IMPORTANCE OF OCEAN HEAT CONTENT TO THE GLOBAL CLIMATE SYSTEM Eileen Maturi1, David Donahue2, Deirdre Bryne1 1. NOAA/NESDIS/STAR 2. NOAA/NESDIS/OSPO Ocean Heat Content (OHC) The Ocean Heat Content is a measure of the integrated vertical temperature from the 26o C isotherm to the sea surface where surface boundary conditions exist (area under the curve in Fig. 1). The 26o C isotherm defines the lower limit at which convection can develop and strengthen. Surface winds generate turbulent mixing within the uppermost part of the ocean; this layer is called the Mixed Layer, and can often reach depths of hundreds of meters. Turbulence associated with the Mixed Layer is responsible for providing a large reservoir of heat energy that can be tapped into by a tropical cyclone. This can intensify and extend the lifetime of the cyclone. Figure 1. Schematic of OHC calculation. The red shading shows the true OHC by integrating the black temperature profile. The dashed blue line shows the approximated temperature profile of the upper ocean. Summary The Madden Julian Oscillation (MJO) and the El Nino/La Nina oscillations have global impacts which affect all the basins. It is important to know the Ocean Heat Content of all the Ocean Basins to predict the rainfall patterns, tropical and mid-latitude cyclones and drought. All these phenomena are components of the Global Climate System. NOAA/NESDIS generates a daily suite of satellite-generated OHC products for the Atlantic and Pacific. There are plans to generate a suite of OHC products for the Indian Ocean. Operational Ocean Heat Content (OHC) Products IMPACTS • The OHC products are important to the monitoring and understanding of Coral Reef systems. Coral reefs are sensitive to unusually warm water. Increased Ocean Heat leads to the destruction of Coral Reefs. • Higher oceanic heat content leads to increased rainfall, which is beneficial for agriculture. • Increased oceanic heat content in the Northern Indian Ocean leads to increased summer monsoon rainfall in India. • Improved ecological forecasting leads to better management of fish stocks, which are an important food source for ocean-bordering countries. There is only one true ocean, the “World Ocean.” For simplicity, the World Ocean is divided into 5 interconnected ocean basins. They are the Atlantic, Pacific, Indian, Arctic, and Southern Oceans. Climatic Variability The Indian Ocean is the warmest of the 5 ocean basins. An Indian OHC product can provide information about the Madden Julian Oscillation (MJO), which is a major factor in determining rainfall, drought, and tropical cyclone patterns in the Eastern Hemisphere. MJO can be visualized as alternating regions of rising air and sinking air. The rising air is associated with tropical rainfall. The sinking air is associated with drier conditions, allowing more solar insolation to reach the ground, inducing drought. It can also play a role in strengthening or weakening tropical cyclones. In addition, the OHC can be used to gauge the strength and duration of the Indian, Asian and North American Summer Monsoons. The MJO typically moves across the tropical Indian Ocean and western Pacific before weakening; though it occasionally circumnavigates the global tropics in 30- 60 days (1-2 months). MJO differs from El Nino/La Nina primarily in that the MJO recurs more frequently (lasting 1-2 months),compared to El Nino/La Nina which recurs less frequently (lasting 6-9 months or longer). The OHC is especially important for the Atlantic and Pacific Basins to help gauge the intensity and duration of El Nino/La Nina, tropical and extratropical (mid- latitude) cyclones, and anomalous rainfall patterns.