The 1.10- and 1.18-μm nightside windows of Venus observed by SPICAV-IR aboard Venus Express     

Bruno Bézard  Anna Fedorova  Jean-Loup Bertaux  Alexander Rodin  Oleg Korablev 《Icarus》2011,216(1):173-183

Observations of the 1.10- and 1.18-μm nightside windows by the SPICAV-IR instrument aboard Venus Express were analyzed to characterize the various sources of gaseous opacity and determine the H₂O mole fraction in the lower atmosphere of Venus. We showed that the line profile model of Afanasenko and Rodin (Afanasenko, T.S., Rodin, A.V. [2007]. Astron. Lett. 33, 203–210) underestimates the CO₂ absorption in the high-wavelength wing of the 1.18-μm window and we derived an empirical lineshape that matches this wing well. An additional continuum opacity is required to reproduce the variation of the 1.10- and 1.18-μm radiances with surface elevation as observed by the VIRTIS-M instrument aboard Venus Express. A constant absorption coefficient of 0.7 ± 0.2 × 10⁻⁹ cm⁻¹ am⁻² best reproduces the observed variation. We compared spectra calculated with different CO₂ and H₂O line lists. We found that the CDSD line list lacks the 5ν₁ + ν₃ series of CO₂ bands, which provide significant opacity in Venus’ deep atmosphere, and we have constructed a composite line list that best reproduces the observations. We also showed for the first time that HDO brings significant absorption at 1140–1190 nm. Using the best representation of the atmospheric opacity we could reach, we retrieved a water vapor mole fraction of ppmv, pertaining to the altitude range 5–25 km. Combined with previous measurements in the 1.74- and 2.3-μm windows, this result provides strong evidence for a uniform H₂O profile below 40 km, in agreement with chemical models.  相似文献   

Raman spectroscopic and calorimetric observations on natural gas hydrates with cubic structures I and II obtained from Lake Baikal     

Akihiro Hachikubo  Oleg Khlystov  Masato Kida  Hirotoshi Sakagami  Hirotsugu Minami  Satoshi Yamashita  Nobuo Takahashi  Hitoshi Shoji  Gennadiy Kalmychkov  Jeffrey Poort 《Geo-Marine Letters》2012,32(5-6):419-426

This study reports measurements of the Raman spectra of Lake Baikal gas hydrates and estimations of the hydration number of methane-rich samples. The hydration number of gas hydrates retrieved from the southern Baikal Basin (crystallographic structure I) was approx. 6.1. Consistent with previous results, the Raman spectra of gas hydrates retrieved from the Kukuy K-2 mud volcano in the central Baikal Basin indicated the existence of crystallographic structures I and II. Measurements of the dissociation heat of Lake Baikal gas hydrates by calorimetry (from the decomposition of gas hydrates to gas and water), employing the hydration number, revealed values of 53.7–55.5?kJ?mol^–1 for the southern basin samples (structure I), and of 54.3–55.5?kJ?mol^–1 for the structure I hydrates and 62.8–64.2?kJ?mol^–1 for the structure II hydrates from the Kukuy K-2 mud volcano.  相似文献   

Thermal anomalies associated with shallow gas hydrates in the K-2 mud volcano, Lake Baikal     

Jeffrey Poort  Oleg M. Khlystov  Lieven Naudts  Albert D. Duchkov  Hitoshi Shoji  Shin’ya Nishio  Marc De Batist  Akihiro Hachikubo  Masato Kida  Hirotsugu Minami  Andrey Y. Manakov  Marina V. Kulikova  Alexey A. Krylov 《Geo-Marine Letters》2012,32(5-6):407-417

