On the Seasonal and Spatial Dependence of Extreme Warm Days in Antarctica

Xu, Mingzhu; Yang, Qinghua; Clem, Kyle R.; Yu, Lejiang; Hu, Xiaoming

doi:10.1029/2022gl102472

Cited by 2 publications

(1 citation statement)

References 25 publications

(27 reference statements)

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“…The role of infrequent, high-intensity events for Antarctic precipitation and temperature extremes has been the subject of numerous recent studies (e.g., Turner et al, 2019;Turner et al, 2021;Wei et al, 2019;Wille et al, 2021;Xu et al, 2023). By contrast, relatively little research has examined the dynamical drivers of variability in coastal winds on daily time-scales.…”

Section: Introductionmentioning

confidence: 99%

Dynamics of extreme wind events in the marine and terrestrial sectors of coastal Antarctica

Caton Harrison,

King,

Bracegirdle

et al. 2024

Quart J Royal Meteoro Soc

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Antarctic coastal surface winds affect ice‐sheet stability, sea ice, and local ecosystems. The strongest coastal winds are especially important due to the nonlinear relationship between wind speed and wind stress. We investigate the dynamics of extreme coastal winds using a simplified momentum budget calculated across the period 2010–2020 from the ERA5 reanalysis. The pressure‐gradient forcing term in the budget is decomposed into a large‐scale component and one associated with the temperature deficit layer. The role of budget terms across the coastal sector is compared for weak and strong winds. We then calculate composites of the top 100 easterly wind events across six east Antarctic coastal sectors, identifying terms responsible for the evolution of coastal extremes. A simple balance of terms exists offshore, dominated by large‐scale forcing, contrasting with the complex balance in the onshore sector where katabatic forcing is large. Large‐scale forcing explains 57% of offshore coastal wind‐speed variance overall, improving to 81% when budget terms associated with the temperature deficit layer and horizontal advection are included, with significant regional variation. The residual term plays an increasingly active role as wind speed increases. Extremes in all coastal sectors are associated with a synoptic‐scale transient dipole of pressure anomalies driving warm‐air advection. Although katabatic forcing is a very large term in magnitude, it is found to play a passive role, declining as wind speeds increase during extreme conditions. In some regions, an anomalous southerly component develops during extremes, which we attribute to an ageostrophic barrier wind. This research underscores the major role for large‐scale forcing in Antarctica's coastal winds, but also reveals a significant regional locally driven component. The results have implications for improving numerical model simulations of coastal easterlies and for studying their impacts on ocean circulation, sea ice, and ice‐shelf basal melt.

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Section: Introductionmentioning

confidence: 99%

Dynamics of extreme wind events in the marine and terrestrial sectors of coastal Antarctica

Caton Harrison,

King,

Bracegirdle

et al. 2024

Quart J Royal Meteoro Soc

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Antarctic Warm Extremes Across Seasons and Their Response to Advection

Xu,

Pithan,

Yang

2024

JGR Atmospheres

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Antarctic warm extremes impact the cryosphere, with very warm extremes driving surface melt on ice shelves. Here, we analyze temperatures exceeding the 90th percentile and the associated circulation patterns and radiation anomalies. ERA5 reanalysis data show positive geopotential height anomalies related to the occurrence of warm extremes. The highest temperature during warm extremes appears on the western periphery of high‐pressure systems, consistent with anticyclonic advection. Temperature anomalies during warm extremes are strongest in winter due to the transport of warm and moist air and a strong meridional temperature gradient. In summer, the weak meridional gradients of top‐of‐atmosphere downward solar radiation flux and surface air temperature contribute to weak temperature anomalies. Warm extremes are associated with positive longwave radiation anomalies in all seasons, but with negative shortwave radiation anomalies at the surface except during polar night. These relationships are verified by station observations. Our results confirm that Antarctic warm extremes are mostly driven by meridional advection of warm air, and suggest that these warm air masses are predominantly moist and cloudy.

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On the Seasonal and Spatial Dependence of Extreme Warm Days in Antarctica

Cited by 2 publications

References 25 publications

Dynamics of extreme wind events in the marine and terrestrial sectors of coastal Antarctica

Dynamics of extreme wind events in the marine and terrestrial sectors of coastal Antarctica

Antarctic Warm Extremes Across Seasons and Their Response to Advection

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