The role of diffuse electron precipitation in forming subauroral polarization streams (SAPS) is investigated with the Multiscale Atmosphere-Geospace Environment (MAGE) model. Diffuse precipitation is derived from the distribution of drifting electrons calculated in MAGE. SAPS manifest themselves as a separate mesoscale flow channel in the duskside ionosphere when diffuse precipitation is implemented in MAGE, whereas it merges with the primary auroral convection when diffuse precipitation is turned off. SAPS overlap with the downward Region-2 field-aligned currents equatorward of diffuse precipitation, where poleward electric fields closing the Pedersen currents are strong due to a low conductance in the subauroral ionosphere. The Region-2 field-aligned currents extend to lower latitudes than diffuse precipitation because the ring current protons penetrate closer to the Earth than the electrons do. This study demonstrates the critical role of diffuse electron precipitation in determining SAPS location and structure.

Abstract: Jason-3 is equipped with an Advanced Microwave Radiometer (AMR) to remove the signal wet delay caused by precipitable water vapor (PWV). In order to investigate the accuracy of PWV from Jason-3 AMR on a global scale, we adopt PWV observations from 263 radiosonde stations and 103 GNSS stations as reference PWV. These reference PWV are recorded during Jason-3 cycles 0 – 119 and are globally distributed in coastal and island regions. Over 60,000 Jason-3 PWV vs radiosonde PWV comparison points and over 380,000 Jason-3 PWV vs GNSS PWV comparison points are used in this study. For GNSS PWV, four retrieval strategies are used to retrieve GNSS PWV: a combination of two different zenith hydrostatic delay (ZHD) modeling methods (Saastamoinen and ECMWF), and two PWV height reduction methods (Kouba empirical method and ECMWF method to reduce PWV from height of station to sea level). The comparison results indicate that the root mean square error (RMSE) of Jason-3 PWV evaluated using radiosonde PWV is 3.4 kg/m, while the RMSE evaluated with PWV from four different GNSS schemes are in the range of 3.0 – 3.5 kg/m. Specifically, Jason-3 PWV has the best agreement (3.0 kg/mof RMSE) with GNSS PWV derived using Saastamoinen ZHD correction and ECMWF PWV height correction. In addition, the accuracy of Jason-3 PWV increases when the latitude of its footprints or the distance from its footprints to land increases. The correlation coefficient of Jason-3 PWV with radiosonde and GNSS PWV are 0.984 and 0.988, respectively.

In 2020, people’s health suffered a great crisis under the dual effects of the COVID-19 pandemic and the extensive, severe wildfire in the western and central United States (U.S.). Parks, including city, national, and cultural parks, offer a unique opportunity for people to maintain their recreation behaviors following the social distancing protocols during the pandemics. However, massive forest wildfires in western and central US, producing harmful toxic gases and smoke, pose significant threats to human health and affect their recreation behaviors and visitations to parks. In this study, we employed the Geographically and Temporally Weighted Regression (GTWR) Models to investigate how COVID-19 and wildfires jointly shaped human visitations to parks, regarding the number of visitors, dwell time, and travel distance from home, during June - September 2020. Our findings indicated that people tended to travel closer from home and spent less time at parks as more COVID-19 cases were reported. However, with the stay-at-home restriction lifted and the reopen of some large national parks, people traveled further distances to those places (e.g., Yellowstone National Park) regardless the peak of pandemics in June 2020. Moreover, we found people intended to decrease the visitations to the parks surrounded by wildfires and shorten the time there. This study provides important insights on people’s responses in recreation and social behaviors when facing multiple serve crises that impact their health and wellbeing, which could support the preparation and mitigation of the health impacts from future pandemics and natural hazards.

Simulations of solar radiation management (SRM) geoengineering using comprehensive general circulation models (GCM) show a residual surface warming at high latitudes. Previous work attributes this to the difference in forcing structure between the increase in greenhouse gases and the decrease in insolation, but this neglects the induced reduction in atmospheric energy transport. Here we show that the difference in vertical structure of temperature change between increasing CO2, decreasing insolation, and decreasing atmospheric energy transport is the dominant reason for the residual near-surface warming at high latitudes. A single column model (SCM) is used to decompose the high latitude temperature change, and shows the importance of the bottom-heavy temperature change from the CO2 increase in explaining the residual polar warming. This model hierarchy invites caution when attributing high latitude surface temperature changes to the lapse rate feedback, as various forcings and nonlocal processes affect the vertical structure of temperature change differently.

