Transition regions and their role in the relationship between sea surface height and subsurface temperature structure in the Atlantic Ocean

Abstract

Expendable bathythermograph (XBT) profiles and TOPEX/Poseidon altimeter data (T/P) are compared for the years 1993 through 1997 to determine how much can be understood about water column variability from XBT's given only sea height anomalies (SHA) from T/P. Our focus is on the annual cycle along two well sampled XBT sections in the Atlantic Ocean from 10°S to 40°N. Regions of transition are identified that separate the mid-latitudes where surface buoyancy fluxes dominate the forcing of sea level, from those in the equatorial region where thermocline effects dominate. Zones of transition occur in the vicinity of troughs where small fluctuations in SHA belie the true nature of water column variability. Here, surface and thermocline variability tend to cancel each other. Thus, the character of SHA in transition regions emphasizes how important direct observations can be in interpreting satellite altimetric observations correctly when both surface and thermocline variability are important but are compensating in nature.