The Impacts of cloud condensation nuclei on the extreme precipitation of a monsoon coastal mesoscale convection system

  • CCN types can impact extreme precipitation and updraft in monsoon coastal convection
  • Polluted simulation has stronger extreme precipitation and updraft
  • Stronger extremes are related to larger snow/graupel and higher cloud diffusion growth

This study investigates the impacts of different types of Cloud Condensation Nuclei (CCN) on the extreme of precipitation and updraft (above the 99th percentile threshold) of a mesoscale convection system occurred over the southwest coast of Taiwan Island under the moist southwesterly monsoon environment using cloud-permitting simulations. The convection system over the Taiwan Strait was observed during the SoWMEX/TiMREX IOP#8 in 2008. Simulations with the maritime type (clean) and the continental type (polluted) CCN are carried out and compared. The polluted simulation exhibits stronger extreme precipitation and updraft. The stronger extreme precipitation is associated with the enhanced size of snow and graupel. The enhanced latent heat release from faster diffusion growth of cloud drops contributes to stronger extreme updraft in the polluted simulation. With smaller rain evaporation rate, cold pool is weaker in the polluted simulation, which also leads to a more optimized convection structure and enhanced extreme updraft. The current results highlight the potential impacts of aerosol loadings on the extreme rainfall of monsoon coastal convection through microphysical, thermodynamics, and dynamical effects.

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