Baroclinic Vortex Interactions with Topographic Obstacles Georgi SUTYRIN Graduate School of Oceanography, University of Rhode Island, USA Email: gsutyrin@gso.uri.edu Long-lived baroclinic vortices with strong potential vorticity anomalies dominate in the ocean dynamics and the transport of tracers. Their interactions with topographic obstacles are often dramatic for the fate of vortices as shown by observations in different regions, e.g., [8], [9]. Multi-layer models are widely used for modeling vortex interactions with continental shelves and slopes, mid-ocean ridges and seamounts. Topography is typically represented by a variable depth with PV gradients in the lower layer, e.g., [4], [5], [11]; or as a vertical wall, e.g., [13], [7]. Recent studies of two-layer baroclinic flows near a step-like finite topography penetrating in the upper layer have shown that the intersection of isopycnals with topogra- phy introduces qualitative new effects [6], [1], [3], [14]. Here we describe a novel approach for modeling baroclinic vortices with isopycnals intersecting sloping bottom and consider examples of vortex-seamount interactions [12]. In a two-layer model with a rigid-lid the layer depths are h 1 = D 1 + η, h 2 = D(x, y) − h 1 , (1) where D(x, y) is the ocean depth, D 1 = D(x, y) over the shallow seamount top if h 2 = 0, otherwise D 1 = const is the average depth of the upper layer, and η is the interface displace- ment. The geopotential (p i , the pressure divided by density) and the interface displacement (η) are related by the hydrostatic equation: g ′ ∇η = ∇(p 1 − p 2 ), (2) where g ′ ≡ g(ρ 2 − ρ 1 )/ρ 1 is the reduced gravity (η is not defined over the shallow seamount top). Focusing on the upper layer dynamics, we assume that the velocity in the lower layer to be much smaller, i.e., we consider an equivalent-barotropic approximation with p 2 = 0. In this case the bathymetry influences the vortex evolution only due to intersection with the upper layer interface. The evolution of p 1 was modeled using the General Geostrophic equations, [10], where the velocity is expressed by p 1 expanding in the Rossby number. This approach is valid for finite variations of the upper layer depth and allows for calculating variable interface position at the sloping bottom from (1)–(2) h 2 = D(x, y) − D 1 − p 1 g ′ =0 (3) The physical mechanism that has the most significant effect on the vortex evolution is the advection by a topographic anticyclone formed after replacement of water over the seamount