Large-scale diurnal variability in the oceans: observation, modelling, assimilation and effects

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More than two-thirds of the Earth's surface is covered by ocean. The current state of the ocean and how it will evolve is of practical importance to weather forecasting and maritime activities. 'Analysis' of the ocean state is the process of using available observations of the ocean to create the best possible picture of the ocean at a given time. The temperature of the surface of the ocean (referred to as SST) is one of the important parameters describing the ocean, and is observed by a limited number of ships and buoys and globally by satellites. One complication is that there is a daily signal in the SST as the near-surface warms in response to heating by sunlight and then cools again as the sun goes down. At present in ocean and weather simulations, this effect is largely ignored, partly because adequate observations of the phenomenon occuring from hour to hour through the day over large areas of ocean have not been available. In this project, we will use new hourly satellite observations of the daily warming and cooling of the ocean surface and of the amount of heating by sunlight to do several things. The first thing is to describe the size and frequency of significant daily warming events in different areas of oceans in different months. Second, we will explore how to correct satellite SSTs for daily warming events when doing SST analysis (using a new analysis system at the UK Met Office). Third, we will verify that we are able to run computer simulations based on the physics of daily heating events that give good estimates of their size. Fourth, we will calculate the importance of the daily variability to the exchange of carbon dioxide between the air and sea (which is sensitive to SST amongst other things). Lastly, we will conduct a case study of how to use the new satellite observations to improve SST analyses such that they capture daily warming for the first time.