Studying the daily evolution of turbulent fluxes modulated by snowfall over the Tibetan Plateau (TP) is of importance to understand the features of the change in the TP heat source/sink. Based on observations from 4 sites of the Third TP Atmospheric Scientific Experiment, the process of surface energy balance impacted by snow is investigated. The results show that the surface albedo increases on the first day of snow and then slowly decreases. Correspondingly, the sensible heat (H) flux sharply decreases after snow and then recovers to the original level during the following approximately 10 days. The latent heat (LE) flux becomes more active and stronger after snowfall and persists for a longer period than H, since the soil moisture may still contribute to a high LE after snowmelt. As the synergistic result of H and LE modulated by snow, the surface turbulent heating (i.e., the sum H and LE) of the TP decreases at the early period of snow events and then even enhances to a higher level after the snowmelt than before snow. Comparison analyses reveal that the impact of snow on the H and LE over the TP is much stronger than over similar latitude low-altitude regions in North America and Europe, which may be partly attributed to the larger and more drastic change of the surface net solar radiation associated with snow processes in the TP. This study may help further understand the detailed physical processes of modulation of snow events on Asian weather processes during winter.

Lightning is observed to incept in thundercloud electric fields below the threshold value $E_k$ for discharge initiation. To explain this, the local enhancement of the electric field by hydrometeors is considered. The conditions for the onset of positive corona discharges are studied in air for ellipsoidal geometries. A hydrometeor is simulated as an individual charged conductor in zero ambient field; there is only a field generated by the charge on the hydrometeor surface. By doing so, the feasibility of corona inception from ellipsoidal hydrometeors can be formulated based on the self-sustaining condition of electron avalanches. For representative hydrometeor volumes and typical thundercloud pressure, values between $1.2\,E_k$ and $37\,E_k$ were found for the onset electric field at the tip of the ellipsoid. From simulations the required ambient electric field for corona onset from an uncharged hydrometeor can then be derived. This results in values between $0.07\,E_k$ and $0.8\,E_k$ for semi-axes aspect ratios between 0.01 and 1. The charge required on the hydrometeor surface for corona onset is minimum for semi-axes aspect ratios between 0.04 and 0.07 depending on the considered hydrometeor volume. For the simulated hydrometeors, the values of this onset charge for typical pressures are between 1500\,pC and 3200\,pC. Including a size-correction for comparison to in situ measurement shows agreement with measured precipitation charges. From the results it is concluded that corona onset from ellipsoidal hydrometeors of a realistic volume can be achieved in thundercloud conditions for certain aspect ratios.

(Ultra)high-pressure metamorphic rocks provide valuable insights into properties of slab-derived fluids. Here, we report CH4-rich fluid inclusions in garnet of a metapelite from the Zermatt-Saas ophiolite, western Alps. Two types of metapelite, a CH4-bearing pelitic schist and a calcareous pelitic schist, were investigated to unravel favorable P-T-fO2 conditions for preservation of CH4 in high-pressure metapelite. In the CH4-bearing pelitic schist, CH4-rich fluid inclusions exclusively occur in the core of garnet (GrtI) rather than the rim (GrtⅡ). GrtI records P-T conditions of ~2.85 GPa and ~555 °C, whereas GrtⅡ records a prograde P-T path from ~1.75 GPa at 510 °C to ~2.0 GPa at 530 °C. Compositional profile of garnet in the calcareous pelitic schist reflects a prograde metamorphic path from ~1.9 GPa at 510 °C to ~2.12 GPa at 545 °C. CH4-rich fluid formation may primarily rise from graphite reduction at high-pressure reduced conditions (ΔFMQ -3.5 to -4, 2.85 GPa, ~550 °C), while graphite and carbonates stabilize in a relatively oxidized environment (ΔFMQ ~ 0, 2.12 GPa, 545 °C). The initial redox budget of subducted sediments is primarily controlled by the amount of sedimentary carbonate and organic carbon, which plays the most important role in deciding the carbon speciation at different subduction depth. CH4 formation in COH fluids could primarily be attributed to the reduction of graphite. Subducted metasediments act as conduits for transporting non-oxidized fluids to arc magmas, which provides crucial evidence to support the heterogeneity for slab-derived COH fluids and offers new insights into the deep carbon cycle.