Due to the progress of the availability of thermodynamic data in the last decades, equilibrium thermodynamics provides the ability to calculate mineral stability relations in the Earth’s lithosphere (and beyond) as well as thermobarometric results. GeoPS (available at http://www.geops.org) is a windows-based interactive visualization program for thermodynamic modeling of phase equilibria. This program provides a wide range of phase equilibrium calculations and illustration facilities base on Gibbs free energy minimization method, which is done automatically with practically no user intervention. Possible applications include calculation various types of phase diagrams, isopleths, and thermodynamic modeling of phase equilibrium along specific P-T path with a progressively changing effective bulk compositions (EBC), such as fluid and melt loss, and chemical fractionation during compositionally zoned minerals growth in a metamorphic process. A novel algorithm with parallel computing makes GeoPS have high efficiency. The easy to use interface, visualization, high efficiency, reliability of GeoPS makes phase equilibrium modeling accessible to any researchers and students of earth sciences, and provides a powerful tool to understand natural systems and plan experimental work.

The plate tectonic history of the hypothesized ‘proto-South China Sea’ (PSCS) ocean basin and surrounding SE Asia since Cenozoic times is controversial. We implement four diverse PSCS plate reconstructions into global geodynamic models to constrain PSCS plate tectonics and possible slab locations. We consider: southward versus double-sided PSCS subduction models; earlier (Eocene) or later (late Oligocene) initiation of Borneo counterclockwise rotations; and, larger or smaller reconstructed Philippine Sea plate sizes. We compare our modeling results against tomographic images by taking into account mineralogical effects and the finite resolution of seismic tomography. All geodynamic models reproduce the tomographically-imaged Sunda slabs beneath Peninsular Malaysia, Sumatra and Java. Southward PSCS subduction produces slabs beneath present Palawan, northern Borneo, and offshore Palawan. Double-sided PSCS subduction combined with earlier Borneo rotations uniquely reproduces sub-horizontal slabs under the southern South China Sea (SCS) at ~400 to 700 km depths; these models best fit seismic tomography. A smaller Philippine Sea (PS) plate with a ~1000 km-long restored Ryukyu slab was superior to a very large PS plate. Taken together, the four end-member plate models predict PSCS slabs at <900 km depths under present-day Borneo, the SCS, the Sulu and Celebes seas, and the southern Philippines. Regardless of plate models, we predicted passive mantle upwellings under Indochina during late Eocene-Oligocene times, and downwellings under the SCS during the late Cenozoic that do not support a deep-origin ‘Hainan plume’. Modeled Sundaland dynamic topography depends strongly on the imposed plate model, varying by several hundred meters.

Enhanced Geothermal Systems could provide a substantial contribution to the global energy demand if their implementation could overcome inherent challenges. Examples are insufficient created permeability, early thermal breakthrough, and unacceptable induced seismicity. Here we report on the seismic response of a meso-scale hydraulic fracturing experiment performed at 1.5 km depth at the Sanford Underground Research Facility. We have measured the seismic activity by utilizing a novel 100 kHz, continuous seismic monitoring system deployed in six 60 m-length monitoring boreholes surrounding the experimental domain in 3-D. The achieved location uncertainty was on the order of 1 m, and limited by the signal-to-noise ratio of detected events. These uncertainties were corroborated by detections of fracture intersections at the monitoring boreholes. Three intervals of the dedicated injection borehole were hydraulically stimulated by water injection at pressures up to 33 MPa and flow rates up to 5 L/min. We located 1933 seismic events during several injection periods. The recorded seismicity delineates a complex fracture network comprised of multi-strand hydraulic fractures and shear-reactivated, pre-existing planes of weakness that grew unilaterally from the point of initiation. We find that heterogeneity of stress dictates the outcome of hydraulic stimulations, even when relying on theoretically well-behaved hydraulic fractures. Once hydraulic fractures intersected boreholes, the boreholes acted as a pressure relief and fracture propagation ceased. In order to create an efficient sub-surface heat exchanger, production boreholes should not be drilled before the end of hydraulic stimulations.

