ALBERT

Description: While the calibration accuracy of Advanced Microwave Sounding Unit-A (AMSU-A) was well characterized during its prelaunch period, its on-orbit performance remains important after the launch of each satellite. In this study, Global Positioning System (GPS) radio occultation (RO) data are used to carry out a postlaunch calibration to obtain an estimate of the accuracy of brightness temperatures measured by an AMSU-A instrument. At each scan angle, the mean difference and a linear regression relationship between AMSU-A observations and GPS RO brightness temperature simulations can firstly be derived using data in clear-sky conditions over ocean. The AMSU-A upper-air sounding channels are then calibrated to GPS RO brightness temperature simulations using either the mean difference or the linear regression relationship. The effect of the above two calibration methods on the biases of AMSU-A data with respect to NCEP GFS 6-h forecast fields is finally examined. It is found that the magnitude and sign of biases vary with channels. After GPS RO calibration, biases are negative and of the same magnitude for all AMSU-A upper-air sounding channels. The negative biases of AMSU-A brightness temperature are associated with a small warm bias in the physical temperature of NCEP GFS 6-h forecasts compared with GPS RO temperature retrieval above the low troposphere.

Description: The main goal of this paper is to estimate the errors involved in applying a quasi-static convection model such as the Rice Convection Model (RCM) or its equilibrium version (RCM-E), which neglect inertial currents, to treat the injection of fresh particles into the inner magnetosphere in a substorm expansion phase. The approach is based on the idea that the dipolarization process involves earthward motion of a bubble that consists of flux tubes that have lower values of the entropy parameter than the surrounding medium. Our tests center on comparing MHD simulations with RCM- and RCM-E-like quasi-static approximations, for cases where the bubble is considered to be a thin ideal-MHD filament. Those quasi-static solutions miss the interchange oscillations that are often a feature of the MHD results. RCM and, to a lesser extent, RCM-E calculations tend to overestimate the westward electric field at the ionospheric footprint of the bubble and underestimate its duration. However, both get the time integral of the E × B drift velocity right as well as the net energization of the particles in the filament. The quasi-static approximation is most accurate if its computed value of the braking time of the bubble's earthward motion is long compared to the period of the relevant interchange oscillation. Comparison of MHD filament simulations of interchange instability with corresponding RCM calculations suggests a similar validity criterion. For plasma sheet conditions, the quasi-static approximation is typically best if the background medium has low β, worst if it consists of highly stretched field lines.

Description: This paper presents a quantitative theory of “interchange oscillations,” which occur as an earthward-moving low-entropy plasma bubble slows and eventually comes to rest. Our theoretical picture is based on an idealized situation where an ideal-MHD magnetic filament moves without friction through a stationary background that represents the plasma sheet. If the relevant region of the background plasma sheet is interchange stable, then the filament usually executes a damped oscillation about an equilibrium position, where its entropy parameter matches the local background. The oscillations are typically dramatic only if the equatorial plasma beta is greater than about one. We derive an approximate analytic formula for the oscillation period, which is not simply related to slow- or intermediate-wave travel times. For an oscillation that Panov and collaborators carefully studied using THEMIS data, our simple theory, though based on an unrealistic 2D background magnetic field, predicted an oscillation period that agrees with the observations within about 40%. The simulations suggest that the ionospheric oscillation should lag behind the magnetospheric one by between 40 and 90 degrees. Ionospheric conductance affects the damping rate, which maximizes for an auroral zone conductance ∼2 S. Adding a friction force acting between the filament and the background increases the decay rate of the oscillation.

Description: Improving the high-temperature strength and stiffness of Ti 3 SiC 2 is the task of many investigations. However, methods for high-temperature strengthening have not been established although various ways are applicable to enhance the room-temperature mechanical properties of Ti 3 SiC 2 . In this work, we report that significant strengthening was realized at both room and high temperatures by incorporating a small amount of W into Ti 3 ( Si , Al ) C 2 . The onsite temperature for the rapid degradation of stiffness and strength moved more than 150°C upward to over 1200°C. The flexural strength of 5 at.% W -doped Ti 3 ( Si , Al ) C 2 is 632.9 MPa at RT and 285 MPa at 1200°C, being 176% and 170% of those for baseline material, respectively.

