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The University of Southampton
Ocean and Earth Science, National Oceanography Centre Southampton

Research project: Evaluation of accuracy and uncertainty of EO parameters for global air-sea fluxes

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The oceans play a key role in the climate system through storing and transporting vast amounts of heat and freshwater. They have naturally long thermodynamic timescales, exerting a moderating influence on changes induced by perturbations in other parts of the climate system, e.g. to the radiation budget. The capacity to detect subtle changes as the ocean responds to global warming will enhance our preparedness to mitigate the impacts of climate change. Earth Observation (EO) methods from satellites provide the spatially detailed, regularly repeated global coverage needed for identifying climatically important variability over the oceans.

Surface fluxes of heat and freshwater connect the atmosphere and the ocean and are poorly quantified, despite being vital forcing fields for models and essential to understand the ocean in a changing climate. In situ-based flux estimates cover less than 50% of the ocean and EO cannot presently measure all of the components of the heat and freshwater budgets with usable accuracy. For example, remotely sensed sensible and latent (evaporative) fluxes contain large uncertainties, mainly due to their poor retrieval of surface air temperature and humidity, but even more established EO parameters such as wind speed do not meet user accuracy requirements for fluxes. We characterise the accuracy and uncertainty of crucial satellite measurements needed to quantify ocean climate variability and change.

A particular focus is the assessment of structural uncertainty in scatterometer measurements of wind velocity over the ocean and the influence of rain on wind datasets. EO wind measurements are generally supposed to be accurate and are thus widely assimilated into models or used to create blended wind products. However, biases between long-term wind datasets exist, indicating where our knowledge is limited and further research required. This is of particular importance since most bulk parameterisations of air-sea fluxes rely on wind.

This work is part of the Climate Theme of the NERC National Centre for Earth Observation (NCEO) and is carried out in close collaboration with researchers at NOC. It links into NCEO work at NOC assessing humidity and sea surface temperature measurements from space and in situ by John Prytherch, Elizabeth Kent and David Berry as well to other NCEO activities in the UK.

NCEO's website is

Funding: NERC March 2008-2013

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