HPC | Joseph Mouallem

Multiple Same-Level and Telescoping Grid Nesting

Tue, 07 Jun 2022 00:00:00 +0000

Motivation

Multi-scale modeling often requires simulations at many different resolutions. This work shows how to couple coarse and fine domains within a single dynamical core, enabling cost-effective high-resolution forecasts of localized phenomena like hurricanes.

Overview

Two-way multiple same-level and telescoping grid nesting capabilities are implemented in FV3 using GFDL’s Flexible Modeling System (FMS).

A nest is an additional grid that zooms in over a region of interest to resolve the small-scale structures needed for better forecasts of localized weather events such as severe storms and hurricanes. A telescoping nest is a nest within a nest, allowing resolution to be refined progressively over the target region.

Nests can be used in both global and regional domains, and each level of the hierarchy can refine the parent resolution by an arbitrary factor.

A telescoping configuration refining a global ~13 km grid down to ~4.3 km, ~1.4 km and ~0.5 km over the region of interest.

Computational design

The nested grids run concurrently on different sets of processors and interact two-way with their parent grids. This provides more accurate results on both the nest and the parent, and reduces load imbalance between processors.

Availability

Starting from the FV3 public release of 2021, multiple same-level and telescoping nests are fully functional and available to the broader scientific community. This drastically improves overall forecast performance and opens the door to numerous research possibilities for scientists and meteorologists alike.

Reference

Mouallem, J., Harris, L., and Benson, R.: Multiple same-level and telescoping nesting in GFDL’s dynamical core, Geoscientific Model Development, 15(11), 4355-4371, 2022. https://doi.org/10.5194/gmd-15-4355-2022

SHiELD-LM4: Coupled Land-Atmosphere Modeling

Fri, 04 Sep 2026 00:00:00 +0000

What I developed

Implicit land-atmosphere coupling between SHiELD and LM4
Integration of the LM4 land component into the SHiELD framework
FMS coupling and exchange-grid infrastructure for conservative water and energy fluxes
High-resolution coupled hydrological simulations
The Hurricane Helene (2024) case study evaluating hydrological extremes

Motivation

Land-atmosphere interactions drive weather and climate extremes. This system integrates advanced atmospheric and land processes to capture how soil moisture, vegetation, and runoff feedback on regional weather patterns, advancing forecast skill for hydrological extremes.

Overview

We present a new high-resolution coupled atmosphere-land model, SHiELD-LM4, which integrates GFDL’s advanced atmospheric model (SHiELD) with the Geophysical Fluid Dynamics Laboratory Land Model (LM4) through the Flexible Modeling System (FMS) coupler. This coupled system enables accurate representation of land-atmosphere interactions, including soil moisture feedbacks, runoff generation, and hydrological extremes.

The model captures critical processes such as precipitation-driven runoff, soil water dynamics, and their impacts on atmospheric evolution during extreme weather events. High-resolution representation is essential for resolving the complex interactions between atmospheric convection and land surface hydrology.

Coupling Infrastructure

The SHiELD-LM4 model employs the Flexible Modeling System (FMS) coupler to facilitate bidirectional exchange between the atmospheric and land components. The exchange grid ensures accurate conservation of water and energy fluxes at the atmosphere-land interface.

Schematic of atmosphere (Atm), exchange grid (Xgrid), and land/ice components showing multi-level coupling infrastructure and flux exchange pathways.

Hurricane Helene (2024): Precipitation and Runoff

A key application of the coupled SHiELD-LM4 system is realistic simulation of extreme precipitation and its hydrological consequences during tropical cyclones. The animation below shows global precipitation and runoff during Hurricane Helene’s landfall, zoomed on the southeastern United States to reveal localized hydrological response.

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Global precipitation (mm/hr), surface runoff, and river discharge (kg/m³/s) during Hurricane Helene (2024). Zoomed panels show detailed runoff and river flow in the southeastern U.S. during landfall.

Soil Moisture and Land Surface Response

The coupling captures soil moisture evolution and its feedback to atmospheric conditions. The animation shows soil liquid water content evolution during an extreme precipitation event, with time series of observed vs. modeled soil moisture at multiple locations.

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Time series of soil liquid water content (kg/m³) at multiple observation sites during Hurricane Helene, illustrating the rapid soil water response to extreme precipitation and subsequent drainage.

Soil Column Interactions

The detailed representation of soil-atmosphere interactions is illustrated through the vertical exchange of water and energy between atmospheric columns and land model soil layers.

Time series of soil liquid content (kg/m³) at four observation locations (Asheville, Buncombe; Busick, Yancey; Boone, Watauga; Jefferson, Ashe) showing hourly evolution during extreme precipitation event.

Key Results

Two-way land-atmosphere coupling effectively captures soil moisture-precipitation feedbacks during extreme events.
Runoff generation and river discharge are accurately simulated at high resolution.
Soil water dynamics show realistic response to precipitation forcing with multi-hour memory effects.
The model demonstrates capability to simulate coupled hydro-atmospheric extremes with kilometer-scale detail.

This work extends coupled modeling capabilities to include detailed land surface hydrology, with implications for weather forecasting, hydrological prediction, and climate research.

