Andrew M. Bradley's research while affiliated with Sandia National Laboratories and other places

Publications (44)

Article
Full-text available
This work documents version two of the Department of Energy's Energy Exascale Earth System Model (E3SM). E3SMv2 is a significant evolution from its predecessor E3SMv1, resulting in a model that is nearly twice as fast and with a simulated climate that is improved in many metrics. We describe the physical climate model in its lower horizontal resolu...
Preprint
Full-text available
This paper provides an overview of the United States (US) Department of Energy's (DOE's) Energy Exascale Earth System Model version 2 (E3SMv2) fully coupled Regionally Refined Model (RRM) and documents the overall atmosphere, land, and river results from the Coupled Model Intercomparison Project 6 (CMIP6) DECK (Diagnosis, Evaluation, and Characteri...
Article
Full-text available
Advection of trace species, or tracers, also called tracer transport, in models of the atmosphere and other physical domains is an important and potentially computationally expensive part of a model's dynamical core. Semi-Lagrangian (SL) advection methods are efficient because they permit a time step much larger than the advective stability limit f...
Article
Full-text available
This paper describes the first implementation of the Δx = 3.25 km version of the Energy Exascale Earth System Model (E3SM) global atmosphere model and its behavior in a 40‐day prescribed‐sea‐surface‐temperature simulation (January 20 through February 28, 2020). This simulation was performed as part of the DYnamics of the Atmospheric general circula...
Preprint
Full-text available
Advection of trace species (tracers), also called tracer transport, in models of the atmosphere and other physical domains is an important and potentially computationally expensive part of a model's dynamical core (dycore). Semi-Lagrangian (SL) advection methods are efficient because they permit a time step much larger than the advective stability...
Article
Full-text available
Previous studies have shown that atmospheric models with a spectral element grid can benefit from putting physics calculations on a relatively coarse finite volume grid. Here we demonstrate an alternative high‐order, element‐based mapping approach used to implement a quasi‐equal‐area, finite volume physics grid in E3SM. Unlike similar methods, the...
Article
Full-text available
We present a new evaluation framework for implicit and explicit (IMEX) Runge–Kutta time-stepping schemes. The new framework uses a linearized nonhydrostatic system of normal modes. We utilize the framework to investigate the stability of IMEX methods and their dispersion and dissipation of gravity, Rossby, and acoustic waves. We test the new framew...
Preprint
Full-text available
We present a new evaluation framework for implicit and explicit (IMEX) Runge-Kutta timestepping schemes. The new framework uses a linearized nonhydrostatic system of normal modes. We utilize the framework to investigate stability of IMEX methods and their dispersion and dissipation for gravity, Rossby, and acoustic waves. We test the new framework...
Article
Full-text available
We present an architecture-portable and performant implementation of the atmospheric dynamical core (High-Order Methods Modeling Environment, HOMME) of the Energy Exascale Earth System Model (E3SM). The original Fortran implementation is highly performant and scalable on conventional architectures using the Message Passing Interface (MPI) and Open...
Article
Full-text available
We present an architecture-portable and performant implementation of the atmospheric dynamical core (HOMME) of the Energy Exascale Earth System Model (E3SM). The original Fortran implementation is highly performant and scalable on conventional architectures using MPI and OpenMP. We rewrite the model in C++ and use the Kokkos library to express on-n...
Conference Paper
Many applications, such as PDE based simulations and machine learning, apply blas/lapack routines to large groups of small matrices. While existing batched blas APIs provide meaningful speedup for this problem type, a non-canonical data layout enabling cross-matrix vectorization may provide further significant speedup. In this paper, we propose a n...
Article
Physics-based models of volcanic eruptions track conduit processes as functions of depth and time. When used in inversions, these models permit integration of diverse geological and geophysical datasets to constrain important parameters of magmatic systems. We develop a 1D steady-state conduit model for effusive eruptions including equilibrium crys...
Article
The geodetically-derived interseismic Moment Deficit Rate (MDR) provides a first-order constraint on earthquake potential, and can play an important role in seismic hazard assessment, but quantifying uncertainty in MDR is a challenging problem that has not been fully addressed. We establish criteria for reliable MDR estimators, evaluate existing me...
Article
Newton–Krylov solvers for ocean tracers have the potential to greatly decrease the computational costs of spinning up deep-ocean tracers, which can take several thousand model years to reach equilibrium with surface processes. One version of the algorithm uses offline tracer transport matrices to simulate an annual cycle of tracer concentrations an...
Article
Full-text available
Albany is a multiphysics code constructed by assembling a set of reusable, general components. It is an implicit, unstructured grid finite element code that hosts a set of advanced features that are readily combined within a single analysis run. Albany uses template-based generic programming methods to provide extensibility and flexibility; it empl...
