VIIRS SST at High Latitudes

Sasha Ignatov, Prasanjit Dash, Bruce Brasnett

NOAA; CIRA; CMC

3 June 2014 ACSPO VIIRS at High Latitudes 1

15th GHRSST Science Team Meeting 2-6 June 2014, Cape Town, South Africa

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

Background

3 June 2014 2ACSPO VIIRS at High Latitudes

VIIRS & in situ drifters coverage – Night

3 June 2014 3ACSPO VIIRS at High Latitudes

ACSPO VIIRS at High Latitudes 4

NIGHT: ACSPO L2 – OSTIA L4

3 June 2014

• ACSPO does not truncate by LAT• Retrievals available up to ±80° +

ACSPO VIIRS at High Latitudes 5

NIGHT: ACSPO L2 – iQuam Drifters

3 June 2014

• These areas either lack or have very sparse coverage by in situ data

VIIRS and in situ drifters coverage – Day

3 June 2014 6ACSPO VIIRS at High Latitudes

ACSPO VIIRS at High Latitudes 7

DAY: ACSPO L2 – OSTIA L4

3 June 2014

• ACSPO does not truncate by LAT• Retrievals available up to ±80° +

ACSPO VIIRS at High Latitudes 8

DAY: ACSPO L2 – iQuam Drifters

3 June 2014

• These areas either lack or have very sparse coverage by in situ data

ACSPO VIIRS at High Latitudes 93 June 2014

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 103 June 2014

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

SST Biases – Night

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ACSPO VIIRS at High Latitudes 12

NIGHT: ACSPO L2 – OSTIA L4

3 June 2014

• 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: ACSPO L2 – iQuam Drifters

3 June 2014

• Biases below 60°S not easy to verify• Above 60°N, there is actually a coldish bias

SST Biases – Day

3 June 2014 14ACSPO VIIRS at High Latitudes

ACSPO VIIRS at High Latitudes 15

DAY: ACSPO L2 – OSTIA L4

3 June 2014

• 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: ACSPO L2 – iQuam Drifters

3 June 2014

• Biases below 60°S not easy to verify• Above 60°N, there is actually a coldish bias

Some Early Results Assimilating ACSPO VIIRS L2P Datasets

Bruce BrasnettCanadian Meteorological CentreMay, 2014

Assessing relative value of 2 VIIRS datasets: NAVO vs. ACSPO

Using ACSPO instead of NAVO improves assimilation3 June 2014 18ACSPO VIIRS at High Latitudes

Warm Bias above 60°N

SOUTHNORTH

Assessing the relative value of 3 datasets for January-March 2014

Using ACSPO improves STD in all LAT bands, except at 10°S3 June 2014 19ACSPO VIIRS at High Latitudes

Warm Bias above 60°N

SOUTHNORTH

Assessing potential benefit of adding VIIRS to CMC analysis

ACSPO improves assimilation in all LAT bands, except hi-lat North (high bias)3 June 2014 20ACSPO VIIRS at High Latitudes

Warm Bias above 60°N

SOUTHNORTH

Summer Sample: Aug. 15- Sept. 9, 2013. VIIRS vs. NAVO AVHRR GAC

ACSPO VIIRS assimilation comparable to NAVO AVHRR, except at hi-lat3 June 2014 21ACSPO VIIRS at High Latitudes

Warm Bias above 60°N

Warm Bias below 60°S?

SOUTHNORTH

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 SST at HL - Observations

3 June 2014 22ACSPO VIIRS at High Latitudes

Back Up Slides

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NAVO SST

VIIRS & in situ drifters coverage – Night

3 June 2014 24ACSPO VIIRS at High Latitudes

ACSPO VIIRS at High Latitudes 25

NIGHT: NAVO L2 – OSTIA L4

3 June 2014

• 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: NAVO L2 – iQuam Drifters

3 June 2014

• NAVO product is more consistent with in situ domain

• Yet, evaluation at HL remains challenging

VIIRS and in situ drifters coverage – Day

3 June 2014 27ACSPO VIIRS at High Latitudes

ACSPO VIIRS at High Latitudes 28

DAY: NAVO L2 – OSTIA L4

3 June 2014

• 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: NAVO L2 – iQuam Drifters

3 June 2014

• NAVO product is better covered by in situ data at HL due to more limited domain

• Nevertheless, evaluation of satellite SST is challenging

SST Biases – Night

3 June 2014 30ACSPO VIIRS at High Latitudes

ACSPO VIIRS at High Latitudes 31

NIGHT: NAVO L2 – OSTIA L4

3 June 2014

• 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: NAVO L2 – iQuam Drifters

3 June 2014

• 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)

SST Biases – Day

3 June 2014 33ACSPO VIIRS at High Latitudes

ACSPO VIIRS at High Latitudes 34

DAY: NAVO L2 – OSTIA L4

3 June 2014

• 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: NAVO L2 – iQuam Drifters

3 June 2014

• 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)