Electric and dielectric properties of forsterite between 400 and 900°C

The electrical impedance of a sintered forsterite sample containing 1 mol percent SiO₂ in excess has been studied as a function of frequency (1–10⁵ Hz) and temperature (400–900°C). The electrical properties are strongly frequency-dependent, requiring both conduction and displacement current for their interpretation. The electrical conductivity is thermally activated with a mean activation energy of 1.15 eV. It is interpreted as being ionic and caused by migration of magnesium ions via a vacancy mechanism. Dielectric data deduced from impedance measurements vary as ω^n?1 (0 < n < 1) at constant temperature. The value of n is different below and above a critical frequency ω_c, which is thermally activated and interpreted as the jump frequency of the migrating species.     

积云动力和电过程二维模式研究 Ⅰ．理论和模式

提出了一个模拟积云动力和电力发展的二维时变轴对称模式。考虑了１０种主要微物理过程，它们包括凝结（凝华）、蒸发、自动转换、粒子间的碰撞以及冰晶核化，次生冰晶等。在起电过程中除了考虑常规的扩散和电导起电外，重点引入了感应和非感应起电，以及次生冰晶起电的作用。作者认为后三个过程是形成积云电结构的主要物理因子。     

Matrix polynomial representation of the anisotropic magnetotelluric impedance tensor

A formalism based upon the equal penetration depth stratification assumption is extended to a layered anisotropic medium, yielding a recursive algorithm for the computation of the magnetotelluric impedance tensor elements. The development of this new procedure requires an appropriate layer-discretization as well as an extension of the reflection coefficient definition for the anisotropic layered model.This method transfers the differential problem into an algebraic one, and is independent of the electric and magnetic field vectors. The technique is a recursive process which gives a rational matrix polynomial representation for the magnetotelluric impedance tensor.The procedure involves the use of second-order matrices, rather than the fourth-order ones normally used for such a case. Using this representation, a separation of the contribution of the model parameters from that of the frequency is achieved. Consequently the elements of the magnetotelluric impedance tensor are computed, for each frequency, using coefficients which are evaluated just once for a given model.     

Vertical distribution of HTO and 125I− transport parameters in Boom Clay in the Essen-1 borehole (Mol,Belgium)

In the frame of the R&D activities performed on the Boom Clay for assessing the suitability of deep clayey formations for radioactive waste disposal, the transferability of the scientific results obtained on the Boom Clay in Mol to the whole Campine Basin is investigated. Boreholes were drilled at different locations (e.g. Mol, Doel, Essen) and cores were sampled over the entire thickness of the Boom Clay formation on which the migration parameters for iodide and tritiated water (HTO) are determined.At Essen, the transport parameters in the Boom Clay can be considered as homogeneous in the range from 159 m to 241 m Below Drilling Table. The average hydraulic conductivity is (5.4 ± 1.7) × 10⁻¹² m/s. The average ηR value for iodide is 0.25 ± 0.03 and 0.42 ± 0.05 for HTO. For HTO, this high value is mainly due to a higher value in the Putte Member (0.46 ± 0.03) compared to the other members (0.39 ± 0.02). The apparent diffusion coefficient is (1.3 ± 0.1) × 10⁻¹⁰ m²/s for HTO and (1.1 ± 0.2) × 10⁻¹⁰ m²/s for iodide. The expected effect of ionic strength (increasing with depth) on the ηR value of iodide is of the same size as the measurement error, what might explain why it was not observed.On a lateral (horizontal) level, the hydraulic conductivity at the Essen-1 borehole (5.4 × 10⁻¹² m/s) lies between that of Boom Clay in Mol-1 (2.5 × 10⁻¹² m/s) and that of Boom Clay in Doel-2b (1.4 × 10⁻¹¹ m/s). For iodide, the higher ηR value in Essen-1 and Doel-2b (ηR ≈ 0.25) than in Mol-1 (ηR ≈ 0.16) can partly be explained by a higher ionic strength of the pore water. Apart from the Putte Member at Essen-1, the HTO porosities of the Terhagen Member and the Transition zone in Essen are in the range of the average porosities observed in Mol and Doel (ηR ≈ 0.37–0.39). For both iodide and HTO, the value of the apparent diffusion coefficient D_app is similar in Mol-1 and in Doel-2b, with a clearly higher value for HTO than for iodide. In Essen-1, the apparent diffusion coefficients for iodide and HTO are nearly equal, and slightly smaller than the iodide value in Mol-1/Doel-2b. Accordingly, the HTO apparent diffusion coefficient is considerably smaller in Essen-1 than in Mol-1/Doel-2b.     