In this paper we review basic elements of Frequentist inference, specifically maximum likelihood (ML) and M-estimation to point out a critical flaw of Bayesian methods for hydrologic model training and uncertainty quantification. Under model misspecification, the sensitivity $\widehat{\mathbf{A}}_{n}$ and variability $\widehat{\mathbf{B}}_{n}$ matrices of the ML model parameter values $\widehat{\bm{\uptheta}}_{n}$ provide conflicting information about the observed Fisher information $\widehat{\boldsymbol{\mathcal{I}}}\vphantom{\overline{\widehat{\boldsymbol{\mathcal{I}}}}}_{n}$ of the data $\omega_{1},\ldots,\omega_{n}$ for $\bm{\uptheta} = (\theta_{1},\ldots,\theta_{d})^{\top}$. As a result, the ML parameter covariance matrix, $\Var(\widehat{\bm{\uptheta}}_{n})$, does not simplify to the matrix inverse of the observed Fisher information, $\widehat{\boldsymbol{\mathcal{I}}}\vphantom{\overline{\widehat{\boldsymbol{\mathcal{I}}}}}_{n}$, as suggested by naive ML estimators and Bayesian MCMC methods but amounts instead to the so-called sandwich matrix $\Var(\widehat{\bm{\uptheta}}_{n}) = \widehat{\boldsymbol{\mathcal{G}}}\vphantom{\overline{\widehat{\boldsymbol{\mathcal{G}}}}}_{n}^{-1} = \fracn \widehat{\mathbf{A}}_{n}^{-1}\widehat{\mathbf{B}}^{\vphantom{-1}}_{n}\widehat{\mathbf{A}}_{n}^{-1}$, where the observed Godambe information $\widehat{\boldsymbol{\mathcal{G}}}\vphantom{\overline{\widehat{\boldsymbol{\mathcal{G}}}}}_{n}$ is the fundamental currency of data informativeness under model misspecification. The \textit{sandwich} matrix is a metaphor for a \textit{meat} matrix $\widehat{\mathbf{B}}_{n}$ between two \textit{bread} matrices $\widehat{\mathbf{A}}_{n}$ and yields asymptotically valid “robust standard errors” even when the likelihood function $L_{n}(\bm{\uptheta})$ (model) is incorrectly specified. The implications of the sandwich variance estimator are demonstrated in three case studies involving the modeling of soil water infiltration, watershed hydrologic fluxes and the rainfall-discharge transformation. First and foremost, our analytic and numerical results demonstrate that the sandwich variance estimator increases substantially hydrologic model parameter and predictive uncertainty. The sandwich estimator is invariant to likelihood stretching practiced by the GLUE method as a remedy for over-conditioning and requires magnitude and/or curvature adjustments to the likelihood function to yield asymptotically valid sandwich parameter estimates and inference via MCMC simulation.

In the ring current dynamics, various loss mechanisms contribute to the ring current decay, including the loss to the upper atmosphere through particle precipitation. This study implements the field-line curvature (FLC) scattering mechanism in a kinetic ring current model and investigates its role in precipitating ions into the ionosphere. The newly included process is solved via a diffusion equation in the model with associated pitch-angle dependent diffusion coefficients. The simulation results indicate that (1) the FLC scattering process exert mostly on energetic ions above 30 keV on the nightside where the magnetospheric configuration is more stretching. Such ion loss thereafter leads to a faster recovery of the ring current. (2) The FLC-associated ion precipitation mainly occurs in the outer region (L>5 for protons and L>4.5 for oxygen ions) on the nightside, and the oxygen ion precipitation takes places in a wider region than protons although its intensity is much lower. Comparisons with POES observations suggest that more precipitation is needed in the inner region, implying that other loss process is required in the model. (3) We further found that the precipitating energy flux of protons due to the FLC scattering can sometimes become comparable to the one from the electrons on the nightside, although electrons usually dominate the ionospheric energy deposit from the midnight eastward towards the dayside. (4) Finally, the FLC scattering process seems to be capable of explaining the formation of the isotropic boundary in the ionosphere.