Reference

Mouallem, J., Malyshev, S., Tan, Z., Shevliakova, E., Gao, K., Harris, L., Benson, R., Cooke, W., Zadeh, N., and Chilutti, L.: Development of a high-resolution coupled SHiELD-MOM6-LM4 – Part 2: Model overview, coupling technique, and evaluation of hydrological extremes during Hurricane Helene, Geoscientific Model Development (accepted), 2026.

SHiELD-MOM6: High-Resolution Coupled Atmosphere-Ocean Modeling

Fri, 26 Sep 2025 00:00:00 +0000

What I developed

The coupling framework connecting SHiELD, MOM6, and SIS2 through FMS
Exchange-grid infrastructure for conservative flux exchange between components
High-resolution coupled atmosphere-ocean-ice model configurations
Evaluation of hurricane-ocean interaction, including Hurricane Helene (2024)

Motivation

Air-sea interactions drive storm intensity and ocean response. This coupled system captures two-way feedback between the atmosphere and ocean at kilometer scales, enabling accurate simulations of hurricane-ocean interactions and coastal impacts.

Overview

We present a new high-resolution coupled atmosphere-ocean model, SHiELD-MOM6, which integrates GFDL’s advanced atmospheric model, the System for High-resolution modeling for Earth-to-Local Domain (SHiELD), the Modular Ocean Model version 6 (MOM6), and the Sea Ice Simulator (SIS2).

The model leverages the Flexible Modeling System (FMS) coupler and its innovative exchange grid to enable a robust and scalable two-way interaction between the atmosphere and ocean. The atmospheric component is built on the non-hydrostatic Finite-Volume Cubed-Sphere Dynamical Core (FV3) with the latest version of the SHiELD physics parametrization suite, while the ocean component is the latest version of MOM, supporting kilometer-scale high-resolution and regional applications.

Coupling infrastructure

The SHiELD-MOM6 model employs the Flexible Modeling System (FMS) coupler, which facilitates the exchange of information between the atmospheric and oceanic components. The exchange grid ensures accurate and efficient communication, enabling the two-way interaction necessary for realistic coupled simulations.

Schematic of a one-dimensional exchange grid and communication map between the atmosphere and ice components at different resolutions. The red sides of the arrow indicate the step where variables are projected from the exchange grid. The light-blue and mauve sides of the arrows represent the projection of variables onto the exchange grid from the atmosphere or ice components, respectively.

Hurricane Helene (2024)

Validation is demonstrated through a suite of experiments, including idealized hurricane simulations and a realistic North Atlantic case study featuring Hurricane Helene 2024. The animation below shows the simulated sea level pressure and 10 m winds (left) alongside the sea surface temperature anomaly and ocean surface currents (right) as the storm crosses the Gulf.

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Hurricane Helene (2024): sea level pressure and surface winds (left); sea surface temperature change and ocean currents (right). The cold wake and upwelling behind the storm are captured by the two-way coupling.

Scalability

Scalability tests have been conducted to evaluate the model’s performance on massively parallel computing systems. The results demonstrate that SHiELD-MOM6 maintains high computational efficiency as the number of processors increases, ensuring that high-resolution coupled simulations can be performed within practical timeframes

Strong scaling (a) and weak scaling (b): actual speedup/efficiency (red circles) compared to ideal speedup/efficiency (black squares) as a function of the number of PEs.

Key results

Air-sea interactions are effectively captured, both in storm intensity and structure and in the ocean response.
The coupling reproduces ocean phenomena such as storm-induced upwelling, the cold wake, and sea level changes.
Scalability tests confirm the model’s computational efficiency on massively parallel systems.

This work establishes a unified, modular cornerstone for advancing high-resolution coupled modeling, with significant implications for weather forecasting and climate research.

Reference

Mouallem, J., Gao, K., Reichl, B. G., Chilutti, L., Harris, L., Benson, R., Zadeh, N., Chen, J., Chen, J.-H., and Zhang, C.: Development of a high-resolution coupled SHiELD-MOM6 model – Part 1: Model overview, coupling technique, and validation in a regional setup, Geoscientific Model Development, 18(18), 6461-6478, 2025. https://doi.org/10.5194/gmd-18-6461-2025

Development of a high-resolution coupled SHiELD-MOM6 model – Part 1: Model overview, coupling technique, and validation in a regional setup

Fri, 26 Sep 2025 00:00:00 +0000

Multiple same-level and telescoping nesting in GFDL's dynamical core

Tue, 07 Jun 2022 00:00:00 +0000

HPC | Joseph Mouallem

Multiple Same-Level and Telescoping Grid Nesting

Motivation

Overview

Progressive refinement

Computational design

Availability

Reference

SHiELD-LM4: Coupled Land-Atmosphere Modeling

What I developed

Motivation

Overview

Coupling Infrastructure

Hurricane Helene (2024): Precipitation and Runoff

Soil Moisture and Land Surface Response

Soil Column Interactions

Key Results

Reference

SHiELD-MOM6: High-Resolution Coupled Atmosphere-Ocean Modeling

What I developed

Motivation

Overview

Coupling infrastructure

Hurricane Helene (2024)

Scalability

Key results

Reference

Development of a high-resolution coupled SHiELD-MOM6 model – Part 1: Model overview, coupling technique, and validation in a regional setup

Multiple same-level and telescoping nesting in GFDL's dynamical core