The records of solar wind and solar flares in aubrites

A large number of individual enstatite crystals of the gas-rich aubrites Khor Temiki, Staroe Pesyanoe and Bustee was analyzed for implanted helium and for steep gradient ion tracks in order to investigate the relation between solar flare irradiation and solar wind implantation with extreme local resolution. Irradiated and non-irradiated crystals coexist within the gas-rich phases of the aubrites investigated. Statistically in a given meteorite the proportion of crystals with implanted solar wind is similar to the proportion of solar flare irradiated crystals. It varies from aubrite to aubrite in the sequence of their bulk contents of trapped rare gases.For nine enstatites, tracks and rare gases were subsequently measured within the same crystal. The results support the intimate association of solar flare tracks and implanted He. The⁴He-surface concentrations of irradiated crystals vary between <5 × 10^?7 and 10^?4 cm³ STP/cm².The absence of saturation effects together with the low degree of elemental gas fractionation indicates very short solar wind exposure times (< 100 yr) rather than strong diffusion losses. The evidence from tracks and rare gases can be understood in terms of an early simultaneous irradiation of aubritic crystals by solar wind and solar flare particles on top of a regolith-covered parent body.     

高温高压下上地幔岩石电导率实验研究

为了建立具有普遍适用性的上地幔电性结构,本文利用Kawai-1000t压机和Solartron IS-1260阻抗/增益-相位分析仪,在4.0~14.0 GPa、873~1673 K的条件下,采用交流阻抗谱法（频率范围10^-1~10⁶Hz）测量了不含水的地幔岩电导率.实验结果显示,岩石的电导率随温度升高而大幅度的增大;在较大的温度范围内岩石的导电机制发生了变化,中低温时为小极化子导电,此时激活焓为0.94 eV （±0.13） eV,激活体积为0.11（±0.92） cm³·mol^-1,高温时为和镁空穴相关的离子导电,此时激活焓为1.6~3.17 eV,激活体积为6.75（±7.43） cm³·mol^-1;本次测量的电导率比低压下岩石的电导率要高,比矿物的电导率也要高.用本次的实验结果回归计算得到Fennoscandian地区的上地幔的一维电导率剖面,发现200 km以上本次实验计算的结果和大地电磁测深的电导率剖面吻合的比较好,在200 km以下本次实验得到的要比野外测量的电导率稍稍高一点,可能是因为实验过程中没有完全避免水的影响.本次的实验结果比用有效均匀介质方法计算得到的pyrolite矿物模型的电导率要高出两个数量级,这样的结果显示只用一种矿物的电导率或是几种矿物理论计算的结果有一定的不合理性.     

Attenuation of Coda Waves in the Saurashtra Region, Gujarat (India)

The attenuation characteristics based on coda waves of two areas—Jamnagar and Junagarh of Saurashtra, Gujarat (India)—have been investigated in the present study. The frequency dependent relationships have been developed for both the areas using single back scattering model. The broadband waveforms of the vertical components of 33 earthquakes (Mw 1.5–3.5) recorded at six stations of the Jamnagar area, and broadband waveforms of 68 earthquakes (Mw 1.6–5) recorded at five stations of the Junagarh area have been used for the analysis. The estimated relations for the Junagarh area are: Q _c?=?(158?±?5)f^(0.99±0.04) (lapse time : 20?s), Q _c?=?(170?±?4.4)f^(0.97±0.02) (lapse time : 30?s) and Q _c?=?(229?±?6.6)f^(0.94±0.03) (lapse time : 40?s) and for the Jamnagar area are: Q _c?=?(178?±?3)f^(0.95±0.05) (lapse time : 20?s), Q _c?=?(224?±?6)f^(0.98±0.06) (lapse time : 30?s) and Q _c?=?(282?±?7)f^(0.91±0.03) (lapse time : 40?s). These are the first estimates for the areas under consideration. The Junagarh area appears to be more attenuative as compared to the Jamnagar area. The increase in Q _c values with lapse time found here for both the areas show the depth dependence of Q _c as longer lapse time windows will sample larger area. The rate of decay of attenuation (Q ^?1) with frequency for the relations obtained here is found to be comparable with those of other regions of the world though the absolute values differ. A comparison of the coda-Q estimated for the Saurashtra region with those of the nearby Kachchh region shows that the Saurashtra region is less heterogeneous. The obtained relations are expected to be useful for the estimation of source parameters of the earthquakes in the Saurashtra region of Gujarat where no such relations were available earlier. These relations are also important for the simulation of earthquake strong ground motions in the region.     