A new seismic velocity model for the south Central Andes is derived from full waveform inversion, covering the Pampean flat and adjacent Payenia steep subduction segments. Strong focused crustal low-velocity anomalies indicate partial melts in the Payenia segment along the volcanic arc, whereas weaker low-velocity anomalies covering a wide zone in Pampean possibly indicates remnant melts in the past. Thinning and tearing of the flat Nazca slab below the Pampean is inferred by gaps in the high-velocity slab along the inland projection of the Juan-Fernandez-Ridge. A high-velocity anomaly in the upper mantle below the flat slab is interpreted as a relic Nazca slab segment, which indicates an earlier slab break-off during the flattening process, triggered by the buoyancy of the Juan-Fernandez-Ridge. In Payenia, large-scale low-velocity anomalies atop and below the re-steepened Nazca slab are associated with the re-opening of the mantle wedge and sub-slab asthenospheric flow, respectively.

A method based on electron magnetohydrodynamics (EMHD) for the reconstruction of steady, two-dimensional plasma and magnetic field structures from data taken by a single spacecraft, first developed by Sonnerup et al. (2016), is extended to accommodate inhomogeneity of the electron density and temperature, electron inertia effects, and guide magnetic field in and around the electron diffusion region (EDR), the central part of the magnetic reconnection region. The new method assumes that the electron density and temperature are constant along, but may vary across, the magnetic field lines. We present two models for the reconstruction of electron streamlines, one of which is not constrained by any specific formula for the electron pressure tensor term in the generalized Ohm’s law that is responsible for electron unmagnetization in the EDR, and the other is a modification of the original model to include the inertia and compressibility effects. Benchmark tests using data from fully kinetic simulations show that our new method is applicable to both antiparallel and guide-field (component) reconnection, and the electron velocity field can be better reconstructed by including the inertia effects. The new EMHD reconstruction technique has been applied to an EDR of magnetotail reconnection encountered by the Magnetospheric Multiscale spacecraft on 11 July 2017, reported by Torbert et al. (2018) and reconstructed with the original inertia-less version by Hasegawa et al. (2019), which demonstrates that the new method better performs in recovering the electric field and electron streamlines than the original version.

Squall lines are known to be the consequence of the interaction of low-level shear with cold pools associated with convective downdrafts. Also, as the magnitude of the shear increases beyond a critical shear, squall lines tend to orient themselves at an angle to the shear. The existing literature suggests that this angle conserves the projection of the shear on the direction perpendicular to the squall line. However, this hypothesis has never been clearly demonstrated. Here, we confront this theory with tropical squall lines obtained by imposing a vertical wind shear in cloud resolving simulations in radiative convective equilibrium. In the sub-critical regime, squall lines are indeed perpendicular to the shear. In the super-critical regime, their orientation optimizes the projection of the background shear, which supports existing theories. We also find that as shear increases, cold pools become more intense. However, this intensification has little impact on the squall line orientation.

The data from the CLUSTER FGM magnetometer, recorded for 20 years at ESA’s Cluster Science Archive, have been used to form a database aligned in time. It allows the calculation of curl(B) over all the life of the mission. The ̵⃗B and J⃗ data are then averaged, as a function of the dipole tilt angle, to form a 3D grid of spatial extend of 20 RE, and for any spatial resolution. From these data grids, maps of the direction of the magnetic field and of the current density are produced, allowing the observation of the average behavior of the magnetic field and the current density on a large scale. The validity of the calculation of J⃗ is discussed. By means of spatial interpolation, the grids are used to provide a measurement of the magnetic field at any point in space where the grid is filled. This allows possibility of ray tracing to obtain empirical plots of the magnetic field lines, i.e. not theoreti-cal, but from experimental data. Field lines near the cusp are visualized, even if they are very smoothed by the averaging of IMF and solar wind parameters. In a future work it would be possible to add other classification than just the dipole tilt angle, such as various activity indicese and solar wind parameters. The prospect of adding data from other missions would extend the regions that have been covered by Cluster, and in-crease the spatial extent of the 3D grid and its resolution.

