Truong et al. (2026) Spectral nudging impacts on precipitation downscaling in the Conformal Cubic Atmospheric Model, version CCAM-2504: insights from summer 2011

Identification

• Journal: Geoscientific model development
• Year: 2026
• Date: 2026-07-30
• Authors: Son C. H. Truong, Marcus J. Thatcher, Phuong Loan Nguyen, Lisa V. Alexander, John Louis McGregor
• DOI: 10.5194/gmd-19-6991-2026

Research Groups

• The Commonwealth Scientific and Industrial Research Organisation (CSIRO)
• Climate Change Research Centre, UNSW Sydney
• ARC Centre of Excellence for the Weather of the 21st Century, UNSW Sydney
• NSW Department of Climate Change, Energy, the Environment and Water

Short Summary

This study evaluates the impacts of spectral nudging on rainfall when dynamically downscaling with the Conformal Cubic Atmospheric Model (CCAM) during the extreme 2010–2011 La Niña event. The results demonstrate that carefully tuned spectral nudging in CCAM preserves large-scale teleconnections associated with La Niña, MJO, and retains mesoscale variability while enhancing the fidelity of both mean and extreme rainfall.

Objective

• Evaluate the ability of CCAM to reproduce large-scale circulation during the extreme 2010–2011 La Niña.
• Quantify the influence of nudging parameter choices on the representation of mean and extreme rainfall.
• Identify parameter combinations that improve the fidelity of regional rainfall simulations over Australasia during the extreme event.

Study Configuration

• Spatial Scale: The study focuses on the CORDEX-Australasia domain at 12.5 km with CCAM nested in ERA-5 reanalysis.
• Temporal Scale: The study period is from December 2010 to March 2011, covering the extreme 2010–2011 La Niña event.

Methodology and Data

• Models used: Conformal Cubic Atmospheric Model (CCAM)
• Data sources:
  • ERA5 reanalysis
  • GPM-IMERG precipitation
  • AGCD v1.0.0 daily rainfall

Main Results

• Spectral nudging substantially improves rainfall representation over continental Australia, reducing large-scale biases and improving spatial and temporal correlations.
• The most robust performance is achieved with configurations at short nudging wavelengths (≈ 500–1500 km), high-frequency updates (1 h), and including pressure, wind, and temperature.
• These setups reduce large-scale rainfall biases, improve spatial and temporal correlations, reproduce vertical structure and moisture convergence more realistically, and achieve the closest agreement with observed mean and extreme rainfall.

Contributions

• This study strengthens confidence in CCAM downscaling for CORDEX-Australasia, with implications extending to other CORDEX domains and applications.
• The results demonstrate that carefully tuned spectral nudging in CCAM preserves large-scale teleconnections associated with La Niña, MJO, and retains mesoscale variability while enhancing the fidelity of both mean and extreme rainfall.

Funding

• This research was funded by the Commonwealth Scientific and Industrial Research Organisation (CSIRO) and the Australian Research Council (ARC).

Citation

@article{Truong2026Spectral,
  author = {Truong, Son C. H. and Thatcher, Marcus J. and Nguyen, Phuong Loan and Alexander, Lisa V. and McGregor, John Louis},
  title = {Spectral nudging impacts on precipitation downscaling in the Conformal Cubic Atmospheric Model, version CCAM-2504: insights from summer 2011},
  journal = {Geoscientific model development},
  year = {2026},
  doi = {10.5194/gmd-19-6991-2026},
  url = {https://doi.org/10.5194/gmd-19-6991-2026}
}