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Kamide Lecture

Kamide Lecture - AS

Yen-Ting HWANG
National Taiwan University

Wed- 31 Jul, 11:30am-12pm
Nicoll 2, Level 3

"Local and Remote Control on Tropical Circulation and Precipitation under Anthropogenic Climate Change"

The local control of sea surface temperature on tropospheric stability and convection in the tropics has long been recognized to play a critical role in determining the position of the tropical rain belt. The newly developed global energetic constraint, on the other hand, has emphasized extratropical influence on tropical precipitation. Confusion arises when constructing a predictive framework for tropical precipitation in global warming scenarios: The local perspective predicts a southward shift of the tropical rain belt toward the equator, caused by an El Niño-like warming pattern in most global climate models; whereas the energetic perspective points to a northward shift of the tropical precipitation due to positive feedbacks over Northern Hemisphere high latitudes and enhanced heat uptake over the Southern Ocean.

Here we point to a structural change in Hadley Circulation when reconciling the two perspectives. Take the Community Earth System Model (CESM) Large Ensemble Project’s historical and RCP8.5 simulations as an example. An intertropical convergence zone (ITCZ) index and a precipitation centroid (PC)index are defined to quantify the meridional displacement of the zonal-mean rainfall peak and the overall tropical precipitation pattern, respectively. Throughout the simulations, both indices show complex transient responses but different turning points in their time series. The ITCZ is initially stationary but begins to shift southward toward an enhanced equatorial warming pattern that appears after the 1990s. On the other hand, the PC first shifts southward when aerosols cool the Northern Hemisphere during the 20th century, and then shifts northward after year 2000 when greenhouse gas warming is larger in the Northern than Southern Hemisphere. The structural changes in Hadley Circulation can also be seen in other global climate models participated in CMIP (the Coupled Model Intercomparison Project of the World Climate Research Program). The ITCZ and the PC shift toward the opposite directions as the climate warms. The global energetic framework has a stronger constraint on the subtropical precipitation changes, as the stability changes less in the subtropics comparing with the deep tropics in climate change scenarios.

Before joining Department of Atmospheric Sciences at National Taiwan University as an Assistant Professor and leading the Global Dynamics and Climate Change research group in 2014, she received her PhD degree at University of Washington in year 2013 (advised by Prof. Dargan Frierson) and worked as a postdoctoral researcher at Scripps Institute of Oceanography (advised by Prof. Shang-Ping Xie) for a year.

Dr. Hwang’s research focuses on the interactions between climate feedbacks and circulations. On one end, her work demonstrates how radiative feedbacks play critical roles in influencing the displacement of inter-tropical convergence zone, the position of midlatitude stormtracks, and the magnitude of poleward energy transport in the global climate models participated in the CMIP (the Coupled Model Intercomparison Project of the World Climate Research Program, WCRP). On the other end, she investigates mechanisms behind these coupling relationships between climate feedbacks and circulations via performing idealized experiments in a hierarchy of models with different complexity.

Dr. Hwang has been serving as a science organizing committee member in a few international research activities, including the Cloud Feedback Model Intercomparison Project (CFMIP) under WCRP, the 2015 WCRP workshop on stormtracks, and the Model Intercomparison Project on Extratropical-Tropical INteraction (ETIN-MIP). She received Young Scholar Fellowship from Taiwan Ministry of Science and Technology in 2018.