How organised convective systems produce more extreme rainfall

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Convective organisation refers to convective systems that cover a larger area and last longer than an individual convective cell. Tropical extreme rain is closely related to convective organisation, but it is unclear how it influences extreme rainfall and whether the extreme rainfall is caused by extreme intensity or duration.

Therefore, in this study we have compared extreme rainfall between organised and unorganised convection with idealised numerical model simulations.

Surprisingly, the extreme instantaneous rain rate does not change when convection is organized, because the reduced water condensation induced by weaker upward motion is balanced by the increase in precipitation efficiency (how much of the water that condenses is converted to rainfall at the surface).

Nonetheless, extreme daily accumulated rainfall is greater when convection is organised, because convection is localised in relatively fixed locations once it’s organised, which increases the accumulated extreme rain over long timescales.

Reference: Bao, J., and Sherwood, S. C. (2019). The role of convective self‐aggregation in extreme instantaneous versus daily precipitation. Journal of Advances in Modeling Earth Systems, 11. https://doi.org/10.1029/2018MS001503.

 

Originally published by CLEX, 7 February 2019.