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Suggested Citation:"Appendix B: Definitions of Key Terms." National Academies of Sciences, Engineering, and Medicine. 2017. Antarctic Sea Ice Variability in the Southern Ocean-Climate System: Proceedings of a Workshop. Washington, DC: The National Academies Press. doi: 10.17226/24696.
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Appendix B
Definitions of Key Terms

Amundsen Sea Low is the climatological area of low pressure located in the South Pacific sector of the Southern Ocean.1

Antarctic Circumpolar Current (ACC) is the world’s largest ocean current, encircling the Antarctic continent, flowing eastward through the southern portions of the Pacific, Atlantic, and Indian Oceans.2

Circumpolar Deep Water (CDW) is the largest water mass by volume transported by the ACC, derived from a mixture of the deep waters from all the world’s oceans.3

Coupled Model Intercomparison Project (CMIP) is an international activity established in 1995 under the auspices of the World Climate Research Programme (WCRP) and the Working Group on Coupled Modelling (WGCM). CMIP is a standard experimental protocol for studying the output of coupled atmosphere-ocean general circulation models. The comparisons use standardized specifications of model inputs and standardized output formats agreed on by an international committee, and an extensive suite of model outputs is archived and made publicly available for the science and applications communities.4,5

Ekman circulation is the net transport of water due to coupling between wind and surface waters, also known as Ekman transport, resulting from the Ekman spiral (how horizontal wind sets surface waters in motion, in which the speed and direction of water motion change with increasing depth).6

El Niño–Southern Oscillation (ENSO) is an interannual variability phenomenon that combines the tropical Pacific Ocean surface water temperature over the eastern equatorial Pacific Ocean with air pressure difference across the tropical western Pacific Ocean basin (the Southern Oscillation). ENSO has two coupled phases: El Niño (warm phase) and La Niña (a cool phase).7

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1 Raphael, M. N., G. J. Marshall, J. Turner, R. L. Fogt, D. Schneider, D. A. Dixon, J. S. Hosking, J. M. Jones, and W. R. Hobbs. 2016. The Amundsen Sea Low: Variability, change, and impact on Antarctic climate. Bulletin of the American Meteorological Society 97(1):111-121.

2 Fyfe, J. C., and O. A. Saenko. 2005. Human-induced change in the Antarctic Circumpolar Current. Journal of Climate 18(15):3068-3073.

3 Dinniman, M. S., J. M. Klinck, and E. E. Hofmann. 2012. Sensitivity of Circumpolar Deep Water transport and ice shelf basal melt along the west Antarctic Peninsula to changes in the winds. Journal of Climate 25(14):4799-4816.

4 NRC (National Research Council). 2012. National Strategy for Advancing Climate Modeling. Washington, DC: The National Academies Press.

5 See http://cmip-pcmdi.llnl.gov.

6 See http://oceanmotion.org/html/background/ocean-in-motion.htm.

7 NASEM (National Academies of Sciences, Engineering, and Medicine). 2016. Frontiers in Decadal Climate Variability: Proceedings of a Workshop. Washington, DC: The National Academies Press. doi: 10.17226/23552.

Suggested Citation:"Appendix B: Definitions of Key Terms." National Academies of Sciences, Engineering, and Medicine. 2017. Antarctic Sea Ice Variability in the Southern Ocean-Climate System: Proceedings of a Workshop. Washington, DC: The National Academies Press. doi: 10.17226/24696.
×

Greenhouse Gases (GHGs) are those gaseous constituents of the atmosphere, both natural and anthropogenic, that absorb and emit radiation at specific wavelengths within the spectrum of infrared radiation emitted by the Earth’s surface, the atmosphere, and clouds. Water vapor (H2O), carbon dioxide (CO2), nitrous oxide (N2O), methane (CH4), and ozone (O3) are the primary greenhouse gases in Earth’s atmosphere.8

Marginal Ice Zone is a transition zone between the ice edge (often defined by the 15% contour of ice concentration) and the boundary of ice having a concentration greater than 80%.9

