Dong et al. (2025) Stratosphere‐Troposphere Exchange of Water Vapor Based on Observations and Reanalyses

⚠️ Warning: This summary was generated from the abstract only, as the full text was not available.

Identification

• Journal: Geophysical Research Letters
• Year: 2025
• Date: 2025-12-17
• Authors: Cong Dong, Qiang Fu
• DOI: 10.1029/2025gl117115

Research Groups

Not specified in the abstract.

Short Summary

This study provides the first global estimates of stratosphere-troposphere exchange (STE) of water vapor (H2O) using an observational mass budget approach, revealing a small net global flux of 0.10 ± 0.04 Pg/yr into the stratosphere and identifying significant biases in reanalysis products (MERRA2, ERA5) compared to observations.

Objective

• To provide the first global estimates of stratosphere-troposphere exchange (STE) of water vapor (H2O) using the lowermost stratosphere mass budget approach.
• To compare observationally derived H2O fluxes with those from reanalysis products (MERRA2 and ERA5).

Study Configuration

• Spatial Scale: Global, encompassing Northern Hemisphere extratropics, Southern Hemisphere extratropics, and the tropics. Focus on the lowermost stratosphere and tropopause region.
• Temporal Scale: Annual averages and seasonal cycles of H2O fluxes.

Methodology and Data

• Models used: MERRA2 (Modern-Era Retrospective analysis for Research and Applications, Version 2), ERA5 (ECMWF Reanalysis 5). These are reanalysis products used for comparison.
• Data sources: Observationally derived H2O fluxes (specific instruments or datasets not detailed in abstract), reanalysis data from MERRA2 and ERA5. The methodology involves a lowermost stratosphere mass budget approach using these data.

Main Results

• Observationally derived H2O fluxes across the isentropic surface fitted to the tropical tropopause are:
  • Northern Hemisphere extratropics: -1.16 ± 0.20 Pg/yr
  • Southern Hemisphere extratropics: -0.94 ± 0.18 Pg/yr
  • Tropics: 2.20 ± 0.36 Pg/yr
• The net global H2O flux into the stratosphere, based on observations, is 0.10 ± 0.04 Pg/yr.
• In contrast, MERRA2 and ERA5 yield global fluxes of -1.84 Pg/yr and -0.27 Pg/yr, respectively, suggesting a net H2O source in the stratospheric overworld from reanalyses.
• Large discrepancies in the seasonal cycle of H2O net fluxes at the tropopause exist between reanalyses and observations.
• These differences are primarily attributed to biases in reanalysis H2O concentrations at the isentropic surface and in the lowermost stratosphere.

Contributions

• Provides the first global estimates of stratosphere-troposphere exchange (STE) of water vapor using an observationally-based mass budget approach.
• Quantifies regional and global H2O fluxes across the tropopause.
• Identifies and quantifies significant biases in H2O concentrations and fluxes in widely used reanalysis products (MERRA2, ERA5) compared to observational estimates, particularly regarding the seasonal cycle and net global flux.
• Highlights the need for improved representation of H2O in reanalysis systems for accurate STE assessment.

Funding

Not specified in the abstract.

Citation

@article{Dong2025StratosphereTroposphere,
  author = {Dong, Cong and Fu, Qiang},
  title = {Stratosphere‐Troposphere Exchange of Water Vapor Based on Observations and Reanalyses},
  journal = {Geophysical Research Letters},
  year = {2025},
  doi = {10.1029/2025gl117115},
  url = {https://doi.org/10.1029/2025gl117115}
}