Atmospheric drivers of ice drift in the Antarctic marginal ice zone

Simple item page
dc.contributor.advisorVichi, Marcello
dc.contributor.authorWomack, Ashleigh Catherine Stevenson
dc.date.accessioned2021-09-20T18:12:53Z
dc.date.available2021-09-20T18:12:53Z
dc.date.issued2021
dc.date.updated2021-09-20T17:59:56Z
dc.description.abstractSea-ice drift in the Antarctic marginal ice zone (MIZ) was investigated using an array of five drifting ice buoys, deployed during the winter sea-ice expansion, in July 2017. An initial 15- day analysis of pancake ice drift is presented, using the cluster of buoys, which shows: (1) exceptionally fast ice drift speeds and increased meandering of the buoys during cyclone activity; (2) high correlation of drift velocities with the surface wind velocities, even at 100% remotely sensed ice concentration, indicating free drift conditions where ice drift is primarily governed by wind; and (3) the presence of a clear energy peak (»13.5 hour period), which is suggested to be excited by the passage of cyclones through the transfer of momentum from wind. Additionally, one of the buoys (buoy U1) drifted for approximately four months from the South Atlantic sector to the Indian Ocean sector of the Southern Ocean. The analysis of this buoy revealed that it remained within the MIZ even during the winter ice expansion, as the mixed pancake-frazil field was maintained. This allowed for a continued assumption of free drift conditions for buoy U1's full drift, where it continued to respond linearly to the momentum transfer from surface winds. The analysis of buoy U1 also indicated a strong inertial signature at a period of 13.47 hours however, the wavelet analysis indicated majority of the power remained within the lower frequencies. This strong influence at the lower (multiday) frequencies has therefore been identified as the primary effect of atmospheric forcing. When these lower frequencies were filtered out using the Butterworth high-pass filter it allowed the inertial oscillations to become more significant within the wavelet power spectrum, where it can be seen that these inertial oscillations were often triggered by the passage of cyclones. The initiation of inertial oscillations of sea ice has therefore been identified as the secondary effect of atmospheric forcing, which dominates ice drift at sub-daily timescales and results in the deviation of ice drift from a straight-line path. This comprehensive analysis suggests that the general concentration-based definition of the MIZ is not enough to describe the sea-ice cover, and that the MIZ, where ice is in free drift and under the influence of cyclone induced inertial motion, and presumably waves, can extend up to »200 km.
dc.identifier.apacitationWomack, A. C. S. (2021). <i>Atmospheric drivers of ice drift in the Antarctic marginal ice zone</i>. (). ,Faculty of Science ,Department of Oceanography. Retrieved from http://hdl.handle.net/11427/33982en_ZA
dc.identifier.chicagocitationWomack, Ashleigh Catherine Stevenson. <i>"Atmospheric drivers of ice drift in the Antarctic marginal ice zone."</i> ., ,Faculty of Science ,Department of Oceanography, 2021. http://hdl.handle.net/11427/33982en_ZA
dc.identifier.citationWomack, A.C.S. 2021. Atmospheric drivers of ice drift in the Antarctic marginal ice zone. . ,Faculty of Science ,Department of Oceanography. http://hdl.handle.net/11427/33982en_ZA
dc.identifier.ris TY - Master Thesis AU - Womack, Ashleigh Catherine Stevenson AB - Sea-ice drift in the Antarctic marginal ice zone (MIZ) was investigated using an array of five drifting ice buoys, deployed during the winter sea-ice expansion, in July 2017. An initial 15- day analysis of pancake ice drift is presented, using the cluster of buoys, which shows: (1) exceptionally fast ice drift speeds and increased meandering of the buoys during cyclone activity; (2) high correlation of drift velocities with the surface wind velocities, even at 100% remotely sensed ice concentration, indicating free drift conditions where ice drift is primarily governed by wind; and (3) the presence of a clear energy peak (»13.5 hour period), which is suggested to be excited by the passage of cyclones through the transfer of momentum from wind. Additionally, one of the buoys (buoy U1) drifted for approximately four months from the South Atlantic sector to the Indian Ocean sector of the Southern Ocean. The analysis of this buoy revealed that it remained within the MIZ even during the winter ice expansion, as the mixed pancake-frazil field was maintained. This allowed for a continued assumption of free drift conditions for buoy U1's full drift, where it continued to respond linearly to the momentum transfer from surface winds. The analysis of buoy U1 also indicated a strong inertial signature at a period of 13.47 hours however, the wavelet analysis indicated majority of the power remained within the lower frequencies. This strong influence at the lower (multiday) frequencies has therefore been identified as the primary effect of atmospheric forcing. When these lower frequencies were filtered out using the Butterworth high-pass filter it allowed the inertial oscillations to become more significant within the wavelet power spectrum, where it can be seen that these inertial oscillations were often triggered by the passage of cyclones. The initiation of inertial oscillations of sea ice has therefore been identified as the secondary effect of atmospheric forcing, which dominates ice drift at sub-daily timescales and results in the deviation of ice drift from a straight-line path. This comprehensive analysis suggests that the general concentration-based definition of the MIZ is not enough to describe the sea-ice cover, and that the MIZ, where ice is in free drift and under the influence of cyclone induced inertial motion, and presumably waves, can extend up to »200 km. DA - 2021 DB - OpenUCT DP - University of Cape Town KW - Oceanography LK - https://open.uct.ac.za PY - 2021 T1 - Atmospheric drivers of ice drift in the Antarctic marginal ice zone TI - Atmospheric drivers of ice drift in the Antarctic marginal ice zone UR - http://hdl.handle.net/11427/33982 ER - en_ZA
dc.identifier.urihttp://hdl.handle.net/11427/33982
dc.identifier.vancouvercitationWomack ACS. Atmospheric drivers of ice drift in the Antarctic marginal ice zone. []. ,Faculty of Science ,Department of Oceanography, 2021 [cited yyyy month dd]. Available from: http://hdl.handle.net/11427/33982en_ZA
dc.language.rfc3066eng
dc.publisher.departmentDepartment of Oceanography
dc.publisher.facultyFaculty of Science
dc.subjectOceanography
dc.titleAtmospheric drivers of ice drift in the Antarctic marginal ice zone
dc.typeMaster Thesis
dc.type.qualificationlevelMasters
dc.type.qualificationlevelMSc
Files
Original bundle
Now showing 1 - 1 of 1
Thumbnail Image
Name:
thesis_sci_2021_womack ashleigh catherine stevenson.pdf
Size:
12.74 MB
Format:
Adobe Portable Document Format
Description:
Download
License bundle
Now showing 1 - 1 of 1
Thumbnail Image
Name:
license.txt
Size:
0 B
Format:
Item-specific license agreed upon to submission
Description:
Download
Collections
Masters