The effect of the Agulhas Current on synthetic aperture radar derived wind fields

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dc.contributor.advisorKrug, Marjolaineen_ZA
dc.contributor.advisorRouault, Mathieuen_ZA
dc.contributor.advisorHansen, Mortenen_ZA
dc.contributor.authorSchilperoort, Daniel Een_ZA
dc.date.accessioned2017-01-23T12:07:23Z
dc.date.available2017-01-23T12:07:23Z
dc.date.issued2016en_ZA
dc.description.abstractIn this study, 5 years (987 swaths) of high resolution wind speeds, derived from Advanced Synthetic Aperture Radar data collected over the Agulhas Current region, are studied to investigate the effect of warm, high intensity currents on the ocean's surface roughness and resulting derived wind fields. The wind data are derived using the CMOD5.n GMF with CFS reanalysis wind data as direction input. The CFS direction data are validated using ASCAT derived wind observations Globcurrent ocean current velocity data is used to investigate the difference between the satellite derived wind speeds compared to surface velocities of the current and the true wind speed. The, so called, current-relative effect is investigated for different wind direction regimes, namely: upcurrent, downcurrent, crosscurrent west and crosscurrent east. Our analyses are conducted for 6 locations of interest, evenly spaced along the Northern Agulhas Current. MODIS, SEVIRI and OSTIA SST data are used as proxy for locating the core of the Agulhas and it's temperature fronts, as well as to investigate wind speed modifications as a result of ocean-atmosphere energy transfer. It is found that higher resolution SAR derived winds have a greater ability to represent higher intensity and smaller scale wind features in comparison to winds derived from Scatterometers. A combination of the current relative effect and SST-atmospheric heating for upcurrent wind directions results in a sharp increase in mean wind speeds over the inshore boundary of the current of between 5m/s and 7m/s (50−60%). Individual events can reach as high as 15m/s (100%) over 10′s of kilometres. For downcurrent winds, the expected current relative effect is overridden by increased wind speeds of up to 5m/s (40%) across the entire current due to the influence of SSTs. The mean effect of SSTs on wind speeds has a stronger effect than the current relative effect on wind speed changes over the current. The wind speed differences are best represented under moderate wind speeds, between 5−15m/s. This investigation will contribute to future satellite wind speed derivations to identifying new wind speed and surface roughness altering effects. It will also serve to increase understanding of high resolution wind features and sharp changes over ocean features.en_ZA
dc.identifier.apacitationSchilperoort, D. E. (2016). <i>The effect of the Agulhas Current on synthetic aperture radar derived wind fields</i>. (Thesis). University of Cape Town ,Faculty of Science ,Department of Oceanography. Retrieved from http://hdl.handle.net/11427/22952en_ZA
dc.identifier.chicagocitationSchilperoort, Daniel E. <i>"The effect of the Agulhas Current on synthetic aperture radar derived wind fields."</i> Thesis., University of Cape Town ,Faculty of Science ,Department of Oceanography, 2016. http://hdl.handle.net/11427/22952en_ZA
dc.identifier.citationSchilperoort, D. 2016. The effect of the Agulhas Current on synthetic aperture radar derived wind fields. University of Cape Town.en_ZA
dc.identifier.ris TY - Thesis / Dissertation AU - Schilperoort, Daniel E AB - In this study, 5 years (987 swaths) of high resolution wind speeds, derived from Advanced Synthetic Aperture Radar data collected over the Agulhas Current region, are studied to investigate the effect of warm, high intensity currents on the ocean's surface roughness and resulting derived wind fields. The wind data are derived using the CMOD5.n GMF with CFS reanalysis wind data as direction input. The CFS direction data are validated using ASCAT derived wind observations Globcurrent ocean current velocity data is used to investigate the difference between the satellite derived wind speeds compared to surface velocities of the current and the true wind speed. The, so called, current-relative effect is investigated for different wind direction regimes, namely: upcurrent, downcurrent, crosscurrent west and crosscurrent east. Our analyses are conducted for 6 locations of interest, evenly spaced along the Northern Agulhas Current. MODIS, SEVIRI and OSTIA SST data are used as proxy for locating the core of the Agulhas and it's temperature fronts, as well as to investigate wind speed modifications as a result of ocean-atmosphere energy transfer. It is found that higher resolution SAR derived winds have a greater ability to represent higher intensity and smaller scale wind features in comparison to winds derived from Scatterometers. A combination of the current relative effect and SST-atmospheric heating for upcurrent wind directions results in a sharp increase in mean wind speeds over the inshore boundary of the current of between 5m/s and 7m/s (50−60%). Individual events can reach as high as 15m/s (100%) over 10′s of kilometres. For downcurrent winds, the expected current relative effect is overridden by increased wind speeds of up to 5m/s (40%) across the entire current due to the influence of SSTs. The mean effect of SSTs on wind speeds has a stronger effect than the current relative effect on wind speed changes over the current. The wind speed differences are best represented under moderate wind speeds, between 5−15m/s. This investigation will contribute to future satellite wind speed derivations to identifying new wind speed and surface roughness altering effects. It will also serve to increase understanding of high resolution wind features and sharp changes over ocean features. DA - 2016 DB - OpenUCT DP - University of Cape Town LK - https://open.uct.ac.za PB - University of Cape Town PY - 2016 T1 - The effect of the Agulhas Current on synthetic aperture radar derived wind fields TI - The effect of the Agulhas Current on synthetic aperture radar derived wind fields UR - http://hdl.handle.net/11427/22952 ER - en_ZA
dc.identifier.urihttp://hdl.handle.net/11427/22952
dc.identifier.vancouvercitationSchilperoort DE. The effect of the Agulhas Current on synthetic aperture radar derived wind fields. [Thesis]. University of Cape Town ,Faculty of Science ,Department of Oceanography, 2016 [cited yyyy month dd]. Available from: http://hdl.handle.net/11427/22952en_ZA
dc.language.isoengen_ZA
dc.publisher.departmentDepartment of Oceanographyen_ZA
dc.publisher.facultyFaculty of Scienceen_ZA
dc.publisher.institutionUniversity of Cape Town
dc.subject.otherOceanographyen_ZA
dc.titleThe effect of the Agulhas Current on synthetic aperture radar derived wind fieldsen_ZA
dc.typeMaster Thesis
dc.type.qualificationlevelMasters
dc.type.qualificationnameMScen_ZA
uct.type.filetypeText
uct.type.filetypeImage
uct.type.publicationResearchen_ZA
uct.type.resourceThesisen_ZA
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