Ozone Hole is a phenomenon whereby every year, during the Southern Hemisphere spring, a very strong depletion of the ozone layer takes place over the Antarctic region, also caused by human-made chlorine and bromine compounds in combination with the specific meteorological conditions of that region.10

Pacific South America (PSA) Pattern is a mode of climate variability in the mid-to-high southern latitudes.11

Passive Microwave Sensors are a type of microwave sensor (radiometer) that relies on the thermal emission of microwave signals from objects. The emission is related to the physical temperature and electrical properties of the sensed surface.12Polynyas are areas of persistent open water where one would expect to find sea ice. The water remains open because of processes that prevent sea ice from forming or that quickly move sea ice out of the region.13

Reanalysis refers to the reprocessing of observational data spanning a historical period using a consistent modern analysis system.14

Representative Concentration Pathways (RCPs) are GHG concentration trajectories used for climate modeling and research.15

Rossby Waves are a natural phenomenon in the ocean and atmosphere that owe their properties to Earth’s rotation. Oceanic Rossby waves move along the thermocline.16

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8 IPCC. 2001. Annex II: Glossary of Terms. In Climate Change 2001: Synthesis Report. A Contribution of Working Groups I, II, and III to the Third Assessment Report of the Integovernmental Panel on Climate Change. R. T. Watson and the Core Writing Team, eds. Cambridge, UK: Cambridge University Press.

9 See http://seaiceatlas.snap.uaf.edu/glossary.

10 IPCC. 2001. Annex II: Glossary of Terms. In Climate Change 2001: Synthesis Report. A Contribution of Working Groups I, II, and III to the Third Assessment Report of the Integovernmental Panel on Climate Change. R. T. Watson and the Core Writing Team, eds. Cambridge, UK: Cambridge University Press.

11 Mo, K. C., and R. W. Higgins. 1998. The Pacific-South American modes and tropical convection during the Southern Hemisphere winter. Monthly Weather Review 126(6):1581-1596.

12 Long, D. G. 2008. Revision. Microwave sensors–active and passive. In Manual of Remote Sensing, Vol. 3: Remote Sensing for the Earth Sciences. R. A. Ryerson and A. N. Rencz, eds. Hoboken, NJ: John Wiley and Sons.

13 See https://nsidc.org/cryosphere/seaice/characteristics/polynyas.html.

14 NASEM (National Academies of Sciences, Engineering, and Medicine). 2016. Frontiers in Decadal Climate Variability: Proceedings of a Workshop. Washington, DC: The National Academies Press. doi: 10.17226/23552.

15 NRC (National Research Council). 2014. Linkages Between Arctic Warming and Mid-Latitude Weather Patterns. Washington, DC: The National Academies Press.

Suggested Citation:"Appendix B: Definitions of Key Terms." National Academies of Sciences, Engineering, and Medicine. 2017. Antarctic Sea Ice Variability in the Southern Ocean-Climate System: Proceedings of a Workshop. Washington, DC: The National Academies Press. doi: 10.17226/24696.
×

Sea Ice Concentration describes the relative amount of area covered by ice, compared to some reference area, typically reported as a percentage.17

Sea Ice Extent is a measurement of the area of ocean where there is at least some sea ice. Usually, scientists define a threshold of minimum concentration to mark the ice edge; the most common cutoff is at 15%.18

Sea Ice Persistence is the percent time sea ice concentrations are greater than 15% in a given time period.19,20

Sea Ice Volume is a measurement that is estimated through calculations of sea ice thickness with sea ice concentration.21

Seasonal Sea Ice is sea ice that melts away and reforms annually. Almost all Southern Ocean or Antarctic sea ice is seasonal sea ice.22

Southern Annular Mode (SAM) is the primary mode of atmospheric variability at high southern latitudes.23

Westerly Winds are winds from the west toward the east in the mid-latitudes (between 30 and 60 degrees).24

___________________

16 NASEM (National Academies of Sciences, Engineering, and Medicine). 2016. Frontiers in Decadal Climate Variability: Proceedings of a Workshop. Washington, DC: The National Academies Press. doi: 10.17226/23552.

