Award Abstract # 1643436
What Processes Drive Southern Ocean Sea Ice Variability and Trends? Insights from the Energy Budget of the Coupled Cryosphere-ocean-atmosphere System

NSF Org: OPP
Office of Polar Programs (OPP)
Recipient: UNIVERSITY OF WASHINGTON
Initial Amendment Date: April 19, 2017
Latest Amendment Date: April 19, 2017
Award Number: 1643436
Award Instrument: Standard Grant
Program Manager: David Sutherland
OPP
 Office of Polar Programs (OPP)
GEO
 Directorate for Geosciences
Start Date: May 1, 2017
End Date: April 30, 2022 (Estimated)
Total Intended Award Amount: $387,742.00
Total Awarded Amount to Date: $387,742.00
Funds Obligated to Date: FY 2017 = $387,742.00
History of Investigator:
  • Aaron Donohoe (Principal Investigator)
    adonohoe@uw.edu
  • Axel Schweiger (Co-Principal Investigator)
Recipient Sponsored Research Office: University of Washington
4333 BROOKLYN AVE NE
SEATTLE
WA  US  98195-1016
(206)543-4043
Sponsor Congressional District: 07
Primary Place of Performance: Applied Physics Lab
1013 NE 40th Street
Seattle
WA  US  98105-6698
Primary Place of Performance
Congressional District:
07
Unique Entity Identifier (UEI): HD1WMN6945W6
Parent UEI:
NSF Program(s): ANT Ocean & Atmos Sciences
Primary Program Source: 0100XXXXDB NSF RESEARCH & RELATED ACTIVIT
Program Reference Code(s): 5113
Program Element Code(s): 511300
Award Agency Code: 4900
Fund Agency Code: 4900
Assistance Listing Number(s): 47.078

ABSTRACT

This project will use observations and coupled climate model simulations to examine the causes of sea ice variability. Sea ice in the Southern Ocean has increased in area over the observational record but researchers have yet to agree on the cause. Researchers suggests that changes in surface winds, upper-ocean freshening, or internal ocean/atmosphere variability could be the main driver for the increase in sea ice area. This project will determine how much of the change in sea ice area from year to year is due to oceanic, atmospheric, and radiative processes. Reconciling the observation-based understanding with model representations of sea ice variability will improve confidence in projections of future changes in Southern Ocean sea ice.

The goal of this proposal is to improve our understanding of the processes that drive Southern Ocean sea ice year-to-year variability and long term trends. This knowledge will provide insight into how Southern Ocean sea ice responded to greenhouse gas and ozone forcing in the past and how it will respond in the future. The energy budget of the coupled cryosphere/ocean/atmosphere climate system will be used as a framework to disentangle drivers and responses during sea ice loss events. The technique consists of: (i) calculating the coupled energy budget of the climate system at the monthly timescale, (ii) isolating the radiative impact of sea ice variability from the radiative impact of cloud variability in the observed satellite radiation record and (iii) analyzing the vertical structure of atmospheric energy transport to determine the vertical profile of energy transport into the atmospheric column. This framework will allow the investigators to distinguish whether ice loss events are triggered by oceanic processes, atmospheric dynamics, or radiative processes. Preliminary results show that a diversity of mechanisms can drive Southern Ocean sea ice variability in coupled climate models whereas observed sea ice variability appears to be dominated by atmospheric dynamics. The exploration of biases between models and observations in both the mean state and in specific processes will yield more accurate projections of the future of sea ice in the Southern Ocean.

PUBLICATIONS PRODUCED AS A RESULT OF THIS RESEARCH

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(Showing: 1 - 10 of 12)
Blanchard-Wrigglesworth, Edward and Ding, Qinghua "Tropical and Midlatitude Impact on Seasonal Polar Predictability in the Community Earth System Model" Journal of Climate , v.32 , 2019 https://doi.org/10.1175/JCLI-D-19-0088.1 Citation Details
BlanchardWrigglesworth, Edward and Donohoe, Aaron and Roach, Lettie A. and DuVivier, Alice and Bitz, Cecilia M. "HighFrequency Sea Ice Variability in Observations and Models" Geophysical Research Letters , v.48 , 2021 https://doi.org/10.1029/2020GL092356 Citation Details
Blanchard-Wrigglesworth, Edward and Roach, Lettie A. and Donohoe, Aaron and Ding, Qinghua "Impact of Winds and Southern Ocean SSTs on Antarctic Sea Ice Trends and Variability" Journal of Climate , v.34 , 2021 https://doi.org/10.1175/JCLI-D-20-0386.1 Citation Details
Cardinale, Christopher J. and Rose, Brian E. and Lang, Andrea L. and Donohoe, Aaron "Stratospheric and Tropospheric Flux Contributions to the Polar Cap Energy Budgets" Journal of Climate , v.34 , 2021 https://doi.org/10.1175/JCLI-D-20-0722.1 Citation Details
Cox, Tyler and Armour, Kyle C. and Roe, Gerard H. and Donohoe, Aaron and Frierson, Dargan M. "Radiative and Dynamic Controls on Atmospheric Heat Transport over Different Planetary Rotation Rates" Journal of Climate , v.34 , 2021 https://doi.org/10.1175/JCLI-D-20-0533.1 Citation Details
Donohoe, A. and Blanchard-Wrigglesworth, E. "CLIVAR Variations: What Processes drive Southern Ocean sea ice variability and trends" Workshop on Climate Variability of the Eastern North Pacific and Western North America , v.13 , 2017 https://doi.org/ Citation Details
Donohoe, Aaron and Armour, Kyle C. and Roe, Gerard H. and Battisti, David S. and Hahn, Lily "The Partitioning of Meridional Heat Transport from the Last Glacial Maximum to CO 2 Quadrupling in Coupled Climate Models" Journal of Climate , v.33 , 2020 https://doi.org/10.1175/JCLI-D-19-0797.1 Citation Details
Donohoe, Aaron and Blanchard-Wrigglesworth, Ed and Schweiger, Axel and Rasch, Philip J. "The Effect of Atmospheric Transmissivity on Model and Observational Estimates of the Sea Ice Albedo Feedback" Journal of Climate , v.33 , 2020 https://doi.org/10.1175/JCLI-D-19-0674.1 Citation Details
Donohoe, Aaron and Dawson, Eliza and McMurdie, Lynn and Battisti, David S. and Rhines, Andy "Seasonal Asymmetries in the Lag between Insolation and Surface Temperature" Journal of Climate , v.33 , 2020 https://doi.org/10.1175/JCLI-D-19-0329.1 Citation Details
Hahn, L. C. and Armour, K. C. and Battisti, D. S. and Donohoe, A. and Pauling, A. G. and Bitz, C. M. "Antarctic Elevation Drives Hemispheric Asymmetry in Polar Lapse Rate Climatology and Feedback" Geophysical Research Letters , v.47 , 2020 https://doi.org/10.1029/2020GL088965 Citation Details
Hahn, L. C. and Armour, K. C. and Zelinka, M. D. and Bitz, C. M. and Donohoe, A. "Contributions to Polar Amplification in CMIP5 and CMIP6 Models" Frontiers in Earth Science , v.9 , 2021 https://doi.org/10.3389/feart.2021.710036 Citation Details
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PROJECT OUTCOMES REPORT