 Net and anthropogenic CO 2 exchange in the Pacific represents a major contribution to the global CO 2 sink.  The Pacific is thought to have turned to a net sink of CO 2 that is growing primarily due to the increasing uptake of anthropogenic CO 2.  The equatorial region is key in determining net and anthropogenic CO 2 uptakes and their trends and variability in the Pacific.

A document by Avelon Gerritsma. Click on the document to view its contents.

The Pacific Ocean, spanning over 30% of the Earth’s surface, provides an ideal setting for studying the surface radiative balance due to its relatively pristine atmospheric conditions, far from anthropogenic emission sources. In this study we investigated the causes for the decadal trends of surface solar radiation (SSR) observed at eight stations scattered across seven islands in the Western Pacific Ocean, and extrapolated the results to the whole Western Pacific region based on the understanding of physical processes. Our results show a contrast between the causes for SSR trends in the northwestern and in the southwestern Pacific. From the tropical Southern Hemisphere to the Equatorial region, changes in cloud cover play a major role in the SSR decadal trends and interannual variability. The cloud cover in these areas is strongly associated with sea surface temperature (SST) anomalies, especially those induced by El Nino Southern Oscillation (ENSO) and the Interdecadal Pacific Oscillation (IPO). Modes of variability such as ENSO and IPO impact the large-scale dynamics of the atmopshere, which is followed by a redistribution of the regions of deep convection such as the South Pacific Convergence Zone. This consecutively impacts the cloud cover on a regional level and therefore SSR. In the Northern Hemisphere, however, anthropogenic aerosol transported from Eastern Asia play a major role in the decadal SSR trends. These results contribute to an improved understanding of the physical processes relevant for the long-term SSR trends in remote regions.

We analyze the drivers of hydroclimate variability in northeast Brazil and southeast Australia using a causal discovery algorithm (CDA). The CDA-based regression models are also generated to assess the predictive skills of this approach. Hydroclimate variability is quantified using the standardized precipitation index and standardized precipitation evapotranspiration index with different time-scales. The CDA highlights the influences of the tropical Atlantic and tropical Pacific on droughts in northeast Brazil. Droughts in southeast Australia are connected to the tropical Pacific and Southern Annual mode. For drought indices with long time-scales, the indices themselves are involved as drivers of hydroclimate conditions reflecting the persistence of long-lasting wet or dry events. The performance of the CDA-based prediction models increases with the time-scales of drought indices and decreases with the lead times of prediction. Overall, our analysis shows the usefulness of CDA to identify causal links in the regional hydroclimate in the southern Hemisphere.

Following best practice in stated preference guidelines we use scientific information to develop a realistic hypothetical scenario for stormwater management and water quality improvements in a stated preference valuation survey. We then provide different treatment levels of the scientific information to survey respondents. Using a hybrid choice model, we find that scientific information has no direct influence on referendum votes in favor of a stormwater management program. However, different levels of scientific information have an indirect influence by changing concern about stormwater runoff or by changing perceived understanding of the stormwater management plan. Both of these effects have implications for valuing a stormwater management plan. We suggest that researchers should be aware of how their choice on the information provided may influence responses to a stated preference survey.

Irradiances from long-lived stratus-type clouds at Alert (Canada), Summit (Greenland), and South Pole, previously measured, show correlations with the day-to-day input to the global atmospheric electric circuit from the solar wind, as well as with the inputs of low- and mid-latitude thunderstorms and shower clouds. We analyze the measured Alert cloud irradiances, and find differences in the responses to 2, 4, or more solar wind sectors per 27-day solar rotation. We find seasonal variations in the correlations, with sign reversal in the summer. The correlation coefficients that were found previously for all-year, all sector types show further increases for just winter months and in addition, for just 2-sector intervals. At high magnetic latitudes the ionospheric potential correlates strongly with the solar wind sector structure, and determines the flow of current density (Jz) to the Earth;s surface that passes through clouds and modifies space charge in them. Parameterizations of the potential distribution near the magnetic pole are used in the correlations. The daily average values depend mainly on the solar wind (interplanetary) magnetic field (IMF) By component, with lesser influence of the solar wind speed and IMF Bz. Mechanisms by which space charge in clouds can affect cloud microphysics and cloud opacity are described and are qualitatively consistent with the correlations, but need quantitative testing.

