IAP2-23-084

Drivers and impacts of extreme high temperature events over coastal Antarctica

Climatic conditions in Antarctica range from the relatively mild maritime northern section of the Antarctic Peninsula to the frigid high plateau of East Antarctica. Antarctica contains 90% of the Earth’s ice and has the potential to make a significant contribution to global mean sea-level rise (Noble et al. 2020). Although most ice sheet melting so far has occurred when warm ocean waters flow under the peripheral ice shelves, high air temperatures have led to significant ice melting in some regions of coastal Antarctica, e.g. the Antarctic Peninsula (Wille et al. 2019). With climate models suggesting that regional air temperatures will increase over the coming decades, a key priority in polar research is to understand the conditions that lead to the extreme high temperature events and their subsequent impacts on surface melting. A better understanding of the process would help us to derive more accurate projections of their future occurrence and better understand their impacts on ice sheet mass balance.

High temperature events can have a major impact of the Antarctic environment and ecosystems (Lu et al. 2023). Warm intrusions into the coastal region can result in surface temperature anomalies of +4-5º C. The synoptic situation at the time often consists of a warm ridge extending towards Antarctica 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). For instance, an atmospheric river reached the high plateau of East Antarctica in March 2022, which resulted in the temperatures up to 39 C above average for the time of year (Siegert et al. 2023). However, it remains 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 the coast (Turner et al. 2021). While many of these events are of short duration, they involve complex interactions between the air, ocean and ice. To date, the dynamical aspects of extreme high temperature events remain poorly understood. As we learn more about the associated circulation patterns, such as the February 2020 Peninsula record temperatures and the East Antarctic March 2022 “heatwave” and how those patterns interact with the ocean and sea ice, we will be able to improve climate models so that such events can be properly reproduced by model simulations. We then can use model predictions to assess the likelihood of such events becoming more common in the future and explore their likely impacts, e.g. on surface melting, supraglacial lakes and the potential for ice shelf hydrofracturing.

The aims of this project are to investigate high temperature events over coastal Antarctica using a combination of station observations, observationally constrained reconstructions assimilated data sets as well as regional climate simulations. It will also examine how these extreme events impact on surface melting of the ice sheet and the development of supraglacial lakes, with potential implications for ice shelf stability via hydrofracturing.

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Image Captions

Significant surface warmings near coastal Antarctica are often linked to regional, high-pressure system with strong downslope winds. This studentship will study the magnitude, frequency, and development of those warm events.,Antarctica, one of the fastest-warming regions in the world, recorded a new maximum temperature of 18.3°C on February 6, 2021.

Methodology

The project aims to address four research questions regarding high temperature events along the coastal Antarctica:

Q1. What is the spatio-temporal variability of high temperature events over the last 50 years?

Q2. What are the key stages of development and dynamical drivers of these events?

Q3. How do such events impact on surface melt and the development of supraglacial lakes?

Q4. How might the spatial and temporal variability of high temperature events evolve under projected climate change?

These four questions will be addressed by four objectives with specific research activities:

1. Categorise past high temperature extreme events since 1979 in terms of the magnitude, duration, frequency, and regional variation using ERA5 reanalysis stored by the JASMIN super-data-cluster. The influences of cyclones, blocking and atmospheric rivers 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.

2. 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 (Turner et al. 2021; Lu et al. 2023). Emphasis will be placed upon the dynamical processes that can be captured by potential vorticity advection, eddy-driven moisture transfer, latent heat release, and the associated vertical motion. High resolution model simulations will be performed to better understand the life cycles of high temperature events analysed using the nested configuration of the UK Met Office Unified Model. Analyse and compare the model output against ERA5 reanalysis and station-based observations. Regional ‘fingerprints’ that link to broad-scale circulation patterns and other key factors that are associated with high temperature events will be identified.

3. Examine the impacts of high temperature events on surface melt rates and the distribution of supraglacial lakes. This objective will examine the impact of high temperature events on surface melt rates and runoff gleaned from regional climate models (e.g. RACMO, MAR). Medium to high-resolution satellite imagery can then be used examine the extent to which high temperature events lead to the development of supraglacial lakes (e.g. Stokes et al., 2019).

4. Link high temperature events to climate trends. This objective will be achieved by utilizing the output from the HighResMIP component of CMIP6 with future climate forcing scenarios to estimate climate change impacts on high temperature events in the context of anthropogenic forcing, natural variability, model and scenario uncertainty.

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 Objective #1, which forms the foundation for paper 1.
Month 9: First-year report (mini-thesis format, 5000 words; thesis committee); official Progress Review.
Month 10: Visit co-supervisor CRS at Durham University.
Month 12: Attend BAS Student Symposium.

Year 2

Months 13-20: Completion of work related to Objective #1 and the first paper submitted.
Month 18: Poster presentation at postgraduate research day & Visit co-supervisor CRS, Durham University.
Month 21-24: Commence work related to Objectives #2 and #3, which forms the foundation for paper 2.
Month 21: Meeting with thesis committee for official Confirmation Review.
Month 24: Poster presentation at the BAS Student Symposium, and paper 1 drafted.

Year 3

Months 25-36: Paper 1 published, Paper 2 submitted, and commence work related to Objective #4.
Month 28: Submission of Summary of Progress and Thesis Outline Plan; thesis committee.
Month 30: Oral presentation at postgraduate research day & Visit co-supervisor CRS, Durham University.
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: Paper 2 is either revised or accepted for publication. Paper 3 is under preparation. Write up the thesis based on the three papers.

Training
& Skills

The successful candidate will be registered at Durham University 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 held at Durham University. The student will attend induction and receive training, e.g. core components of the Postgraduate Training Programme. The student will also be assigned a “Thesis committee” who will interact directly with the student throughout the PhD programme. In addition, the student will be supported by BAS Student Office and undertake BAS induction programme.

Dr Hua Lu will be the primary supervisor. The supervision will be provided jointly with co-supervisors Prof. Chris Stokes at Durham University and Dr. Thomas Bracegirdle at BAS. The student will receive training in polar meteorology, atmospheric dynamics, air-sea-ice interactions, extreme temperature event impact on melting of ice shelves, and possible connection between high temperature events and supraglacial lakes along the coastal Antarctica. The training will be supplemented by summer schools, workshops, and seminars held at BAS and Cambridge University. The student will gain other generic research skills, i.e., data analysis and visualization, literature review, scientific writing/publication, and oral presentation. The student will present their work at BAS Student Symposiums, internal workshops/seminar series at Durham University, 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

Lu, H., Orr, A., King, J., Phillips, T., Gilbert, E., Colwell, S., and Bracegirdle, T. J. (2023) Extreme warm events in the South Orkney Islands, Southern Ocean: Compounding influence of atmospheric rivers and föhn conditions. Q. J. R. Meteorol., doi: 10.1002/qj.4578.
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.
Siegert M.J. (2023) Antarctic extreme events. Front. Environ. Sci. 11:1229283. doi: 10.3389/fenvs.2023.1229283.
Stokes, C.R., Sanderson, J.E., Miles, B.W.J., Jamieson, S.S.R and Leeson, A.A. (2019) Widespread distribution of supraglacial lakes around the margin of the East Antarctic Ice Sheet. Scientific Reports, 9:13823.
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.

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