IAP-25-012

Stratosphere–Troposphere Coupling and Its Role in Antarctic Coastal Melt Events and Supraglacial Lake Formation

Summary: Antarctica is undergoing accelerated ice melt, especially along its coastal margins. While long-term ocean-driven thinning remains the dominant contributor, short-term surface melt events during austral spring and summer can significantly increase ice shelf vulnerability (Andreasen et al., 2023). These episodic events are often linked to large-scale atmospheric circulation anomalies and upper-level dynamical processes such as stratosphere–troposphere exchange (STE). This project investigates how STE contributes to extreme temperature anomalies and katabatic wind intensification that may trigger surface melting and supraglacial lake formation.

Background: Surface melt events in Antarctica are often linked to large-scale atmospheric circulation anomalies, governed on sub-seasonal to seasonal timescales by tropospheric modes such as the Southern Annular Mode (SAM) and the Amundsen Sea Low (ASL) (Fogt and Marshall, 2020; Turner et al., 2013; 2021). These modes influence regional heat transport, surface winds, and precipitation patterns.

Their variability is shaped by upper-level dynamical processes, including downward propagation of zonal-mean anomalies, stratospheric final warming, and mixing near the tropopause (Domeisen and Butler, 2020). These disturbances modify jet streams and storm tracks, enhancing poleward heat transport and increasing the likelihood of surface warming episodes that may trigger coastal melt events (Choi et al., 2024). Lu et al. (2021) showed that stratospheric regime behavior precede persistent changes in jet streams and surface temperature, highlighting the need to understand its impact on Antarctic melt and supraglacial hydrology. Although recent studies link the stratospheric polar vortex to sea ice variability (Cordero et al., 2023; Mezzina et al., 2025), the role of stratosphere–troposphere exchange (STE) near the tropopause in surface melt remains underexplored.

Aim and Benefits: This interdisciplinary project bridges atmospheric dynamics and cryosphere processes to assess the role of upper-level air dynamics in driving Antarctic coastal warming. It investigates how STE contributes to extreme temperature anomalies and katabatic winds that may trigger supraglacial lake formation—key processes associated with hydrofracturing and ice shelf collapse (Banwell et al., 2013; Stokes et al., 2019). It also explores whether such melt events are likely to become more frequent or intense under future climate scenarios. The findings will improve short-term forecasting and strengthen long-term climate projections related to Antarctic ice mass loss.

By integrating ECMWF reanalysis data, satellite observations, and high-resolution climate model simulations, the project aims to answer three specific research questions:

1. To what extent does stratosphere–troposphere exchange (STE) influence extreme coastal temperature anomalies and katabatic wind intensification in Antarctica?
2. How do specific circulation regimes associated with STE contribute to the timing, intensity, and duration of surface melt episodes along Antarctic coastal margins?
3. What is the role of STE-driven warm episodes in modulating the formation, variability, and spatial distribution of supraglacial lakes, and how does this affect ice shelf vulnerability through hydrofracturing?

We propose three tasks to address these research questions.
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Task 1: Diagnose and Characterize STE Events
Use ECMWF ERA5 reanalysis data to identify and characterize stratosphere–troposphere exchange (STE) events in the Southern Hemisphere, focusing on their frequency, intensity, and spatial distribution near the Antarctic coast. Validate diagnosed STE signals using satellite datasets such as AIRS (Atmospheric Infrared Sounder) and COSMIC (Constellation Observing System for Meteorology, Ionosphere, and Climate). Employ LAGRANTO trajectory modeling to trace the evolution and transport pathways of STE-related air masses.
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Task 2: Link STE to Surface Melt Drivers
Assess the impact of these intrusions on surface temperature anomalies by analysing vertical cross-sections of potential vorticity, temperature, and wind fields. Quantify the thermodynamic and dynamic impacts of STE-associated circulation regimes on surface conditions, particularly extreme temperature anomalies and katabatic wind intensification. Use station observations from BAS and SCAR networks to ground-truth model simulations and reanalysis-based diagnostics. Assess how these regimes influence the duration and intensity of warm episodes relevant to surface melt.
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Task 3: Assess Impact on Supraglacial Lake Formation
Investigate the role of STE-driven warm episodes in modulating the likelihood, timing, and spatial distribution of supraglacial lake (SGL) formation, using methods and datasets consistent with Arthur et al. (2022). Integrate satellite-derived lake observations with modeled surface energy balance and melt metrics to evaluate interannual variability and vulnerability across key ice shelf regions, such as the Shackleton Ice Shelf.

Year 1

• Month 1: Induction programmes of IAPETUS & BAS .
• Months 1–3: Literature review; familiarisation with data, computing facilities, diagnostics, and programming.
• Month 3: Preliminary literature review and aims/objectives report.
• Months 2–12: Begin work on Tasks T1.
• Month 6: First-year progress report.
• Month 9: Presentation at first-year postgraduate conference, Durham, or a targeted national conference.
• Month 10: Visit co-supervisor SC at Durham.
• Month 12: Attend BAS Student Symposium.

Year 2

• Months 13–17: Complete work related to Tasks T1.
• Month 18: Submit Publication #1 on STE diagnostics and validation.
• Month 19: Present at International Conference #1 (e.g., EGU or AGU or equivalent).
• Month 20–22: Industrial placement, e.g. Met Office, another university, a satellite data provider or policy organisation.
• Month 23: Poster presentation at BAS Student Symposium.
• Months 23–24: Work on Task T2 and submit second year progress report to both Durham and BAS.

Year 3

• Months 25–30: Continue work on Tasks T2 and revise publication #1 according to reviewers comments.
• Month 30: Oral presentation at Durham postgraduate research day.
• Month 32: Submit Publication #2 on STE-driven melt episodes and SGL formation.
• Months 33-36: Work on Task T3
• Month 33: Present at International Conference #2 (e.g., SCAR Conference).

Year 3.5

• Months 37-40: continue working on Task T3
• Month 40: submit Publication #3 synthesising findings and implications for forecasting and ice shelf vulnerability.
• Months 41-42: Writing and organizing thesis based on three publications, one published, one accepted or under revision; and one in draft or about to submit.

The successful candidate will be registered at Durham University and primarily based at the British Antarctic Survey (BAS) in Cambridge, within the Atmospheric, Ice and Climate team. They will join a vibrant cohort of ~40 PhD students at BAS, spanning five DTP programmes.
The IAPETUS2 DTP will provide cross-disciplinary training and development, including core components of Postgraduate Training Programme and induction programme.
At BAS, Dr Hua Lu will be the primary supervisor, with Dr Thomas Bracegirdle as co-supervisor. Together, they will provide training in atmospheric circulation, stratosphere-troposphere coupling, polar meteorology, air–sea–ice interactions, extreme temperature diagnostics, and data analysis/visualisation. The student will spend time at Durham University, receiving supervision from Prof. Chris Stokes, an expert in glaciology and cryosphere processes, particularly in the context of supraglacial lake dynamics and ice shelf vulnerability. Additional training will be supplemented by summer schools, workshops provided by NERC, and seminars both at BAS and Durham.
The student will also gain essential research skills in literature review, scientific writing/publication, and oral presentation. They will present their work at BAS Student Symposiums, internal workshops at Durham, and national/international conferences.

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