Disclaimer

This Project Outcomes Report for the General Public is displayed verbatim as submitted by the Principal Investigator (PI) for this award. Any opinions, findings, and conclusions or recommendations expressed in this Report are those of the PI and do not necessarily reflect the views of the National Science Foundation; NSF has not approved or endorsed its content.

Sea ice extent in the Southern Ocean has shown a modest long-term increase over the satellite era (1979-present). In contrast, state of the art climate models unanimously simulate a reduction of sea ice extent over the Southern Ocean as would be expected from the build up of greenhouse gases and global warming. This project investigated mechanism of Southern Ocean sea ice loss in climate models and observations in search of the missing or poorly represented physics in the models that are responsible for the observational/model mismatch of the historical trend. Our work covered mechanisms of sea ice loss at time scales ranging from days to year-to-year variability to long-term forced trends. We found that models have too little sea ice variability at the time scale of weather events (less than 10 days). We leveraged this finding to probe mechanisms of model biases in sea ice variability across timescales in hopes that the physics responsible for well sampled day-to-day variability might also impact long-term trends.

Our project analyzed three primary mechanisms of sea ice loss and evaluated whether these processes are biased in climate models.

Radiative impact of sea ice loss: Sea ice melting exposes the darker ocean surface to the sun resulting in additional heating of the surface which can melt more ice. We evaluated the magnitude of this positive feedback using satellite radiation data and climate model output from over 20 models. We found that models differ by a factor of two in the radiative impact of sea ice loss due to differences in the thickness of clouds in the Southern Ocean. However, models are not, on average, biased relative to observations. Thus, the radiative impact of sea ice leads to inter-model diversity in the sensitivity of sea-ice loss to warming but does not lead to a model bias.

Impact of observed winds and sea surface temperatures in sea ice variability: We developed a novel technique to make the winds in a climate model match those observed over the 1979-2020 period. We found that the model with observed winds nearly replicated the observed year-to-year variability of Southern Ocean sea ice. The long-term sea ice trend of the model with observed winds showed smaller reductions than the model with free running winds but still showed a reduction in sea ice (a mismatch to the observed expansion). When we additionally forced the sea surface temperatures in the mid-latitudes of the Southern Ocean to match those observed (which show a modest cooling trend), the model nearly replicated the long-term expansion of the sea ice. These results indicate that the year-to-year variability of Southern Ocean sea ice is primarily forced by wind variability whereas both winds and sea surface temperature impact long-term trends in sea ice. The model bias toward long-term sea ice loss is primarily due to faster than observed warming of the Southern Ocean simulated by the models.

Impact of atmospheric heat transport on sea ice loss: We demonstrated that sea ice loss events in models are initiated by anomalous atmospheric heat transport into the region above the sea ice loss which heats the atmosphere and subsequently melts ice.  The atmospheric heat transport peaks 10 days before the ice loss. During and after the ice loss, the open ocean serves as a source of energy to the atmosphere and additionally heats the atmosphere. As a result, the atmosphere removes energy from the region during and after the ice loss. The opposing atmospheric heat fluxes before and after the event average to a very small change in atmospheric heat transport. This result cautions against interpreting long term changes in atmospheric heat transport as a climate forcing and, instead, suggests that the long-term changes in atmospheric heat transport represent a delicate balance of remote forcing and feedback to the ice loss. In future work we hope to analyze whether models are biased in the amplitude of atmospheric heat transport events at short (less than 10 days) timescales and whether these biases could explain the model biases in sea ice variability at the timescale of weather events.  


Last Modified: 06/08/2022
Modified by: Aaron Donohoe

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