Thermal expansion of stishovite

The thermal expansion of stishovite has been determined by an X-ray camera technique in a temperature range of 18 – 600°C at an atmospheric pressure. The thermal-expansion coefficients along the crystallographic a- and c-axes at 300 K are α_a = (6.0 ± 0.6) · 10^?6K^?1 and α_c = (1.4 ± 0.5) · 10^?6K^?1, respectively. The volume coefficient at 300 K is α_ν = (13.5 ± 0.6) · 10^?6K^?1.     

Observations of fluid‐dependent shear‐wave splitting in synthetic porous rocks with aligned penny‐shaped fractures‡

P‐ and S‐wave velocity and attenuation coefficients (accurate to ±0.3% and ±0.2 dB/cm, respectively) were measured in synthetic porous rocks with aligned, penny‐shaped fractures using the laboratory ultrasonic pulse‐echo method. Shear‐wave splitting was observed by rotating the S‐wave transducer and noting the maximum and minimum velocities relative to the fracture direction. A block of synthetic porous rock of fracture density 0.0201 ± 0.0068 and fracture size 3.6 ± 0.38 mm (measured from image analysis of X‐ray CT scans) was sub‐sampled into three 20–30 mm long, 50 mm diameter core plugs oriented at 0°, 45° and 90° to the fracture normal (transversely isotropic symmetry axis). Full waveform data were collected over the frequency range 500–1000 kHz for both water and glycerin saturated cores to observe the effect of pore fluid viscosity at 1 cP and 100 cP, respectively. The shear‐wave splitting observed in the 90° core was 2.15 ± 0.02% for water saturated and 2.39 ± 0.02% for glycerin saturated, in agreement with the theory that suggests that the percentage splitting should be 100 times the fracture density and independent of the saturating fluid. In the 45° core, by contrast, splitting was 0.00 ± 0.02% for water saturation and ?0.77 ± 0.02% for glycerin saturation. This dependence on fracture orientation and pore fluid viscosity is consistent with the poro‐visco‐elastic theory for aligned, meso‐scale fractures in porous rocks. The results suggest the possible use of shear‐ or converted‐wave data to discriminate between fluids on the basis of viscosity variations.     

Experimental measurements of the streaming potential and seismoelectric conversion in Berea sandstone

The streaming potential across a porous medium is induced by a fluid flow due to an electric double layer between a solid and a fluid. When an acoustic wave propagates through a porous medium, the wave pressure generates a relative movement between the solid and the fluid. The moving charge in the fluid induces an electric field and seismoelectric conversion. In order to investigate the streaming potential and the seismoelectric conversion in the same rock sample, we conduct measurements with Berea sandstone saturated by NaCl solutions with different conductivities. We measure the electric voltage (streaming potential) across a cylindrical sample in NaCl solutions with different conductivities and under different pressures to determine the DC coupling coefficients. We also measure the seismoelectric signals induced by acoustic waves with a Berea sandstone plate at different frequencies and solution conductivities. The pressures of the acoustic waves are calibrated with a standard hydrophone (Brüel & 8103) at different frequencies (15–120 kHz). We calculate the quantitative coupling coefficients of the seismoelectric conversion at DC and at high frequencies with samples saturated by solutions with different conductivities. When the Berea sandstone sample is saturated by the NaCl solution with 0.32 mS/m in conductivity, for example, the DC and seismoelectric coupling coefficients at 15 kHz are 0.024 μV/Pa and 0.019 μV/Pa, respectively. The seismoelectric coupling coefficient is an important and helpful parameter for designing a seismoelectric tool. More experimental measurements of seismoelectric coupling coefficients in the frequency range of 100 Hz to 15 kHz are needed in the future.     

