Submitted as: model evaluation paper 29 Dec 2020

Submitted as: model evaluation paper | 29 Dec 2020

Review status: this preprint is currently under review for the journal GMD.

Development and evaluation of spectral nudging strategy for the simulation of summer precipitation over the Tibetan Plateau

Ziyu Huang1, Lei Zhong1,2,3, Yaoming Ma4,5,6, and Yunfei Fu1 Ziyu Huang et al.
  • 1School of Earth and Space Sciences, University of Science and Technology of China, Hefei 230026, China
  • 2CAS Center for Excellence in Comparative Planetology, Hefei 230026, China
  • 3Jiangsu Collaborative Innovation Center for Climate Change, Nanjing 210023, China
  • 4Key Laboratory of Tibetan Environment Changes and Land Surface Processes, Institute of Tibetan Plateau Research, Chinese Academy of Science, Beijing 100101, China
  • 5CAS Center for Excellence in Tibetan Plateau Earth Sciences, Beijing 100101, China
  • 6College of Earth and Planetary Sciences, University of Chinese Academy of Science, Beijing 100049, China

Abstract. Precipitation is the key component determining the water budget and climate change of the Tibetan Plateau (TP) under a warming climate. This high-latitude region is regarded as the Third Pole of the Earth and the Asian Water Tower and influences the eco-economy of downstream regions. However, the intensity and diurnal cycle of precipitation are inadequately depicted by current reanalysis products and regional climate models (RCMs). Spectral nudging is an effective dynamical downscaling method used to improve precipitation simulations of RCMs by preventing simulated fields from drifting away from large-scale reference fields, but the most effective manner of applying spectral nudging over the TP is unclear. In this paper, the effects of spectral nudging parameters (e.g., nudging variables, strengths and levels) on summer precipitation simulations and associated meteorological variables were evaluated over the TP. The results show that using a conventional continuous integration method with a single initialization is likely to result in the overforecasting of precipitation events and the overforecasting of horizontal wind speeds over the TP. In particular, model simulations show clear improvements in their representations of downscaled precipitation intensity and its diurnal variations, atmospheric temperature and water vapor when spectral nudging is applied towards the horizontal wind and geopotential height rather than towards the potential temperature and water vapor mixing ratio. This altering to the spectral nudging method not only reduces the wet bias of water vapor in the lower troposphere of the ERA-Interim reanalysis (when it is used as the reference fields) but also alleviates the cold bias of atmospheric temperatures in the upper troposphere, while maintaining the accuracy of horizontal wind features for the simulated fields. The conclusions of this study imply how reference fields errors impact model simulations, and these results may improve the reliability of RCM results used to study the long-term regional climate change.

Ziyu Huang et al.

Status: open (until 23 Feb 2021)
Status: open (until 23 Feb 2021)
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Ziyu Huang et al.

Ziyu Huang et al.


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Short summary
Spectral nudging is an effective dynamical downscaling method used to improve precipitation simulations of regional climate models (RCMs). However, the biases of the reference fields over the Tibetan Plateau (TP) would possibly introduce extra biases when spectral nudging is applied. Results show that the precipitation simulations were significantly improved when limiting the application of spectral nudging towards the potential temperature and water vapor mixing ratio over the TP.