An Operational Lake Surface Water Temperature Analysis using the OSTIA System
Fiedler, Emma; McLaren, Alison; Martin, Matthew; Roberts-Jones, Jonah

Operational analyses of Lake Surface Water Temperature (LSWT) have many potential uses including as boundary conditions in Numerical Weather Prediction (NWP) models. LSWT is now included as part of the Sea Surface Temperature (SST) field in the UK Met Office daily Operational SST and Sea Ice Analysis product, OSTIA, for 248 lakes globally. The OSTIA analysis procedure for SSTs, which has been optimised for oceans, is also used for the lakes. Infra-red satellite observations of lakes and in situ measurements are assimilated. The satellite observations are based on retrievals optimised for SST which may introduce inaccuracies into the LSWT analysis but are currently the only near-real-time satellite information available. It is demonstrated using independent data from the ESA ARC-Lake project at the University of Edinburgh that the OSTIA LSWT analysis has a global RMS error of 1.31 K and a bias of 0.45 K. It is also shown that the OSTIA LSWT is an improvement over the use of climatology to capture the day-to-day variation in global lake surface temperatures. Recent improvements to this product currently in pre-operational testing include a lake ice field as part of the OSTIA global ice concentration field.