ALBERT

Description: In this study, high-resolution projections of temperature and precipitation changes over Canada were developed through the PRECIS model under Representative Concentration Pathways (RCPs). In detail, the PRECIS model was employed to conduct simulations for the historical period over the entirety of Canada, driven by the boundary conditions from both ERA-Interim (1979 -2011) and HadGEM2-ES (1959 - 2005). The performance of PRECIS simulations in reproducing historical climatology of Canada was then validated through comparison with observed temperature and precipitation over the baseline period (1986 - 2005). The boundary conditions from HadGEM2-ES under RCP4.5 and RCP8.5 will be used to drive PRECIS for simulating climatic variables over Canada for the period of 2005 - 2099. Future climate projections of temperature and precipitation as well as their extreme indices over two time slices (i.e., 2046 - 2065 and 2076 - 2095) were extracted and analyzed. The results could help investigate how the regional climate over Canada will respond to global warming as well as the spatiotemporal characteristics of plausible climate changes in the Canadian context. The validation results demonstrate that the PRECIS model is effective in reproducing the historical climatological patterns of annual mean temperature and total precipitation across Canada. Projections of temperature and precipitation for the two future periods indicate that there will be an apparent increasing pattern over Canada. The projected changes derived in this study can provide decision-makers with valuable information to evaluate possible impacts on economic, social, and environmental sectors at regional and local scales.

Description: Some mafic granulites in the Sanggan area of the northern Trans-North China Orogen (TNCO) have a relatively simple mineralogy with low energy grain shapes that are compatible with an assumption of equilibrium, but the rock-forming minerals show variations in composition that create challenges for thermobarometry. The mafic granulites, which occur as apparently disrupted dyke-like bodies in tonalite–trondhjemite–granodiorite gneisses, are divided into two types based on petrography and chemical composition. Type 1 mafic granulites are fine- to medium-grained with an equilibrated texture and an assemblage of plagioclase+clinopyroxene+ garnet+magnetite+ilmenite and sometimes minor hornblende±orthopyroxene. Type 2 mafic granulites are coarse-grained and hornblende-bearing with a peak assemblage of garnet+ clinopyroxene+plagioclase+hornblende and coronae and symplectites of plagioclase+ hornblende+orthopyroxene partially replacing porphyroblastic garnet±clinopyroxene. SIMS U–Pb dating of metamorphic zircon from two type 1 mafic granulites yields metamorphic ages of c . 1.84 and 1.83 Ga, consistent with published ages of the type 2 mafic granulites. Based on phase equilibrium modelling, we use the common overlap of P–T fields defined by the mineral assemblage limits, and the mole proportion and composition isopleths of different minerals in each sample to quantify the metamorphic conditions. For type 1 granulites, overlap of the mineral proportion and composition fields for each of three samples yields similar P–T conditions of 710–880 °C at 0.57–0.79 GPa, 820–850 °C at 0.59–0.63 GPa, 800–860 °C at 0.59–0.68 GPa. For the type 2 granulites, overlaying the peak assemblage fields for three samples yields common P–T conditions of 870–890 °C at 1.1–1.2 GPa. For the retrograde assemblage, overlap of the mineral proportion and composition fields for each sample yields similar P–T conditions of 820–840 °C at 0.85–0.88 GPa, 860–880 °C at 0.83–0.86 GPa, 880–930 °C at 0.89–0.95 GPa. The P–T conditions appear distinct between the two types of mafic granulite, with the mineralogically simple type 1 mafic granulites recording the lowest pressures. However, there are significant uncertainties associated with these results. For the granulites, there are uncertainties related to the determination of modes and composition of the equilibration volume, particularly estimation of O and H 2 O contents, and in the phase equilibrium modelling there are uncertainties that propagate through the calculation of mole proportions and mineral compositions. The compound uncertainties on pressure and temperature for high-temperature granulites are large and the results of our study show that it may be unwise to rely on P–T conditions determined from the simple intersection of calculated mineral composition isopleths alone. Since the samples in this study are from a limited area—a few hundred square metres—we infer that they record a single P–T path involving both decompression and cooling. However, there is no evidence of the high-pressure granulite facies event at 1.93 – 1.90 Ga that is recorded elsewhere in the TNCO, which suggests that the precursor basic dykes were emplaced late during the assembly of the North China Craton. This article is protected by copyright. All rights reserved.

