Performance of Arctic Cloud Products in the CLARA-A2 AVHRR Dataset from CMSAF

Performance of Arctic cloud products in the CLARA-A2 AVHRR dataset from CMSAF

Karl-Göran Karlsson SMHI, Norrköping

Presentation at APVE II workshop, 27-28 October 2015, Norrköping 1 EUMETSAT CMSAF project

Consortium: 6 partners

• Deutscher Wetterdienst (DWD), Germany (Leading entity) • Swedish Meteorological and Hydrological Institute (SMHI), Sweden • Koninklijk Nederlands Meteorologisch Instituut (KNMI), The Netherlands • Meteorological Office, United Kingdom • Finish Meteorological Institute, Finland • Federal Office of Meteorology and Climatology (MeteoSwiss), Switzerland • Royal Meteoroligical Institute, Belgium

More info at: www.cmsaf.eu 2 AVHRR climatologies from 30+ years

CLARA – CMSAF’s cloud, surface albedo and radiation dataset: New version (CLARA-A2) covering 1982-2014 in production

NOAA-19 since February 2009

Metop-A since July 2007

Metop-B since October 2012

Basic cloud products from NWC SAF PPS cloud software (Dybbroe et al., 2005, Karlsson et al., 2013) Courtesy of Andrew Heidinger, NOAA 3 CLARA-A2 Arctic mean cloudiness

Achieved sample results for Januari 2008: Consistent results for all satellites!

NOAA-15 NOAA-16 NOAA-17

NOAA-18 METOP-A

4 Upgraded results in the Arctic

Example for January 2008:

CLARA-A1 CLARA-A2 CALIPSO

(Plot from Stefan Stapelberg, DWD) The amount of false clouds have been reduced which leads to very low cloud amounts (reflecting that many Arctic clouds are not detectable using AVHRR during the polar night!)

5 Extensive validation from CALIPSO

Recent extended validation effort based on CALIPSO-CALIOP cloud masks. Simultaneous (within 3 minutes) observation of the same spot on Earth.

For CLARA-A1 we compared to 99 closely matched NOAA-18 orbits 2006-2009. For CLARA-A2 we have now compared to more than 10000 orbits 2006-2014 for all available satellites (NOAA-17, NOAA-18, NOAA-19, METOP-A, METOP-B).

Results for NOAA-18 (with channel 3b at 3.7 micron) and METOP-A (with channel 3a at 1.6 micron) will be shown here for the Polar (Arctic+Antarctic) area. 6 CLARA-A2 cloud mask performance over the Arctic and Antarctic regions (above 75°) for NOAA-18 and METOP-A 2006-2014 – POLAR DAY NOAA-18 (3.7 µm) METOP-A (1.6 µm) Difference

Number of orbits 2 753 2 366 +387

Matched FOVs 673 651 149 017 + 524 634 Mean error cloud -7.9 % -10.2 % + 2.3 % amount (bias)

POD cloudy 79.2 % 78.5 % +0.7 % POD clear 83.1 % 84.7 % -1.6 % FAR cloudy 10.0 % 7.9 % +2.1 % FAR clear 32.6 % 36.5 % - 3.9 % Kuipers score 0.62 0.63 -0.01 Hit Rate 80.5 % 80.4 % +0.1 % CLARA-A2 cloud mask performance over the Arctic and Antarctic regions (above 75°) for NOAA-18 and METOP-A 2006-2014 – POLAR NIGHT

NOAA-18 (3.7 µm) METOP-A (3.7 µm) Difference

Number of orbits 2 753 2 366 +387

Matched FOVs 843 538 214 013 + 629 525 Mean error cloud -37.4 % -34.7 % - 2.7 % amount (bias)

POD cloudy 43.3 % 45.7 % -2.4 % POD clear 94.2 % 92.2 % +2.0 % FAR cloudy 5.7 % 7.3 % -1.6 % FAR clear 57.5 % 56.2 % + 1.3 % Kuipers score 0.37 0.38 - 0.01 Hit Rate 59.0 % 60.3 % -1.3 % Conclusions

• Cloudmasks from the CMSAF CLARA-A2 dataset have been matched with more than 10000 CALIPSO orbits and with observations made within 3 minutes from corresponding AVHRR observations in the period 2006-2014.

• Over the Polar area results from AVHRRs with channel 3b (NOAA-18) and channel 3a (METOP-A) have been inter-compared for more than 5000 orbits.

• Results during Polar day are as good as over non-Polar areas (e.g. bias ≈ -10 %, hitrate ≈ 80 %) for both AVHRR configurations

• Results during Polar night are significantly worse (e.g. bias ≈ -35 %, hitrate ≈ 60 %)

• Same exercise will now be repeated for corresponding results from the ESA-CLOUD-CCI project including also validation of cloud top height and cloud phase (ice or water). 9 Transition from cloud masks to probabilities

Demonstration case of derived AVHRR cloud probabilities

Part of an AVHRR GAC orbit from NOAA-17 over Greenland on 4th of June 2009.

Left: Colour composite (RGB) with two visual and one thermal channels (AVHRR channels 1,2 and 4).

Right: Corresponding cloud analysis expressed in probabilities of a cloudy pixel in greyshades (where black-to- white displays the range 0-100 % cloud probability).

(Karlsson and Johansson, Rem. Sens.of Env., 2015)