoclimate studies, cosmogenic isotopes are frequently used as proxy indicators of past variations in solar irradiance on centennial and millennial timescales. These isotopes are spallation products of galactic cosmic rays (GCRs) impacting Earth's atmosphere, which are deposited and stored in terrestrial reservoirs such as ice sheets, ocean sediments and tree trunks. On timescales shorter than the variations in the geomagnetic field, they are modulated by the heliosphere and thus they are, strictly speaking, an index of heliospheric variability rather than one of solar variability. Strong evidence of climate variations associated with the production (as opposed to the deposition) of these isotopes is emerging. This raises a vital question: do cosmic rays have a direct influence on climate or are they a good proxy indicator for another factor that does (such as the total or spectral solar irradiance)? The former possibility raises further questions about the possible growth of air ions generated by cosmic rays into cloud condensation nuclei and/or the modulation of the global thunderstorm electric circuit. The latter possibility requires new understanding about the required relationship between the heliospheric magnetic fields that scatter cosmic rays and the photospheric magnetic fields which modulate solar irradiance.     

Geochemistry of Carbonates on Mars: Implications for Climate History and Nature of Aqueous Environments

Ongoing research on martian meteorites and a new set of observations of carbonate minerals provided by an unprecedented series of robotic missions to Mars in the past 15 years help define new constraints on the history of martian climate with important crosscutting themes including: the CO₂ budget of Mars, the role of Mg-, Fe-rich fluids on Mars, and the interplay between carbonate formation and acidity. Carbonate minerals have now been identified in a wide range of localities on Mars as well as in several martian meteorites. The martian meteorites contain carbonates in low abundances (<1 vol.%) and with a wide range of chemistries. Carbonates have also been identified by remote sensing instruments on orbiting spacecraft in several surface locations as well as in low concentrations (2–5 wt.%) in the martian dust. The Spirit rover also identified an outcrop with 16 to 34 wt.% carbonate material in the Columbia Hills of Gusev Crater that strongly resembled the composition of carbonate found in martian meteorite ALH 84001. Finally, the Phoenix lander identified concentrations of 3–6 wt.% carbonate in the soils of the northern plains. The carbonates discovered to date do not clearly indicate the past presence of a dense Noachian atmosphere, but instead suggest localized hydrothermal aqueous environments with limited water availability that existed primarily in the early to mid-Noachian followed by low levels of carbonate formation from thin films of transient water from the late Noachian to the present. The prevalence of carbonate along with evidence for active carbonate precipitation suggests that a global acidic chemistry is unlikely and a more complex relationship between acidity and carbonate formation is present.     

关于飞船的动态稳定问题

本文研究了以平衡攻角为中心作俯仰振荡的飞船,其动态稳定形态随来流马赫数Ｍ∞Ｒ ＹＯ ＷＸ 。     

The seasonal cycle of water on Mars

A review of the behavior of water in the Mars atmosphere and subsurface is appropriate now that data from the Mariner and Viking spacecraft have been analyzed and discussed for several years following completion of those missions. Observations and analyses pertinent to the seasonal cycle of water vapor in the atmosphere of Mars are reviewed, with attention toward transport of water and the seasonal exchange of water between the atmosphere and various non-atmospheric reservoirs. Possible seasonally-accessible sources and sinks for water include water ice on or within the seasonal and residual polar caps; surface or subsurface ice in the high-latitude regions of the planet; adsorbed or chemically-bound water within the near-surface regolith; or surface or subsurface liquid water. The stability of water within each of these reservoirs is discussed, as are the mechanisms for driving exchange of the water with the atmosphere and the timescales for exchange. Specific conclusions are reached about the distribution of water and the viability of each mechanism as a seasonal reservoir. Discussion is also included of the behaviour of water on longer timescales, driven by the variations in solar forcing due to the quasi-periodic variations of the orbital obliquity. Finally, specific suggestions are made for future observations from spacecraft which would further define or constrain the seasonal cycle of water.     

