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Abstract Understanding the natural petrologic and tectonic processes, such as slab subduction, requires accurate determination of the metamorphic pressure (P) and temperature (T) conditions of the exhumed rocks. Recent development of elastic thermobarometry based on the difference between the thermoelastic properties of mineral inclusions and their hosts allows constraining the formation P-T conditions of the inclusion/host system without assuming thermodynamic equilibrium. However, the reliability of elastic thermobarometry heavily depends on the accurate determination of the high P-T single-crystal elastic properties of relevant minerals. In this study, we performed the first high P-T single-crystal elasticity measurements of zircon, which is one of the most common inclusion/host minerals in metamorphic rocks, using Brillouin spectroscopy at pressures up to 7 GPa and temperatures up to 700 K. The single-crystal elastic properties of zircon at ambient conditions were determined as: ρ0 = 4.6674(4) g/cm3; KS = 231(3) GPa; G = 108(11) GPa; C11 = 428(2) GPa; C33 = 484(3) GPa; C44 = 113.5(8) GPa; C66 = 46.9(8) GPa; C12 = 75(2) GPa; and C13 = 151(1) GPa. We also obtained the P and T derivatives of the elastic moduli as ∂KS0/∂P = 5.0(2), ∂KS0/∂T = −0.019(2) GPa/K, ∂G0/∂P = 0.73(6), and ∂G0/∂T = −0.011(1) GPa/K. Compared with other common rock-forming minerals (e.g., quartz, pyroxene, olivine), zircon is extremely incompressible (high KS) and its stiffness (KS) has relatively small T dependence, making it an ideal mineral for the application of elastic thermobarometry. Finally, we utilized the high P-T single-crystal elasticity data of zircon and garnet to evaluate the potential applications of zircon-in-garnet in elastic thermobarometry via elastic modeling. 

The search for high-temperature superconductivity among pressure-stabilized hydrides has received great interest since theory-directed clathrate hydrides, such as CaH6, YH6, YH9, and LaH10, were synthesized and shown to exhibit a superconducting critical temperature (Tc) above 200 K. However, further tuning the superconductivity and stability of these prominent hydrides to enhance their applicability remains a significant challenge. Here, we take the sodalite-like clathrate prototype MH6 (M = Ca, Y, etc.) as an example to investigate the stability and superconductivity of multicomponent metal hydrides containing four different metal atoms for each structure. High-throughput simulations of 1820 ABCDH24 quinary hydrides with initial symmetry of F4" 3m, where A, B, C, and D represent different metal atoms were performed. The calculations reveal 119 structures that are dynamically stable at 300 GPa and 67 structures exhibit superconductivity exceeding 200 K, and 20 are found to have Tcs above 260 K. Notable among these quinary alloy hydrides, (Na,Zr,Mg,Hf)H6 is predicted to have a Tc approaching room temperature at 250 GPa. Both configurational and vibrational entropy play important roles in stabilizing these alloy structures. (Na,Y,Zr,Hf)H6, (Mg,Zr,Sc,Y)H6, and (Mg,Hf,Ca,Zr)H6 were computed to be thermodynamically stable, making them promising candidates for experimental synthesis. These quinary superconducting hydrides may facilitate realization of very high-temperature superconductors that are stable over a broader range of conditions than those found for binary or ternary systems. 

The space hurricane is a newly discovered large-scale three-dimensional magnetic vortex structure that spans the polar ionosphere and magnetosphere. It has been suggested to open a fast energy transport channel for the solar wind to invade Earth’s magnetosphere under northward interplanetary magnetic field (IMF) conditions. It is, therefore, an important phenomenon to understand the solar wind–magnetosphere–ionosphere coupling process under northward IMF conditions. In this study, we report the three-dimensional ionospheric plasma properties of a space hurricane event in the Northern Hemisphere observed by multiple instruments. Based on the convection velocity observations from ground-based radars and polar satellites, we confirm that the major modulation to the polar cap convection called a space hurricane rotates clockwise at the altitude of the ionosphere. Ground-based incoherent scatter radar and polar satellite observations reveal four features associated with the space hurricane: 1) strong plasma flow shears and being embedded in a clockwise lobe convection cell; 2) a major addition to the total energy deposition in the ionosphere–thermosphere system by Joule heating; 3) downward ionospheric electron transport; and 4) multiple ion-temperature enhancements in the sunward velocity region, likely from the spiral arms of the space hurricane. These results present, first, the impact of space hurricane on the low-altitude ionosphere and provide additional insights on the magnetospheric impact on structuring in the polar ionosphere. 

The space hurricane is a newly discovered large-scale three-dimensional magnetic vortex structure that spans the polar ionosphere and magnetosphere. At the height of the ionosphere, it has a strong circular horizontal plasma flow with a nearly zero-flow center and a coincident cyclone-shaped aurora caused by strong electron precipitation associated with intense upward magnetic field-aligned currents. By analyzing the long-term optical observation onboard the Defense Meteorological Satellite Program (DMSP) F16 satellite from 2005 to 2016, we found that space hurricanes in the Northern Hemisphere occur in summer and have a maximum occurrence rate in the afternoon sector around solar maximum. In particular, space hurricanes are more likely to occur in the dayside polar cap at magnetic latitudes greater than 80°, and their MLT (magnetic local time) dependence shows a positive relationship with the IMF (interplanetary magnetic field) clock angle. We also found that space hurricanes occur mainly under dominant positive IMF By and Bz and negative Bx conditions. It is suggested that the stable high-latitude lobe reconnection, which occurs under the conditions of a large Earth’s dipole tilt angle and high ionosphere conductivity in summer, should be the formation mechanism of space hurricanes. The result will give a better understanding of the solar wind–magnetosphere–ionosphere coupling process under northward IMF conditions.