Subtropical Western Boundary Currents (WBCs) are often associated with hotspots of global warming, with certain WBC extension regions warming 3-4 times faster than the global mean. In the Southern Hemisphere strong warming over the WBC extensions has been observed over the last few decades, with enhanced warming projected into the future. This amplified warming has primarily been linked to poleward intensification of the mid-latitude westerly winds in the Southern Hemisphere. Changes in these winds are often thought of as being zonally symmetric, however, recent studies show that they contain strong zonal asymmetries in certain ocean basins. The importance of these zonal asymmetries for the Southern Ocean has not yet been investigated. In this study, we use an ocean-sea-ice model forced by prescribed atmospheric fields to quantify the contribution of projected zonally asymmetric atmospheric changes in generating future ocean warming and circulation changes in the subtropical WBC regions of the Southern Hemisphere. We find that the projected zonally asymmetric component of atmospheric change can explain more than 30% (>2°C) of the SST warming found in the Tasman Sea and southern Australia region and a sizeable fraction of warming in the Agulhas Current region. These changes in SST in both the Indian and Pacific Ocean basins are found to be primarily driven by changes in the large-scale subtropical ocean gyres, which in turn can largely be explained by changes in the surface wind stress patterns.

We report a new series of experiments to explore the phenomenon of low-temperature annealing of fission tracks in apatite that feature a number of improvements over previous work. Grain mounts were pre-irradiated Cf to increase confined track detection and allow briefer thermal neutron irradiation. We co-irradiated and etched four apatite varieties (Durango, Fish Canyon, Renfrew, Tioga) over five time steps equally spaced from 3.66 to 15 ln(s). A length standard was co-etched with all experiments to ensure that subtle differences are within detection limits. Finally, we used a standard etching protocol, allowing the data to be co-modeled with extensive high-temperature data sets and recent analyses of induced tracks that underwent ambient-temperature annealing over year-to-decade time scales. Ambient-temperature annealing occurs at two different rates, with faster annealing at early stages that decreases to a slower rate that converges with empirical fanning linear or curvilinear models. The nature of this decrease varies among the apatite species examined, but no patterns could be determined. The fitted models make geological time-scale predictions consistent with those based on high-temperature data only, and also make predictions consistent with reasonable inferred low-temperature histories for all four apatite varieties. The empirical fanning curvilinear equation encompasses low-temperature annealing at month-to-decade time scales, but low-temperature annealing at shorter time scales may occur by a distinct mechanism. We consider but rule out annealing by radiation from short-lived activated isotopes. We also reconsider the notion of the initial track length, and the appropriate length for normalizing confined track length measurements.

Utilizing historical data from the U.S. nuclear test program and freely available barometric pressure data, we performed an analytical barometric-pumping efficiency analysis to determine factors resulting in late-time radionuclide gas seeps from underground nuclear explosions. We considered sixteen underground nuclear explosions with similar geology and test setup, of which five resulted in the measurement of late-time radionuclide gas concentrations at the ground surface. The factors we considered include barometric frequency and amplitude, depth of burial, air-filled porosity, intact-rock permeability, fracture aperture, and fracture spacing. The analysis indicates that the best discriminators of late-time radionuclide gas seeps for these explosions are barometric frequency and amplitude and air-filled porosity. While geologic information on fracture aperture and spacing is not available for these explosions, the sensitivity of barometric-pumping efficiency to fracture aperture indicates that fracture aperture would likely also be a good discriminator.

To determine hydrologic changes in a warmer climate, we impose precipitation and potential evaporation perturbations on hydrologic response functions constructed from precipitation and satellite soil moisture observations across the United States. Despite nonlinearities in the evaporation (E) and drainage (D) responses and opposing-sign perturbations, changes in individual fluxes are superposable. Empirical frameworks (Budyko) can misrepresent changes in E/D partitioning by neglecting shifts/trends in hydrologic regime and subseasonal precipitation dynamics. E/D both increase to balance mean precipitation (P) increases, and increased E reduces soil moisture. E and D are generally more elastic to changes in P than E. The results suggest that (1) the impacts of regional hydrologic perturbations may allow for simple superposition/scaling, (2) changes in timing/intensity of precipitation may have substantial impacts on mean moisture states and fluxes, and (3) changes to the distribution of surface moisture states are likely more relevant for E/D partitioning than common aridity indices.