Thermal measurements and hydrate mapping in the vicinity of the K-2 mud volcano in Lake Baikal have revealed a particular type of association of thermal anomalies (29–121?mW?m^–2) near hydrate-forming layers. Detailed coring within K-2 showed that hydrates are restricted to two distinct zones at sub-bottom depths exceeding 70–300?cm. Temperature data from stations with hydrate recovery and degassing features all display low thermal gradients. Otherwise, the thermal gradients within the mud volcano are generally increased. These findings imply a more complicated thermal regime than often assumed for mud volcanoes, with important roles for both fluids and hydrates. The coexistence of neighbouring low and high thermal anomalies is interpreted to result from discharging and recharging fluid activity, rather than hydrate thermodynamics. It is suggested that hydrates play a key role in controlling the fluid circulation pattern at an early stage. At a later stage, the inflow of undersaturated lake water would favour the dissolution of structure I hydrates and the formation of structure II hydrates, the latter having been observed on top of structure I hydrates in the K-2 mud volcano.  相似文献   

Quasi-stationary striations in basin-scale oceanic circulation: vorticity balance from observations and eddy-resolving model     

Oleg V. Melnichenko  Nikolai A. Maximenko  Niklas Schneider  Hideharu Sasaki 《Ocean Dynamics》2010,60(3):653-666

Recently, prominent jet-like features of the ocean circulation, called striations, with a meridional scale of O(300–500 ;km) and extending for thousands of kilometers in length, have been detected in satellite and in situ observations and in high-resolution numerical models. In this paper, we study quasi-stationary striations, which are best seen in the multi-year time-averaged velocity fields. Using 1993–2002 mean dynamic ocean topography, satellite altimeter observations, and output of the Ocean General Circulation Model for the Earth Simulator, the dynamics of the quasi-stationary striations in the eastern parts of the subtropical North and South Pacific are examined by assessing individual terms in the time-averaged equations of relative and potential vorticity. While non-linear effects are found to be essential in the dynamics of the striations, rejecting some linear hypotheses forwarded in the earlier studies, the relevance of the Rhines mechanism is not confirmed. Eddy flux does not act as a relative vorticity source for the striations. Using the potential vorticity (PV) diagnostics, we show that the time-mean PV is not conserved along the time-mean streamlines, and on the scale of the striations these changes in PV are largely induced by the eddy flux of layer thickness. The fact that eddy fluxes contribute to the striations’ time-mean PV budget suggests that the striations are not a kinematical artifact of time-averaging of westward-propagating eddies.  相似文献   

Experimental and petrological constraints on local-scale interaction of biotite-amphibole gneiss with H2O-CO2-（K, Na）Cl fluids at middle-crustal conditions： Example from the Limpopo Complex, South Africa   总被引：1，自引：1，他引：0  

Oleg G. Safonov  Elizaveta I. Kovaleva  Svetlana A. Kosova  H.M. Rajesh  Georgy A. Belyanin  Maria A. Golunova  Dirk D. Van Reenen 《地学前缘(英文版)》2012,3(6):829-841

Reaction textures and fluid inclusions in the～2.0 Ga pyroxene-bearing dehydration zones within the Sand River biotite-hornblende orthogneisses（Central Zone of the Limpopo Complex） suggest that the formation of these zones is a result of close interplay between dehydration process along ductile shear zones triggered by H₂O-CO₂-salt fluids at 750—800℃and 5.5—6.2 kbar.partial melting,and later exsolution of residual brine and H₂O-CO₂ fluids during melt crystallization at 650—700℃.These processes caused local variations of water and alkali activity in the fluids,resulting in various mineral assemblages within the dehydration zone.The petrological observations are substantiated by experiments on the interaction of the Sand River gneiss with the H₂O-CO-2-（K,Na）Cl fluids at 750 and 800℃and 5.5 kbar.It follows that the interaction of biotite-amphibole gneiss with H₂O-CO₂-（K.Na）Cl fluids is accompanied by partial melting at 750—800℃.Orthopyroxene-bearing assemblages are characteristic for temperature 800℃and are stable in equilibrium with fluids with low salt concentrations,while salt-rich fluids produce clinopyroxene-bearing assemblages.These observations arc in good agreement with the petrological data on the dehydration zones within the Sand River orthoeneisses.  相似文献   

