2050年前长江流域地表水资源变化趋势

 利用ECHAM5/MPI-OM气候模式预估2001-2050年长江流域不同排放情景（SRES-A2,A1B,B1）下径流深的变化,分析了长江流域地表水资源量的时空变化特征。结果表明：3种排放情景下长江流域多年平均地表水资源量相差不大,但不同排放情景下年际变化特征较为复杂,且变化趋势有所不同。其中,A2高排放情景下地表水资源量呈缓慢减小的趋势,A1B中等排放情景下变化趋势不明显,B1低排放情景下呈相对最为显著的增加趋势。地表水资源量年代际变化波动幅度也较大,2001-2030年3种情景下地表水资源量总体呈现下降特征,但从2030年起,则均表现出不同程度的增加,最高增幅达7.47%,其中尤以夏季和冬季增加显著。模式预估长江流域未来水资源量仍保持目前水平,水资源空间分布不均匀特征仍较为突出。     

A Comparison Between Modelled and Measured Mixing-Layer Height Over Munich

An attempt is made to correlate the mixing heights, derived from ceilometer and Sodar measurements, to those simulated by different atmospheric boundary-layer parameterization schemes. The comparison is performed at two sites (one suburban and one rural) close to Munich, Germany for two spring and two winter days. It is found that, under convective conditions, the mixing height determined, by both Sodar and ceilometer, corresponds to the middle or the top of the entrainment zone, respectively, as calculated from the eddy-viscosity profiles. Under stable conditions, the measured mixing height is related to the height where eddy viscosities attain their minimum values (Sodar) or to the height of residual mechanical turbulence (ceilometer). During a foehn case with weak turbulence, the measured mixing height from both Sodar and ceilometer is better inferred by considering the eddy-viscosity profiles during daytime and the height of the low-level jet during nighttime.     

A more accurate scheme for calculating Earth’s skin temperature

The theoretical framework of the vertical discretization of a ground column for calculating Earth’s skin temperature is presented. The suggested discretization is derived from the evenly heat-content discretization with the optimal effective thickness for layer-temperature simulation. For the same level number, the suggested discretization is more accurate in skin temperature as well as surface ground heat flux simulations than those used in some state-of-the-art models. A proposed scheme (“op(3,2,0)”) can reduce the normalized root–mean–square error (or RMSE/STD ratio) of the calculated surface ground heat flux of a cropland site significantly to 2% (or 0.9 W m^?2), from 11% (or 5 W m^?2) by a 5-layer scheme used in ECMWF, from 19% (or 8 W m^?2) by a 5-layer scheme used in ECHAM, and from 74% (or 32 W m^?2) by a single-layer scheme used in the UCLA GCM. Better accuracy can be achieved by including more layers to the vertical discretization. Similar improvements are expected for other locations with different land types since the numerical error is inherited into the models for all the land types. The proposed scheme can be easily implemented into state-of-the-art climate models for the temperature simulation of snow, ice and soil.     

The stability of hercynite at high pressures and temperatures

The stability of hercynite (FeAl₂O₄) has been investigated experimentally between 7 and 24 GPa and 900 and 1,700°C. Hercynite breaks down to its constituent oxides at 7–8.5 GPa and temperatures >1,000°C. The incorporation of a small magnetite component in the hercynite necessitated a small correction to fix the location of the endmember reaction: FeAl₂O₄  = Al₂O₃ + FeO in P–T space. After making this correction, the position of the phase boundary was used to evaluate thermodynamic data for hercynite. Our results support a relatively large S ₂₉₈^° for hercynite, on the order of 115 J mol⁻¹ K⁻¹. Experiments up to 24 GPa and 1,400°C failed to detect any high-pressure polymorph of FeAl₂O₄; only corundum + wüstite were detected. This behaviour contrasts with that observed for the analogous MgAl₂O₄ system where the constituent oxides recombine at high pressure to produce “post-spinel” phases with CaFe₂O₄-type and CaTi₂O₄-type structures.     

