Sharp Frontal Interfaces in Near-Surface Layer of the Ocean in the Western Equatorial Pacific Warm Pool

Alexander Soloviev*
and
Roger Lukas

Department of Oceanography
University of Hawaii
1000 Pope Road
Honolulu, HI 96822

Abstract
 During the TOGA COARE we observed rich horizontal temperature and salinity variability of the near-surface layer of the ocean in the western Pacific warm pool. High resolution measurements were made by probes mounted on the bow of the vessel in an undisturbed region at ~1.5-m depth during four COARE cruises of the R/V Moana Wave in Feb-Mar 93 and in Mar-May 94. We observed several tens of cases of periodic sharp frontal interfaces of 1-100 m width and of 1-60 km separation. Maneuvers of the ship were conducted to determine the spatial orientation of a sharp frontal interface. The sharp frontal interfaces were mainly observed in frontal regions and on periphery of freshwater puddles. They were presumably associated with buoyancy adjustment of the stratified near-surface layer of the ocean to variable wind stress and rain events. Their structural form had some similarity to that of the internal surge previously observed in long stably-stratified lake (Fig. 1). The dynamically active interfaces were mainly observed when the wind stress had a component in the direction of buoyant spreading of the front.

The sharp frontal interfaces in the warm pool region may develop due to nonlinear evolution of longwave disturbances on the so called "barrier layers" that are an intrinsic feature of the surface layer in the western equatorial Pacific warm pool. A model is based on equation of Korteweg-deVries-Burgers type describing the dynamics of a nonlinear system with dispersion and dissipation. A nondimensional number of Reynolds type is a criteria of transition from wave train solution to dissipative shock wave structure. The model predicts spatial anisotropy depending on the relative angle between the wind stress and horizontal density gradient.

*Visiting staff. Permanent affiliation is the P.P.Shirshov Institute of Oceanology Russian Academy of Sciences

Reference:

Soloviev, A. and R. Lukas, 1997: Sharp frontal interfaces in the near-surface layer of the ocean in the western equatorial Pacific warm pool. J. Phys. Oceanogr., 27, 999-1017.

Last modified: October 16, 1997