The canonical picture of the magnetotail of unmagnetized planets consists of draped interplanetary magnetic fields (IMF) forming opposite-directed lobes, separated by the current sheet. \citet{DiBraccio2018twisted} showed that Mars’ magnetotail has a twist departing from this picture. Magnetohydrodynamic (MHD) results suggest that open field lines connected to the planet that populate portions of the tail cause the apparent twist. To validate this interpretation, we compare the tail topology determined from MHD simulations to that inferred from data collected by the Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft, in particular how each topology responds to the upstream IMF orientation. The occurrence rates for open topology from both data and MHD varies with IMF polarities in a similar fashion as the tail twisting. This suggests that Mars’ crustal fields have a global effect on the magnetosphere configuration, supporting the picture of a “hybrid” magnetotail that is partly induced/draped and partly intrinsic/planetary in origin.

Substantial changes have occurred in the Arctic Ocean in the last decades. Not only sea ice has retreated significantly, but also the ocean at mid-depth showed a warming tendency. By using simulations we identified a mechanism that intensifies the upward trend in ocean heat supply to the Arctic Ocean through Fram Strait. The reduction in sea ice export through Fram Strait induced by Arctic sea ice decline increases the salinity in the Greenland Sea, which lowers the sea surface height and strengthens the cyclonic gyre circulation in the Nordic Seas. The Atlantic Water (AW) volume transport to the Nordics Seas and Arctic Ocean is consequently strengthened. This enhances the warming trend of the Arctic AW layer, potentially contributing to the “Atlantification” of the Eurasian Basin. Therefore, the Nordic Seas can play the role of a switchyard for the Arctic sea ice decline to influence the Arctic heat budget at mid-depth.

The January 15, 2022 phreatomagmatic eruption of the submarine Hunga Tonga-Hunga Ha’apai (HTHH) volcano (Tonga) generated an explosion of historic magnitude, and was preceded by ~1 month of Surtseyan eruptive activity and two precursory explosive eruptions. We present an analysis of ultraviolet (UV) satellite measurements of volcanic sulfur dioxide (SO2) between December 2021 and the climactic January 15, 2022 eruption, comprising an unprecedented record of Surtseyan eruptive emissions. UV measurements from the Ozone Monitoring Instrument (OMI) on NASA’s Aura satellite, the Ozone Mapping and Profiler Suite (OMPS) on Suomi-NPP, the Tropospheric Monitoring Instrument (TROPOMI) on ESA’s Sentinel-5P, and the Earth Polychromatic Imaging Camera (EPIC) aboard the Deep Space Climate Observatory (DSCOVR) are combined to yield a consistent multi-sensor record of SO2 emissions during the eruptive sequence. We estimate SO2 emissions during the key phases of the eruption: the initial December 19, 2021 eruption (~0.01 Tg SO2); continuous SO2 emissions from December 20, 2021-early January 2022 (~0.12 Tg SO2); the January 13, 2022 stratospheric eruption (0.06 Tg SO2); and the paroxysmal January 15, 2022 eruption (~0.4-0.5 Tg SO2); yielding a total SO2 emission of ~0.6-0.7 Tg SO2 for the entire eruptive episode. We interpret the vigorous SO2 emissions observed prior to the January 2022 eruptions, which were significantly higher than measured in the 2009 and 2014 HTHH eruptions, as strong evidence for a rejuvenated magmatic system. High cadence DSCOVR/EPIC SO2 imagery permits the first UV-based analysis of umbrella cloud spreading and volume flux in the January 13, 2022 eruption, and also tracks early dispersion of the stratospheric SO2 cloud injected by the January 15 eruption. The ~0.4-0.5 Tg SO2 discharged by the paroxysmal January 15, 2022 HTHH eruption is low relative to other eruptions of similar magnitude, and a review of previous submarine eruptions of the satellite era indicates that such modest SO2 yield may be characteristic of these events, with the emissions and atmospheric impacts likely dominated by water vapor (WV). The origin of the low SO2 loading awaits further investigation but scrubbing of SO2 in the water-rich eruption plumes and rapid conversion to sulfate aerosol are highly plausible, given the exceptional WV emission measured in the January 15, 2022 HTHH eruption.