Presented on September 21, 2022, by

Dr. Shaocheng Xie
Research Scientist, Group Leader
Cloud Processes Research and Modeling
Atmospheric, Earth & Energy Division (L103)
Lawrence Livermore National Laboratory


Dominant summertime disturbances along the subtropical Meiyu front are eastward-propagating synoptic-scale waves that are coupled with precipitation and moisture under a moderate background vertical shear. To what extent the intensity and structure of such synoptic disturbances change under global warming is investigated by diagnosing 18 models from Phase 6 of the Coupled Model Intercomparison Project. The model diagnosis reveals that there is a robust increase in the intensity of synoptic-scale activity along the Meiyu front, while the wavelength and phase speed remain unchanged. The cause of such changes of the synoptic-scale variability in the future warmer climate is investigated through the analysis of a moist baroclinic instability model framework. It is found that the growth rate of the most unstable mode strengthens in the future warmer climate, while the zonal wavenumber and phase speed of the most unstable mode remain unchanged, which is consistent with the CMIP6 future projections. The enhanced synoptic-scale variability is primarily attributed to the increase of background meridional and vertical moisture gradients under a warmer climate through strengthened positive moisture-convection-circulation feedback, while the changes of background vertical shear and convective adjustment times are insignificant.