ALBERT

Description: The clumped-isotope composition of oxygen, denoted by Δ〈sub〉36〈/sub〉, measures the proportional abundance of two heavy oxygen isotopes, 〈sup〉18〈/sup〉O〈sup〉18〈/sup〉O in oxygen, and is sensitive to photochemical and thermal properties of the atmosphere. Ozone photochemistry controls Δ〈sub〉36〈/sub〉 values via isotope exchange reactions, yielding a higher abundance of 〈sup〉18〈/sup〉O〈sup〉18〈/sup〉O than would be expected for a stochastic distribution. Colder temperatures increase this preference for 〈sup〉18〈/sup〉O〈sup〉18〈/sup〉O formation at equilibrium by 0.013‰/K. If tropospheric ozone and stratosphere-troposphere exchange fluxes remain unchanged, Δ〈sub〉36〈/sub〉 would record changes in free-tropospheric temperatures to provide a high-resolution record of upper tropospheric (UT) temperatures on glacial-interglacial timescales. We present an ice core record of Δ〈sub〉36〈/sub〉 values measured in the West Antarctic Ice Sheet Divide ice core spanning 15–8ka BP. Measured Δ〈sub〉36〈/sub〉 values decrease to Early Holocene (EH; 8-11ka BP)/Pre-industrial (PI; 1850CE) levels at the onset of the Bølling Allerød (BA; 14.7–12.9ka BP) warm period, and continues into the Younger Dryas (YD; 12.9-11.7ka BP). Δ〈sub〉36〈/sub〉 values reach PI/EH when global-mean surface temperatures are still colder than those of PI/EH. This indicates either a change in the lapse rate feedback, or a significant increase in tropospheric ozone burden. Our investigations reveal no evidence for increased O〈sub〉3〈/sub〉 and that the decrease in Δ〈sub〉36〈/sub〉 is coeval with rapid decreases in Northern Hemisphere ice sheet elevation. Previous work highlights the influence of changing ice sheet elevation on the thermal structure of the atmosphere. A plausible explanation for our observation is that during periods of abrupt climate change the cryosphere plays a predominant role in governing UT temperatures.

Description: Mingantu Spectral Radioheliograph (MUSER), is an aperture-synthesis imaging telescope, dedicated to observing the Sun, operating on multiple frequencies in the dm to cm range. MUSER is located in Mingantu Town, Inner Mongolia of China, about 400 km northwest of Beijing. MUSER is composed of two arrays of 40 4.5m antennas covering 400MHz -2 GHz, and 60 2m antennas covering 2 - 15 GHz including outdoor devices with antennas, LNBs, and indoor devices including receivers, correlators, etc. In the period of 2014-2019, about 94 solar radio burst events have been registered by MUSER. During the rising phase of the 25th solar cycle, MUSER also records some new events. The project to extend MUSER to the 40 - 400 MHz frequency regime with 224 log-periodic dipole antennas is under construction. The construction of a new 3-site Interplanetary Scintillation (IPS) telescope with the main site having three 140 m by 40m cylinder antennas at MUSER site and 2 sub-sites having 30 m parabolic antennas about 200 km apart has been approved and is under construction. All these are due to complete within a couple of years. We present the recent progress of the solar radio spectroscopy-imaging results from these facilities, including near-future developments and upgrades, as well as the progress of the IPS telescopes under construction in China. The MUSER and IPS telescopes at Mingantu Observing Station, National Space Science Center of the Chinese Academy of Sciences will play important role in solar and heliospheric physics.

Description: Based on the data of Mingantu Spectral Radioheliograph (MUSER) at 0.4-2.0GHz, the EUV images of the Atmospheric Imaging Assembly (AIA) and the magnetic field data of Helioseismic Magnetic Imager (HMI), we carried out a detailed study of solar bursts with a fan-spine structure that occurred on December 17, 2014. The results show that during the low active level of the active region, there are usually two radio sources, one is around zero point of the fan-spine structure and the other is related to the spine. However, when the M7.8 flare occurred, the location of the radio sources changed dramatically. The high frequency source became one source and moves to the left side of the fan, but the low frequency sources usually displays two sources. The stronger one of which is located on the left side of the fan whereas the weaker one settled at the far end of the spine. These results might shine light on understanding the morphology of three-dimensional magnetic reconnection as well as the acceleration of electrons and the radio emissions caused by them.