Dynamics of hourly sea level at Hillarys Boat Harbour,Western Australia: a chaos theory perspective     

Rahman Khatibi  Mohammad Ali Ghorbani  Mohammad Taghi Aalami  Kasim Kocak  Oleg Makarynskyy  Dina Makarynska  Mahdi Aalinezhad 《Ocean Dynamics》2011,61(11):1797-1807

Water level forecasting using recorded time series can provide a local modelling capability to facilitate local proactive management practices. To this end, hourly sea water level time series are investigated. The records collected at the Hillarys Boat Harbour, Western Australia, are investigated over the period of 2000 and 2002. Two modelling techniques are employed: low-dimensional dynamic model, known as the deterministic chaos theory, and genetic programming, GP. The phase space, which describes the evolution of the behaviour of a nonlinear system in time, was reconstructed using the delay-embedding theorem suggested by Takens. The presence of chaotic signals in the data was identified by the phase space reconstruction and correlation dimension methods, and also the predictability into the future was calculated by the largest Lyapunov exponent to be 437 h or 18 days into the future. The intercomparison of results of the local prediction and GP models shows that for this site-specific dataset, the local prediction model has a slight edge over GP. However, rather than recommending one technique over another, the paper promotes a pluralistic modelling culture, whereby different techniques should be tested to gain a specific insight from each of the models. This would enable a consensus to be drawn from a set of results rather than ignoring the individual insights provided by each model.  相似文献   

A physicochemical model for the formation of gas hydrates of different structural types in K-2 mud volcano (Kukui Canyon,Lake Baikal)     

A.Yu. Manakov  O.M. Khlystov  A. Hachikubo  A.G. Ogienko 《Russian Geology and Geophysics》2013,54(4):475-482

Earlier, the coexistence of spatially separated layers of gas hydrates of cubic structures I and II (CS-I, CS-II) in the bottom sediment cores from K-2 mud volcano (Kukui Canyon, Lake Baikal) was described. The layers of gas hydrates of different structural types were situated at different depths and overlain by the lacustrine sediments. Hydrate of CS-II contained 13–15 mol.% ethane, whereas CS-I hydrate contained only 3–4 mol.% ethane. We present a physicochemical model explaining the formation of such an unusual natural object. The model suggests that only CS-I hydrate was originally present at the sampling site. Some geologic event (tectonic shifts, landslide, etc.) stopped natural-gas emanation from the mud volcano or increased the heat flow in the hydrate pool. As a result, CS-I hydrate began to dissolve in interstitial water. We assume that the ethane-enriched CS-II hydrate is an intermediate product of the dissociation (dissolution) of CS-I hydrate.  相似文献   

A fragmentation criterion for highly viscous bubbly magmas estimated from shock tube experiments     

Takehiro Koyaguchi  Bettina Scheu  Noriko K. Mitani  Oleg Melnik 《Journal of Volcanology and Geothermal Research》2008

When a highly viscous bubbly magma is sufficiently decompressed, layer-by-layer fracturing propagates through the magma at a certain speed (fragmentation speed). On the basis of a recent shock tube theory by Koyaguchi and Mitani [Koyaguchi, T., Mitani, N. K., 2005. A theoretical model for fragmentation of viscous bubbly magmas in shock tubes. Journal of Geophysical Research 110 (B10), B10202. doi:10.1029/2004JB003513.], gas overpressures at the fragmentation surface are estimated from experimental data on fragmentation speed in shock tube experiments for natural volcanic rocks with various porosities. The results show that gas overpressure at the fragmentation surface increases as initial sample pressure increases and sample porosity decreases. We propose a new fragmentation criterion to explain the relationship between the gas overpressure at the fragmentation surface, the initial pressure and the porosity. Our criterion is based on the idea that total fragmentation of highly viscous bubbly magmas occurs when the tensile stress at the midpoint between bubbles exceeds a critical value. We obtain satisfactory agreement between our simulation and experiment when we assume that the critical value is inversely proportional to the square root of bubble wall thickness. This fragmentation criterion suggests that long micro-cracks or equivalent flaws (e.g., irregular-shaped bubbles) that reach the midpoints between bubbles are a dominant factor to determine the bulk strength of the bubbly magma.  相似文献   

