Kwon et al. (2025) Synoptic systems influence the effectiveness of spectral nudging in high-resolution simulations of extreme precipitation

Identification

• Journal: npj Climate and Atmospheric Science
• Year: 2025
• Date: 2025-10-10
• Authors: Daehee Kwon, Ga‐Yeong Seo, Seung‐Ki Min, Seok‐Woo Son, Young‐Hee Ryu, Eun‐Soon Im, Dong‐Hyun Cha, Jinuk Kim, Young‐Hwa Byun, Kyung-On Boo
• DOI: 10.1038/s41612-025-01224-4

Research Groups

• Division of Environmental Science and Engineering, Pohang University of Science and Technology, Pohang, South Korea
• Institute for Convergence Research and Education in Advanced Technology, Yonsei University, Seoul, South Korea
• School of Earth and Environmental Sciences, Seoul National University, Seoul, South Korea
• Department of Atmospheric Sciences, Yonsei University, Seoul, South Korea
• Department of Civil and Environmental Engineering, The Hong Kong University of Science and Technology, Hong Kong SAR, China
• Division of Environment and Sustainability, The Hong Kong University of Science and Technology, Hong Kong SAR, China
• Department of Civil Urban Earth and Environmental Engineering, Ulsan National Institute of Science and Technology, Ulsan, South Korea
• Climate Change Research Team, National Institute of Meteorological Sciences, Jeju, South Korea

Short Summary

This study investigates the effectiveness of spectral nudging (SN) in convection-permitting model simulations of warm-season extreme precipitation in South Korea, finding that SN improves simulations by maintaining synoptic circulations consistent with observations, with its effectiveness depending on synoptic conditions, domain size, and the dominant wave scales of the event.

Objective

• Investigate the effectiveness of spectral nudging (SN) in convection-permitting model simulations of three typical warm-season extreme precipitation events in South Korea.
• Analyze how the effects of SN depend on the synoptic conditions of extreme precipitation events and the model domain size.

Study Configuration

• Spatial Scale:
  • Model horizontal resolution: 3 kilometers.
  • Three different domain sizes: approximately 4500 kilometers (Domain1), 3000 kilometers (Domain2), and 1800 kilometers (Domain3) wide.
  • Spectral nudging (SN) cut-off wavelength: approximately 1000 kilometers.
• Temporal Scale:
  • Three warm-season extreme precipitation events in South Korea (August 2021, July 2020, September 2010).
  • Simulations performed five times for each experiment, with initialization times delayed by 6-hour intervals to create ensemble members.
  • Analysis period: centered on the time of maximum hourly precipitation observed at surface stations for each event.

Methodology and Data

• Models used:
  • Weather Research and Forecasting (WRF) model version 4.4 (convection-permitting simulation).
• Data sources:
  • Initial and Lateral Boundary Conditions: European Center for Medium-Range Weather Forecasts reanalysis fifth generation (ERA5).
  • Synoptic Observation Data: ERA5.
  • Precipitation Evaluation:
    • Korea Meteorological Administration (KMA) 500 meter gridded data (for time series evaluation over South Korean land area).
    • Integrated Multi-Satellite Retrievals for Global Precipitation Measurement (IMERG) (0.1° resolution, half-hourly, for spatial distribution evaluation).

Main Results

• Spectral nudging (SN) generally improves the spatial distribution and hourly peak simulations of extreme precipitation, particularly for events driven by upper-level troughs and strong baroclinic instability (e.g., 202108 and 202007 events).
• SN's effectiveness increases with increasing model domain size, especially for events where synoptic-scale Rossby waves are well-resolved within the domain and exceed the SN cut-off wavelength.
• SN influences moisture transport (Integrated Vapor Transport, IVT) and local ascent by restricting the upper-level trough, which in turn affects the baroclinic structure and surface cyclone development.
• The impact of SN is less pronounced for events primarily influenced by surface processes or mesoscale disturbances rather than upper-level dynamics (e.g., 201009 event).
• SN contributes to reducing ensemble spread in simulations, making them more consistent with observations.
• The most effective configuration for simulating extreme precipitation events where SN is beneficial is proposed to be a domain approximately 3000 kilometers wide (Domain2) with SN applied.

Contributions

• Provides a comprehensive, mechanism-based analysis of spectral nudging (SN) effectiveness, considering both the synoptic characteristics of extreme precipitation events and the model domain size.
• Quantitatively demonstrates how SN, by constraining upper-level dynamics, indirectly influences mid-to-lower tropospheric baroclinic structures, moisture transport, and vertical ascent, leading to improved precipitation simulations.
• Offers practical guidance for optimizing SN configuration in high-resolution regional climate modeling, suggesting an optimal domain width for events sensitive to SN.
• Highlights the importance of matching the dominant horizontal wave scale of an event with the model domain size and SN cut-off wavelength for maximizing SN benefits.

Funding

• KMA Research and Development Program (Grant RS-2024-00403386)
• Human Resource Program for Sustainable Environment in the 4th Industrial Revolution Society
• National Center for Meteorological Supercomputer of the Korea Meteorological Administration (KMA) (for model simulation and data transfer support)

Citation

@article{Kwon2025Synoptic,
  author = {Kwon, Daehee and Seo, Ga‐Yeong and Min, Seung‐Ki and Son, Seok‐Woo and Ryu, Young‐Hee and Im, Eun‐Soon and Cha, Dong‐Hyun and Kim, Jinuk and Byun, Young‐Hwa and Boo, Kyung-On},
  title = {Synoptic systems influence the effectiveness of spectral nudging in high-resolution simulations of extreme precipitation},
  journal = {npj Climate and Atmospheric Science},
  year = {2025},
  doi = {10.1038/s41612-025-01224-4},
  url = {https://doi.org/10.1038/s41612-025-01224-4}
}