Description: The contrasting fates of continental collisional orogens, i.e., deep subduction or collision cessation, are widely recognized by petrological, paleomagnetic and geophysical observations. However, the mechanisms of such different collisional modes, especially the dynamics of continental deep subduction, are controversial. In this study, we integrate the phase transition-induced density evolution into a thermo-mechanical numerical model. Combing the systematic petrological-thermo-mechanical models with force balance analyses, we find that the favorable conditions of continental deep subduction include high metamorphic transformation degree, mildly depleted mantle composition of the subcontinental lithosphere, long preceding oceanic slab, as well as the rheologically weak continental crust and asthenospheric mantle. Otherwise, the collision cessation mode is favored. The further calculations of slab negative buoyancy indicate that the phase transition-induced metamorphic densification of the subducted continental crust and mildly to moderately depleted continental lithospheric mantle can provide a great slab pull force to sustain the self-driven continental deep subduction; however, the positive buoyancy of highly depleted Archean lithospheric mantle impedes deep subduction and causes collision cessation. Based on these systematic numerical models, we also evaluate the crustal mass balance or deficit in continental collisional system, which indicates that a large amount of felsic crust can be subducted deeply with the sinking slab in the regime of continental subduction. In contrast, the recycled felsic crust is negligible in the regime of collision cessation. Thus, the different modes of continental collision play a crucial role in the global crustal recycling and related mantle heterogeneities.

Description: An important source of noise in the current global monthly time-varying gravity field obtained on the basis of GRACE-like missions (GRACE, GRACE-FO) is the error due to the aliasing of the high frequency non-tidal atmospheric and oceanic mass changes (AOD error). And due to the orbital configuration, the inter-satellite ranging system (K-band ranging system, KBR; laser interferometer, LRI) of gravity satellites is under-sampled in the east-west direction, leading to striping errors in the north-south direction. In our study, we introduced a new independent observational quantity called the angular velocity of the line-of-sight (LOS), i.e. the orientation change of the LOS caused by the gravity field, which has complementary information perpendicular to the LOS obtained from KBR/LRI. We call the combination of angular velocity sensing (AVS) and ranging observations GRACE-3D because it contains three-dimensional gravity observations, not just along the line-of-sight as in GRACE. We developed observation equations for AVS based on the dynamic approach and on the acceleration approach and solved them jointly with the observation equations generated by GPS and KBR/LRI using two independent software suites for cross-validation. The simulation results show that the AVS-based gravity field can reduce the effect of AOD error and significantly improve the north-south strip error when compared to the results obtained using only a combination of KBR/LRI and GPS. And the optimum results are achieved when GPS, LRI and AVS are combined. Finally, We will also briefly discuss how AVS measurements could be obtained in future missions.

Description: Understanding the impact forces exerted by debris flows is limited by a lack of direct field measurements and validated numerical models. In this study, we use real-time impact-force measurements and field observations of debris flows recorded by a sensor network in Jiangjia Ravine, China, to quantify the impact-force distribution of natural debris flows. We observed one debris flow event during and after a storm on August 25, 2004, including 42 short-duration surges and seven long-duration surges, and impact-force signals were successfully recorded for 38 surges. Our observed debris flows comprise high-viscosity laminar flows with high sediment concentration and frequent solid-to-solid interactions. We identified a large magnitude (up to 1 kN), high-frequency (greater than 1 Hz) fluctuating component of the impact force that we interpret as solid particle impact on the sensors. The variability of particle impact forces increases with the mean impact force. Our results show that a log-logistic distribution can describe the probability density distribution of impact forces. Solid-dominated surges and fluid-dominated intersurge flows have similar impact-force distributions, but surges usually have heavy tails. We created a dimensionless number to describe the impact force and correlated it against existing dimensionless parameters. Finally, we develop a simple particle impact model to understand the relationship between flow dynamics and the impact force inside debris flows that could be applied to improve debris-flow flume experiments and design debris-flow hazard mitigation measures.

