Seminar Talk----"The "known knowns" and the "known unknowns of the Indonesian hydroclimate”
Speaker：Dr. Mahyar Mohtadi
Time：Dec.6(Tues.) 10:00a.m.-12:00 a.m.
Venue：B3-202 ，Zhou long bldg
Hosts：Stephan Steinke and Selvaraj Kandasamy
Lecture----Forcing and feedback of tropical circulation
Speaker：Dr. Mahyar Mohtadi
Time：Dec.7(Wed.) 15:00p.m.-17:00 p.m.
Venue：C2-403,Xi ping bldg
Hosts：Stephan Steinke and Selvaraj Kandasamy
Brief intro:
Dr. Mahyar Mohtadi
MARUM – Center for Marine Environmental Sciences
University of Bremen
Bremen, Germany
Dr. Mahyar Mohtadi is a palaeooceanographer and palaeoclimatologist specializing in past climate change with an emphasis on the mid- and low-latitude climate, particularly in the following areas: Western Pacific Warm Pool hydrology, past climate of the Indonesian Archipelago and East Asian monsoon variability. He is currently a Senior Scientist at the Center of Marine Environmental Sciences (MARUM), University of Bremen, Germany. Dr. Mohtadi is author and co-author of over 40 articles in scientific journals such as Nature, Nature Geoscience, PNAS and Paleoceanography.
Abstract：
1."The "known knowns" and the "known unknowns of the Indonesian hydroclimate”
Results from one decade of research on past Indonesian climate, particularly the trends and variability in hydrological cycle and its forcing mechanisms are discussed. Consistent with instrumental and historical records, solar forcing, ENSO, and the position of the rainbelt largely control the Holocene climate variability of Indonesia. The role of volcanic forcing and the Indian Ocean Dipole remain to be explored in future studies and require climate archives with very high temporal resolution, such as corals, stalagmites or varve sediments that are not yet available. Large differences exist between the hydroclimate of the deep tropics and the monsoon regions at various timescales, owing to the different feedbacks of these regions to the same, or a combination of forcing mechanisms. Records off Sumatra suggest a gradual drying trend over the course of the Holocene that reverses during the past 2000 years, while records from the monsoonal Indonesia show no trend during the Holocene but an abrupt two-step increase at about 3000 and 1000 years ago. Records from northern and eastern Indonesia are equivocal and do not show a coherent change over the Holocene and the past 2000 years, owing to different local feedback mechanisms and a limited understanding of the present and past behavior of the proxies used for hydroclimate reconstructions. A deeper understanding of these proxies is essential for a more reliable projection of future changes in Indonesian hydroclimate.
2. Forcing and feedback of tropical circulation
Climate models predict a slowdown of the zonal and meridional atmospheric overturning circulation over the tropics (the Walker and Hadley circulations) for the twenty-first century with severe consequences for tropical and global climate. However, debate exists on the appropriate interpretation of historical records and observations over the twentieth century, such as ENSO and the IOD, and necessitates longer records of past changes in tropical circulation to test the model results. Several records of continental rainfall, sea surface and thermocline temperatures extending back to the last glacial period suggest a stronger-than-today glacial zonal circulation in the tropics. Changes in the meridional circulation occurred through a number of forcings and feedbacks: while model simulations underscore the sensitivity of tropical circulation to temperature change, among other forcings, they remain equivocal and in part, inconsistent with proxy evidence. Untangling the (competing) impacts of meridional and zonal circulation changes on tropical hydroclimate, and whether and how these changes are reflected by different proxies at different sites, remains a critical task for both climate reconstructions and simulations.
Contact:
陈敬艳 Chen Jingyan, chenjy@xmu.edu.cn