ALBERT

Description: During the interval from 06:15 to 07:30 UT on 24 August 2005, the Chinese Tan-Ce 1 (TC1) satellite observed the multiple responses of the near-Earth magnetotail to the combined changes in solar wind dynamic pressure and interplanetary magnetic field (IMF). The magnetotail was highly compressed by a strong interplanetary shock because of the dynamic pressure enhancement (∼15 nPa), and the large shrinkage of magnetotail made a northern lobe and plasma mantle move inward to the position of the inbound TC1 that was initially in the plasma sheet. Meanwhile, the dynamic pressure fluctuations (∼0.5–3 nPa) behind the shock drove the quasi-periodic oscillations of the magnetopause, lobe-mantle boundary, and geomagnetic field at the same frequencies: one dominant frequency was around 3 mHz and the other was around 5 mHz. The quasi-periodic oscillations of the lobe-mantle boundary caused the alternate entries of TC1 into the northern lobe and the plasma mantle. In contrast to a single squeezed or deformed magnetotail by a solar wind discontinuity moving tailward, the compressed and oscillating magnetotail can better indicate the dynamic evolution of magnetotail when solar wind dynamic pressure increases and fluctuates remarkably, and the near-Earth magnetotail is quite sensitive even to some small changes in the solar wind dynamic pressure when it is highly compressed. Furthermore, it is found that a considerable amount of oxygen ions (O+) appeared in the lobe after the southward turning of IMF.

Description: [1]  When a barchan dune migrates, the sediment trapped on its lee side is later mobilized when exposed on the stoss side. Then, sand grains may undergo many dune turnover cycles before their ejection along the horns, but the amount of time a sand grain contributes to the dune morphodynamics remains unknown. To estimate such a residence time, we analyze sediment particle motions in steady-state barchans by tracking individual cells of a 3D cellular automaton dune model. The overall sediment flux may be decomposed into advective and dispersive fluxes to estimate the relative contribution of the underlying physical processes to the barchan shape. The net lateral sediment transport from the center to the horns indicates that dispersion on the stoss slope is more efficient than the convergent sediment fluxes associated with avalanches on the lee slope. The combined effect of these two antagonistic dispersive processes restricts the lateral mixing of sediment particles in the central region of barchans. Then, for different flow strengths and dune sizes, we find that the mean residence time of sediment particles in barchans is equal to the surface of the central longitudinal dune slices divided by the input sand flux. We infer that this central slice contains most of the relevant information about barchan morphodynamics. Finally, we initiate a discussion about sediment transport and memory in the presence of bed forms using the advantages of the particle tracking technique.

Description: Abstract The Yellow River flow has decreased substantially in recent decades, and the river often dried up in the lower reach and failed to reach the sea. Climate change and human disruption have been suggested as major causes of the flow reduction, but quantification of their relative contribution is challenging due to limited instrumental records and disturbance by dams. Here we use a basin‐wide tree ring network to reconstruct the Yellow River flow for the past 1,200 years and show that the flow exhibits marked amplitude variations that are closely coupled to the hydrological mean state swings at multidecadal to centennial timescales. Recent flow should have increased to the highest level of the past 1,200 years if there were no human disruption. However, human activities have caused a loss of nearly half of natural flow since the late 1960s and are the main culprit for recent downstream flow reduction.

Description: Abstract Omphacite is a major mineral phase of eclogite, which provides the main driving force for the slab subduction into the Earth's interior. We have measured the single‐crystal elastic moduli of omphacite at high pressures for the first time up to 18 GPa at ambient temperature using Brillouin spectroscopy. A least‐squares fit of the velocity‐pressure data to the third‐order finite strain equation of state yields KS0'=4.5(3), G0'=1.6(1) with ρ0=3.34(1) g/cm3, KS0=123(3) GPa, and G0=74(2) GPa. In addition, the synchrotron single‐crystal X‐ray diffraction data have been collected up to 18 GPa and 700 K. The fitting to Holland‐Powell thermal‐pressure equation of state yields KT0'=4.6(5) and α0=2.7(8) ×10‐5 K‐1. Based on the obtained thermoelastic parameters of omphacite, the anisotropic seismic velocities of eclogite are modeled and compared with pyrolite between 200 to 500 km. The largest contrast between the eclogite and pyrolite in terms of seismic properties is observed between ~310 to 410 km.

