Date: 22nd Feb 2023, Wednesday (11:00am – 12:00pm)
Presenter: Xiangzhong (Remi) Luo (National University of Singapore)
Topic: Climate change impacts on global photosynthesis: perspectives from cross scale observations

Abstract:
Vegetation photosynthesis is the largest carbon flux in the global carbon cycle, removing CO2 from the atmosphere and contributing to climate change mitigation. Meanwhile, climate change, characterised by elevated CO2 concentration, rising temperature, and shifted rainfall, has caused considerable changes in global photosynthesis, though the magnitude – and even sometimes the direction – of the change are uncertain. In this talk, I will introduce our recent works in quantifying the response of vegetation photosynthesis to climatic drivers over short and long terms, using multiple observations across spatial scales (i.e. leaf traits, eddy covariance, remote sensing, atmospheric CO2 observation), as well as process-based land surface models and ecological theories.

Date: 22nd Mar 2023, Wednesday (11:00am – 12:00pm)
Presenter: Jennifer Weeks (UK Met Office)
Topic: The Evolution of Sea-level Projections and Future Sea-level Rise in Southeast Asia

Abstract:
The methods used to generate process-based global and local mean sea-level projections have evolved substantially over the last fifteen years, including improved process understanding, advances in ice-sheet modelling, the use of emulators and further development of high-end scenarios. This talk will present an evolution of process-based local mean sea-level projections for the UK and for Southeast Asia, comparing projections and their methods generated using two approaches: (1) UK Climate Projections 2018 (UKCP18) (available to 2300), where projections are rooted in Coupled Model Intercomparison Project Phase 5 (CMIP5) models and in methods used in the Intergovernmental Panel on Climate Change (IPCC) Fifth Assessment Report (AR5); and (2) IPCC Sixth Assessment Report (AR6) (available to 2150), where projections are rooted in CMIP6 models. Understanding decadal-to-centennial future sea levels across Southeast Asia is important due to the region’s densely populated and low-lying coastlines. Relative sea level change in Southeast Asia is complicated by tectonic activity and/or intensive groundwater extraction leading to Vertical Land Movement (VLM). Comparisons between the two approaches reveal the projections are broadly consistent, but the representation of VLM component in studies can lead to significant differences in projected relative sea-level at a given location (e.g. ~30cm at Sembawang, Singapore). Alongside scientific advancements in generating process-based sea-level projections, there has been an increasing need to improve the utility of projections in coastal adaptation planning and decision-making. This talk will also demonstrate a framework in which physically consistent high-end storylines can be generated for locations in Southeast Asia. This allows for a pragmatic approach to high-end sea-level rise where risk tolerances and decisions made in Southeast Asia may vary considerably over the coming centuries.

Date: 5th Apr 2023, Thursday (11:00am – 12:00pm)
Presenter: Shilpa Manandhar (A*STAR)
Topic: Precision Time Driven Solution for an Accurate Estimation of GNSS Signal Delays for Meteorological Applications

Abstract:
Singapore is a tropical island which often experiences heavy convective rainfall events. There has been continued research on accurate estimation and prediction of rainfall events. Prediction of rising sea-levels is another interesting and challenging research area. Weather stations and Radars are few of the technologies that are currently used in gathering data for these purposes. However, Weather stations are limited by its spatial resolution and the Radars have poor vertical resolution and are also expensive solution to be implemented at multiple locations. To counter such challenges, our cutting-edge approach is to use GNSS signals, which has higher spatial coverage and is cheaper technology, to estimate the water vapor content of the atmosphere and hence use it in climatological applications like prediction of rainfall and sea-level heights. The approach has already shown to work well with more that 85% of true detection rate for rainfall prediction [1-2].

Here, the accuracy of the GNSS signal delays play an important role in determining the prediction results. Hence our focus at NMC, A*STAR is to better estimate the GNSS signal delays. We have identified, the GNSS receiver clock bias errors as one of the significant parameters in deteriorating the accuracy. The receiver clock bias error is related to the receiver clock stability. For a receiver with crystal oscillators (cheap), which have lower stability compared to atomic clocks (expensive), the clocks drift with temperature over a period of time, and hence the clock bias error increases. The increment in the clock bias results in an additional distance between the satellite and a receiver. This in turn affects the range and hence the GNSS signals. To improve this, our centre is conducting research to use the precision timing information from our time & frequency lab. The precision time is being generated by a highly maintained fountain of atomic clocks (Caesium clocks and Hydrogen Maser). The goal is to disseminate the precision timing information to the mobile GNSS receivers stationed at multiple locations and continuously monitor the GNSS signals to apply it for different meteorological applications. Moving forward, the precision timings will be based on optical clock standards, which is currently being developed in NMC. Optical clocks have better performance compared to the current atomic clocks, which will help to further improve prediction results.