创业氛围与环境优化

创业环境的优化是一个内外协同演进的共生过程,培育一定的创业氛围是其中至关重要的中间环节。创业环境包括两个组成部分：内生决定的创业氛围和外部影响的创业条件。现阶段,决定我国创业水平的环境因素是创业氛围,它表现为显在与潜在的创业者行为方式,是一种主观的生态环境。不同区域创业环境优化的政策思路应当有别,落后的中西部地区创业环境建设的关键在于形成一定的创业氛围,否则,客观的创业条件再怎么改善也很难有效刺激创业活动。     

Creating Habitable Zones, at all Scales, from Planets to Mud Micro-Habitats, on Earth and on Mars

The factors that create a habitable planet are considered at all scales, from planetary inventories to micro-habitats in soft sediments and intangibles such as habitat linkage. The possibility of habitability first comes about during accretion, as a product of the processes of impact and volatile inventory history. To create habitability water is essential, not only for life but to aid the continual tectonic reworking and erosion that supply key redox contrasts and biochemical substrates to sustain habitability. Mud or soft sediment may be a biochemical prerequisite, to provide accessible substrate and protection. Once life begins, the habitat is widened by the activity of life, both by its management of the greenhouse and by partitioning reductants (e.g. dead organic matter) and oxidants (including waste products). Potential Martian habitats are discussed: by comparison with Earth there are many potential environmental settings on Mars in which life may once have occurred, or may even continue to exist. The long-term evolution of habitability in the Solar System is considered.     

Interstellar-Terrestrial Relations: Variable Cosmic Environments, The Dynamic Heliosphere, and Their Imprints on Terrestrial Archives and Climate

In recent years the variability of the cosmic ray flux has become one of the main issues interpreting cosmogenic elements and especially their connection with climate. In this review, an interdisciplinary team of scientists brings together our knowledge of the evolution and modulation of the cosmic ray flux from its origin in the Milky Way, during its propagation through the heliosphere, up to its interaction with the Earth’s magnetosphere, resulting, finally, in the production of cosmogenic isotopes in the Earth’ atmosphere. The interpretation of the cosmogenic isotopes and the cosmic ray – cloud connection are also intensively discussed. Finally, we discuss some open questions.     

Thermospheric X-Ray and Euv Heating by the Young Sun on Early Venus and Mars

In view of the low H₂O abundance in the present Venusian and Martian atmospheres several observations by spacecraft and studies suggest that both planets should have lost most of their water over the early active period of the young Sun. During the first Gyr after the Sun arrived at the Zero- Age-Main-Sequence high X-ray and EUV fluxes between 10 and 100 times that of the present Sun were responsible for much higher temperatures in the thermosphere-exosphere environments on both planets. By applying a diffusive-gravitational equilibrium and thermal balance model for investigating radiation impact on the early thermospheres by photodissociation and ionization processes, due to exothermic chemical reactions and cooling by CO₂ IR emission in the 15μm band we found expanded thermospheres with exobase levels between about 200 km (present) and 2000 km (4.5 Gyr ago). The higher temperatures in the upper atmospheres of both planets could reach “blow-off” conditions for H atoms even at high CO₂ mixing ratios of 96%. Lower CO₂/N₂ mixing ratio or higher contents of H2O vapor in the early atmospheres could have had a dramatic impact from the loss of atmosphere and water on both planets. The duration of this phase of high thermal loss rates essentially depended on the mixing ratios of CO₂, N₂, and H₂O in the early atmospheres and could have lasted between about 150 and several hundred Myr.     

The Influence of Total Solar Irradiance on Climate

To estimate the effect of the solar variability on the climate, two estimates of the solar intensity variations during the last three centuries have been used as forcing in numerical simulations. The model employed to carry out the experiments was the same coupled global ocean-atmosphere model used in a number of studies to assess the effect of the anthropogenic greenhouse gases on climate. The near surface temperature and the tropospheric temperature distribution shows a clear response to the variability of the solar input. Even the thermohaline circulation reacts on the large amplitudes in the forcing. In the stratosphere, the response pattern is similar as in the observations, however, the 11-year cycle found in the forcing data does not excite an appreciable response. This might be due to the missing parameterisation of the increase in the UV-radiation at the solar cycle maximum and the connected increase of the stratospheric ozone concentration.     

低密度气凝胶复合材料的火星环境适应性研究

针对航天器的使用要求,研制了密度≤30 kg/m~3轻质高效的二氧化硅气凝胶复合材料。针对深空探测的应用环境,对低密度气凝胶复合材料在不同条件下的热导率、热循环、热真空和电离总剂量等环境试验进行测试。结果表明,低密度气凝胶复合材料服役温度可达到-145～85℃,在1 kPa CO_2气氛下热导率可达到6.6 mW/(m·K)。获得了不同气氛和不同温度条件下以及同种气氛、不同压力条件下低密度气凝胶复合材料的热导率变化规律,并测试批次性材料热导率,结果表明批次热导率稳定性良好。热循环、热真空和电离辐照试验前后热导率和尺寸收缩率均未变化,表明低密度气凝胶复合材料在深空环境下保持良好的结构和稳定的隔热性能。