The ocean upper layer heat content is important during the passage of hurricane events, in which a sea surface temperature above 26 degree C is one of the necessary conditions to maintain the hurricane. Sea surface temperature and the vertical temperature gradient becomes a factor in estimating the upper layer heat content. Sea surface temperature from AVHRR imagery only provides temperature of the upper few cm or less of the ocean. Hydrographic measurements from XBT's and buoys are scarce in time and space. On the other hand, sea surface height derived from altimetry provides a global and almost continuous measurement of the oceanic dynamics, which is closely related to surface and subsurface thermal structure.
Radar altimeter-derived sea height anomaly data from NASA's TOPEX/POSEIDON mission provides information to identify the main dynamic features, where anticyclonic (cyclonic) circulation is usually identified by positive (negative) values of sea height anomalies. The combination of the altimeter data with historical hydrographic measurements, based upon a two-layer ocean model, provides a means to monitor the depth of the thermocline, its relationship with the depth of the 26 degree isotherm, and the upper layer heat content.
A high resolution (0.25 x 0.25 degrees) Levitus hydrographic data set is merged with TOPEX/POSEIDON-derived sea height anomalies in the NW Atlantic Ocean. The location of the Gulf Stream, its meanders and warm anticylonic rings are easily observed from their values of thermocline depth, taken here to be the depth of the 20 degree C isotherm. The WOCE hydrographic data set is also used to explore the relationship between the depth of the 20 degree C and 26 degree C isotherms, and the horizontal distribution of the mean vertical gradient of temperature in the region. The computation of the hurricane heat content is then obtained from the values of the depth of the 26 degree C isotherm and the vertical temperature gradient. Estimates of this parameter, its spatial and temporal variability, and the errors are presented to provide insights into the complexities of the upper ocean circulation.