Wang et al. (2025) Moist orographic gravity wave drag parameterization reduces the bias of summer rainfall over the Tibetan Plateau

Identification

• Journal: npj Climate and Atmospheric Science
• Year: 2025
• Date: 2025-11-17
• Authors: Yingjie Wang, Xin Xu, Xiangrong Yang, Peng Wei, Congyuan Li, Jian Wu, Kaijun Ren
• DOI: 10.1038/s41612-025-01245-z

Research Groups

• College of Computer Science and Technology, National University of Defense Technology, Changsha, Hunan, China
• College of Meteorology and Oceanography, National University of Defense Technology, Changsha, Hunan, China
• State Key Laboratory of Severe Weather Meteorological Science and Technology, Key laboratory of Mesoscale Severe Weather/Ministry of Education, and School of Atmospheric Sciences, Nanjing University, Nanjing, Jiangsu, China

Short Summary

This study revises the orographic gravity wave drag (OGWD) parameterization in the Weather Research and Forecasting (WRF) model by incorporating moisture effects. Seasonal simulations demonstrate that this modification significantly reduces the persistent wet biases in summer precipitation over the southeastern Tibetan Plateau by altering monsoon circulation and water vapor transport.

Objective

• To revise the existing orographic gravity wave drag (OGWD) parameterization scheme (Kim and Doyle, 2005) in the Weather Research and Forecasting (WRF) model by incorporating the moisture effect of saturated air on the buoyancy frequency.
• To investigate the influence of this revised moist OGWD scheme on summer precipitation over the Tibetan Plateau (TP) and assess its ability to reduce simulation biases.

Study Configuration

• Spatial Scale: Tibetan Plateau (TP) and surrounding South Asia, including the Indian Peninsula and the Bay of Bengal. The model domain covers this region with a horizontal resolution of 0.5°.
• Temporal Scale: Seasonal simulations for summer (June–July–August, JJA) conducted annually from 2003 to 2023. Each simulation period runs from May 25 to August 31.

Methodology and Data

• Models used:
  • Weather Research and Forecasting (WRF) model.
  • Revised Kim and Doyle (KD05) Orographic Gravity Wave Drag (OGWD) parameterization scheme, incorporating moist buoyancy frequency based on Durran and Klemp (1982).
  • WRF single-moment three-class microphysics scheme.
  • Yonsei University planetary boundary layer scheme.
  • Tiedtke scheme for cumulus convection.
  • Rapid Radiative Transfer Model for Global Climate Models (RRTMG) radiation schemes.
  • Mesoscale Model version 5 similarity scheme for the surface layer.
  • Noah land surface model.
• Data sources:
  • Initial and Boundary Conditions: European Center for Medium-Range Weather Forecasts (ECMWF) global atmospheric reanalysis (ERA-Interim for 2003–2019, ERA5 for after 2019).
  • Sea Surface Temperature Forcing: Derived from ERA-Interim/ERA5 reanalysis data.
  • Precipitation Evaluation: Climate Prediction Center Morphing Technique (CMORPH) precipitation data (3-hour, 0.25° resolution).

Main Results

• The revised moist OGWD scheme (MOIST experiment) significantly reduces summer precipitation and wet biases over the southeastern and eastern Tibetan Plateau compared to the original dry scheme (CTRL experiment).
• The areal mean wet bias over the southeastern and eastern TP (24–35°N, 90–110°E) is reduced by approximately 8.2% (from 3.91 mm to 3.59 mm).
• The moisture effect initially increases lower-tropospheric OGWD over the Indian Peninsula, leading to a weakening of local low-level winds.
• This initial wind deceleration subsequently reduces the surface gravity wave momentum flux and OGWD, which in turn gradually strengthens the low-level flow and intensifies the South Asian monsoon circulation over the Bay of Bengal (BOB).
• During mid-to-late summer, this monsoon intensification is continuously enhanced through a positive feedback mechanism (Conditional Instability of the Second Kind, CISK) between circulation and precipitation.
• The strengthened cyclonic circulation over the BOB induces an anomalous easterly flow south of the TP, which opposes the climatological southwesterly monsoon, thereby decreasing water vapor transport toward the TP.
• The total water vapor budget in the main rainfall wet bias area over the southeastern TP decreases by approximately 26.59% in the MOIST experiment (from 60.03 × 10^5 kg s^-1 to 44.07 × 10^5 kg s^-1).

Contributions

• This study presents a novel revision of the Kim and Doyle (2005) OGWD parameterization scheme by explicitly incorporating the moisture effect (latent heating from saturated moist air) on the buoyancy frequency, considering both dry and moist adiabatic processes.
• It provides compelling evidence that this moist OGWD parameterization effectively reduces persistent summer precipitation wet biases over the Tibetan Plateau, a common challenge in numerical models.
• The research elucidates a complex atmospheric feedback mechanism: moist OGWD initially weakens local winds, which then indirectly strengthens the Bay of Bengal monsoon, leading to reduced water vapor transport and precipitation over the southeastern TP.
• The findings offer valuable insights for model developers aiming to improve OGWD parameterizations, particularly in moisture-rich, complex terrain regions influenced by monsoons.

Funding

• National Key Research and Development Program of China (Grant 2023YFC3007502)
• The Fundamental Research Funds for the Central Universities (Grant 14380222)
• The National Natural Science Foundation of China (Grant 42375158)
• The National University of Defense Technology innovation project (Grant XJZH20240004)

Citation

@article{Wang2025Moist,
  author = {Wang, Yingjie and Xu, Xin and Yang, Xiangrong and Wei, Peng and Li, Congyuan and Wu, Jian and Ren, Kaijun},
  title = {Moist orographic gravity wave drag parameterization reduces the bias of summer rainfall over the Tibetan Plateau},
  journal = {npj Climate and Atmospheric Science},
  year = {2025},
  doi = {10.1038/s41612-025-01245-z},
  url = {https://doi.org/10.1038/s41612-025-01245-z}
}