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Arctic Sea Ice Loss in Different Regions Leads to Contrasting Northern Hemisphere Impacts (2018)

McKenna, Christine M. ; Bracegirdle, Thomas J. ; Shuckburgh, Emily F. ; [et al.]

American Geophysical Union

In: Geophysical Research Letters. 2018; 45(2): 945-954. Published 2018 Jan 19. doi: 10.1002/2017gl076433.

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Publication Date: 2018-01-19

Description: To explore the mechanisms linking Arctic sea ice loss to changes in midlatitude surface temperatures, we conduct idealized modeling experiments using an intermediate general circulation model and with sea ice loss confined to the Atlantic or Pacific sectors of the Arctic (Barents-Kara or Chukchi-Bering Seas). Extending previous findings, there are opposite effects on the winter stratospheric polar vortex for both large-magnitude (late 21st century) and moderate-magnitude sea ice loss. Accordingly, there are opposite tropospheric Arctic Oscillation (AO) responses for moderate-magnitude sea ice loss. However, there are similar strength negative AO responses for large-magnitude sea ice loss, suggesting that tropospheric mechanisms become relatively more important than stratospheric mechanisms as the sea ice loss magnitude increases. The midlatitude surface temperature response for each loss region and magnitude can be understood as the combination of an “indirect” part induced by the large-scale circulation (AO) response, and a residual “direct” part that is local to the loss region. ©2017. American Geophysical Union. All Rights Reserved.

Print ISSN: 0094-8276

Electronic ISSN: 1944-8007

Topics: Geosciences , Physics

Published by American Geophysical Union

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Do CMIP5 Models Reproduce Observed Low-Frequency North Atlantic Jet Variability? (2018)

Bracegirdle, Thomas J. ; Lu, Hua ; Eade, Rosie ; [et al.]

American Geophysical Union

In: Geophysical Research Letters. 2018; 45(14): 7204-7212. Published 2018 Jul 20. doi: 10.1029/2018gl078965.

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Publication Date: 2018-07-20

Description: The magnitude of observed multidecadal variations in the North Atlantic Oscillation (NAO) in winter is at the upper end of the range simulated by climate models and a clear explanation for this remains elusive. Recent research shows that observed multidecadal winter NAO variability is more strongly associated with North Atlantic (NA) jet strength than latitude, thus motivating a comprehensive comparison of NA jet and NAO variability across the Coupled Model Intercomparison Project Phase 5 (CMIP5) models. Our results show that the observed peak in multidecadal jet strength variability is even more unusual than NAO variability when compared to the model-simulated range across 133 historical CMIP5 simulations. Some CMIP5 models appear capable of reproducing the observed low-frequency peak in jet strength, but there are too few simulations of each model to clearly identify which. It is also found that an observed strong multidecadal correlation between jet strength and NAO since the mid-nineteenth century may be specific to this period. ©2018. American Geophysical Union. All Rights Reserved.

Print ISSN: 0094-8276

Electronic ISSN: 1944-8007

Topics: Geosciences , Physics

Published by American Geophysical Union

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Unprecedented springtime retreat of Antarctic sea ice in 2016 (2017)

Turner, John ; Phillips, Tony ; Marshall, Gareth J. ; [et al.]

American Geophysical Union

In: Geophysical Research Letters. 2017; 44(13): 6868-6875. Published 2017 Jul 10. doi: 10.1002/2017gl073656.

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Publication Date: 2017-07-10

Description: During austral spring 2016 Antarctic sea ice extent (SIE) decreased at a record rate of 75 × 103 km2 d−1, which was 46% faster than the mean rate and 18% faster than in any previous spring season during the satellite era. The decrease of sea ice area was also exceptional and 28% greater than the mean. Anomalous negative retreat occurred in all sectors of the Antarctic but was greatest in the Weddell and Ross Seas. Record negative SIE anomalies for the day of year were recorded from 3 November 2016 to 9 April 2017. Rapid ice retreat in the Weddell Sea took place in strong northerly flow after an early maximum ice extent in late August. Rapid ice retreat occurred in November in the Ross Sea when surface pressure was at a record high level, with the Southern Annular Mode at its most negative for that month since 1968. ©2017. Crown copyright. This article is published with the permission of the Controller of HMSO and the Queen's Printer for Scotland.

Print ISSN: 0094-8276

Electronic ISSN: 1944-8007

Topics: Geosciences , Physics

Published by American Geophysical Union

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Back to the Future: Using Long-Term Observational and Paleo-Proxy Reconstructions to Improve Model Projections of Antarctic Climate (2019)

Bracegirdle, Thomas J. ; Colleoni, Florence ; Abram, Nerilie J. ; [et al.]

Molecular Diversity Preservation International

In: Geosciences. 2019; 9(6): 255. Published 2019 Jun 07. doi: 10.3390/geosciences9060255.

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Publication Date: 2019-06-07

Description: Quantitative estimates of future Antarctic climate change are derived from numerical global climate models. Evaluation of the reliability of climate model projections involves many lines of evidence on past performance combined with knowledge of the processes that need to be represented. Routine model evaluation is mainly based on the modern observational period, which started with the establishment of a network of Antarctic weather stations in 1957/58. This period is too short to evaluate many fundamental aspects of the Antarctic and Southern Ocean climate system, such as decadal-to-century time-scale climate variability and trends. To help address this gap, we present a new evaluation of potential ways in which long-term observational and paleo-proxy reconstructions may be used, with a particular focus on improving projections. A wide range of data sources and time periods is included, ranging from ship observations of the early 20th century to ice core records spanning hundreds to hundreds of thousands of years to sediment records dating back 34 million years. We conclude that paleo-proxy records and long-term observational datasets are an underused resource in terms of strategies for improving Antarctic climate projections for the 21st century and beyond. We identify priorities and suggest next steps to addressing this.

Electronic ISSN: 2076-3263

Topics: Geosciences

Published by Molecular Diversity Preservation International

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