Description: A two-step microreactor for the investigation of glucose oxidation is presented. A model is created to pre-judge the changes in concentrations of the reactants in the straight channels of the microreactor. The structure of the rapid mixing-reaction units of the microreactor was optimized, and the optimal parameters were found to be p  = 1:3, r  = 1:1, and w s  = 60 μm. The model and the optimization method can facilitate the design of microreactors. A two-step micro-reactor was designed to investigate glucose oxidation. A model was established to assess any changes in the concentrations of the reactants in the straight channels of the microreactor. The model and the optimization method can be used in the design of micro-reactors.

Description: Using version 2.0 of the TIMED/SABER kinetic temperature data, we have conducted a study on the annual and inter-annual variations of 6.5DWs at 20-110 km, from 52°S-52°N for 2002-2016. First, we obtained global annual variations in the spectral power and amplitudes of 6.5DWs. We found that strong wave amplitudes emerged from 25°S/N-52°S/N, and peaked in the altitudes of the stratosphere, mesosphere and the lower thermosphere. The annual variations in the 6.5DWs are similar in both hemispheres but different at various altitudes. At 40-50 km, the annual maxima emerge mostly in winters. In the MLT, annual peaks occurred twice every half year. At 80-90 km, 6.5DWs appeared mainly in equinoctial seasons and winters. At 100-110 km, 6.5DWs emerged mainly in equinoctial seasons. Second, we continued the study of the inter-annual variations in 6.5DW amplitudes from 2002-2016. Frequency spectra of the monthly mean amplitudes showed that main dynamics in the long-term variations of 6.5DWs were AO and SAO in both hemispheres. In addition, 4-month period signals were noticed in the MLT of the NH. The amplitudes of SAO and AO were obtained using a bandpass filter and were found to increase with altitude, as do the 6.5DW amplitudes. In both hemispheres, the relative importance of SAO and AO changes with altitude. At 40-50 and 100-110 km, AO play a dominant role, while at 80-90 km, they’re weaker than SAO. Our results show that both the annual and inter-annual variations in 6.5DWs are mainly caused by the combined action of SAO and AO.

Description: We have performed an experiment to compare as directly as realizable, the ionization production rate by HF radio-wave energy vs. by solar EUV. We take advantage of the commonality that ionization production by both ground-based high power HF radio waves and by solar EUV, are driven by primary and secondary supra-thermal electrons near and above ~20 eV. Incoherent scatter radar (ISR) plasma-line (PL) amplitudes are used as a measure of supra-thermal electron fluxes for ISR wavelengths near those for 430 MHz, and are indeed a clean measure of such for those fluxes sufficiently weak to have negligible self-damping. We present data from an HF heating experiment on November 2015 at Arecibo, which even more directly confirm the only prior mid-latitude estimate, of order 10% efficiency for conversion of HF energy to ionospheric ionization. We note the theoretical maximum possible is ~1/3, while ~1% or less reduces the question to near practical irrelevance. Our measurements explicitly confirm the prediction [Carlson, 1993] that radio-frequency production of artificial ionospheres can be practicable, even at mid latitudes. Furthermore, that this mid-latitude efficiency is comparable to efficiencies measured at high latitudes [Pedersen et al., 2009] (which include enhancements unique to high latitudes including magnetic zenith effect, gyro-frequency multiples and double resonances) requires reexamination of current theoretical thinking about soft-electron acceleration processes in weakly magnetized plasmas. The implications are that electron acceleration by any of a variety of processes may be a fundamental underpinning to energy redistribution in space plasmas.

