Tuesday, 31 May - ICTP/UniTN/UniAQ Seminar Series on Weather and Climate

[Earth System Physics Section]

*ICTP/UniTN/UniAQ Joint International Seminar Series
on Weather and Climate: From Fundamentals to Applications*

**31 May at 15:30 CET

Speaker: *Kathleen Schiro*
University of Virginia, Charlottesville, U.S.A.

Title: Impacts of Deep Convection on the Tropical Low Cloud Feedback and 
Climate Sensitivity

Register in advance for this meeting:
https://zoom.us/meeting/register/tJAuce-orjIuGdY-H52Uoj03paRhzpIoIwBl


*Abstract*
Climate model simulations are known to be sensitive to parameter choices 
in the sub grid-scale representation of deep convection, as deep 
convection plays a critical role in the transport of heat and momentum 
globally. Over the years, it has also become evident that the intermodel 
spread in the warming response to anthropogenic forcing is largely 
driven by uncertainties in the magnitude of the cloud feedback in the 
tropics, specifically the low cloud feedback. In this talk, I will 
discuss how parameterization differences among models and changes to 
deep convection in response to anthropogenic warming are likely 
contributing significantly to the intermodel spread in the tropical 
cloud feedback. I will present evidence of two physical pathways linking 
deep convection to low clouds and their response to anthropogenic 
forcing: the "Radiation-Subsidence" Pathway and the "Stability" Pathway. 
In a warmer world, the tropical overturning circulation is projected to 
weaken. We find that the overturning circulation does not weaken as much 
in climate models with more stable tropospheres, which ultimately leads 
to a more positive low cloud feedback (Stability Pathway). Differences 
in deep convective parameterization modifying deep convection onset 
thresholds – such as the fractional rate of entrainment into convective 
updrafts – can contribute significantly to this intermodel spread in 
static stability. Additionally, changes to the total area occupied by 
deep convection in the tropics modify the high cloud fraction, which is 
linked to subsidence changes and the low cloud feedback 
(Radiation-Subsidence Pathway). Results from both the Coupled Model 
Intercomparison Project (CMIP6) and a perturbation physics ensemble in 
the Community Earth System model (NCAR CESM) will be presented and 
discussed.