A140-01
PIRE and Ice - Multiscale Modeling of Cirrus in the Tropical Tropopause Layer
Monday, 14 December 2020: 04:00
Virtual
Christopher Stephen Bretherton1,2, Jacqueline Nugent3, Samantha Turbeville3, Rachel Atlas2, Blaž Gasparini3, Zeyuan Hu4, Fayçal Lamraoui5, Peter N Blossey3, Zhiming Kuang6, Thomas P Ackerman7, Stephan Fueglistaler8 and Elisabeth J Moyer9, (1)Vulcan, Inc., Climate Modeling, Seattle, WA, United States, (2)University of Washington Seattle Campus, Seattle, WA, United States, (3)University of Washington, Seattle, WA, United States, (4)Harvard University, Department of Earth and Planetary Sciences, Cambridge, MA, United States, (5)Harvard University, Cambridge, MA, United States, (6)Harvard University, Department of Earth and Planetary Sciences and School of Engineering and Applied Sciences, Cambridge, MA, United States, (7)Univ of WA--JISAO, Seattle, WA, United States, (8)Princeton University, Department of Geosciences, Princeton, NJ, United States, (9)University of Chicago, Department of the Geophysical Sciences, Center for Robust Decision-making on Climate and Energy Policy (RDCEP), Chicago, IL, United States
Abstract:
The tropical tropopause layer (TTL, about 14-17 km in elevation) plays a key role in setting stratospheric water vapor and supports extensive cirrus important to the global radiation balance and climate change feedbacks.
Much of the cirrus is generated as outflow from deep convection that spreads, thins, develops internal turbulent circulations, and interacts with larger-scale waves and circulations.
The TTL poses a formidable modeling challenge because of its range of scales and uncertainties in ice microphysics.
An NSF-supported PIRE to advance understanding of TTL cirrus is exploring these challenges using global storm-resolving models (GSRMs, 2-5 km horizontal and 200-500 m vertical grid spacing in the TTL) and finer-resolution process models focused on regional and idealized studies.
These models are compared with satellite and in-situ observations and with each other.
For both model types, ice microphysical parameterizations are a dominant uncertainty. They lead to large differences in simulated TTL cloud radiative properties and water vapor profiles, suggesting opportunities for future model improvement.
Cirrus and cumulus convection were analyzed in nine GSRMs from an international intercomparison called DYAMOND aimed at realistic simulation of a 40-day period in Aug.-Sep. 2016. The updraft statistics of deep cumulus convection were more consistently represented than the TTL cirrus; all GSRMs produced a larger flux of water into the TTL in the form of ice rather than vapor. The PDF of ice water path across representative tropical regions differed dramatically between models. Idealized simulations of radiative-convective equilibrium over a uniformly warm ocean surface using several ice microphysical parameterizations in the same cloud-resolving model gave similar results. Regional simulations of TTL cirrus observed around the Himalayas during the SE Asian monsoon allow detailed comparison with a unique in-situ dataset from StratoClim, but they also highlight the horizontal complexity of the clouds that make this comparison challenging.
