Unravelling Disparities in Eulerian and Lagrangian Moisture Tracking Models in Monsoon- and Westerlies-dominated Basins Around the Tibetan Plateau
Abstract. Beyond traditional meteorological and (paleo)climatological analyses, numerical moisture tracking provides a quantitative diagnosis of moisture sources to the Tibetan Plateau (TP). While existing studies predominantly employ either the Eulerian or Lagrangian method, the potential differences in their simulations and the underlying causes of these discrepancies remain unexplored. In this study, we compare the applications of the most widely used Eulerian (WAM-2layers) and Lagrangian (FLEXPART-WaterSip) models in the TP, specifically in an Indian Summer Monsoon (ISM)-dominated basin (Yarlung Zangbo River Basin, YB) and a westerlies-dominated basin (upper Tarim River Basin, UTB). Compared to FLEXPART-WaterSip, WAM-2layers generally estimates higher moisture contributions from westerlies-dominated and distant source regions but lower contributions from local recycling. However, WAM-2layers simulations can be improved by using higher spatial-temporal resolution forcing data. The inherent ability in WAM-2layers to distinguish between evaporation and precipitation makes it more effectively in identifying varying moisture contributions arising from distinct surface evaporation sources. In contrast, in regions heavily influenced by smaller-scale convective systems with high spatial heterogeneity, such as the UTB when compared to the YB, simulations from FLEXPART-WaterSip tend to be more reliable. However, FLEXPART-WaterSip is prone to introducing additional errors when using specific humidity information in particles to infer moisture uptake and loss, although it accurately depicts the three-dimensional movement of air particles.
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