Heat Content from Gliders and Satellites: Eastern Mediterranean Case Study

Heat content measured directly by ocean gliders in the Eastern Mediterranean (EM) Sea is compared to heat content inferred from remotely sensed sea surface properties, assuming a simple reduced-gravity model. Since the Middle East is one of the most responsive regions to climate changes, expected to be warmer and dryer, monitoring and studying the sea heat capacity and the effects on the local weather regime is of great importance. For example, EM heat content during fall was found to be significant in predicting the amount of precipitation over Israel in the following winter. Heat content is a function of both the mixed layer thickness and its mean temperature. Using temperature profiles observed by gliders, we can verify heat content inferred from remotely sensed sea surface temperature and sea level anomalies under reduced-gravity approximation and study its spatial and temporal variability. Sea gliders missions, conducted in high temporal resolution, provide detailed information on the water column thermal structure along its path. The comparison between the heat content obtained from gliders and the heat content calculated from remotely sensed properties shows that there are places and periods where a distinct separation between the surface and subsurface is found in the EM. This separation occurs when a subsurface dynamical eddy, e.g., is observed in the profiles collected by the glider but has no surface signature, hence is not detected by satellites. Furthermore, satellite products seem to poorly represent the heat content of coastal water which exhibit a different thermal structure than an open-water thermal structure. Another finding from the heat content comparison, obtained by two different methods, is that the subsurface is better represented by the surface during summer than during winter. This indicates that the strength of the stratification is also crucial when remotely monitoring heat content. In summary, heat content obtained directly by gliders, remotely by satellites, and the comparison between the two provides several important insights about water column thermal structure variability in one of the most sensitive regions to climate change. Ocean gliders mapping is needed when accurate heat content estimation is required.