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The Santa Cruz Eddy. Part II: Mechanisms of Formation CRISTINA L. ARCHER AND MARK Z. JACOBSON

Summary: The Santa Cruz Eddy. Part II: Mechanisms of Formation
Stanford University, Stanford, California
(Manuscript received 25 March 2004, in final form 1 February 2005)
The formation mechanism of the Santa Cruz eddy (SCE) is investigated using the fifth-generation
Pennsylvania State University­National Center for Atmospheric Research Mesoscale Model (MM5). Simu-
lations of 25­26 August 2000 showed that two eddy instances formed on that night, a finding supported by
observations. The two eddies had similar behavior: they both formed in the sheltered Santa Cruz, Califor-
nia, area and then moved southeastward, to finally dissipate after 7­11 h. However, the first eddy had
greater vorticity, wind speed, horizontal and vertical extents, and lifetime than the second eddy. Numerical
simulations showed that the SCEs are formed by the interaction of the main northwesterly flow with the
topographic barrier represented by the Santa Cruz Mountains to the north of Monterey Bay. Additional
numerical experiments were undertaken with no diurnal heating cycle, no (molecular or eddy) viscosity, and
no horizontal thermal gradients at ground level. In all cases, vertical vorticity was still created by the tilting
of horizontal vorticity generated by the solenoidal term in the vorticity equation. This baroclinic process
appeared to be the fundamental formation mechanism for both SCEs, but more favorable conditions in the
late afternoon (including a south-to-north pressure gradient, flow turning due to the sea breeze, and an
expansion fan) coincided to intensify the first eddy.
1. Introduction


Source: Archer, Cristina Lozej - Department of Civil and Environmental Engineering, Stanford University


Collections: Geosciences; Renewable Energy