A comparison of SSM/I and TOVS column water vapor data over the global oceans

Summary This paper presents a comparison of column water vapor (CWV) information derived from both infrared measurements as part of the TIROS-N Operational Vertical Sounder (TOVS) and Special Sensor Microwave/Imager (SSM/I) in an attempt to assess the relative merits of each kind of data. From the analyses presented in this paper, it appears that both types of satellite data closely reproduce the bulk climatological relationships introduced in earlier studies using different data. This includes both the bulk relationship between CWV and the sea surface temperature and the annual variation of CWV over the world's oceans. The TOVS water vapor data tends to be systematically smaller than the SSM/I data and when averaged over the ocean covered regions of the globe this difference is between 2–3 kgm^–2. Using a cloud liquid water threshold technique to establish clear sky values of SSM/I water vapor, we conclude that the differences between TOVS and SSM/I are largely a result of the clear sky bias in TOVS sampling except in the subsidence regions of the subtropics. The clear sky bias is considerably smaller than previously reported and we attribute this improvement to the new physical retrieval scheme implemented by NOAA NESDIS. While there is considerable agreement between the two types of satellite data, there are also important differences. In regions where there is drying associated with large scale subsidence of the atmosphere, the TOVS CWV's are too moist relative to both radiosonde and SSM/I data and this difference may exceed 10 kgm^–2. The explanation for this difference lies in the limitations of infrared radiative transfer. By contrast, in regions of deep convection, such as in the ITCZ, TOVS CWV is systematically lower than the SSM/I CWV. Both TOVS and SSM/I data demonstrate similar kinds of gross effects of large scale circulation on the water vapor except in these subsidence regions where TOVS data leads to an under-prediction of the effects of subsidence drying.With 11 Figures     

塔里木西克尔基性麻粒岩捕虏体的发现及其地质意义

在塔里木西部新生代碧玄岩中新发现了基性麻粒岩捕虏体。其原生矿物组合为Cpx+Opx+Pl (An=30~50)+Sp+Ilm+Tim,次生矿物组合为Ol+Pl (An>50)+alkaline feldspar+glass。原生矿物组合的温度和压力分别为1005~1059℃ 和 0.6~1.1GPa; 次生矿物组合形成于近等温减压过程和固相线上熔融以及之后的近地表快速冷却。这些麻粒岩捕虏体代表了早期底侵到塔里木板块下地壳的幔源岩浆。     

Dislocation recovery in fine-grained polycrystalline olivine

The rate of static dislocation recovery in Fo₉₀ olivine has been studied under conditions of high temperature and controlled atmosphere in compressively deformed polycrystals hot-pressed from synthetic (sol–gel) and natural (San Carlos) precursor powders. The sol–gel olivine, containing a small fraction of orthopyroxene, was deformed to a final strain of 19% with a maximum differential stress of 266 MPa whereas the San Carlos specimen was deformed to 15% strain and 260 MPa differential stress. Small samples cut from these deformed materials were annealed under high-temperature, controlled atmosphere conditions, for different durations to allow partial recovery of the dislocation sub-structures. Oxidative-decoration of the microstructural features, followed by backscattered electron imaging at 5 kV and image analysis, was used to determine dislocation density. The variation of dislocation density ρ with time t at absolute temperature T was fitted to a second-order rate equation, in integral form, 1/ρ(t) − 1/ρ(0) = kt with k = k ₀ exp(−E _a/RT). The activation energy E _a of the recovery process is 240 ± 43 and 355 ± 81 kJ mol⁻¹ for sol–gel and San Carlos olivine polycrystals, respectively. The measured rates are one to two orders of magnitude lower than those reported in previous studies on natural single crystal olivine. The difference may be explained by several factors such as high dislocation densities measurable from large areas at high magnification for the SEM and the technique used to estimate dislocation densities. Comparison between fine-grained sol–gel olivine and the coarser-grained San Carlos olivine aggregate did not indicate that grain boundaries play an important role in dislocation recovery, but the absence of grain boundaries might also have contributed to the high dislocation recovery rates previously measured for single crystals.     

