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Extreme high temperature events in the South Orkney islands: the role atmospheric rivers and localised Föhn winds

Urheber*innen

Lu,  Hua
IUGG 2023, General Assemblies, 1 General, International Union of Geodesy and Geophysics (IUGG), External Organizations;

Orr,  Andrew
IUGG 2023, General Assemblies, 1 General, International Union of Geodesy and Geophysics (IUGG), External Organizations;

King,  John
IUGG 2023, General Assemblies, 1 General, International Union of Geodesy and Geophysics (IUGG), External Organizations;

Phillips,  Tony
IUGG 2023, General Assemblies, 1 General, International Union of Geodesy and Geophysics (IUGG), External Organizations;

Gilbert,  Ella
IUGG 2023, General Assemblies, 1 General, International Union of Geodesy and Geophysics (IUGG), External Organizations;

Colwell,  Steve
IUGG 2023, General Assemblies, 1 General, International Union of Geodesy and Geophysics (IUGG), External Organizations;

Briacegirdle,  Thomas
IUGG 2023, General Assemblies, 1 General, International Union of Geodesy and Geophysics (IUGG), External Organizations;

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Zitation

Lu, H., Orr, A., King, J., Phillips, T., Gilbert, E., Colwell, S., Briacegirdle, T. (2023): Extreme high temperature events in the South Orkney islands: the role atmospheric rivers and localised Föhn winds, XXVIII General Assembly of the International Union of Geodesy and Geophysics (IUGG) (Berlin 2023).
https://doi.org/10.57757/IUGG23-2964


Zitierlink: https://gfzpublic.gfz-potsdam.de/pubman/item/item_5018893
Zusammenfassung
We present the first comparison of extreme near-surface high temperatures in the South Orkney Islands using synoptic meteorological observations from the Signy and Orcadas stations. Based on the station records above the top 5th percentile thresholds, the key features of the extremes are examined. We find that extreme warm events at both stations often involve the combined effect of synoptically driven atmospheric rivers (ARs) and localized Föhn winds. Their characteristics however differ distinctly between these two stations. The extreme warm events at Signy primarily involve ARs originated from the Andes and/or the Southern Atlantic Ocean, where the warm moist-rich airs are advected towards the islands rapidly by strong northerly winds. Extreme warm events at Orcadas nevertheless mainly involve ARs originated from the Pacific Ocean. To better understand the development of the typical extreme warm events, high resolution model simulations are performed using the nested MetUM configuration that is forced by ERA5. We demonstrate that the typical warm event at Signy involves a steep descent of upper-level warm air on the leeside of Coronation Island. The low-level cold airs are instead blocked, explaining the large difference in the observed temperature between Signy and Ocardas. A typical warm event at Orcadas entails two stages, i.e. the warm Pacific airs being first advected by ARs to the Drake Passage and then brought to flow Coronation Island by strong westerlies in the following day. These results demonstrate the complexity of sub-Antarctic temperature extremes and implications on surface melt.