Date: 3rd Jan 2025, Friday (2:00pm – 3:00pm)
Presenter: Isaac Tan (Monash University)
Topic: Wet and Dry Cold Surges over the Maritime Continent

Abstract:
Cold surges are synoptic weather systems that originate from a large anticyclone over Siberia during the boreal winter. Southward intrusions of cold air often result in sudden surges of northerly to north-easterly winds that extend over the South China Sea and Maritime Continent region, and temperature falls of a few degrees over several days. Over the Maritime Continent, cold surges are often accompanied by heavy prolonged rainfall and flooding but in other cases, suppressed convection. We investigate the synoptic structure and development of cold surges through composites of dry, moderate, and wet surges. Each surge category is defined by the distribution of precipitation averaged within a specified domain over the equatorial South China Sea. Over a 20-year analysis period, cold surges account for approximately 30% of the total rainfall. Dry surges are characterised by cross-equatorial flow and positive mean sea-level pressure anomalies that reach the Southern Hemisphere, and enhanced descent or weaker ascent. Wet surges are characterised by limited cross-equatorial flow, low-pressure anomalies over the equator, and enhanced moisture and ascent. Moreover, dry and moderate (wet) surges usually occur in the suppressed (active) phases of the Madden Julian Oscillation and are sometimes linked to convectively active phases in the Australian summer monsoon.

Speaker Profiles:
Isaac Tan recently completed his PhD at Monash University, focusing on “The Dynamics of Cold Surges over the Maritime Continent” under the supervision of Professor Michael Reeder. One of the chapters of his thesis, titled “Wet and Dry Cold Surges over the Maritime Continent,” has been published in the Journal of Geophysical Research (JGR) Atmospheres. Isaac’s research interests encompass extreme rainfall events and tropical monsoon weather systems.

Date: 7th Jan 2025, Tuesday (11:00am – 12:00pm)
Presenter: Simon Peatman (CCRS)
Topic: Physical mechanisms of scale interactions in the Maritime Continent

Abstract:
The chief form of variability of precipitation in the Maritime Continent is the diurnal cycle. The diurnal cycle amplitude is controlled by many large-scale drivers including the MJO, ENSO, IOD and equatorial waves. I shall give an overview of these scale interactions and discuss the physical mechanisms by which the large-scale environment modulates the local-scale diurnal cycle, with a particular focus on the phenomenon of convection propagating offshore overnight from Maritime Continent islands, especially to the south-west of Sumatra.

Speaker Profiles:
Simon read Physics at the University of Oxford before his PhD in tropical meteorology with Adrian Matthews at the University of East Anglia. He has since worked as a post-doc in the tropical group at the University of Reading and the dynamics group at the University of Leeds. His research has covered the diurnal cycle, the MJO, scale interactions, modelling of equatorial waves, air-sea interactions, the Indian summer monsoon, tropical cyclones and propagating convection. His recent work has focused on investigating tropical processes using convection-scale modelling with the MetUM. He joined CCRS in October 2024 in the Seasonal and Subseasonal Prediction branch.

Date: 14th Jan 2025, Tuesday (4:00pm – 5:00pm)
Presenter: Cathryn Birch (University of Leeds)
Topic: Understanding and predicting humid heat extremes across the global (sub)tropics

Abstract:
The role of humidity in extreme heat events is a growing area of interest and research. This seminar summarises recent results from the Humid heat extremes in the Global (Sub)Tropics (H2X) project on the role of rainfall and soil moisture in humid heat extremes. Results show that there are distinct categories of processes in the lead up to events, where in the semi-arid sub-tropics evaporation of recent rainfall is a key driver but in the equatorial tropics drier days with increased shortwave heating are more important. The seminar will finish with an outlook towards developing Early Warning Systems for humid and dry heat extremes.

Speaker Profiles:
Cathryn Birch is Professor of Meteorology and Climate at University of Leeds. Cathryn works to better understand the causes of high impact weather to improve weather forecasts, flood forecasts and Early Warning System capability. She currently leads the Humid heat extremes in the Global (Sub)Tropics (H2X) project, which aims to quantify the atmospheric and surface drivers of humid heatwaves. Whilst historically a tropical meteorologist, her research has broadened recently to include climate-health topics. Cathryn previously worked as a Senior Scientist at the Met Office and has continued to collaborate closely with them on a wide range of projects.

