Sea-surface dynamics diagnosed from satellite data and coupled models

Johns Hopkins University, Baltimore MD

Investigators

Abstract

A central question in oceanography and climate dynamics concerns the evolution of surface anomalies of a wide range of properties. Sea surface temperature anomalies regulate the exchange of heat between the upper ocean and the atmosphere, profoundly influencing ocean circulation, weather, the seasonal cycle, low-frequency climate variability, and climate change. In high latitudes, sea surface salinity anomalies have been associated with such variability, and with variability in ecosystems. It is unclear how to interpret the development and propagation of sea surface temperature anomalies, however, which are often analyzed in terms of spatiotemporally-lagged correlations. This ambiguity makes it difficult to constrain the underlying mechanisms, both in observations and in models. The main goal of this project is to diagnose, quantify, and understand the mechanisms controlling the propagation of ocean surface anomalies in temperature and salinity. This study will train one graduate student and its results will be disseminated broadly to scientists and the general public. This project applies a new framework developed by the investigators to understand how and why surface anomalies propagate and evolve. In particular, this new method to infers sea surface temperature transport fields greatly improves on earlier approaches by decomposing sea surface temperature evolution into advective, diffusive and relaxation components. Preliminary results applying this new method to historical North Atlantic sea surface temperature data and coupled climate model output motivate this study. The researchers intend to continue the sea surface temperature analysis to quantify anomaly dynamics using global observations, especially satellite imagery, as well as numerical models. The new framework also applies to other surface property fields, such as sea surface salinity. Three questions emerge from this work: Why do sea surface temperature anomalies apparently propagate at different speeds to the underlying currents? Why do sea surface temperature and sea surface salinity anomalies behave differently? and What determines the variations in the lateral diffusivity inferred from them? The researchers will use a hierarchy of models, including coupled climate models, to identify the mechanisms controlling anomaly evolution in these fields.