Meeting Documents

Topography Effects on the Seasonal Variability of Ocean Bottom Pressure in the North Pacific Ocean and North Atlantic Ocean

Abstract

Ocean bottom pressure p_B is an important oceanic variable that is dynamically related to the abyssal ocean circulation through geostrophy. In this study we examine the seasonal p_B variability in the North Pacific Ocean and the North Atlantic Ocean by analyzing satellite gravimetric observations from the GRACE program and a data-assimilated ocean-state estimate from ECCOv4. The seasonal p_B variability of the North Pacific Ocean is characterized by alternations of low and high anomalies among three regions, the subpolar and subtropical basins as well as the equatorial region. A linear two-layer wind-driven model is used to examine forcing mechanisms and topographic effects on seasonal p_B variations of the North Pacific Ocean and a three-layer model will be used for the North Atlantic Ocean considering the three-layer structure of transport. The model control run, which uses a realistic topography, is able to simulate a basinwide seasonal p_B variability that is remarkably similar to that from GRACE and ECCOv4. Since the model is driven by wind stress alone, the good model-data agreement indicates that wind stress is the leading forcing for seasonal changes in p_B. An additional model simulation was conducted by setting the water depth uniformly at 5000m. The magnitude of seasonal p_B anomaly is amplified significantly in the flat-bottom simulation as compared with that in the control run. The difference can be explained in terms of the topographic Sverdrup balance. In addition, the spatial pattern of the seasonal p_B variability is also profoundly affected by topography especially on continental margins, ridges and trenches. In the North Atlantic Ocean, the seasonal variation of deep water transport is profoundly affected by the Mid-Atlantic Ridge and weaken the dominance of the deep western boundary current. Such differences are due to topographic effects on the propagation pathways of Rossby waves.View Document (AGU) »