Graduate Thesis Or Dissertation
 

Ocean surface wind divergence and vorticity co-variability and statistical differences between QuikSCAT and ERA5

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/r781wq265

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  • I examine the strong co-variability between the surface divergence and vorticity and how it varies with latitude in the Pacific Ocean using surface vector winds from reanalysis and satellite scatterometer observations. This analysis was motivated in part by a significant correlation between divergence and vorticity over the global oceans that had not been previously identified. For this exploration, I developed a novel method to examine the co-variability. In this method, an angle α^' is derived from the surface divergence and vorticity and shown to succinctly summarize the co-variability between divergence and vorticity in context of Ekman dynamics, which governs the large-scale surface winds to first order. Steady-state Ekman dynamics predicts a strong correlation between divergence and vorticity which varies with latitude. Next, I examined the statistical differences in divergence and vorticity between QuikSCAT and ERA5, which also utilized the aforementioned method. This model predicts two steady-state conditions which are easily identifiable in the α^' Probability Distribution Functions (PDFs): 1) diverging with negative vorticity or 2) converging with positive vorticity. I found that the statistical distributions of the surface divergence and vorticity of the horizontal winds over the ocean are consistent with steady-state Ekman dynamics. Significant differences are apparent in the divergence and vorticity fields that cannot be readily explained by the simple model Ekman employed. One of the main differences identified is that the reanalysis data of ERA5 follows Ekman dynamics more closely than the satellite scatterometers. In the ensuing work, I showed that atmospheric gravity waves are a significant source of the variability by use of the natural coordinate decomposition of the divergence and vorticity. The surface signature of gravity waves are more easily identified in the natural coordinate system than just divergence and vorticity. Finally, I identified that QuikSCAT has a clearer response in the divergence field to variations in the background/steady-state wind field caused by gravity waves, while ERA5 over dampens gravity waves strengthening the steady-state wind field.
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  • This research was funded by the National Aeronautics and Space Administration’s Future Investigators in NASA Earth and Space Science and Technology.
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