| dc.description.abstract | The dissertation seeks to elucidate the interaction of Amazon Plume Barrier Layer (BL) with hurricanes using a combination of observational analysis and high-resolution regional coupled model simulations. Firstly, multiple observational datasets, including 905 qualified in-situ Argo floats and two shipment cruise datasets, were used to characterize the climatological spatial structure of the BL associated with the Amazon plume. BL is more prominent in the horizontal boundary region of the plume, where the horizontal salinity gradients are the greatest, than in the plume interior, where the freshwater volume is larger. That’s because the strong stratification there could levitate temperature Mixed Layer Depth (T-MLD) to as shallow as the density Mixed Layer Depth (D-MLD). This process has been underestimated in the previous studies.
Then, 64 pairs of Argo float profiles coincident in time and space with the passage of a hurricane has been compared to examinate the relationship between SST cooling and BL thickness. Each pair captured the vertical profiles before and after each Hurricane arrival. Our analysis finds more evidence for reduced SST cooling due to the BL effect in the plume boundary region than in the plume interior, especially for slow-moving hurricanes. Also, the reduced cooling is seen mostly in the cool hurricane wake, reducing the possibility of a feedback on hurricane intensity.
In order to examine the direct feedback of the reduced SST cooling on Hurricane intensification. 21 Hurricanes were simulated by the Regional Coupled Earth System Model (RCESM) running at 10km spatial resolution, which has crossed over the Plume region. In addition to carrying out control simulations to reproduce the observed evolution of hurricanes, two sensitivity simulations were carried for each hurricane case: a BL- simulation that eliminated the barrier by removing the freshwater; a BL+ simulation that enhanced the BL by adding more freshwater in order to check the saturation of the BL effect, and other conditions were kept the same (to the extent possible). Analysis of the suite of simulations shows that, for strong hurricanes, the model is able to simulate the reduced SST cooling due to the BL effect in the Hurricane cold wake. But the reduced SST cooling has only a modest effect on the hurricane intensity, because of the fast translation speed of the Hurricanes in the Plume region. The area-averaged SST cooling is observed near 0.1°C 12 hours after Hurricane passed by, by then hurricanes have moved 200-300km away, making it too late to have an impact. Moreover, the quantitively analysis shows that the Hurricane intensity measured by the Sea Level Pressure only changed 2 hpa, with a 0.1°C change in the SST. | |
