VIIRS SST at High Latitudes Sasha Ignatov, Prasanjit Dash, Bruce Brasnett NOAA; CIRA; CMC

1. 15th GHRSST Science Team Meeting2-6 June 2014, Cape Town, South Africa VIIRS SST at High Latitudes Sasha Ignatov, Prasanjit Dash, Bruce Brasnett NOAA; CIRA; CMC ACSPO VIIRS at High Latitudes

2. Background • Jacob asked to review VIIRS SST performance at HL • Until Recently, no major issues have been identified in ACSPO @ HLs • Recently received feedback from CMC Bruce Brasnett • Initially, ACSPO used Reynolds ice mask. Now switching over to CMC ice & 1st guess SST • Started looking at various ice analyses: OSTIA (OSISAF); CMC; and NCEP (Grumbine) Factors affecting satellite SST products at HL • Cloud screening • Ice identification • SST algorithms • Lack of in situ data for Cal/Val Today’s presentation • ACSPO VIIRS SST performance at HL as seen in SQUAM • No in depth analyses of contributing factors ACSPO VIIRS at High Latitudes

3. VIIRS & in situ drifters coverage – Night ACSPO VIIRS at High Latitudes

4. NIGHT:ACSPO L2 – OSTIA L4 • ACSPO does not truncate by LAT • Retrievals available up to ±80° + ACSPO VIIRS at High Latitudes

5. NIGHT:ACSPO L2 – iQuam Drifters • These areas either lack or have very sparse coverage by in situ data ACSPO VIIRS at High Latitudes

6. VIIRS and in situ drifters coverage – Day ACSPO VIIRS at High Latitudes

7. DAY:ACSPO L2 – OSTIA L4 • ACSPO does not truncate by LAT • Retrievals available up to ±80° + ACSPO VIIRS at High Latitudes

8. DAY:ACSPO L2 – iQuam Drifters • These areas either lack or have very sparse coverage by in situ data ACSPO VIIRS at High Latitudes

9. Feedback from Bruce Brasnett – ACSPO Coverage • “It was noted from examination of the ACSPO VIIRS dataset that the region north of 60N benefitted from a larger increase in coverage relative to AVHRR compared to other regions. The global average coverage with VIIRS was 2.9 times the AVHRR19 coverage, but this ratio increased to 3.4 north of 60N, based on data from Feb 1, 2014. This improved coverage at high latitudes could account for some of the gain seen in fig. 6 in this region.” ACSPO VIIRS at High Latitudes

10. Feedback from Bruce Brasnett – ACSPO Biases • “The only issue that will have to be monitored is the tendency for the ACSPO VIIRS retrievals to be too warm north of 60N, a trend seen both in summer and winter.” • Analyses in SQUAM suggest two observations • We do not have long term comparisons of ACSPO with CMC yet. However, we do see warm biases at HL wrt. OSTIA • On the contrary, there appears to be a coldish (rather than warm) ACSPO bias in the Northern HL ACSPO VIIRS at High Latitudes

11. SST Biases – Night ACSPO VIIRS at High Latitudes

12. NIGHT:ACSPO L2 – OSTIA L4 • Below 60°S: slight biases up to ±0.5K • Above 60°N: warm seasonal bias up to 1K ACSPO VIIRS at High Latitudes

13. NIGHT:ACSPOL2 – iQuam Drifters • Biases below 60°S not easy to verify • Above 60°N, there is actually a coldish bias ACSPO VIIRS at High Latitudes

14. SST Biases – Day ACSPO VIIRS at High Latitudes

15. DAY:ACSPO L2 – OSTIA L4 • Below 60°S: slight biases up to ±0.5K • Above 60°N: warm seasonal bias up to 1K ACSPO VIIRS at High Latitudes

16. DAY:ACSPOL2 – iQuam Drifters • Biases below 60°S not easy to verify • Above 60°N, there is actually a coldish bias ACSPO VIIRS at High Latitudes

