Formation of Tropical Anvil Clouds by Slow Evaporation

TitleFormation of Tropical Anvil Clouds by Slow Evaporation
Publication TypeJournal Article
Year of Publication2019
AuthorsSeeley, Jacob T., Jeevanjee Nadir, Langhans Wolfgang, and Romps David M.
JournalGeophysical Research Letters
Volume46
Number1
Pages492 - 501
Abstract / Summary

Tropical anvil clouds play a large role in Earth’s radiation balance, but their effect on global warming is uncertain. The conventional paradigm for these clouds attributes their existence to the rapidly-declining convective mass flux below the tropopause, which implies a large source of detraining cloudy air there. Here, we test this paradigm by manipulating the sources and sinks of cloudy air in cloud-resolving simulations. We find that anvils form in our simulations because of the long lifetime of upper tropospheric cloud condensates, not because of an enhanced source of cloudy air below the tropopause. We further show that cloud lifetimes are long in the cold upper troposphere because the saturation specific humidity is much smaller there than the condensed water loading of cloudy updrafts, which causes evaporative cloud decay to act very slowly. Our results highlight the need for novel cloud-fraction schemes that align with this decay-centric framework for anvil clouds.

URLhttps://doi.org/10.1029/2018GL080747
DOI10.1029/2018GL080747
Journal: Geophysical Research Letters
Year of Publication: 2019
Volume: 46
Number: 1
Pages: 492 - 501

Tropical anvil clouds play a large role in Earth’s radiation balance, but their effect on global warming is uncertain. The conventional paradigm for these clouds attributes their existence to the rapidly-declining convective mass flux below the tropopause, which implies a large source of detraining cloudy air there. Here, we test this paradigm by manipulating the sources and sinks of cloudy air in cloud-resolving simulations. We find that anvils form in our simulations because of the long lifetime of upper tropospheric cloud condensates, not because of an enhanced source of cloudy air below the tropopause. We further show that cloud lifetimes are long in the cold upper troposphere because the saturation specific humidity is much smaller there than the condensed water loading of cloudy updrafts, which causes evaporative cloud decay to act very slowly. Our results highlight the need for novel cloud-fraction schemes that align with this decay-centric framework for anvil clouds.

DOI: 10.1029/2018GL080747
Citation:
Seeley, JT, N Jeevanjee, W Langhans, and DM Romps.  2019.  "Formation of Tropical Anvil Clouds by Slow Evaporation."  Geophysical Research Letters 46(1): 492 - 501.  https://doi.org/10.1029/2018GL080747.