Attenuation of P- and S-waves in the Chamoli Region, Himalaya, India

The attenuation properties of the crust in the Chamoli region of Himalaya have been examined by estimating the frequency-dependent relationships of quality factors for P waves (Q_α) and for S waves (Q_β) in the frequency range 1.5–24 Hz. The extended coda normalization method has been applied on the waveforms of 25 aftershocks of the 1999 Chamoli earthquake (M 6.4) recorded at five stations. The average value of Q_α is found to be varied from 68 at 1.5 Hz to 588 at 24 Hz while it varies from 126 at 1.5 Hz to 868 at 24 Hz for Q_β. The estimated frequency-dependent relations for quality factors are Q_α = (44 ± 1)f^(0.82±.04) and Q_β = (87 ± 3)f^(0.71±.03). The rate of increase of Q(f) for P and S waves in the Chamoli region is comparable with the other regions of the world. The ratio Q_β/Q_α is greater than one in the region which along with the frequency dependence of quality factors indicates that scattering is an important factor contributing to the attenuation of body waves in the region. A comparison of attenuation relation for S wave estimated here (Q_β = 87f^0.71) with that of coda waves (Q_c = 30f^1.21) obtained by Mandal et al. (2001) for the same region shows that Q_c > Q_β for higher frequencies (>8 Hz) in the region. This indicates a possible high frequency coda enrichment which suggests that the scattering attenuation significantly influences the attenuation of S waves at frequencies >8 Hz. This observation may be further investigated using multiple scattering models. The attenuation relations for quality factors obtained here may be used for the estimation of source parameters and near-source simulation of earthquake ground motion of the earthquakes, which in turn are required for the assessment of seismic hazard in the region.     

The KVVN-7 multifunction digital measuring station for electromagnetic monitoring of seismoactive zones

The portable highly sensitive measuring station KVVN-7 has been designed. It enables us to perform frequency sounding with controllable sources and audio-magnetotelluric sounding in the field of natural variations in an electromagnetic field within one session. Signal recording is made by seven channels (three magnetic and four electric ones) in a broad frequency spectrum (0.1–2000 Hz) with elimination of frequencies on the edges of the set frequency range and in the odd harmonics of industrial frequency (up to the ninth harmonic). The station incorporates the system of band-stop filters and anti-alias filters at resistors having a low temperature coefficient of resistance (TCR is lower than 25 × 10⁻⁶ °C⁻¹) and capacitors having a low temperature coefficient of capacity (TCC is lower than ±30 × 10⁻⁶ °C⁻¹). Application of the KVVN-7 station allows the electric conductivity and fluid regime of the upper crust to be studied for both implementation of geological tasks and tasks related to electromagnetic monitoring of seismoactive zones in combination with seismic methods. The example of practical application of the KVVN-7 station in the Lovozero-Pulozero profile (Kola Peninsula) has been presented. A high effectiveness of a station has been demonstrated when study of a fluid-saturated layer with conductivity of a dilatancy-diffuse origin (“DD layer”) in the upper crust. The further perfection of the KVVN-7 measuring station is aimed at the design of a completely automated recording system through data recording to a built-in data medium (flash memory). Additionally, it is suggested to use a built-in analog-to-digital converter of high resolution (24 bit) for every channel in order to broaden the dynamical range of the station.     

Mineralogy and stable isotope geochemistry of hydrothermally altered oceanic rocks

Data for the diffusion of cations in pyroxenes are relevant to a variety of sub-solidus processes including order-disorder and exsolution. Similar data must also be available if the reliability of geobarometers and geothermometers involving pyroxenes is to be assessed. Two types of diffusion experiment have been performed to determine cation diffusion rates in pyroxenes: (1) interdiffusion between single crystals of diopside and polycrystalline sinters enriched in Al and Fe, and (2) interdiffusion between single crystals of diopside and a glass of the same composition which was isotopically enriched in²⁶Mg and⁴³Ca. Following high-temperature annealing for periods up to several hundred hours, analysis of the diffusion couples, using an electron microprobe and an ion microprobe respectively, failed to show any measurable diffusion profiles. From these “null result” experiments the diffusion coefficients (D) for Al and Fe in diopside are estimated to be less than4×10^?14cm²s^?1 at 1200°C, and values ofD for Ca and Mg in diopside are estimated to be less than7 × 10^?14cm²s^?1 at 1250°C. These rates are significantly slower than published tracer-type diffusion data for Ca and Al.A review of studies of order-disorder, microstructural coarsening, and diffusion in pyroxenes suggest that activation energies for cation exchange are typically in excess of 60 kcal mol^?1. Transport rates will be assisted, and activation energies lowered by sample non-stoichiometry, inhomogeneities, high dislocation densities and the presence of water.The collective data for Al, Mg and Ca diffusion in diopside indicate diffusion coefficients? 10^?15cm²s^?1 at 1200°C. A comparison with data for diffusion in garnet, olivine and spinel suggests that pyroxenes may have the highest blocking temperatures.     