Bulk chemical compositions of Al-rich objects from Rumuruti (R) chondrites: Implications for their origin

R chondrites are a distinct group of chondritic meteorites with unique mineralogical and chemical compositions. They contain various types of Al-rich objects [Ca,Al-rich inclusions (CAIs), Al-rich chondrules and fragments], whose mineralogical compositions and classifications were previously determined by Rout and Bischoff (2008). Here, we report on the bulk compositions of 126 such Al-rich objects determined by broad-beam electron probe microanalysis.Most of the CAIs, except a few, are significantly altered by complex nebular and/or parent body processes and the determination of their pristine composition is difficult. We found that the simple concentric spinel-rich inclusions have high Al₂O₃ (21–72 wt%) correlated with their high modal spinel. The subgroup of simple concentric spinel-rich CAIs have a high Al₂O₃ (21–57 wt%) and also sometimes high FeO (up to 36 wt%), due to a high hercynitic component in the spinel. One simple concentric spinel- and hibonite-rich CAI H030/L, identified as a HAL-type CAI by isotopic studies reported elsewhere, has a highly refractory composition (Al₂O₃～72 wt%). Most of the simple concentric spinel- and fassaite-rich CAIs have consistently high CaO (～2.5–17 wt%) compared to other simple concentric spinel-rich inclusions group, where only some inclusions have high CaO (up to 15 wt%). Simple concentric spinel- and Na,Al-alteration product-rich CAIs are heavily altered and have high Na₂O (up to ～12.5 wt%).The three analyzed fassaite-rich spherules have high CaO and Al₂O₃, and complex spinel- and fassaite-rich CAIs have high CaO (up to 23 wt%) and SiO₂ (up to 41 wt%). Most of the complex spinel- and plagioclase-rich CAIs are altered and contain high amounts of secondary oligoclase. However, a few are less affected by secondary alteration and these are characterized by relatively high CaO (up to 24 wt%) and Al₂O₃ (18–33 wt%); complex spinel and Na,Al-alteration product-rich CAIs are similar to the concentric spinel- and Na,Al-alteration product-rich CAIs. Due to Fe- and alkali-metasomatism, the vast majority of the inclusions in this subgroup were heavily altered, either in a nebular or parent body environment. As a result of this alteration, they contain high FeO and Na₂O+K₂O+Cl.Almost all inclusions have a Ca/Al-ratio below the solar ratio. This suggests that significant Ca/Al fractionation occurred during the formation of most CAIs, most probably due to disequilibrium condensation of spinel prior to melilite. However, a distillation process cannot be ruled out for some CAIs in producing the spinel enrichment. Some porous and fine grained CAIs may have been produced by agglomeration of refractory dust rich in spinel and fassaite. The HAL-type CAI, H030/L, most likely formed by distillation, similar to most of the HAL-type inclusions. Phase equilibrium analysis, in the CMAS system, shows that the fassaite-bearing spherules most likely formed by metastable crystallization and disequilibrium processes. Al-rich chondrules are characterized by >10 wt% Al₂O₃, and most of these also have high FeO and Na₂O. Considering their bulk compositions, their precursors seem to have been a mixture of a ferromagnesian chondrule component rich in olivine and an anorthite–spinel–pyroxene–nepheline-rich CAI component. The mineral assemblages of some of the less altered Al-rich chondrules conform to those predicted by phase equilibrium studies.     

