Drivers of extreme high temperature events over coastal Antarctica

Overview

Climatic conditions of Antarctica range from the relatively warm maritime northern section of the Antarctic Peninsula to the frigid high plateau of East Antarctica. Antarctica contains 90% of the Earth’s ice. Ice melt along its coastal margins has the potential to make a significant contribution to global sea-level rise (Noble et al. 2020). Although most melt so far has occurred when warm ocean waters flow under the peripheral ice shelves, high air temperatures have led to significant ice melt on the eastern side of the Antarctic Peninsula. With climate models suggesting that regional air temperatures will rise over the coming decades, a high priority in polar research is to understand the conditions that lead to coastal extreme temperature events and subsequent surface melt and derive projections of their future occurrence.

High temperature events along coastal Antarctica result in surface temperature anomalies of +4-5º C with extensive surface melt. While many of these events are of short duration, they involve complex interactions between the air, ocean and ice. The synoptic situation at the time of the high temperature events often consists of a warm ridge extending towards the Antarctic in association with strong meridional flow. Large magnitude, more persistent events have been linked to atmospheric rivers, which are narrow bands of warm, moist air originating in lower latitudes (Wille et al., 2019). It is puzzling that some of the high temperature events have been preceded by downslope flow from the interior of Antarctica, where the air is normally much colder than that on the coast (Turner et al. 2021). To date, the dynamical aspects of these extremes remain poorly understood.

This project will investigate high temperature events in the coastal Antarctica using hourly ERA5 reanalysis in combination with the latest CMIP6 model outputs and the nested configuration of the UK Met Office Unified Model. The aim is to improve our understanding of the high temperature events and make projections of the likelihood of future changes.

Methodology

The project aims to answer two questions:

Q1. What are the key stages and dynamical drivers of the high temperature events along coastal Antarctica?

Q2. To what extent is projected climate change linked to high temperature events?

These two questions will be addressed by undertaking the following research tasks:

T1. Categorise past high temperature extreme events in terms of in terms of magnitude, duration, frequency, and regional variation using ERA5 reanalysis stored by the JASMIN super-data-cluster. The influences of blocking and moist transfer in enhancing such events will be investigated. Meteorological observations from the Antarctic stations assembled by the READER project of the Scientific Committee on Antarctic Research (SCAR) will be used for validation.

T2. Undertake case studies to elucidate the life cycle of representative high temperature events for a few selected regions using and further developing the existing diagnostics (Byrne et al. 2018; Turner et al. 2021). Emphasis will be placed upon the dynamical processes that can be captured by potential vorticity advection, moist eddy transfer, latent heat release, and associated vertical motion.

T3. Perform model simulations to better understand the life cycle of high temperature events analysed via T2 using the nested configuration of the UK Met Office Unified Model with high-resolution (~5-10 km). Analyse and compare the model output against ERA5 reanalysis and station-based observations.

T4. Develop regional ‘fingerprints’ between the key meteorological variables affecting the high temperature events and the broader-scale circulation patterns based on knowledge obtained from T1-T3. Identify the key factors that have led to certain cluster / behaviour of high temperature events and their interannual to multidecadal variability.

T5. Linking high temperature events to climate trends. Because large samples are needed to achieve statistical significance, the linkage cannot be reliably assessed based on observations. This task will utilize the output from the High Resolution Model Intercomparison Project (HighResMIP) of The Coupled Model Intercomparison Project 6 (CMIP6) with future climate scenarios to estimate climate change impact on the high temperature events in the context of anthropocentric contribution, natural variability, model and scenario uncertainty.

T1-T3 aim to answer Q1 and T4-5 will answer Q2.

Project Timeline

Year 1

Month 1: Core induction programmes of IAPETUS2.
Months 1-3: Literature review and gain basic understanding of data, computing facilities, diagnostics, and programming.
Month 3: Project aims report (3000 words; thesis committee)
Months 2-12: Commence work relating to tasks T1-2
Month 9: First-year report (mini-thesis format, 5000 words; thesis committee); official Progress Review.
Month 10: Visit co-supervisor MB
Month 12: Attend BAS Student Symposium

Year 2

Months 13-20: Completion of work related to tasks T1-2
Month 18: Poster presentation at postgraduate research day, St. Andrews
Month 21-24: Commence work related to T3
Month 21: Meeting with thesis committee for official Confirmation Review
Month 24: Poster presentation at the BAS Student Symposium

Year 3

Months 25-36: Commence work related to tasks T4-5.
Month 28: Submission of Summary of Progress and Thesis Outline Plan; thesis committee.
Month 30: Oral presentation at postgraduate research day, St. Andrews
Month 33: Meeting with Thesis Committee for the official Completion Review. Submission of Thesis Plan with timetable for completion and submission
Month 36: Oral presentation at the BAS Student Symposium

Year 3.5

Months 37-42: Thesis writing

Training
& Skills

The successful candidate will be registered at the University of St. Andrews in the Deportment of Earth & Environmental Sciences but based primarily at the British Antarctic Survey (BAS) in Cambridge, within the Atmospheric, Ice and Climate team. They will join a cohort of ~40 PhD students in total at BAS, spread over five DTP programmes.

The IAPETUS2 DTP programme will provide cross-disciplinary training and development, most of which will be held at the University of Durham. The student will also undertake the induction programme at BAS and core components of the Postgraduate Training Programme at St Andrews. Thereafter the student will be assigned a “Thesis committee” within Deportment of Earth & Environmental Sciences at St. Andrews who will interact directly with the student throughout the PhD programme. The student will spend additional time at St. Andrews learning moisture-dynamical coupled processes under the supervision of Dr Byrne.

At BAS, Dr Lu will be the primary supervisor. She and co-supervisor Prof Turner will jointly provide training in polar meteorology, atmospheric circulation, air-sea-ice interactions, extreme temperature event diagnostics, data analysis and visualisation, supplemented by summer schools, workshops, and seminars held at BAS and Cambridge University. The student will gain other generic research skills, i.e., literature review, scientific writing/publication, and oral presentation. The student will present their work at BAS Student Symposiums, internal workshops at St Andrews, and national and international conferences.

Person specification
We are looking for enthusiastic, self-reliant, and self-motivated candidates with a numerical background, mathematics, physics, or environmental sciences. Previous programming experience and proven ability in scientific writing would be advantageous.

References & further reading

Byrne, M.P., Pendergrass, A.G., Rapp, A.D. et al. 2018. Response of the Intertropical Convergence Zone to Climate Change: Location, Width, and Strength. Curr. Clim. Change Rep., 4, 355–370.
Noble, T.L. et al. 2020. The Sensitivity of the Antarctic Ice Sheet to a Changing Climate: Past, Present, and Future. Rev. Geophys., 58, e2019RG000663.
Turner, J., Lu, H., King, J., Marshall, G. J., Phillips, T., Bannister, D., & Colwell, S. 2021. Extreme Temperatures in the Antarctic, J. Clim., 34, 2653-2668
Wille, J. D., et al. 2019. West Antarctic surface melt triggered by atmospheric rivers. Nat. Geosci., 12, 911–916.

Further Information

Dr Hua Lu, hlu@bas.ac.uk
Dr Michael Byrne, mpb20@st-andrews.ac.uk
Prof John Turner, jtu@bas.ac.uk

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