Description: Petrological evidence is provided for anatexis of ultrahigh-pressure (UHP) metamorphic quartzite in the Sulu orogen. Some feldspar grains exhibit elongated, highly cuspate shapes, or occur as interstitial, cuspate phases constituting interconnected networks along grain boundaries. Elongated veinlets composed of plagioclase + quartz ± K-feldspar also occur in grain boundaries. These features provide compelling evidence for anatexis of the UHP quartzite. Zircon grains from impure quartzite are all metamorphic growth with highly irregular shape. They contain inclusions of coesite, jadeite, rutile and lower pressure minerals, including multiphase solid inclusions that are composed of two or more phases of muscovite, quartz, K-feldspar and plagioclase. All zircon grains exhibit steep REE patterns, similar U-Pb ages and Hf isotope compositions with a weighted mean of 218±2 Ma. Most of them have similar δ 18 O values of -0.6 to 0.1‰, but a few of them fall in a range of -5.2 to -4.3‰. Thus, these zircon grains would have grown from anatectic melts at various pressures. Zircon O isotope difference indicates that anatectic melts were derived from different sources with contrasting O isotopes but similar Hf isotopes, i.e., one from the quartzite itself and the other probably from the country rock granitic gneiss. Zircon grains from pure quartzite contain relict magmatic cores and significant metamorphic overgrowths. Domains that contain eclogite-facies minerals exhibit flat HREE patterns, no Eu anomalies and concordant U-Pb ages of c . 220 Ma. Similar U-Pb ages are also obtained for domains that contain lower pressure minerals and exhibit steep REE patterns and marked negative Eu anomalies. These observations indicate that zircon records subsolidus overgrowth at eclogite-facies conditions but suprasolidus growth at lower pressures. Zircon enclosed by garnet gave consistent U-Pb ages of c . 214 Ma. Such garnet is interpreted as a peritectic product of the anatectic reaction that involves felsic minerals and possibly amphibole and titanite. The REE patterns of epidote and titanite also record multistage growth and metasomatism by anatectic melts. Therefore, the anatexis of UHP metamorphic rocks is evident during continental collision in the Triassic. © 2012 Blackwell Publishing Ltd

Description: [1]  In Chen and Shearer (2011), we compared well injection data from the Salton Sea geothermal site with nearby seismicity. The detailed injection record for each injection well can be downloaded from the ‘geostream for geothermal resources’ website and include total injection volume and duration for each month. However, we incorrectly interpreted the duration to be the starting date of discrete injection events, which we compared with the occurrence time of individual seismicity swarms. This misinterpretation led to apparently more precise temporal correlations between injection times and swarm activity than can obtained from the injection data. The injection activities are continuous and the exact injection start and stop times for each well are not included in the records that we obtained. This error does not affect our main results, including the longer-term correlations between injection activities and seismicity, as well as the stress drop behavior with distance from injection wells. [2]  The specific corrections are as follows: [3]  (1) In Figure 8 in Chen and Shearer [2011] (Figure 1), The lines indicating exact timing for injection are removed from Figure 8(c). [4]  (2) In section 6.3, the sentence: ‘The swarms are located within the Salton Sea and Brawley geothermal fields, close to geothermal wells, especially the three swarms that started shortly after nearby injection events’ should be changed to ‘The swarms are located within the Salton Sea and Brawley geothermal fields, close to geothermal wells, especially the three swarms that occurred within active injection periods.’ [5]  (3) In paragraph 34, the opening sentence: ‘The large swarm in August, 2005 started less than 10 hours after a cluster of injection events, and exhibits NE-SW migration during the initial 10 hours’ should be changed to ‘The large swarm in August, 2005, is located within an area with a cluster of continuous injection wells, and exhibits NE-SW migration during the initial 10 hours.’ [6]  (4) In paragraph 34, the phrase in the last sentence: ‘The increased pore fluid pressure from multiple injection events prior to the seismicity may have’ should be changed to: ‘The increased fluid pressure from multiple injection wells nearby may have’ [7]  (5) In paragraph 37, the reference to Figure 8c in the last sentence should be removed. However, the fact that multiple injection wells are active at the same time remains a valid point.

Description: Several types of multiphase solid (MS) inclusions are identified in garnet from ultrahigh-pressure (UHP) eclogite in the Dabie orogen. The mineralogy of MS inclusions ranges from pure K-feldspar to pure quartz, with predominance of intermediate types consisting of K-feldspar + quartz ± silicate (plagioclase or epidote) ± barite. The typical MS inclusions are usually surrounded with radial cracks in the host garnet, similar to where garnet contains relict coesite. Barite aggregates display significant heterogeneity in major element composition, with total contents of only 57–73% and highly variable SiO 2 contents of 0.32–25.85% that are positively correlated with BaO and SO 3 contents. The occurrence of MS inclusions provides petrographic evidence for partial melting in the UHP metamorphic rock. The occurrence of barite aggregates with variably high SiO 2 contents suggests the coexistence of aqueous fluid with hydrous melt under HP eclogite facies conditions. Thus, local dehydration melting is inferred to take place inside the UHP metamorphic slice during continental collision. This is ascribed to phengite breakdown during ‘hot’ exhumation of the deeply subducted continental crust. As a consequence, the aqueous fluid is internally buffered in chemical composition and its local sink is a basic trigger to the partial melting during the continental subduction-zone metamorphism.

