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Abstract. The recent changes and record lows in Antarctic sea ice extent illustrate the need for longer estimates beyond the short satellite observation period commencing around 1979. However, Antarctic sea ice extent reconstructions since 1900 based on paleo-records and those generated based on instrumental observations from the Southern Hemisphere midlatitudes are markedly different, especially prior to 1979. Here, these reconstructions are examined with the goal of understanding the relative strengths and limitations of each reconstruction better so that researchers using the various datasets can interpret them appropriately. Overall, it is found that the different spatial and temporal resolutions of each dataset play a secondary role to the inherent connections each reconstruction has with its implied atmospheric circulation. Five Southern Hemisphere pressure reconstructions spanning the 20th century are thus examined further. There are different variabilities and trends poleward of 60∘ S between proxy-based and station-based 20th century pressure reconstructions, which are connected to the disagreement between the Antarctic sea ice extent reconstructions examined here. Importantly, reconstructions based on only coral records provide the best agreement between the early pressure reconstructions, suggesting that a contributing role of tropical variability is present in the station-based pressure (and therefore sea ice) reconstructions. In contrast, ice-core-only reconstructions provide a local, high-latitude constraint that creates differences between the proxy-based and station-based reconstructions near Antarctica. Our results reveal the greatest consistencies and inconsistencies in available datasets and highlight the need to better understand the relative roles of the tropics versus high latitudes in historical sea ice variability around Antarctica.
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An assessment of early 20th century Antarctic pressure reconstructions using historical observations
Abstract While gridded seasonal pressure reconstructions poleward of 60°S extending back to 1905 have been recently completed, their skill has not been assessed prior to 1958. To provide a more thorough evaluation of the skill and performance in the early 20th century, these reconstructions are compared to other gridded datasets, historical data from early Antarctic expeditions, ship records, and temporary bases. Overall, the comparison confirms that the reconstruction uncertainty of 2–4 hPa (evaluated after 1979) over the Southern Ocean is a valid estimate of the reconstruction error in the early 20th century. Over the interior and near the coast of Antarctica, direct comparisons with historical data are challenged by elevation‐based reductions to sea level pressure. In a few cases, a simple linear adjustment of the reconstruction to sea level matches the historical data well, but in other cases, the differences remain greater than 10 hPa. Despite these large errors, comparisons with continuous multi‐season observations demonstrate that aspects of the interannual variability are often still captured, suggesting that the reconstructions have skill representing variations on this timescale, even if it is difficult to determine how well they capture the mean pressure at these higher elevations. Additional comparisons with various 20th‐century reanalysis products demonstrate the value of assimilating the historical observations in these datasets, which acts to substantially reduce the reanalysis ensemble spread, and bring the reanalysis ensemble mean within the reconstruction and observational uncertainty.
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- Award ID(s):
- 1744998
- PAR ID:
- 10454611
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- International Journal of Climatology
- Volume:
- 41
- Issue:
- S1
- ISSN:
- 0899-8418
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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