The lithospheric mantle beneath the Kerguelen Islands (Indian Ocean): petrological and petrophysical characteristics of mantle mafic rock types and correlation with seismic profiles

Deep-seated meta-igneous xenoliths brought to the surface by alkali basaltic magmas from the Kerguelen Islands reveal that basaltic magmas have intruded the upper mantle throughout their geological evolution. These xenoliths record volcanic activity associated with their early South East Indian Ridge location and subsequent translation to an intraplate setting over the Kerguelen Plume. The meta-igneous xenoliths sample two distinctive geochemical episodes: one is tholeiitic transitional and one is alkali basaltic. Geothermobarometry calculations provide a spatial context for the rock type sequence sampled and for interpreting petrophysical data. The garnet granulites equilibrated over a pressure range of 1.15 to 1.35 GPa and the garnet pyroxenite at 1.8 GPa. Ultrasonic measurements of compressional wave speed V_P have been carried out at pressures up to 1 GPa, and densities measured for representative samples of meta-igneous xenoliths and for a harzburgite that represents the peridotitic mantle. V_P and density have also been calculated using modal proportions of minerals and appropriate elastic properties for the constituent minerals. Calculated and measured V_P agree well for rock types with microstructures not complicated by kelyphitic breakdown of garnet and/or pervasive grain-boundary cracking. Pyroxene granulites have measured and calculated V_P within the range 7.37-7.52 km/s; calculated velocities for the garnet granulites and pyroxenites range from 7.69 to 7.99 km/s, whereas measured and calculated V_P for a mantle harzburgite are 8.45 and 8.29 km/s respectively. The seismic structure observed beneath the Kerguelen Islands can be explained by (1) a mixture of underplated pyroxene granulites and ultramafic rocks responsible for the 2-3 km low velocity transitional zone below the oceanic layer 3, (2) varying proportions of granulites and pyroxenites in different regions within the upper mantle producing the lateral heterogeneities, and (3) intercalation of the granulites and pyroxenites throughout the entire upper mantle column, along with elevated temperatures, accounting for the relatively low mantle velocities (7.70-7.95 km/s).     

MEG Investigation of Low Pressure Silica — Shell model for polarization

We present a two-shell polarization model for the α-quartz and α-cristobalite structures. By allowing for polarization, we correct problems encountered in purely ionic bonding treatments of tetrahedrally coordinated silica phases. The shell model predicts zero pressure structures in very good agreement with experiment using no empirical parameters. The behavior of the shell model α-quartz lattice upon compression shows dramatic improvement over the distorted, rigid lattice given by the ionic model.     

东昆仑牦牛山组流纹岩锆石U-Pb年龄及构造意义

东昆仑水泥厂地区造山后火山-沉积盆地内形成的牦牛山组磨拉石建造不整合覆盖在前泥盆系地层之上,其形成时代的研究对限定东昆仑早古生代洋盆关闭的时间具有重要意义。应用激光烧蚀多接收器电感耦合等离子体质谱仪(LAMC-ICPMS)方法,对火山-沉积盆地内牦牛山组不同层位的流纹岩夹层进行了精确的锆石U-Pb定年研究。结果表明,盆地北缘牦牛山组底砾岩之上的流纹岩(B743-2)中岩浆锆石~(206)Pb/~(238)U年龄平均值为423.2±1.8Ma,盆地西缘牦牛山组底砾岩之上的流纹岩(B820-1)中岩浆锆石~(206)Pb/~(238)U年龄平均值为408.2±2.4Ma,盆地西缘和南缘牦牛山组中上部碎屑岩中流纹岩夹层(B705-1和B656-1)的岩浆锆石~(206)Pb/~(238)U年龄平均值分别为404.9±4.8Ma和399.6±2.8Ma。它们代表了牦牛山组不同层位火山岩的形成年龄,由此可以限定水泥厂地区牦牛山组形成时间为400～423Ma。上述年代学结果较为精确地限定了东昆仑早古生代洋盆关闭的构造年代。流纹岩中2486～920Ma元古代继承锆石的发现,说明东昆仑南的变质基底和扬子板块变质基底类似,是晋宁期0.9～1.0Ga罗迪尼亚超大陆形成时发育起来的。