Description: We detect 17 seismic events in Antarctica from 1997 to 2009 by applying a surface wave detector to global seismic data. We locate these events using a waveform cross-correlation method and find that most occurred near the coast of Antarctica and are clustered in three regions: four events are on the Ronne Ice Shelf, close to the location of a 1998 calving event; five events are near the Vanderford Glacier; and eight events are near the Ninnis Glacier. The observed Rayleigh and Love waves for these events have similar amplitudes and a two-lobed radiation pattern, matching the expected amplitude behavior of a single-force source model. Using such a model, we obtain best fitting horizontal force directions for the 14 events that have relatively better signal-to-noise ratios. Analysis of coastline changes from MODIS images before and after the detected events show that two events on Vanderford Glacier and one event near Ninnis Glacier are likely associated with calving events. Moreover, the inferred force directions for the seismic events appear consistent with local ice flow directions. Both satellite observations and modeling results strongly suggest a link between seismic events and calving processes in the two regions. However, the force directions on the Ronne Ice Shelf are aligned with observed rift propagation directions, suggesting that these events may arise from rifting processes.

Description: Laser ablation inductively coupled plasma mass spectrometry analyses of U–Pb isotopes and trace elements in zircon and titanite were carried out on epoxy mounts and thin sections for ultrahigh-pressure (UHP) eclogite in association with paragneiss in the Dabie orogen. The results provide a direct link between metamorphic ages and temperatures during continental subduction-zone metamorphism. Zircon U–Pb dating gives two groups of concordant ages at 242 ± 2 to 239 ± 5 Ma and 226 ± 2 to 224 ± 6 Ma, respectively. The Triassic zircon U–Pb ages are characterized by flat heavy rare earth element (HREE) patterns typical of metamorphic growth. Ti-in-zircon thermometry for the two generations of metamorphic zircon yields temperatures of 697 ± 27 to 721 ± 8 °C and 742 ± 19 to 778 ± 34 °C, respectively. We interpret that the first episode of zircon growth took place during subduction prior to the onset of UHP metamorphism, whereas the second episode in the stage of exhumation from UHP to HP eclogite facies regime. Thus, the continental subduction-zone metamorphism of sedimentary protolith is temporally associated with two episodes of fluid activity, respectively, predating and postdating the UHP metamorphic phase. The significantly high Ti-in-zircon temperatures for the younger zircon at lower pressures indicate the initial ‘hot’ exhumation after the peak UHP metamorphism. There are two types of titanite. One exhibits light rare earth element (LREE) enrichment, steep MREE–HREE patterns and no Eu anomalies, and yields Zr-in-titanite temperatures of 551 to 605 °C at 0.5 GPa, and the other shows LREE depletion and flat MREE–HREE patterns, and gives Zr-in-titanite temperatures of 782–788 °C at 2.0 GPa. The former is amenable for U–Pb dating, yielding a discordia lower intercept age of 252 ± 3 Ma. Thus, the first type of titanite is interpreted to have grown in the absence of garnet and plagioclase and thus in the early stage of subduction. In contrast, the second one occurs as rims surrounding rutile cores and thus grew in the presence of garnet during the ‘hot’ exhumation. Therefore, there is multistage growth of zircon and titanite during the continental subduction-zone metamorphism. The combined studies of chronometry and thermobarometry provide tight constraints on the P–T–t path of eclogites during the continental collision. It appears that the mid- T /UHP eclogite facies zone would not only form by subduction of the continental crust in a P–T path slightly below the wet granite solidus, but also experience decompression heating during the initial exhumation.

Description: The ecological situation of the Tarim River basin in China seriously declined since the early 1950's, mainly due to a strong increase in water abstraction for irrigation purposes. In order to restore the ecological system and support sustainable development of the Tarim River basin region in China, more hydrological studies are demanded to properly understand the processes of the watershed and efficiently manage the water resources. Such studies are, however, complicated due to the limited data availability, especially in the mountainous headwater regions of the Tarim River basin. This study investigated the usefulness of remote sensing (RS) data in order to overcome that lack of data in the spatially distributed hydrological modelling of the basin. Complementary to the conventional station based (SB) data, the RS products that are directly used in this study include precipitation, evapotranspiration and leaf area index (LAI). They are derived from raw image data of the Chinese Fengyun meteorological satellite and from the Moderate Resolution Imaging Spectroradiometer (MODIS). The MODIS land surface temperature was used to calculate the atmospheric temperature lapse rate to describe the temperature dependency on topographical variations. Moreover, MODIS based snow cover images were used to obtain model initial conditions and as validation reference for the snow model component. Comparison of model results based on RS input versus conventional SB input exhibited similar results in terms of high and low river runoff extremes, cumulative runoff volumes in both runoff and snow melting seasons, and spatial and temporal variability of snow cover. During summer time, when the snow cover shrinks in the permanent glacier region, it was found that the model resolution influences the model results dramatically; hence showing the importance of detailed (RS based) spatially distributed input data. Copyright © 2011 John Wiley & Sons, Ltd.