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<p>The Tibetan Plateau (TP) significantly influences regional and even global climate mainly due to its high altitude and unique topography. Therefore, the planetary boundary layer (PBL) scheme is important for regional climate simulations in the TP. In this study, the impact of the PBL schemes (PBLSs; i.e., the YSU, MYJ, QNSE, and ACM2 schemes) on simulated surface air temperature (SAT) in the TP is investigated using the Weather Research and Forecasting model (WRF) for the summer of 2003. Overall, the PBLSs can generally reproduce the SAT spatial distributions in the TP. Significant differences are found between local closure schemes (MYJ and QNSE) and nonlocal ones (YSU and ACM2). For example, QNSE produces the most significant cold bias of -4.9&#xa0;°C, with the largest difference of 1.8&#xa0;°C between QNSE and ACM2, which simulate the lowest and the highest SAT values, respectively. Based on the temperature change equation, the adiabatic (i.e. convection) and diabatic terms are dominant in the PBLS choice-induced SAT change, whereas the advection is less important. The PBLSs can also greatly change land surface fluxes and PBL parameters, thereby influencing SAT. Additionally, the PBLSs tend to produce an unrealistically long super-adiabatic state, which alleviates the convergence of near-surface sensible heat and decreases the SAT. Due to overestimation of surface albedo, all these schemes underestimate the SAT, and the simulated higher SATs are consistent with higher downward longwave flux and lower albedo values. All these help understand the SAT simulation for the TP by regional climate models. </p> Graphical Abstract <p></p> <p>This graphical summary illustrates how different planetary boundary layer parameterization schemes (PBLSs) influence the simulation of summer surface air temperature (SAT) over the Tibetan Plateau, based on the Weather Research and Forecasting (WRF) model with a 12-member ensemble simulation. All four evaluated PBLSs produce notable cold biases in simulated SAT. The local PBLSs (i.e. MYJ and QNSE) exhibit average cold biases of 4–5&#xa0;°C, which are approximately 3&#xa0;°C larger than those of the non‑local PBLSs (i.e. YSU and ACM2). Compared with non‑local PBLSs, the local PBLSs tend to simulate a thicker and more unstable planetary boundary layer, accompanied by stronger adiabatic (or convective) heating and diabatic cooling processes near the surface. These processes lead to enhanced surface sensible and latent heat fluxes in the local‑scheme simulations, which dominate the SAT variation. Furthermore, owing to the high‑altitude environment of the Tibetan Plateau, the lower SAT produced by local schemes results in expanded snow and ice coverage and consequently higher surface albedo. This albedo feedback further amplifies the cold biases in local PBL simulations.</p>

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Sensitivity of Summer Surface Air Temperature to Planetary Boundary Layer Parameterization over the Tibetan Plateau: A Process-based Analysis

  • 期刊论文

  • 发表日期：

    2026年6月26日

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  • Shuaibing Shao,
  • Xin-Min Zeng,
  • Ning Wang,
  • Chunxiang Shi,
  • Shuai Sun,
  • Irfan Ullah,
  • Yiqun Zheng,
  • Fengge Su

摘要

The Tibetan Plateau (TP) significantly influences regional and even global climate mainly due to its high altitude and unique topography. Therefore, the planetary boundary layer (PBL) scheme is important for regional climate simulations in the TP. In this study, the impact of the PBL schemes (PBLSs; i.e., the YSU, MYJ, QNSE, and ACM2 schemes) on simulated surface air temperature (SAT) in the TP is investigated using the Weather Research and Forecasting model (WRF) for the summer of 2003. Overall, the PBLSs can generally reproduce the SAT spatial distributions in the TP. Significant differences are found between local closure schemes (MYJ and QNSE) and nonlocal ones (YSU and ACM2). For example, QNSE produces the most significant cold bias of -4.9 °C, with the largest difference of 1.8 °C between QNSE and ACM2, which simulate the lowest and the highest SAT values, respectively. Based on the temperature change equation, the adiabatic (i.e. convection) and diabatic terms are dominant in the PBLS choice-induced SAT change, whereas the advection is less important. The PBLSs can also greatly change land surface fluxes and PBL parameters, thereby influencing SAT. Additionally, the PBLSs tend to produce an unrealistically long super-adiabatic state, which alleviates the convergence of near-surface sensible heat and decreases the SAT. Due to overestimation of surface albedo, all these schemes underestimate the SAT, and the simulated higher SATs are consistent with higher downward longwave flux and lower albedo values. All these help understand the SAT simulation for the TP by regional climate models.

Graphical Abstract

This graphical summary illustrates how different planetary boundary layer parameterization schemes (PBLSs) influence the simulation of summer surface air temperature (SAT) over the Tibetan Plateau, based on the Weather Research and Forecasting (WRF) model with a 12-member ensemble simulation. All four evaluated PBLSs produce notable cold biases in simulated SAT. The local PBLSs (i.e. MYJ and QNSE) exhibit average cold biases of 4–5 °C, which are approximately 3 °C larger than those of the non‑local PBLSs (i.e. YSU and ACM2). Compared with non‑local PBLSs, the local PBLSs tend to simulate a thicker and more unstable planetary boundary layer, accompanied by stronger adiabatic (or convective) heating and diabatic cooling processes near the surface. These processes lead to enhanced surface sensible and latent heat fluxes in the local‑scheme simulations, which dominate the SAT variation. Furthermore, owing to the high‑altitude environment of the Tibetan Plateau, the lower SAT produced by local schemes results in expanded snow and ice coverage and consequently higher surface albedo. This albedo feedback further amplifies the cold biases in local PBL simulations.