Speaker
Description
Water vapor in the Upper Troposphere and Lower Stratosphere (UTLS) is critical to climate feedback mechanisms through its influence on radiation, chemistry, and atmospheric dynamics. The amount of water vapor entering the stratosphere is sensitive to the cold point temperature (CPT), which makes the Northern Hemisphere summer monsoons more favorable for transporting high-water vapor mixing ratios into the lower stratosphere during boreal summer. In this study, we use Lagrangian methods to reconstruct water vapor over the Asian summer monsoon (ASM) and North American monsoon (NAM), aiming to understand their contributions to stratospheric water vapor. The Lagrangian method, which tracks individual air parcels and focuses on large-scale flow behaviors, identifies the relevant CPT based on the coldest temperature encountered along each parcel's trajectory, contrasting with the Eulerian approach that identifies the CPT along local vertical temperature profiles.We validate the reconstructed water vapor fields against the satellite observations from the Stratospheric Aerosol and Gas Experiment III on the International Space Station (SAGE III/ISS) and NASA’s Aura Microwave Limb Sounder (MLS), while also comparing the SAGE and MLS observations with each other. Observations from SAGE III/ISS reveal stratospheric water vapor anomalies within the ASM and NAM anticyclones that are largely consistent with MLS data but exhibit stronger moisture enhancements. The Lagrangian trajectory-based advection-condensation approach, although systematically dry-biased compared to SAGE III/ISS and MLS observations, effectively reconstructs the water vapor concentrations in the UTLS (correlation coefficient about 0.75) and captures the moist anomalies in the ASM, but less well in the NAM. Our analysis reveals that UTLS water vapor mixing ratios in the ASM are influenced by large-scale tropopause temperatures (Lagrangian CPTs), similarly to the deep tropics. Furthermore, UTLS water vapor mixing ratios in the NAM are found to be significantly affected by long-range transport from Asia. However, some large-scale effects of convection, such as the drying and moistening effects of east-west shifts within the ASM, are not captured by the trajectory-based method, likely due to unresolved temperature variability and ice microphysics within the deep convection in the ERA5 meteorology. Despite limitations such as dry biases and computational demands, the Lagrangian method offers valuable insights into atmospheric water vapor transport processes, providing a robust tool for analyzing UTLS water vapor distribution.
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