Summary: The Santa Cruz Eddy. Part I: Observations and Statistics
CRISTINA L. ARCHER, MARK Z. JACOBSON, AND FRANCIS L. LUDWIG
Stanford University, Stanford, California
(Manuscript received 25 March 2004, in final form 30 August 2004)
A shallow cyclonic circulation that occurs in the summertime over the Monterey Bay (California) is
investigated. Since it is often centered offshore from the city of Santa Cruz and has never been studied in
detail before, it is named the Santa Cruz eddy (SCE) in this study. Its horizontal size is 1040 km, and its
vertical extent is 100500 m. The SCE is important for local weather because it causes surface winds along
the Santa Cruz coast to blow from the east instead of from the northwest, the latter being the climatological
summer pattern for this area. As a consequence of the eddy, cool and moist air is advected from the south
and southeast into the Santa Cruz area, bringing both relief from the heat and fog to the city.
The SCE is unique in its high frequency of occurrence. Most vortices along the western American coast
form only during unusual weather events, whereas the SCE forms 78%79% of the days during the summer.
The SCE frequency was determined after analyzing two years of data with empirical orthogonal functions
(EOFs) from a limited observational network and satellite imagery. An explanation of the formation
mechanism of the SCE will be provided in Part II of this study.
Atmospheric eddies (or vortices) of various sizes and
lifetimes have been observed and studied in several ar-