17. Some Early Results Assimilating ACSPO VIIRS L2P Datasets Bruce Brasnett Canadian Meteorological Centre May, 2014

18. Assessing relative value of 2 VIIRS datasets: NAVO vs. ACSPO Warm Bias above 60°N NORTH SOUTH Using ACSPO instead of NAVO improves assimilation ACSPO VIIRS at High Latitudes

19. Assessing the relative value of 3 datasets for January-March 2014 Warm Bias above 60°N NORTH SOUTH Using ACSPO improves STD in all LAT bands, except at 10°S ACSPO VIIRS at High Latitudes

20. Assessing potential benefit of adding VIIRS to CMC analysis Warm Bias above 60°N NORTH SOUTH ACSPO improves assimilation in all LAT bands, except hi-lat North (high bias) ACSPO VIIRS at High Latitudes

21. Summer Sample: Aug. 15- Sept. 9, 2013. VIIRS vs. NAVO AVHRR GAC Warm Bias above 60°N Warm Bias below 60°S? NORTH SOUTH ACSPO VIIRS assimilation comparable to NAVO AVHRR, except at hi-lat ACSPO VIIRS at High Latitudes

22. ACSPO VIIRS SST at HL - Observations • ACSPO VIIRS provides superior coverage at high latitudes • Bruce Brasnett, based on his assimilation in CMC L4, observed a warm ACSPO bias above 60°N • SQUAM shows a warm bias wrt. OSTIA at HL (South & North) • However, VAL against in situ drifters in SQUAM does not appear to support this observation, and suggests a slightly cold bias in the Northern Hemisphere • In the Southern hemisphere, in situ data may suggest a slightly warm bias • However, statistically significant validation at HL remains challenging, due to limited in situ data ACSPO VIIRS at High Latitudes

23. Back Up Slides NAVO SST ACSPO VIIRS at High Latitudes

24. VIIRS & in situ drifters coverage – Night ACSPO VIIRS at High Latitudes

25. NIGHT:NAVOL2 – OSTIA L4 • NAVO retrievals available from 70°S to 80°N (truncation by LAT?) • Similar LAT truncation was implemented in NOAA historical pre-ACSPO system (prototype of SEATEMP ) ACSPO VIIRS at High Latitudes

26. NIGHT:NAVOL2 – iQuam Drifters • NAVO product is more consistent with in situ domain • Yet, evaluation at HL remains challenging ACSPO VIIRS at High Latitudes

27. VIIRS and in situ drifters coverage – Day ACSPO VIIRS at High Latitudes

28. DAY:NAVOL2 – OSTIA L4 • NAVO retrievals available from 70°S to 80°N (truncation by LAT?) • Similar LAT truncation was implemented in NOAA pre-ACSPO system (SEATEMP prototype) ACSPO VIIRS at High Latitudes

29. DAY:NAVOL2 – iQuam Drifters • NAVO product is better covered by in situ data at HL due to more limited domain • Nevertheless, evaluation of satellite SST is challenging ACSPO VIIRS at High Latitudes

30. SST Biases – Night ACSPO VIIRS at High Latitudes

31. NIGHT:NAVOL2 – OSTIA L4 • NAVO also shows a warm bias up to +0.5K below 50°S • And warm bias up to 1K above 50°N ACSPO VIIRS at High Latitudes

32. NIGHT:NAVOL2 – iQuam Drifters • Warm bias in NAVO wrt. drifters below -50°S is a little larger than in ACSPO • Above 60°N, the bias is small (if any) ACSPO VIIRS at High Latitudes

33. SST Biases – Day ACSPO VIIRS at High Latitudes

34. DAY:NAVOL2 – OSTIA L4 • Below -50°S: NAVO shows a warm bias up to +1K wrt. OSTIA • Above +50°N: Biases are also warmer than in ACSPO ACSPO VIIRS at High Latitudes

35. DAY:NAVOL2 – iQuam Drifters • Warm bias in NAVO wrt. drifters below -50°S is a little larger than in ACSPO • Above +50°N, the bias is small (if any) ACSPO VIIRS at High Latitudes