PhD Oral Defense of Yudha Setiawan Djamil: Mid-Holocene climate change over the Maritime Continent: Impact, attribution, and mechanisms

PhD Oral Defense of Yudha Setiawan Djamil: Mid-Holocene climate change over the Maritime Continent: Impact, attribution, and mechanisms

Event Type: 

  • Oral Defense

Venue: 

ASE 3D Visualisation Laboratory (N2-B1c-16c)

Date: 

28 March, 2019 - 14:00 to 17:00

About the Event: 

Speleothem oxygen stable isotope (δ18O) records suggest that precipitation over the Maritime Continent changed significantly during the mid-Holocene, a time interval about 6,000 years ago. These precipitation proxy datasets show that climatic conditions became wetter over Borneo, but drier over Flores. Such changes were hypothesised to be caused by the northward migration of the Inter-tropical Convergence Zone (ITCZ) and/or the weakening of the El Niño-Southern Oscillation (ENSO). These two phenomena are mainly driven by changes in the incoming solar radiation (insolation) and also responding to the feedback of sea surface temperature (SST). However, the exact mechanisms through which the two physical quantities contributed to changing the precipitation over the Maritime Continent are still debated, and hence they are investigated here using General Circulation Models (GCMs). The Community Climate System Model version 4 (CCSM4) attributes the higher precipitation in the mid-Holocene to higher annual variability in its monthly climatology, which is associated with the ITCZ and concentrated over the large islands. The robustness of the mid-Holocene annual precipitation signal is further confirmed by its persistence in climate experiments without the ENSO, using the Community Atmospheric Model version 4 (CAM4). The mid-Holocene higher precipitation over landmass is caused by stronger insolation rather than SST-feedbacks, as suggested by the numerical experiments using CAM4. The stronger insolation increases landmass surface temperature and triggers stronger convection. Then, the low-level southerly wind converges over the landmass and increases humidity, which further strengthens convection over the landmass, suppresses oceanic convection over the South China Sea, and weakens the local Hadley cell.

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Members of the Examination Committee:

  • Professor John Chiang (External Examiner), UC Berkeley, USA
  • Dr. Liong Shie-Yui (External Examiner), NUS, Singapore
  • Assistant Professor Mikinori Kuwata (Internal Examiner), NTU, Singapore

Oral Examination Committee:

  • Associate Professor Fidel Costa Rodriguez (Chairman), NTU, Singapore
  • Assistant Professor Caroline Bouvet De La Maisonneuve (Oral Examiner), NTU, Singapore 
  • Assistant Professor Mikinori Kuwata (Oral Examiner), NTU, Singapore
  • Dr. Liong Shie-Yui, National University of Singapore
  • Dr. Tri Wahyu Hadi, Bandung Institute of Technology, Indonesia
  • Dr. Rosbintarti Kartika Lestari, Ronin Institute

Advisors:

  • Associate Professor Wang Xianfeng, Nanyang Technological University, Singapore

About the Speaker: 

Yudha Setiawan Djamil

Yudha Setiawan Djamil received his BSc in Meteorology from the School of Geophysics and Meteorology, Bandung Institute of Technology (ITB), Indonesia. His BSc final year project focused on identifying a positive trend of the dry season in eastern Java. This work was published and cited by the IPCC-AR5. In 2012, he worked as a Research Assistant at the Earth Observatory of Singapore. He joined the Asian School of the Environment in 2013, working under the supervision of Associate Professor Koh Tieh Yong. Later in 2016, he joined Associate Professor Wang Xianfeng’s group. In his PhD work, he used atmosphere General Circulation Model (AGCM) experiments to explain the fundamental mechanisms of precipitation change between the pre-Industrial and the mid-Holocene eras over the Maritime Continent.

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