Spatio-temporal Variability of the SST from Drifters and Satellites

Sea Surface Temperature (SST) is a key variable in coupled ocean-atmosphere interactions and for the marine ecosystem, modulating the distribution of marine biota and various biogeochemical reactions. Satellite-derived reanalysis products are routinely used to measure SST, but questions remain about how representative these measurements are of in-situ ocean temperatures. Here we employ Lagrangian observations to assess the relation, using surface drifter data from the Nordic Seas, Atlantic Subpolar Gyre and the Indian Ocean. We find that daily ERA-interim reanalysis successfully captures the intraseasonal temperature fluctuations observed by the drifters. At daily-to monthly frequencies, the spectra from both the drifter temperatures and the ERA temperatures interpolated onto the drifter trajectories display a
clear w^(-2) slope. The same slope is recovered with a set of synthetic stochastic trajectories, indicating it is random. Further information about the spatial coherence can be inferred from temperatures on pairs of nearby drifters; the ERA-SST results are again comparable on time scales longer than weekly, and over spatial scales exceeding 100 km. The results support the fidelity of the reanalysis data in climate studies but also shed light on the turbulent fluctuations occurring at smaller spatial and temporal scales.