# Sea Surface Temperature in Global Analyses: Gains from the Copernicus Imaging Microwave Radiometer
## 3 Results  
### Error Statistics  
The mean and standard deviation of the error in the daily analysis of the SST were formed via comparison with the original \"truth\" dataset for the day. Histograms of the distribution and global maps of these statistics are shown for January in Figures 4 and 5, respectively, for the perfect input data cases. Similar comparisons using input data with realistic errors are shown in Figures 6 and 7. The change in the root-mean-square error (RMSE) resulting from the addition of the CIMR data to the analysis inputs is shown in Figure 8. Results for July are similar to those for January and so just the maps of the errors statistics are shown for the data with realistic errors and the change in RMSE in Figures 9 and 10. Both Figures 4 and 6 show a clear improvement in the error distributions with the addition of the CIMR data and imply an improved ability of the analyses to reproduce the \"truth\" dataset. As might be expected, the OSTIA analyses in Figures 5, 7 and 9 show patches of larger error standard deviations in regions of dynamical SSTs, such as around the Aghulas Current and the Gulf Stream. More widely, for the infrared-only reconstructions, the error standard deviations appeared to be larger in the southern hemisphere in January and the northern hemisphere in July. This is counter-intuitive as one might expect summer to result in decreased cloudiness and thus improved coverage. In January, for the southern hemisphere, AVHRR and SLSTR had \(16.1\pm 0.9\%\) and \(14.5\pm 0.9\%\) daily hemisphere coverage, respectively, compared to \(11.5\pm 0.8\%\) and \(10.1\pm 0.5\%\), respectively, for the northern hemisphere. However, in July, there was a more mixed coverage picture: \(13.0\pm 1.1\%\) and \(12.0\pm 0.8\%  
Figure 5: Maps of the January error statistics: **(a)** mean error with perfect IR data only, **(b)** standard deviation of the error with perfect IR data only, **(c)** mean error with combined perfect IR and CIMR data and **(d)** standard deviation of the error with combined perfect IR and CIMR data. Figure 6: Statistics of the differences between the analysis of January SST fields and the original “truth” SST for IR-only (red) and combined IR and MW (blue) input data with realistic errors: **(a)** mean error and **(b)** standard deviation of the error. Figure 7: Maps of the error statistics during January for input data with realistic errors: **(a)** mean error with IR data only, **(b)** standard deviation of the error with IR data only, **(c)** mean error with combined IR and CIMR data and **(d)** standard deviation of the error with combined IR and CIMR data. A summary of the RMSE in different regions for each of the configurations is given in Table 2. During validation of current operational OSTIA products, the RMS difference relative to reference observations is typically in the range 0.3-0.5 [14; 29], so a similar magnitude of results in this table suggests that this simulation study is performing realistically. The addition of CIMR data resulted in a marked decrease in RMSE in all regions except the coast. The coastal region (defined as cells less than 0.3-0.5) is also included in the range 0.3-0.5. Figure 8: Change in the RMS error of the reconstructed SST field in January from adding CIMR data to the input for: (**a**) perfect input data and (**b**) input data containing realistic errors. Figure 10: Change in the RMS error of the reconstructed SST field in July from adding CIMR data to the input for: (**a**) perfect input data and (**b**) input data containing realistic errors. Figure 9: Maps of the error statistics during July for input data with realistic errors: (**a**) mean error with IR data only, (**b**) standard deviation of the error with IR data only, (**c**) mean error with combined IR and CIMR data and (**d**) standard deviation of the error with combined IR and CIMR data. 25 km from land) showed only small improvements with the addition of the CIMR data.