A 3D S-velocity model for the crust and upper-mantle beneath the South China Sea and Indonesia is presented in this paper, determined by means of Rayleigh-wave analysis, in the depth range from zero to 400 km. From this model, the most conspicuous features of the crust and upper mantle structure will be revealed for this study area, which are not so visible in other previous studies because of their low resolution. Also, this model will allow the confirmation of the principal structural features revealed in other previous studies. The results determined in the present study will allow to solve an open question largely time debated: if the northern continental margin of the South China Sea is volcanic or nonvolcanic. The final conclusion is that this continental margin is nonvolcanic.

The local scale of rotating convection, ℓ, is a fundamental parameter in many turbulent geophysical and astrophysical fluid systems, yet it is often poorly constrained. Here we conduct rotating convection laboratory experiments analogous to convecting flows in planetary cores and subsurface oceans to obtain measurements of the local scales of motion. Utilizing silicone oil as the working fluid, we employ shadowgraph imagery to visualize the flow, from which we extract values of the characteristic cross-axial scale of convective columns and plumes. These measurements are compared to the theoretical values of the critical onset length scale, ℓ_crit, and the turbulent length scale, ℓ_turb. Our experimentally-obtained length scale measurements simultaneously agree with both the onset and turbulent scale predictions across three orders of magnitude in convective supercriticality ($10^2\lesssim \widetilde{Ra}\lesssim10^5$), a correlation that is consistent with inferences made in prior studies. We further explore the nature of this correlation and its implications for geophysical and astrophysical systems.Abstract content goes here

The North Qilian Ocean (NQO) was the northernmost branch of the Proto-Tethys separating the Central Qilian Terrane (CQT) from the North China Block (NCB) since the Neoproterozoic Rodinia breakup. An enhanced knowledge on its evolutionary history would greatly improve our understanding on the tectonics of the Proto-Tethys and the assembly of the East Asia. However, the timing of the NQO closure onset remains unsolved with assumptions ranging from the end-Ordovician to the Devonian. To address this issue, integrated studies of stratigraphy, petrology and geochronology were conducted on the Ordovician strata in the SWNCB and the eastern North Qilian Accretionary Belt (ENQAB). Stratigraphic and paleontologic syntheses demonstrate that the pre-Katian strata in the SWNCB are shallow-marine deposits containing abundant benthonic faunas, while the Katian successions atop an unconformity are dominated by deep-water calcareous debrites and siliciclastic turbidites with the dominance of planktonic graptolites. Provenance analysis reveals an evolving source from the NCB basement to the CQT orogen since the Katian. The pre-Katian quartz arenites in the SWNCB contain zircons of ca. 1600–2800 Ma significantly older than their depositional timing, in contrast, the Katian turbidites in the SWNCB and the ENQAB display similar age patterns dominated by ca. 450–900 Ma ages. These clues imply a noteworthy basin-filling shift from passive margin to underfilled peripheral foreland separated by a forebulge unconformity at the Sandbian/Katian boundary. The first arrival of CQT-originated detritus onto the SWNCB at ca. 453 Ma is the oldest stratigraphic constraint for the initial elimination of the northern Proto-Tethys.