The inversion of the data of magnetotelluric sounding and electromagnetic frequency sounding with horizontal electric dipole

On the basis of the dispersion relation of magnetotelluric response functions (MTRF), a filter coefficient algorithm has been made, with which the corresponding impedance phase data can be estimated using a set of apparent resistivity data. The tests of theoretical models and observed magnetotelluric (MT) data show that this algorithm is effective. Comparing the impedance phase estimated using dispersion relation with the observed phase, it can be checked whether the dispersion relation between the observed apparent resistivities and phase data was satisfied. The use of phase data corrected using the dispersion relation in the joint inversion for MT impedance is advantageous to obtain more reliable inversion results. The problems on the one-dimensional joint inversion for the (MT) apparent resistivity and the apparent resistivity of the frequency electromagnetic sounding (FEMS) with horizontal electric dipole, whose observed frequency bands are linked up each other, are studied. The observed data of two kinds of electromagnetic (EM) methods at two sites are used to inverse, the comparison with the drilling data show the results are more reliable. To supply the phase data of FEMS using the dispersion relation, for the apparent resistivity-phase data and impedance real part-imaginary part apparent resistivities of two kinds of EM methods the imitated MT joint inversions are made, and more similar results also are obtained. The Chinese version of this paper appeared in the Chinese edition ofActa Seismologica Sinica,15, 91–96, 1993. The projects sponsored by the Chinese Joint Seismological Science Foundation.     

Studies in diffusion,II. Oxygen in phlogopite mica

Self-diffusion of oxygen in a natural phlogopite mica (annite 4%) has been measured under hydrothermal conditions at 2000 bars pressure and from 500 to 800°C using water enriched in¹⁸O. Diffusional transport is dominantly parallel to the c crystallographic axis. A linear Arrhenius plot was obtained with a pre-exponential term = (1.03 ± 0.38) × 10^?9cm²sec^?1 a and an activation energy of 29 ± 2kcal/g-atom O. The difference in transport rate between oxygens in the OH groups and those in tetrahedral sites is small to non-existent unless the OH oxygens diffuse much more slowly than the other oxygens, which we consider unlikely. A typical phlogopite crystal, 0.2 mm thick by 1 mm across will lose radiogenic argon faster than it will exchange oxygen at temperatures above 435°C, but the reverse holds at lower temperatures if the diffusion mechanism can be extrapolated to temperatures below 500°C. Such a crystal will lose only 5% of its argon if held at 380°C for 1 m.y., but could exchange 27% of its oxygen in that time. The rate at which phlogopite will undergo deformation by diffusional creep does not appear to be controlled by oxygen diffusion.     

Influence of the crystal field effect on chemical transport in Earth's mantle: Cr3+ and Ga3+ diffusion in periclase

Experiments were performed to determine concentration-dependent diffusion coefficients of Cr³⁺ and Ga³⁺ in periclase at temperatures of 1563–2273 K. Diffusion profiles measured in the quenched samples are consistent with a theoretical model in which the mobile species is a bound M³⁺-vacancy pair, and each profile was fitted to determine the binding energy and diffusion coefficient of the pair. Trivalent chromium-vacancy pairs diffuse more slowly than Ga³⁺-vacancy pairs, and with higher migration energy, 237 kJ/mol vs. 190 kJ/mol. Cation vacancies also bind less tightly to Cr³⁺ than to Ga³⁺, with average binding free energies of ?22 and ?83 kJ/mol, respectively. At all concentrations and temperatures, Cr³⁺ diffuses much more slowly than Ga³⁺, by up to two orders of magnitude. The differences between Cr³⁺ and Ga³⁺ cannot be explained by differences in ionic radius or dipole polarizability, but are consistent with the influence of the crystal field on the partially occupied 3d orbitals of Cr³⁺. The crystal field splitting stabilizes Cr³⁺ on the octahedral cation site, increasing the energy required for Cr³⁺ to exchange positions with an adjacent vacancy. It also makes Cr³⁺-vacancy pairs less favorable, with the presence of a nearest-neighbor vacancy disrupting the symmetry of the octahedral site, thus diminishing the crystal field stabilization. Trends in the diffusion of first-row divalent transition metals in periclase can also be explained by the crystal field effect. High-spin to low-spin transitions in Fe²⁺, Co²⁺ or Mn²⁺ would significantly enhance their crystal field stabilization in periclase, and if such spin transitions occur in the deep mantle, they would be expected to slow the diffusivity of these ions significantly, perhaps by several orders of magnitude.     

