Wind changes above warm Agulhas Current eddies

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dc.contributor.authorRouault, M
dc.contributor.authorVerley, P
dc.contributor.authorBackeberg, B
dc.date.accessioned2021-10-08T07:08:31Z
dc.date.available2021-10-08T07:08:31Z
dc.date.issued2016
dc.description.abstractSea surface temperature (SST) estimated from the Advanced Microwave Scanning Radiometer E onboard the Aqua satellite and altimetry-derived sea level anomalies are used south of the Agulhas Current to identify warm-core mesoscale eddies presenting a distinct SST perturbation greater than to 1 °C to the surrounding ocean. The analysis of twice daily instantaneous charts of equivalent stability-neutral wind speed estimates from the SeaWinds scatterometer onboard the QuikScat satellite collocated with SST for six identified eddies shows stronger wind speed above the warm eddies than the surrounding water in all wind directions, if averaged over the lifespan of the eddies, as was found in previous studies. However, only half of the cases showed higher wind speeds above the eddies at the instantaneous scale; 20 % of cases had incomplete data due to partial global coverage by the scatterometer for one path. For cases where the wind is stronger above warm eddies, there is no relationship between the increase in surface wind speed and the SST perturbation, but we do find a linear relationship between the decrease in wind speed from the centre to the border of the eddy downstream and the SST perturbation. SST perturbations range from 1 to 6 °C for a mean eddy SST of 15.9 °C and mean SST perturbation of 2.65 °C. The diameter of the eddies range from 100 to 250 km. Mean background wind speed is about 12 m s<sup>−1</sup> (mostly southwesterly to northwesterly) and ranging mainly from 4 to 16 m s<sup>−1</sup>. The mean wind increase is about 15 %, which corresponds to 1.8 m s<sup>−1</sup>. A wind speed increase of 4 to 7 m s<sup>−1</sup> above warm eddies is not uncommon. Cases where the wind did not increase above the eddies or did not decrease downstream had higher wind speeds and occurred during a cold front associated with intense cyclonic low-pressure systems, suggesting certain synoptic conditions need to be met to allow for the development of wind speed anomalies over warm-core ocean eddies. In many cases, change in wind speed above eddies was masked by a large-scale synoptic wind speed deceleration/acceleration affecting parts of the eddies.
dc.identifier.apacitationRouault, M., Verley, P., & Backeberg, B. (2016). Wind changes above warm Agulhas Current eddies. <i>Ocean Science</i>, 12(2), 495 - 506. http://hdl.handle.net/11427/34598en_ZA
dc.identifier.chicagocitationRouault, M, P Verley, and B Backeberg "Wind changes above warm Agulhas Current eddies." <i>Ocean Science</i> 12, 2. (2016): 495 - 506. http://hdl.handle.net/11427/34598en_ZA
dc.identifier.citationRouault, M., Verley, P. & Backeberg, B. 2016. Wind changes above warm Agulhas Current eddies. <i>Ocean Science.</i> 12(2):495 - 506. http://hdl.handle.net/11427/34598en_ZA
dc.identifier.issn1812-0784
dc.identifier.issn1812-0792
dc.identifier.ris TY - Journal Article AU - Rouault, M AU - Verley, P AU - Backeberg, B AB - Sea surface temperature (SST) estimated from the Advanced Microwave Scanning Radiometer E onboard the Aqua satellite and altimetry-derived sea level anomalies are used south of the Agulhas Current to identify warm-core mesoscale eddies presenting a distinct SST perturbation greater than to 1 °C to the surrounding ocean. The analysis of twice daily instantaneous charts of equivalent stability-neutral wind speed estimates from the SeaWinds scatterometer onboard the QuikScat satellite collocated with SST for six identified eddies shows stronger wind speed above the warm eddies than the surrounding water in all wind directions, if averaged over the lifespan of the eddies, as was found in previous studies. However, only half of the cases showed higher wind speeds above the eddies at the instantaneous scale; 20 % of cases had incomplete data due to partial global coverage by the scatterometer for one path. For cases where the wind is stronger above warm eddies, there is no relationship between the increase in surface wind speed and the SST perturbation, but we do find a linear relationship between the decrease in wind speed from the centre to the border of the eddy downstream and the SST perturbation. SST perturbations range from 1 to 6 °C for a mean eddy SST of 15.9 °C and mean SST perturbation of 2.65 °C. The diameter of the eddies range from 100 to 250 km. Mean background wind speed is about 12 m s<sup>−1</sup> (mostly southwesterly to northwesterly) and ranging mainly from 4 to 16 m s<sup>−1</sup>. The mean wind increase is about 15 %, which corresponds to 1.8 m s<sup>−1</sup>. A wind speed increase of 4 to 7 m s<sup>−1</sup> above warm eddies is not uncommon. Cases where the wind did not increase above the eddies or did not decrease downstream had higher wind speeds and occurred during a cold front associated with intense cyclonic low-pressure systems, suggesting certain synoptic conditions need to be met to allow for the development of wind speed anomalies over warm-core ocean eddies. In many cases, change in wind speed above eddies was masked by a large-scale synoptic wind speed deceleration/acceleration affecting parts of the eddies. DA - 2016 DB - OpenUCT DP - University of Cape Town IS - 2 J1 - Ocean Science LK - https://open.uct.ac.za PY - 2016 SM - 1812-0784 SM - 1812-0792 T1 - Wind changes above warm Agulhas Current eddies TI - Wind changes above warm Agulhas Current eddies UR - http://hdl.handle.net/11427/34598 ER - en_ZA
dc.identifier.urihttp://hdl.handle.net/11427/34598
dc.identifier.vancouvercitationRouault M, Verley P, Backeberg B. Wind changes above warm Agulhas Current eddies. Ocean Science. 2016;12(2):495 - 506. http://hdl.handle.net/11427/34598.en_ZA
dc.language.isoeng
dc.publisher.departmentDepartment of Oceanography
dc.publisher.facultyFaculty of Science
dc.sourceOcean Science
dc.source.journalissue2
dc.source.journalvolume12
dc.source.pagination495 - 506
dc.source.urihttps://dx.doi.org/10.5194/os-12-495-2016
dc.subject.otherAgulhas Current eddies
dc.subject.otherWind changes
dc.subject.otherClimate research
dc.subject.otherArticle
dc.titleWind changes above warm Agulhas Current eddies
dc.typeJournal Article
uct.type.publicationResearch
uct.type.resourceJournal Article
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