RAMSSA - An operational, high-resolution, Regional Australian Multi-Sensor Sea surface temperature Analysis over the Australian region

Abstract

An operational, high-resolution, Regional Australian Multi-Sensor Sea surface temperature Analysis (RAMSSA) system has been developed at the Australian Bureau of Meteorology as part of the BLUElink Ocean Forecasting Australia project. The pre-existing operational, 1/4° resolution, regional sea surface temperature (SST) analysis system has been modified to produce 1/12° resolution, daily SST analyses over the Australian region (20°N-70°S, 60°E-170°W). The new RAMSSA system combines SST data from infrared and microwave sensors on polar-orbiting satellites with in situ measurements to produce daily 'foundation' SST estimates, free of nocturnal cooling and diurnal warming effects. The RAMSSA analyses exhibited significantly less standard deviation than the pre-existing regional SST analyses when compared with independent buoy SST observations for the period 1 October 2007 to 31 March 2008 (0.42 °C compared with 0.55 °C) and agreed closely with those from daily foundation SST analyses produced by the UK Met Office and Ifremer using similar data sources (0.39 °C and 0.49 °C, respectively). The major differences between RAMSSA and these other foundation SST analyses relate to RAMSSA's method for creating super-observations and assigning weights to the various input data streams, and Ifremer and the Met Office analysis systems' bias-correction of all satellite input data using SST data from the Advanced Along Track Scanning Radiometer (AATSR). The lack of bias-correction of data input into RAMSSA has minimal effect north of 40°S where RAMSSA is on average within ±0.07 °C of other multi-sensor SST analyses. South of 40°S, RAMSSA is on average 0.09 °C to 0.25 °C warmer than bias-corrected analyses studied, mainly due to systematic biases over this region in satellite SST data streams from the Advanced Very High Resolution Radiometer (AVHRR) and Advanced Microwave Scanning Radiometer - Earth Observing System (AMSR-E) input into the analyses.