Description: [1]  During the interval ~07:45:36–07:54:24UT on 24 August 2005, Cluster satellites (C1 and C3) observed an obvious loss of energetic electrons (~3.2-95 keV) associated with the growth of whistler mode waves inside some bursty bulk flows (BBFs) in the midtail plasma sheet ( X GSM  ~ −17.25R E ). However, the fluxes of the higher-energy electrons (≥128 keV) and energetic ions (10-160 keV) were relatively stable in the BBF-impacted regions. The energy-dependent electron loss inside the BBFs is mainly due to the energy-selective pitch angle scatterings by the whistler mode waves within the scattering time scales from several seconds to several minutes, and the pitch angle evolutions of the resonant electrons in different initial distributions are different in the wave growth regions. The low-energy plasma sheet electrons (~0.073-2.1 keV) have initially a field-aligned pitch angle distribution (0 o  ≤  α  ≤ 30 o and 150 o  ≤  α  ≤ 180 o ) in the absence of the whistler mode waves, and the loss of the low-energy electrons in field-aligned directions is accompanied by their increase in quasi-perpendicular directions (30 o  〈  α  〈 150 o ) in the intense wave growth regions inside the BBFs, indicating that the resonant electrons in a field-aligned pitch angle distribution can be scattered by the waves simultaneously into the loss cone and towards the larger pitch-angles. Due to the limits of the small loss cone ( α c  ~ 0.8-1.3 o ) and double-direction scatterings in field-aligned distributions, the loss of the low-energy electrons inside the BBFs is not obvious in the presence of their large background fluxes. Unlike the low-energy electrons, the plasma sheet energetic electrons (~3.2-95 keV) have mainly a quasi-perpendicular pitch angle distribution (30 o  〈  α  〈 150 o ) during the expansion-to-recovery development of a substorm ( AE index decreased from 1677nT to 1271nT), and their loss can occur at almost all pitch angles in the intense wave growth regions inside the BBFs, indicating that the resonant electrons in a quasi-perpendicular pitch angle distribution are always scattered by the waves from the larger pitch angles to the loss cone. Finally, the growth of whistler mode waves causes the net loss of the quasi-perpendicular distribution electrons inside the BBFs. These observations indicate that the anisotropic distribution energetic electrons mainly undergo the rapid pitch angle scattering loss because of the growth of whistler mode waves inside the BBFs with a highly compressed equatorial magnetic field (~tens of nT), but the final loss effect of the wave-induced pitch angle scatterings on resonant electrons depends on their initial pitch angle distributions.

Description: We construct a rice paddy biogeochemical cycle model to investigate processes governing rice mercury sources, and to understand factors influencing spatiotemporal variability in Chinese rice mercury concentrations. The rice paddy model takes atmospheric mercury deposition, simulated from a global atmospheric-chemistry-transport model (GEOS-Chem), and soil and irrigable surface water mercury concentrations obtained from literature, and calculates rice inorganic (IHg) and methylmercury (MeHg) concentrations. We use ranges of GEOS-Chem simulated future atmospheric mercury deposition-- no-policy and strict-policy to regulate mercury emissions from Chinese coal-fired power plants under the Minamata Convention on Mercury -- to simulate future rice IHg and MeHg concentrations. Sensitivity analyses suggest that rice IHg and MeHg concentrations are more sensitive to the process of soil desorption compared to infiltration of recently introduced mercury (atmospheric and irrigation source). The rate of internal methylation via microbial activity has the largest modeled influence on rice MeHg concentration. We find that soil mercury, rather than atmospheric deposition, explains observed spatial variability in rice IHg and MeHg concentrations and captures locations of rice mercury hotspots (〉 20 ng/g; China National Standard Limit). Under our future scenarios, the Chinese median rice IHg and MeHg concentrations increase by 13% and decrease by 18% under no-policy and strict-policy, respectively. Regions with the largest percentage decline in rice IHg and MeHg concentrations under strict-policy are in central China, which demonstrate high rice mercury concentrations, rice production, and consumption. Our study suggests that addressing Chinese rice mercury contamination requires attention to contaminated soil and regulation of anthropogenic mercury emissions.

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.