SHARP FRONTAL INTERFACES IN THE NEAR-SURFACE LAYER OF THE OCEAN IN THE WESTERN EQUATORIAL PACIFIC WARM POOL

During the TOGA COARE rich horizontal temperature and salinity variabi lity of the near-surface layer of the ocean in the western Pacific war m pool was observed. High-resolution measurements were made by probes mounted on the bow of the vessel in an undisturbed region at similar t o 1.7-m depth during four COARE cruises of the RN Moana Wave. The auth ors observed several tens of cases of periodic sharp frontal interface s of width 1-100 m and separation 0.2-60 km. The sharp frontal interfa ces were often found in frontal regions and on the periphery of freshw ater puddles. Maneuvers of the ship were conducted to determine the sp atial orientation of a sharp frontal interface. The interfaces reveale d anisotropy with respect to the wind direction. They were most sharp when the wind stress had a component along the buoyant spreading of th e front. A possible origin of the sharp frontal interfaces is discusse d. These interfaces may develop by nonlinear evolution of long-wave di sturbances on the near-surface pycnocline that is often observed in th e warm poor area. A shallow-water model may describe some features of the observations. A dimensionless number of the Reynolds type is a cri terion of transition from wave train solution to dissipative shock-wav e structure. The model predicts spatial anisotropy depending on the re lative angle between the wind stress and horizontal density gradient.