The Polar Cap (PC) indices: Relations to solar wind parameters and global magnetic activity     

P. Stauning  Oleg Troshichev  Alexander Janzhura 《Journal of Atmospheric and Solar》2008,70(18):2246-2261

The polar geomagnetic activity resulting from solar wind–magnetosphere interactions can be characterized the Polar Cap (PC) indices, PCN and PCS. PC index values are derived from polar magnetic variations calibrated on a statistical basis such that the index approximate values in units of mV/m of the interplanetary “geo-effective” (or “merging”) electric field (E_M) conveyed by the solar wind. The timing and amplitude relations of the PC index to solar wind plasma and magnetic field parameters are reported. The solar wind effects are parameterized in terms of the geo-effective electric field (E_M) and the dynamical pressure (P_DYN). The PC index has a delayed and damped response to E_M variations and display saturation-like effects for E_M values exceeding 10 mV/m. Steady or slowly varying levels of solar wind dynamical pressure have little or no impact on the PC index above the effects related to E_M for which the solar wind velocity is also a factor. Sharp increases in the dynamical pressure generate impulsive variations in the PC index comprising a initial negative impulse of 5–10 min duration followed by a positive impulse lasting 10–20 min. Typical amplitudes of both the negative and the positive impulses are 0.2–0.5 units. A sharp decrease in the pressure produces the inverse sequence of pulses in the PC index. Auroral substorm activity represented by the AL index level has a marked influence on the average PC/E_M level at the transition from very quiet (AL0 nT) to disturbed conditions while more or less disturbed conditions (AL<−100 nT) have no systematic effect on the average PC/E_M values. At distinct substorm events the PC/E_M ratio has a minimum (0.8) in the pre-onset phase at around 20 min before substorm onset. The average ratio gradually increases in the expansion phase to reach a maximum value (1.1) at around 40 min after substorm onset (or 20 min after the largest (negative) peak in AL). At substorm recovery during the next 2 h the PC/E_M ratio decreases. Finally, we report on the application of polar magnetic variations to model the disturbance storm time (Dst) index development during magnetic storms by using the PC index as a source function to quantify the energy input to the ring current representing accumulated storm energy and characterized by the Dst index.  相似文献   

Multi-Wavelength Synchrotron Radiation XRF Determination of U and Th in Sedimentary Cores from Lake Baikal   总被引：1，自引：0，他引：1  

Michael A. Phedorin  Evgeny L. Goldberg  Vladislav A. Bobrov  Oleg M. Khlystov  Michael A. Grachev 《Geostandards and Geoanalytical Research》2000,24(2):217-226

A new technique for the determination of uranium and thorium in lacustrine sediments is based on non-destructive synchrotron radiation X-ray fluorescence analysis (SR-XRF) of sediment samples using monochromatic beams of different energies as excitation sources, with the recording and subsequent iterative processing of the X-ray fluorescence spectra. The technique has a multielement capability and enables fast, simultaneous analysis of a few tens of elements. The proposed SR-XRF technique was tested against INAA and ICP-MS methods and showed a number of advantages with a generally good correlation of results by the three methods. Uranium and Th profiles have been measured at a time resolution of 2 kyr in a drill core (BDP-96) from Lake Baikal bottom sediments deposited between 780 and 40 kyr B P. During this time span, peaks in the U and U/Th concentration marked warm climates. Oscillations of U and U/Th in Baikal bottom sediments during the Brunhes chron reflect climate-induced global change in the volume of polar ice, controlled by long-term cyclicity of the Earths orbital parameters. The response of these warm periods is similar to that observed earlier in shorter cores that span the two last interglacials (220-0 kyr BP).  相似文献