17 See https://nsidc.org/cryosphere/seaice/data/terminology.html.

18 See https://nsidc.org/cryosphere/seaice/data/terminology.html.

19 Finkl, C. W., J. M. Grebmeier, and W. Maslowski. 2015. The Pacific Arctic Region: Ecosystem Status and Trends in a Rapidly Changing Environment. Dordrecht: Springer Netherlands.

20 Stammerjohn, S. E., D. G. Martinson, R. C. Smith, and R. A. Iannuzzi. 2008. Sea ice in the western Antarctic Peninsula region: Spatio-temporal variability from ecological and climate change perspectives. Deep Sea Research Part II: Topical Studies in Oceanography 55(18):2041-2058.

21 See http://www.metoffice.gov.uk/research/areas/cryosphere-oceans/sea-ice/measure.

22 See https://nsidc.org/cryosphere/sotc/sea_ice.html.

23 Raphael, M. N., G. J. Marshall, J. Turner, R. L. Fogt, D. Schneider, D. A. Dixon, J. S. Hosking, J. M. Jones, and W. R. Hobbs. 2016. The Amundsen Sea Low: Variability, change, and impact on Antarctic climate. Bulletin of the American Meteorological Society 97(1):111-121.

24 NASEM (National Academies of Sciences, Engineering, and Medicine). 2016. Frontiers in Decadal Climate Variability: Proceedings of a Workshop. Washington, DC: The National Academies Press. doi: 10.17226/23552.

Suggested Citation:"Appendix B: Definitions of Key Terms." National Academies of Sciences, Engineering, and Medicine. 2017. Antarctic Sea Ice Variability in the Southern Ocean-Climate System: Proceedings of a Workshop. Washington, DC: The National Academies Press. doi: 10.17226/24696.
×

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Suggested Citation:"Appendix B: Definitions of Key Terms." National Academies of Sciences, Engineering, and Medicine. 2017. Antarctic Sea Ice Variability in the Southern Ocean-Climate System: Proceedings of a Workshop. Washington, DC: The National Academies Press. doi: 10.17226/24696.
×
Page 47
Suggested Citation:"Appendix B: Definitions of Key Terms." National Academies of Sciences, Engineering, and Medicine. 2017. Antarctic Sea Ice Variability in the Southern Ocean-Climate System: Proceedings of a Workshop. Washington, DC: The National Academies Press. doi: 10.17226/24696.
×
Page 48
Suggested Citation:"Appendix B: Definitions of Key Terms." National Academies of Sciences, Engineering, and Medicine. 2017. Antarctic Sea Ice Variability in the Southern Ocean-Climate System: Proceedings of a Workshop. Washington, DC: The National Academies Press. doi: 10.17226/24696.
×
Page 49
Suggested Citation:"Appendix B: Definitions of Key Terms." National Academies of Sciences, Engineering, and Medicine. 2017. Antarctic Sea Ice Variability in the Southern Ocean-Climate System: Proceedings of a Workshop. Washington, DC: The National Academies Press. doi: 10.17226/24696.
×
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The sea ice surrounding Antarctica has increased in extent and concentration from the late 1970s, when satellite-based measurements began, until 2015. Although this increasing trend is modest, it is surprising given the overall warming of the global climate and the region. Indeed, climate models, which incorporate our best understanding of the processes affecting the region, generally simulate a decrease in sea ice. Moreover, sea ice in the Arctic has exhibited pronounced declines over the same period, consistent with global climate model simulations. For these reasons, the behavior of Antarctic sea ice has presented a conundrum for global climate change science.

The National Academies of Sciences, Engineering, and Medicine held a workshop in January 2016, to bring together scientists with different sets of expertise and perspectives to further explore potential mechanisms driving the evolution of recent Antarctic sea ice variability and to discuss ways to advance understanding of Antarctic sea ice and its relationship to the broader ocean-climate system. This publication summarizes the presentations and discussions from the workshop.

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