Article
[1] Dike intrusions both deform Earth's surface and induce propagating earthquake swarms. We develop methods to utilize both deformation and seismicity from brittle, volcano-tectonic earthquakes to image time-dependent dike propagation. Dieterich's (1994) seismicity-rate theory is used to relate dike-induced stress changes to seismicity rate and is...
Article
Deep aseismic roots of faults play a critical role in transferring tectonic loads to shallower, brittle crustal faults that rupture in large earthquakes. Yet, until the recent discovery of deep tremor and creep, direct inference of the physical properties of lower-crustal fault roots has remained elusive. Observations of tremor near Parkfield, CA p...
Article
Slow slip events (SSE) in many subduction zones incrementally stress the adjacent locked megathrust, suggesting that they could potentially either trigger or evolve into damaging earthquakes. We explore this with 2D quasi-dynamic simulations with rate-state friction, dilatancy, and coupled 1D pore-fluid and heat transport. Steady-state weakening fr...
Article
Geophysical observations have shown that transient slow slip events, with average slip speeds v on the order of 10(-8) to 10(-7) m/s, occur in some subduction zones. These slip events occur on the same faults but at greater depth than large earthquakes (with slip speeds of order similar to 1 m/s). We explore the hypothesis that whether slip is slow...
Article
It is believed that faults sustain large shear stresses during the nucleation phase, but slip at much lower stresses during earthquakes. The nucleation phase is typically characterized by rate- and state-dependent friction, in which slip accelerates after shear stress τ grows to about 0.6 to 0.9 times the effective normal stress σeff. During earthq...
Article
Full-text available
Episodic Tremor and Slip (ETS), involving transient deformations accompanied by emergent, low-frequency tremor occurs in subduction zones around the world. ETS events increase the shear stress on locked megathrusts and may potentially trigger damaging earthquakes. Despite the clear association of tremor and slip the physical relationship between th...
Article
Shear heating-induced thermal pressurization has long been thought to be a significant weakening mechanism during earthquake rupture. Recent work has shown that, in some cases, thermal pressurization may become the dominant weakening mechanism during the quasi-static nucleation phase of an earthquake, well before the onset of seismic radiation. The...
Article
Motivated by the hypothesis that dilatancy plays a critical role in faulting in subduction zones, we are developing FDRA, a software package to simulate two-dimensional quasi-dynamic faulting that includes rate-state friction, thermal pressurization, dilatancy (following Segall and Rice [1995]), and flash heating [Rice, 2006]. FDRA accommodates ful...
Article
Seismic and geodetic observations are consistent with slow-slip events (SSE) occurring down-dip of the locked megathrust in regions of anomalously high pore pressure p. We hypothesize that at low effective normal stress (sigma -p), dilatancy stabilizes velocity weakening faults, whereas at higher (sigma -p), thermal pressurization overwhelms dilata...
Article
Low frequency earthquakes (LFEs) and tremor have been observed in a number of subduction zones in conjunction with slow slip events (SSEs). However, the physics of LFEs and why they are different from high frequency earthquakes is poorly understood. Segall et al. [2010] proposed that dilatant reductions in the pore-pressure p promote the occurrence...
Article
Full-text available
The mechanics of slow slip events (SSE) in subduction zones remains un-resolved. We suggest that SSE nucleate in areas of unstable friction under drained con-ditions, but as slip accelerates dilatancy reduces pore-pressure p quenching instability. Competition between dilatant strengthening and thermal pressurization may control whether slip is slow...
Article
Seismic and geodetic observations indicate that slow-slip events (SSE) occur down-dip of locked megathrusts, in areas of high pore-pressure, p. We suggest that at low effective stress (sigma -p) dilatancy stabilizes rate-weakening faults, whereas at higher (sigma -p) thermal pressurization overwhelms dilatancy leading to dynamic slip. 2D simulation...
Article
Recent work has suggested that shear heating-induced thermal pressurization may become the dominant fault weakening mechanism during the quasi-static nucleation phase of an earthquake, well before the onset of seismic radiation. For the ``aging'' form of rate- and state-dependent friction, Schmitt & others [AGU, 2007] confirmed this hypothesis usin...
Article
We model the orbital debris environment by a set of differential equations with parameter values that capture many of the complexities of existing three-dimensional simulation models. We compute the probability that a spacecraft gets destroyed in a collision during its operational lifetime, and then define the sustainable risk level as the maximum...