Frequency-Dependent Attenuation of Coda Waves in the Crust in Southwest Anatolia (Turkey)

The attenuation of coda waves in the earth’s crust in southwest (SW) Anatolia is estimated by using the coda wave method, which is based on the decrease of coda wave amplitude in time and distance. A total of 159 earthquakes were recorded between 1997 and 2010 by 11 stations belonging to the KOERI array. The coda quality factor Q _c is determined from the properties of scattered coda waves in a heterogeneous medium. Firstly, the quality factor Q ₀ (the value of Q _c at 1 Hz.) and its frequency dependency η are determined from this method depending on the attenuation properties of scattered coda waves for frequencies of 1.5, 3.0, 6.0, 8.0, 12 and 20 Hz. Secondly, the attenuation coefficients (δ) are estimated. The shape of the curve is controlled by the scattering and attenuation in the crustal volume sampled by the coda waves. The average Q _c values vary from 110 ± 15 to 1,436 ± 202 for the frequencies above. The Q ₀ and η values vary from 63 ± 7 to 95 ± 10 and from 0.87 ± 0.03 to 1.04 ± 0.09, respectively, for SW Anatolia. In this region, the average coda Q–f relation is described by Q _c = (78 ± 9)f ^0.98±0.07 and δ = 0.012 km^?1. The low Q ₀ and high η are consistent with a region characterized by high tectonic activity. The Q _c values were correlated with the tectonic pattern in SW Anatolia.     

Effect of deposit feeders on migration of137Cs in lake sediments

Illite clay particles with adsorbed¹³⁷Cs were added as a submillimeter layer to the surface of silt-clay sediments contained in rectangular Plexiglas cells stored in a temperature-regulated aquarium, in order to trace the effect of the oligochaete, Tubifex tubifex, and the amphipod, Pontoporeia hoyi, on mass redistribution near the sediment-water interface. A well-collimated NaI gamma detector scanned each sediment column (～10 cm deep) at daily or weekly intervals for six months, depicting the time evolution of radioactivity with and without added benthos. In a cell with tubificids (～5 × 10⁴ m^?2), which feed below 3 cm and defecate on surface sediments, the labeled layer was buried at a rate of 0.052 ± 0.007 cm/day (20°C). When labeled particles entered the feeding zone,¹³⁷Cs reappeared in surface sediments creating a bimodal activity profile. In time, the activity tended toward a uniform distribution over the upper 6 cm, decreasing exponentially below to undetectable levels by 9 cm. In a cell with amphipods (～1.6 × 10⁴ m^?2) uniform activity developed rapidly (～17 days) down to a well-defined depth (1.5 cm). The mixing of sediments by Pontoporeia is described by a simple quantitative model of eddy diffusive mixing of sediment solids. The value of the diffusion coefficient, 4.4 cm²/yr (7°C) was computed from a least squares fit of theoretical to observed profile broadening over time. In a cell without benthos, small but measurable migration of¹³⁷Cs indicated an effective molecular diffusion coefficient of 0.02 cm²/yr.     

Distribution of some trivalent ions between melt and single crystals of Mg2SiO4 grown by the Czochralski method

Partition coefficients for trace amounts of trivalent ions between artificial single crystals of Mg₂SiO₄ grown by the Czochralski method and the coexisting melt have been determined by neutron activation analysis. They are found to vary greatly with the amount of visible imperfections in the crystal and slightly with the concentration of the ions in the melt. Plots of the partition coefficients against ionic radius of the trace ions give a pattern which agrees qualitatively with that found in a natural olivine phenocryst-groundmass pair.     

Characteristics of aerosol optical depth and Ångström parameters over Mohal in the Kullu Valley of Northwest Himalayan Region,India

The measurements using a ground based multi wavelength radiometer (MWR) at Mohal (31°54′N, 77°07′E, 1154 m AMSL) in the Kullu valley of Northwestern Himalayan region show that the spectral aerosol optical depth (AOD) and turbidity coefficient, β, are high in summer, moderate in monsoon season, low in winter and lowest in autumn, while wavelength exponent, α, has an opposite trend. Average annual value of AOD at 500 nm is 0.24±0.01, 0.43±0.02, and 0.28±0.02; that of β is 0.14±0.01, 0.22±0.02, and 0.17±0.03; and that of α is 1.06±0.09, 1.16±0.10, and 0.86±0.13, respectively, for clear, hazy and partially clear sky days. The considerably greater value of β on hazy days indicates more coarse particles in mountain haze. The fractional asymmetry factor (AF) is more negative in summer and autumn months. The AOD and β have significantly positive correlation with temperature and wind speed, suggesting high AODs and turbidity on hot and windy days.