A variable-resolution global model is helping meteorologists understand the water cycle across the Tibetan Plateau

The Tibetan Plateau (TP) is known as the third pole of the world due to the vast highlands with an average elevation of over 4 km. Its unique mid-latitude climate and high elevation, which provides headwaters for many of Asia’s major rivers, allows the TP to play an important role in the hydrological cycle and regional ecology.

Throughout the TP, summer precipitation reaches its annual maximum primarily due to moisture transport driven by the South Asian summer monsoon. The TP topography, particularly influenced by the Himalayas, is highly complex and contributes to unique precipitation patterns across the plateau. Due to this terrain, numerical weather and climate models should simulate the water cycle process with a spatial resolution of a few kilometers so that the topography can be recorded accurately.

Prof. Zhao Chun and his team – a group of researchers at the University of Science and Technology of China (USTC) Laboratory of Advanced Computing for Atmospheric Research (LACAR) – conducted numerical experiments with regional refinement over the TP in a 4 km horizontal by resolution using a non-hydrostatic model with global variable resolution. This allowed the team to study for the first time the effects of complex topography on TP moisture transport and summer precipitation. The study was published in advances in atmospheric science.

“Our study shows that a variable-resolution global simulation at a few kilometers can reproduce the main meteorological fields over the summer TP,” said Prof. Zhao, the corresponding author of the study. “Complex topography increases net moisture transport into the TP by about 11% and significantly modulates the spatial distribution of precipitation over the Himalayas.”

dr Zhao noted that despite the regional changes in the simulated precipitation distribution, when considering the average precipitation across the entire TP, the resolved topography results in a negligible simulation difference compared to the coarse spatial resolution topography. However, the new findings on modeling the influence of individual topography features are of great use.

“Previous studies mainly performed small-scale simulations with high spatial resolution using regional models, which may not fully simulate the effects of complex topography on large-scale circulation and thus moisture transport,” said Prof. Zhao. “…impacts are limited due to confinement by lateral (horizontal) boundaries.”

According to Prof. Zhao and his research team, global variable resolution simulation can avoid this problem and improve the ability to account for the influence of terrain on meteorological fields throughout the Himalayas and Tibetan Plateau.

“Compared to the smooth topography, in the complex topography, more pointed southern slopes of the Himalayas shift the uplifted airflow to the north, and more small-scale valleys that serve as channels for moisture transport are resolved,” said lead author Li Gudongze. “Both effects shift precipitation northward.”

The variable-resolution global simulation approach appears promising for future weather and regional climate simulations across the TP. Upcoming research will focus on applying the new method to the water cycle, energy cycle and studies of the atmospheric environment across the TP, including topographical impacts on regional climate and air quality.

Provided by the University of Science and Technology of China