Using velocities from a state estimate, Lagrangian analysis maps the global routes of North Atlantic Deep Water (NADW) exiting the Atlantic and reentering the upper branch of the Atlantic Meridional Overturning Circulation (AMOC). Virtual particle trajectories followed for 8100 years highlight an upper route (32%) and a lower route (68%). The latter samples σ2 > 37.07 and is further divided into subpolar (20%) and abyssal cells (48%). Particles in the abyssal cell detour into the abyssal North Pacific before upwelling in the Southern Ocean. NADW preferentially upwells north of 33°S (67%). Total diapycnal transformations are largest in the lower route but of comparable magnitudes in the upper route, challenging its previous characterization as “adiabatic.” Typical transit times are 300, 700, and 3600 years for the upper route, subpolar, and abyssal cells, respectively. The AMOC imports salinity into the Atlantic, indicating its potential instability to high-latitude freshwater perturbations.

https://advances.sciencemag.org/content/advances/7/21/eabf5478.full.pdf

Coupling of the mid-depth and abyssal components of the global overturning circulation according to a state estimate

Ocean observations are expensive and difficult to collect. Designing effective ocean observing systems therefore warrants deliberate, quantitative strategies. We leverage adjoint modeling and Hessi...

/pdf/leveraging-uncertainty-quantification-to-design-ocean-nymba0vt78.pdf

Leveraging Uncertainty Quantification to Design Ocean Climate Observing Systems

Abstract A string of fierce fires broke out in Chile in the austral summer 2023, just six years after the record-breaking 2017 fire season. Favored by extreme weather conditions, fire activity has dramatically risen in recent years in this Andean country. A total of 1.7 million ha. burned during the last decade, tripling figures of the prior decade. Six of the seven most destructive fire seasons on record occurred since 2014. Here, we analyze the progression during the last two decades of the weather conditions associated with increased fire risk in Central Chile (30°–39° S). Fire weather conditions (including high temperatures, low humidity, dryness, and strong winds) increase the potential for wildfires, once ignited, to rapidly spread. We show that the concurrence of El Niño and climate-fueled droughts and heatwaves boost the local fire risk and have decisively contributed to the intense fire activity recently seen in Central Chile. Our results also suggest that the tropical eastern Pacific Ocean variability modulates the seasonal fire weather in the country, driving in turn the interannual fire activity. The signature of the warm anomalies in the Niño 1 + 2 region (0°–10° S, 90° W–80° W) is apparent on the burned area records seen in Central Chile in 2017 and 2023. 

Extreme fire weather in Chile driven by climate change and El Niño–Southern Oscillation (ENSO)

Reduced order models (ROMs) are computational models whose dimension is significantly lower than those obtained through classical numerical discretizations (e.g., finite element, finite difference, finite volume, or spectral methods). Thus, ROMs have been used to accelerate numerical simulations of many query problems, e.g., uncertainty quantification, control, and shape optimization. Projection-based ROMs have been particularly successful in the numerical simulation of fluid flows. In this brief survey, we summarize some recent ROM developments for the quasi-geostrophic equations (QGE) (also known as the barotropic vorticity equations), which are a simplified model for geophysical flows in which rotation plays a central role, such as wind-driven ocean circulation in mid-latitude ocean basins. Since the QGE represent a practical compromise between efficient numerical simulations of ocean flows and accurate representations of large scale ocean dynamics, these equations have often been used in the testing of new numerical methods for ocean flows. ROMs have also been tested on the QGE for various settings in order to understand their potential in efficient numerical simulations of ocean flows. In this paper, we survey the ROMs developed for the QGE in order to understand their potential in efficient numerical simulations of more complex ocean flows: We explain how classical numerical methods for the QGE are used to generate the ROM basis functions, we outline the main steps in the construction of projection-based ROMs (with a particular focus on the under-resolved regime, when the closure problem needs to be addressed), we illustrate the ROMs in the numerical simulation of the QGE for various settings, and we present several potential future research avenues in the ROM exploration of the QGE and more complex models of geophysical flows.

Reduced Order Models for the Quasi-Geostrophic Equations: A Brief Survey

Indexes for the assessment of bacterial pollution in bathing waters from point sources: The northern Adriatic Sea CADEAU service.

/pdf/xclim-xarray-based-climate-data-analytics-vinl0lds.pdf

Xclim: Xarray-based Climate Data Analytics

MITgcm/MITgcm: checkpoint67m

MITgcm/MITgcm: mid 2020 version


 Decision-making regarding adaptation to climate hazards frequently requires a quantitative assessment of the likelihood of future hazards. This is typically done using climate model projections conditional on future greenhouse gas (GHG) and aerosol concentrations, as well as land-use changes. This leaves decision makers with the responsibility to select the concentration pathway corresponding to their risk tolerance, with little guidance from the scientific community. Here we propose a climate service estimating the occurrence of future climate hazards based on a weighted mixture distribution calibrated on an ensemble of hundreds of simulations from different global climate models and GHG concentration pathways. Each simulation is weighted according to its performance over the historical period, the equilibrium climate sensitivity of climate models, and the likelihood of future GHG concentrations. A prototype implementation for Canada was evaluated by groups of professionals from engineering firms and governments to collect criticism and suggestions. This feedback underlines the interest for climate products that integrate seamlessly with established risk-based frameworks familiar to decision makers.

Delivering probabilistic climate hazards assessments

The Ouranos CRCM5-CMIP6 ensemble: A dynamically downscaled ensemble of CMIP6 simulations over North America

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