Date: 24th Jan 2025, Friday (2:00pm – 3:00pm)
Presenter: Bernhard Mayer (NTU)
Topic: Modelling the Fate of Terrestrial Dissolved Organic Carbon and its Effect on Ocean Acidification in the Sunda Shelf Sea

Abstract:
The flux of organic carbon from land to sea is an important net transfer within the global carbon cycle. The biogeochemical fate of this carbon remains poorly understood and is usually neglected in ocean models, even though it can significantly impact coastal biogeochemistry. Owing to the extensive tropical peatlands, Southeast Asian Seas receive approximately 10% of global land–ocean tDOC flux. We applied a 3D numerical model system to simulate the transport and remineralization of terrestrial dissolved organic carbon (tDOC) from rivers through the Sunda Shelf Sea into the open ocean. Our model is based on the regional ocean circulation and ecosystem models HAMSOM and ECOHAM. River discharge of freshwater was calculated based on a global–regional hydrological model combination (HydroPy and HD), and riverine inputs of chemical constituents, especially tDOC and terrestrial chromophoric dissolved organic matter (tCDOM), were calculated based on field data from Southeast Asia. The remineralization of tDOC in our model is calculated according to a new light-driven parameterization that accounts for photochemical, microbial, and photochemical–microbial interactive remineralization processes. We will introduce our model system, and present data from realistic hindcast simulations for 1958–2022 regarding the import of tDOC to the Sunda Shelf via the rivers, the export to the open ocean as well as the degradation of tDOC on the Sunda Shelf demonstrating its impact on the ocean acidification – including trends derived from our 65 years model results. We will close our seminar with our ideas for future research
.

Speaker Profiles:
Dr. Bernhard Mayer is a Senior Research Fellow at the Asian School of the Environment, Nanyang Technological University (NTU), Singapore. He holds a Diploma in Oceanography and a PhD in Geosciences from the University of Hamburg. His career spans roles as a scientist at the University of Hamburg’s Institute of Oceanography, where he focused on modelling ocean circulation, marine carbonate system, and suspended particulate matter, as well as experience in IT consulting and project management in private companies. Before joining NTU, he was a Visiting Senior Research Fellow at the National University of Singapore. His current research involves modelling ocean circulation and the fate of terrestrial dissolved organic carbon on the Sunda Shelf.

Date: 4th Feb 2025, Tuesday (11:00am – 12:00pm)
Presenter: Zhihuo Xu (CCRS)
Topic: Traffic Road Visibility Retrieval in the Internet of Video Things through Physical Feature Based Learning Network

Abstract:
Singapore, a major transportation hub, faces significant challenges due to visibility, which impacts transportation safety. This study explores whether road visibility can be estimated from video networks in the Internet of Video Things (IoVT). Estimating visibility from video frames is complex due to the inverse problem of indirect inference. The study models the effects of fog on images and finds that the first and second eigenvalues of the image matrix approximate those of airlight under foggy conditions. A four-step framework is proposed, including scatterer definition, background and airlight separation via singular value decomposition (SVD), key feature extraction, and a hybrid convolutional long short-term memory (LSTM) network for accurate visibility estimation. Comparative methods (Koschmieder law, CNN, deep LSTM) show improved results with the proposed method, which achieves the highest correlation (0.9484) and lowest error (681m). The study also emphasizes the importance of responsibly optimizing deep learning models to reduce energy consumption and environmental impact.

Speaker Profiles:
Dr. Zhihuo Xu is an internationally recognized scientist, originally from China, and a Senior Member of IEEE. His research spans advanced meteorological radar, synthetic aperture radar (SAR) for Earth observation, millimeter-wave radar for autonomous driving, and intelligent observation and sensing technologies.

Date: 18th Feb 2025, Tuesday (11:00am – 12:00pm)
Presenter: Chin-Hsien Cheng (NTU)
Topic: Methane-Climate Feedback is Dominantly Dependent on Rate of Changing Temperature and Precipitation

Abstract:
Rapidly rising atmospheric methane concentration in recent years is alarming. While increasing wetland emission was proposed to be a major driver, we still need a consistent explanation how changing climate affects the methane sources and sinks throughout different timescales. By analyzing data from seasonal, interannual, to multidecadal scales, we classify the instantaneous methane-climate feedback into 8 (23) categories: rate- vs. state-dependent, temperature vs. precipitation dependent, and positively vs. negatively correlated. Seasonal feedback is found to be weakly negative, consistent to the interannual state-dependent feedback. This is mainly driven by the temperature effect on atmospheric methane sink. However, the net interannual and long-term methane-climate feedbacks are positive and stronger than IPCC’s estimate, driven by the changing rate (rate-dependent) instead of the absolute change (state-dependent) of temperature and precipitation. The rate-dependency is mainly due to interactions between sources and sinks. Such interactions should be incorporated into future process-based Earth system models (ESMs).

Speaker Profiles:
Dr. Chin-Hsien Cheng is a research fellow from Nanyang Technological University. His research focus is on biogeochemical Earth system feedbacks, in particular, how climate change affects the methane and carbon cycles. His earlier publication, ‘Impact of interannual and multidecadal trends on methane-climate feedbacks and sensitivity’, revealed the oscillating influence of interannual and multidecadal climate on the rate of rising atmospheric methane. His research highlighted that the oscillating positive feedback with stronger sources during warming years (e.g. El Niño years) followed by negative feedback with weaker sinks during cooling years (e.g. La Niña years), results in stronger positive methane-climate feedback in long term. In addition to research on Earth system feedbacks, he also look into negative emission technologies to draw down atmospheric CO2 or accelerate the atmospheric methane oxidation. His journey on climate change mitigation solutions started decades ago, with experience working on energy efficiency and transboundary haze pollution during his past service in National Environment Agency.