Salt fingers occur throughout a large fraction of the World Ocean and can have substantial effects on large-scale mixing processes, such as the Meridional Overturning Circulation (see, e.g., Zhang et al., 1998). However, most numerical and laboratory studies of this phenomenon occur in quiescent environments. We simulate salt fingers in the presence of constant and oscillating shear in order to quantify the mixing of heat and salt by these systems under the impacts of large-scale internal waves. The code used in these simulations (the “Rocking Ocean Modeling Environment” or ROME) is a new pseudo-spectral hydrodynamic model which incorporates a steady or oscillatory background shear flow with a spatially uniform background velocity gradient. This configuration presents a challenge for modeling via Fourier-based algorithms because the typical evolution of such a flow is incompatible with the periodic boundary conditions at the vertical extremities of the computational domain. This complication is addressed by reformulating the governing equations in a new, temporally varying “tilting” coordinate system associated with the background flow as has been done in the past in the field of homogenous turbulence. Generally, it is shown that the application of shear can reduce fluxes by a factor of 2 or 3 for typical amplitudes of near-inertial waves and that the impact of shear decreases as the frequency of the applied shear increases. Though the focus of this study is on the effects of shear on double-diffusive systems, ROME is well-suited to a wide range of problems involving sheared stratified systems.

We characterize $117$ seismic events occurred in Chile and registered at the Wetzell Geodetic Observatory (BWLRAS) in Germany in terms of rotational seismic parameters. Using the Minimum Curvature Interpolation method, we create a $2$D map with the Vertical Rotation Rate (VRR) divided in three zones from the Chilean Coast: Northern, Central, and Southern area. In order to describe the behavior of VRR along time, we create a timeline and seismic moment model showing events in these areas with different values of VRR. The analyzed data includes four large earthquakes occurred in different zones with magnitudes greater than $M_w$7.5. We focus our analysis in the values of the rotational velocity for these earthquakes and show that the VRR does not have a clear relation with the seismic moment magnitude. Our results open a new way to describe and study seismic events. It can be useful to generate a deeper understanding of the dynamics in the underlying processes involved in the earthquake occurrence. As well, our results could serve to improve safety regulations in construction and mining, since important rotational movements may be present even within low moment magnitude events.

To reveal the spatial distribution of major active faults and structural discontinuities in the Himalayan-Tibetan orogen, this paper presents wavelet multiscale analysis of the Bouguer gravity field and solves the total horizontal derivatives of each wavelet detail. The results show that, in general, the crustal discontinuities on the Pamir Plateau and in the Himalayan tectonic zone are significant. On the northern margin of Tibet, active faults are mostly visible only in the deep crust. In eastern Tibet, crustal discontinuities decrease as depth increases. The Himalayan crust is undergoing E-W extension, and material discontinuities are significant along N-S-trending normal faults. The Sangri-Nacuo fault is the tectonic boundary between the Himalayan tectonic zone and the eastern Himalayan syntaxis and cuts off the entire lithosphere of Tibet. The spatial structural distributions of the western and eastern Himalayan syntaxes are very different. The former is relatively intact and extends deeper in the lithosphere, while the latter is more complex and shallower than the Mohorovicic discontinuity, and its overlying crust has deformed intensely from the collision between the Indian and Eurasian plates. Further, the structural distribution in the upper mantle reveals that the wedging Indian plate in the western Himalayan syntaxis almost reaches the SW margin of the Tarim basin and forms a closed structure in western Tibet, which could help to explain the eastward extrusion of the Tibetan Plateau.

The three Swarm satellites provide an optimum, low Earth orbit (LEO) and multi-spacecraft platform, to explore for the first time the local correlation between field-aligned currents (FACs), auroral electrojets, and magnetic perturbations at the Earth’s surface. By Swarm and ground magnetic field data together, one can investigate systematically the full correlation chain, whose final link controls the ground induced currents and related space weather effects. We introduce an integrated FAC product, the Sheet FAC (SFAC) index, as a convenient measure of the in-situ FAC data, and check the correlations SFAC-AE, SFAC-PEJ and SFAC-dH, with AE the standard auroral electrojet index, PEJ the local, Swarm based, polar electrojet index, and dH the horizontal magnetic field perturbation at the Earth’s surface. Given the good SFAC-dH correlation, we also suggest an extension of SFAC to higher LEO satellites, which cannot observe any more the electrojet currents, but are fully capable to monitor SFAC.