Description: The GRACE Follow-On satellite mission measures distance variations between its two satellites in order to derive monthly gravity field maps, indicating mass variability on Earth on a scale of a few 100 km originating from hydrology, seismology, climatology and other sources. This mission hosts two ranging instruments, a conventional microwave system based on K(a)-band ranging (KBR) and a novel laser ranging instrument (LRI), both relying on interferometric phase readout. In this paper, we show how the phase measurements can be converted into range data using a time-dependent carrier frequency (or wavelength) that takes into account potential intraday variability in the microwave or laser frequency. Moreover, we analyze the KBR-LRI residuals and discuss which error and noise contributors limit the residuals at high and low Fourier frequencies. It turns out that the agreement between KBR and LRI biased range observations can be slightly improved by considering intraday carrier frequency variations in the processing. Although the effect is probably small enough to have little relevance for gravity field determination at the current precision level, this analysis is of relevance for detailed instrument characterization and potentially for future more precise missions.

Description: Numerous projects are releasing ice velocity data, with increasing spatial and temporal resolution. However, the study of the intra-annual dynamics of glaciers remains difficult over large scales because observations contain gaps and artifacts in areas of strong surface changes, shadow casting, clouds, or featureless regions. Moreover, this amount of data is complex to analyze since velocities span different temporal baselines, are derived from different sensors and possibly different processing chains. There is a need to find a consensus between different sources of information, which are not necessarily in agreement. Therefore, a question arises : how is it possible to fuse the available multi-temporal, multi-sensor and multi-source glacier velocity observations to derive ice velocity time series with a high temporal resolution and a reduced uncertainty? The proposed approach relies on an inversion of the displacement observation network based on a new formulation of the temporal closure. Because the observations have different uncertainties, not necessarily known, the inversion is solved using an Iterative Reweighted Least Square with a robust downweighting function. We discuss a strategy that takes into account that ice velocities from different sources can have different spatial sampling and can be impacted by systematic errors. The results are shown over the Kyagar glacier in the Karakoram. They reveal the seasonality of the glacier velocities, from the upper part of the western tributaries to the terminus, with a reduced uncertainty. This work opens perspectives for the study of glacier intra-annual dynamics and the joint exploitation of different ice velocity datasets.

Description: Saline water is a common fluid on the Earth‘s surface and in ice planets. Potassium chloride (KCl) is a common salt and is expected to be a ubiquitous solute in salt water in the Universe; however, few studies investigated the behavior of KCl-H2O system at high pressures and temperatures. In this study, powder and single-crystal X-ray diffraction (SC-XRD), Raman and Brillouin scattering combined with diamond anvil cells were used to investigate the phase relation in the KCl-H2O system for different KCl concentrations at 0–4 GPa and 298–405 K. The results of powder X-ray diffraction and Raman scattering demonstrate that a novel KCl hydrate is formed when KCl aqueous solutions transform to solid ice-VI and ice-VII at high pressure. Simultaneously, the single-crystal of KCl hydrate is synthesized from a supersaturated KCl solution at 298 K and 1.8 GPa. The structure is solved by SC-XRD, indicating a KCl monohydrate with the P21/n space group is formed. We have verified the phase stability of KCl monohydrate by using Raman spectroscopy and density functional theory. Our results indicate that KCl monohydrate is a stable phase under pressure and temperature conditions between 1.6 and 2.4 GPa and 298–359 K. By considering the thermal profile and composition of icy moons, we hypothesize that the formation and decomposition of KCl monohydrate might induce mantle convection in these moons.