Upper Ocean Heat Content Variability in the Pacific Ocean

Upper ocean heat has considerable importance in air-sea exchanges in areas such as tropical cyclone interactions and El Niño events in the Pacific Ocean that have global consequences. That is, the sea surface temperatures (SST) dominate the surface buoyancy flux by a factor of four compared to salinity effects as part of the air-sea exchange processes. However, the SST is only one component of the upper ocean heat content (OHC), and the tropical oceans can often mask the underlying warm structures associated with fronts and eddies. Combining SST with sea surface height anomaly (SSHA) measurements exploits the sources and sinks of OHC in the basins when combined with background climatologies and in situ measurements from multiple platforms. OHC, integrated thermal structure from the surface layer to a particular isotherm level, is important for tropical cyclone forecasting, assessing seasonal to annual climate variability, and tracking El Niño events in the equatorial Pacific. Here we discuss one approach in understanding OHC and its linkage to short and long term weather events.

Combining ocean climatology with SSHA and SST, OHC variability was estimated for the Pacific basin within the construct of a 2.5 layer model. Mean isotherm depths of 20°C and 26°C, reduced gravities, and mixed layer depth were estimated from blended temperature and salinity fields from the World Ocean Atlas and the Generalized Digital Environmental Model. Together with the blended climatology, SST from geostationary and polar orbiting radiometers and daily tracks of SSHA from polar orbiting radar altimeters were used to estimate OHC. Monthly, seasonal, and yearly time scales are investigated for the nearly two decades of SST and evaluated OHC estimates from space. Identifying variability and trends in upper ocean heat and their relationship to oceanic circulation features and weather is crucial to understand their impacts on short and long-term climate variations.