Dynamics of a Catalina Eddy Revealed by Numerical Simulation

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Abstract
Through numerical simulations with the Pennsylvania State University–NCAR Mesoscale Model the dynamics of a Catalina Eddy event that formed during the period 26–30 June 1988 off the coast of southern California is examined. A strengthening and veering of the low-level synoptic-scale winds, from climatological northwesterlies to northerlies, results in a more pronounced effect of the coastal orography around the California bight region. In particular, relative vorticity formed by flow over the coastal terrain remains offshore. Prior to the formation of a quasi-steady eddy within the bight, the northerlies are strong enough to advect anomalously high vorticity out of the region. The formation of a mature Catalina eddy relies on a rapid deceleration of the synoptic-scale northerlies on 30 June, such that vorticity, once formed, remains in the bight. The eddy is also strongly modulated by the diurnal cycle. Northwesterly flow around 500 m above mean sea level impinging on the mountains north of the b... Abstract Through numerical simulations with the Pennsylvania State University–NCAR Mesoscale Model the dynamics of a Catalina Eddy event that formed during the period 26–30 June 1988 off the coast of southern California is examined. A strengthening and veering of the low-level synoptic-scale winds, from climatological northwesterlies to northerlies, results in a more pronounced effect of the coastal orography around the California bight region. In particular, relative vorticity formed by flow over the coastal terrain remains offshore. Prior to the formation of a quasi-steady eddy within the bight, the northerlies are strong enough to advect anomalously high vorticity out of the region. The formation of a mature Catalina eddy relies on a rapid deceleration of the synoptic-scale northerlies on 30 June, such that vorticity, once formed, remains in the bight. The eddy is also strongly modulated by the diurnal cycle. Northwesterly flow around 500 m above mean sea level impinging on the mountains north of the b...

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