A Numerical Modeling Study of the Catalina Eddy

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  • 1 Physics Department, Gonzaga University, Spokane, Washington
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Abstract

A numerical modeling study of the Catalina Eddy was performed to investigate the causes of his occasional vortex over the Bight of California. The eddy was successfully simulated by imposing over the mesoscale domain a strong northwesterly flow resembling one that was associated with a June 1988 occurrence. In the simulation, a low pressure center form in the Ice of the San Rafael Mountains, that is, over the northern bight. The low forms because of leeside subsidence warning; daytime diabatic heating of the flow that traverses the mountains is insignificant. In response to the leeside low, the large-scale northwesterly flow turns cyclonically around Point Conception, strengthening the westerly component of the flow over the bight. The coastal mountains south of Los Angeles are a barrier to the large-scale northwesterlies and to the westerly flow over the bight, causing marine air to pool below the mountains' mean height. The pooled marine air replaces much warmer air in the strongly inverted layer and forms a mesoscale pressure ridge along the coast. The eddy is formed when the pooled marine air begins to flow down the pressure gradient toward the leeside low near Santa Barbara. In a simulation without the southern coastal mountains, no coastal ridging develops and therefore no eddy occurs. If daytime solar heating is turned off, eliminating the sea-breeze and heated-slope circulations, the eddy forms several hours sooner than if solar heating is fully simulated.

Abstract

A numerical modeling study of the Catalina Eddy was performed to investigate the causes of his occasional vortex over the Bight of California. The eddy was successfully simulated by imposing over the mesoscale domain a strong northwesterly flow resembling one that was associated with a June 1988 occurrence. In the simulation, a low pressure center form in the Ice of the San Rafael Mountains, that is, over the northern bight. The low forms because of leeside subsidence warning; daytime diabatic heating of the flow that traverses the mountains is insignificant. In response to the leeside low, the large-scale northwesterly flow turns cyclonically around Point Conception, strengthening the westerly component of the flow over the bight. The coastal mountains south of Los Angeles are a barrier to the large-scale northwesterlies and to the westerly flow over the bight, causing marine air to pool below the mountains' mean height. The pooled marine air replaces much warmer air in the strongly inverted layer and forms a mesoscale pressure ridge along the coast. The eddy is formed when the pooled marine air begins to flow down the pressure gradient toward the leeside low near Santa Barbara. In a simulation without the southern coastal mountains, no coastal ridging develops and therefore no eddy occurs. If daytime solar heating is turned off, eliminating the sea-breeze and heated-slope circulations, the eddy forms several hours sooner than if solar heating is fully simulated.

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