Citations

... L. Lombardozzi et al., 2020). To address this shortcoming and to improve the simulation of carbon and water fluxes, several land model components of ESMs are now simulating major crops, including the Community Land Model Levis et al., 2012), E3SM land model (Golaz et al., 2022), Joint UK Land Environment Simulator (JULES) (Osborne et al., 2015), Noah-MP-Crop (Liu et al., 2016), Organizing Carbon and Hydrology In Dynamic Ecosystems (ORCHIDEE) (Wu et al., 2016), and Simple Biosphere Model (Lokupitiya et al., 2009). ...
... CC BY 4.0 License.in E3SMv2(Ma et al., 2022;Golaz et al., 2022) because these parameters are subject to large uncertainty depending on the ...
... Nevertheless, NARRM reduces the underestimation of maximum diurnal cycle magnitude by over 2x (6.71 mm/day vs. 3.10 mm/day). This result suggests that a resolution of ∼25 km is not adequate to capture the physics driving propagating MCSs, which probably require convection-permitting atmospheric simulations to achieve a good agreement with observations (Caldwell et al., 2021). ...
... EAMv2 uses the lowest-order Islet basis set, the one for n p = 4. Because the model code was frozen before the Islet bases were finalized, the formulation of the n p = 4 stable basis set is slightly different than reported in Bradley et al. (2021), but this difference has essentially no impact. To achieve global mass conservation, shape preservation, and mass-tracer consistency, Islet uses element-local and global versions of the communication-efficient density reconstructor (CEDR) described in Algorithm 3.1 of Bradley et al. (2019). ...
... The dynamics grid has an average grid spacing of 110 km, while the parameterizations grid and, as a result, the land grid have an average grid spacing of 165 km. Hannah et al. (2021) describe the remap algorithms to transfer data between the grids and the new topography file format to support these grids. The grids are the same as introduced in Herrington et al. (2019), but in EAMv2, the high-order remap method is local to each element except for some halo data for extremal mixing ratio values. ...
... The Simple Cloud Resolving E3SM Atmosphere Model (SCREAM) is being developed for the Energy Exascale Earth System Model (E3SM) project. SCREAM models nonhydrostatic fluid dynamics and includes a turbulence/ cloud fraction scheme, a microphysics scheme, a radiation scheme, an energy fixer, and prescribed-aerosol functionality, described in Caldwell et al. (2021). The energy fixer adjusts the temperature by a small global constant after each timestep (Williamson et al. 2015). ...
... The atmospheric dynamics is solved using the High Order Method Modeling Environment (HOMME; J. Dennis et al., 2005; J. M. Dennis et al., 2012;Evans et al., 2013), which provides both the hydrostatic (H) spectral element dynamical core used by E3SMv1 Golaz et al., 2019;Rasch et al., 2019) and the Community Earth System Model (Lauritzen et al., 2018;S. Zhang et al., 2020;Small et al., 2014), as well as the new HOMME NH (HOMME-NH; Bertagna et al., 2020;Taylor et al., 2020) spectral element dynamical core developed for SCREAM. In this section, we focus specifically on the differences between the H and NH model. ...
... For the time-stepping algorithm, the H simulations utilize the third order KGU53 explicit method described in Guerra and Ullrich (2016). NH simulations use a Horizontally Explicit Vertically Implicit approach (HEVI; Satoh, 2002), discretized with an IMplicit-EXplicit (IMEX) Runge Kutta method (Ascher et al., 1997), which combines an explicit KGU53 method for all horizontal derivatives and an implicit method for terms responsible for vertically propagating acoustic waves, similar to the IMEX methods constructed in Guba et al. (2020). ...
... It is the "physics" update-effectively computing q 1 and q 2 -that implements the various schemes that capture the effect of unresolved dynamical and thermodynamic processes (e.g., turbulence transport including that of convective updrafts, various boundary layer processes, cloud microphysics, and radiation) on the resolved scales. Physics parameterizations in SOTA climate models tends to be one of the most computationally intensive parts (e.g., see Bosler et al., 2019;Bradley et al., 2019). Furthermore, since traditional parameterizations are based on our limited understanding of the complex subgrid-scale processes, significant inaccuracies persist in the representation of microphysics, cumulus, boundary layer, and other processes (e.g., Sun and Barros, 2014). ...
... Because the model code was frozen before the Islet bases were finalized, the formulation of the n p = 4 stable basis set is slightly different than reported in Bradley et al. (2021), but this difference has essentially no impact. To achieve global mass conservation, shape preservation, and mass-tracer consistency, Islet uses element-local and global versions of the communication-efficient density reconstructor (CEDR) described in Algorithm 3.1 of Bradley et al. (2019). The global version is sometimes called a "mass fixer," but note that, in combination with the element-local version, it also enforces grid-point-local, time-dependent lower and upper bounds on tracer mixing ratios to enforce shape preservation and mass-tracer consistency. ...