Description: We present a statistical analysis of phase space density data from the first 26 months of the Van Allen Probes mission. In particular we investigate the relationship between the 10s-100s keV seed electrons and 〉1 MeV core radiation belt electron population. Using a cross correlation analysis, we find that the seed and core populations are well correlated with a coefficient of ≈ 0.73 with a time lag of 10-15 hours. We present evidence of a seed population threshold that is necessary for subsequent acceleration. The depth of penetration of the seed population determines the inner boundary of the acceleration process. However, we show that an enhanced seed population alone is not enough to produce acceleration in the higher energies, implying that the seed population of 100s of keV electrons is only one of several conditions required for MeV electron radiation belt acceleration.

Description: Most natural sediment is invariably covered by biofilms in reservoirs and lakes, which have significant influence on bedform dynamics and sediment transport, and also play a crucial role in natural river evolution, pollutant transport, and habitat changes. However, most models for sediment transport are based on experiments using clean sediments without biological materials. In this study, a three-dimensional mathematical model of hydrodynamics and sediment transport is presented with a comprehensive consideration of the biofilm effects. The changes of the bed resistance mainly due to the different bedform dynamics of the biofilm-coated sediment (bio-sediment), which affect the hydrodynamic characteristics, are considered. Moreover, the variations of parameters related to sediment transport after the biofilm growth are integrated, including the significant changes of the incipient velocity, settling velocity, reference concentration and equilibrium bed-load transport rate, etc. The proposed model is applied to evaluate the effects of biofilms on the hydrodynamic characteristics and sediment transport in laboratory experiments. Results indicate that the mean velocity increases after the biofilm growth, and the turbulence intensity near the river bed decreases under the same flow condition. Meanwhile, biofilm inhibits sediment from moving independently. Thus, the moderate erosion is observed for bio-sediment resulting in smaller suspended sediment concentrations. The proposed model can reasonably reflect these sediment transport characteristics with biofilms, and the approach to integration of the biological impact could also be used in other modeling of sediment transport, which can be further applied to provide references for the integrated management of natural aqueous systems.

Description: [1]  Plasma bubbles are regions of depleted plasma density in the nighttime equatorial ionosphere. Plasma enhancements, also referred as plasma blobs, are regions where the plasma density is increased. It has not been well understood whether and how plasma enhancements are related to plasma bubbles. In this paper, we present the observations of plasma bubbles and enhancements by the Communication/Navigation Outage Forecasting System (C/NOFS) satellite during 2008 and 2009. In some cases, C/NOFS first detected plasma bubbles near the magnetic equator and then plasma enhancements at the same longitudes but at higher latitudes during subsequent orbits. In other cases, C/NOFS first detected plasma enhancements at off-equatorial locations and then plasma bubbles near the magnetic equator at the same longitudes. It is also found that plasma enhancements existed just above plasma depletions. We propose a unified scenario to describe the evolution of plasma bubbles and the formation of plasma enhancements. In the proposed scenario, plasma enhancements can occur at different latitudes and altitudes during the early, intermediate, and late stages of the bubble evolution. This scenario provides a reasonable explanation of the observations.

Description: [1]  GRACE satellite-derived total water storage can be obscured by glacial isostatic adjustment. In order to solve this problem for the Nelson River drainage basin in Canada, a gravity rate map from 110 months (June 2002- October 2011) of GRACE gravity data was corrected for glacial isostatic adjustment using an independent gravity rate map derived from updated GPS vertical velocities. The GPS-based map was converted to equivalent gravity rate using a transfer function developed from GPS and absolute-g data at co-located sites. The corrected GRACE gravity rate map revealed a major positive anomaly within the drainage basin, which was independently shown by hydrological data to be due to changes in water storage. The anomaly represents a cumulative increase at its center of about 340 mm of water, reflecting a progression from extreme drought to extremely wet conditions.