Pyroclast loss or retention during explosive volcanism on asteroids: Influence of asteroid size and gas content of melt

Abstract– We review the conditions under which explosive volcanism took place on early‐forming differentiated asteroids. The pressure‐dependent solubility of typical asteroid volatiles in melts implies that the gas driving explosive volcanism on asteroids less than approximately 100 km in diameter was probably present mainly as a free phase capable of accumulating into large gas bodies and, thus, causing slug flow in melts approaching the surface. In contrast, in asteroids larger than approximately 100 km the gas was probably present largely as a dispersion of small bubbles. We show that these gas distributions have implications for the size distribution of the pyroclastic droplets produced in explosive eruptions at the surface. All pyroclastic melt droplets are accelerated by the expanding gases, but their speeds lag the gas speed by a finite amount that is a function of the droplet size and density and the asteroid size and, hence, acceleration due to gravity. We compute pyroclast speeds and, by comparing them with escape velocities, we identify the critical pyroclast diameter on a given‐size asteroid that distinguishes droplets lost to space from droplets that return to the surface. Identification of asteroidal pyroclasts and measurements of their sizes could throw light on the amounts of gas driving eruptions.     

The Sierra Ballena Shear Zone in the southernmost Dom Feliciano Belt (Uruguay): evolution, kinematics, and deformation conditions

The Sierra Ballena Shear Zone (SBSZ) is part of a high-strain transcurrent system that divides the Neoproterozoic Dom Feliciano Belt of South America into two different domains. The basement on both sides of the SBSZ shows a deformation stage preceding that of the transcurrent deformation recognized as a high temperature mylonitic foliation associated with migmatization. Grain boundary migration and fluid-assisted grain boundary diffusion enhanced by partial melting were the main deformation mechanisms associated with this foliation. Age estimate of this episode is >658 Ma. The second stage corresponds to the start of transpressional deformation and the nucleation and development of the SBSZ. During this stage, pure shear dominates the deformation, and is characterized by the development of conjugate dextral and sinistral shear zones and the emplacement of syntectonic granites. This event dates to 658–600 Ma based on the age of these intrusions. The third stage was a second transpressional event at about 586 to <560 Ma that was associated with the emplacement of porphyry dikes and granites that show evidence of flattening. Deformation in the SBSZ took place, during the late stages, under regional low-grade conditions, as indicated by the metamorphic paragenesis in the supracrustals of the country rocks. Granitic mylonites show plastic deformation of quartz and brittle behavior of feldspar. A transition from magmatic to solid-state microstructures is also frequently observed in syntectonic granites. Mylonitic porphyries and quartz mylonites resulted from the deformation of alkaline porphyries and quartz veins emplaced in the shear zone. Quartz veins reflect the release of silica associated with the breakdown of feldspar to white mica during the evolution of the granitic mylonites to phyllonites, which resulted in shear zone weakening. Quartz microstructures characteristic of the transition between regime 2 and regime 3, grain boundary migration and incipient recrystallization in feldspar indicate deformation under lower amphibolite to upper greenschist conditions (550–400°C). On the other hand, the mylonitic porphyries display evidence of feldspar recrystallization suggesting magmatic or high-T solid-state deformation during cooling of the dikes.     

Comparison of atmospheric turbulence characteristics and turbulent fluxes from two urban sites in Essen, Germany

From September 2006 to September 2007, the intersite variability of turbulence characteristics and turbulent heat fluxes was analysed at two urban stations in Essen, Germany. One site was situated within an urban residential setting while the other was located at the border of an urban park and suburban/urban residential housing. Therefore, the surroundings at both sites contributing to surface–atmosphere exchange differed in terms of surface cover and surface morphology. During the 1-year measurement period, 19% of data were characterised by stable atmospheric stratification. Since observations of urban turbulence characteristics under stable stratification are scarce, so far, this work adds additional input to this discussion. Turbulence characteristics, i.e. normalised standard deviations of wind components, were in agreement to empirical fits from other urban observations under both instable and stable atmospheric stratification. However, differences in magnitude of turbulence characteristics between sites were observable. Comparison of turbulent heat fluxes indicated typical urban features in the site located in the urban setting with increased surface heating and higher surface heat fluxes by about 30%. Also the temporal evolution of heat fluxes on the diurnal course was affected. Differences in momentum flux were of minor magnitude with about 6% variation on average between sites. Findings indicate that multiple urban flux measurements within one city may be characterised by general similarities in terms of turbulent characteristics but are still significantly influenced by differences in the surface cover of the flux footprint.