By Anthony Barone, Class of 2029
Figure 1. Topographical map of the Tibetan Plateau
Orographic drag is the phenomenon in which momentum is exchanged between the uneven topography and the atmosphere, causing momentum fluxes and large-scale circulation alterations. This drag directly affects the amount of precipitation that a region receives. Current climate models use a 2D scheme that does not accurately represent anisotropy, directional dependence. Jinbo Xie from Princeton and Minghua Zhang from the Stony Brook School of Marine and Atmospheric Sciences teamed up to implement a 3D climate parameterization within an existing model to better account for the terrain and more accurately predict rainfall in mountainous regions.
A simulation was conducted in East Asia using the climate parameterization, 3D orographic anisotropy (3D oro). This parameterization modified the transport of moisture and wind stress as a result of orographic drag that was left out of the 2D scheme. Two simulations were conducted to test the system’s accuracy against the older scheme. One set was a medium-range forecast, which was a 10-day simulation, and a seasonal forecast, which lasted 3 months. Climate data collected by stations across East Asia were compiled to gauge the accuracy of the 3D oro scheme.
When the seasonal simulation data from the 2D and 3D-oro schemes were compared, the 3D-oro model alleviated some of the overestimation of precipitation in the Tibetan Plateau from the 2D scheme by approximately 2 mm/day. For the medium range simulation, precipitation bias was in Eastern China with reduction of approximately 1.5 mm/day and the Tibetan Plateau with alleviation of approximately 0.5 mm/day. The data indicates that when the orographic anisotropy is taken into consideration, a more accurate precipitation estimate could be obtained.
This study indicated that a 3D scheme could be implemented that takes into account the orographic anisotropy to better estimate the amount of precipitation in a region. Precipitation affects billions of people across the world and being able to accurately determine how much rain a place will get could help with flood preparation and safety.
Work’s Cited:
[1] Xie, J., & Zhang, M. (2025). Impact of Orographic Drag Schemes on East Asia Rainfall. Journal of Geophysical Research: Atmospheres, 130(18). https://doi.org/10.1029/2024jd041336
[2] Image retrieved from: https://commons.wikimedia.org/wiki/File:Tibet_and_surrounding_areas_topographic_map_2.png
