Canadian contribution to the Year of Polar Prediction: deterministic and ensemble coupled atmosphere-ice-ocean forecasts

Transcription

1 Canadian contribution to the Year of Polar Prediction: deterministic and ensemble coupled atmosphere-ice-ocean forecasts G.C. Smith, F. Roy, J.-F. Lemieux, F. Dupont, J-M Belanger and the CONCEPTS team GEM Environment and Climate Change Canada, Dorval, Québec, Canada NEMO CICE

2 ECCC polar forecasts for YOPP Coupled CAPS-RIOPS Arctic/N.Atl., fully-coupled A-I-O, 3km(A)-3-8km(IO), 2day GDPS-GIOPS Global, fully-coupled A-I-O, 15km(A)-1/4deg(IO), 10day GIOPS Ensembles Global, 1/4deg, 32 day, 20 member Seasonal Predictions (CanSIPS) CanCM3/4 & GEM-NEMO-CICE CICE : Global, 1deg, 10 members Page 2 November-8-17

3 Global Ice-Ocean Prediction System (GIOPS) Produces daily ice-ocean analyses and 10day coupled A-I-O forecasts (2/day) NEMO-CICE (~1/4 ), < 15km in Arctic Mercator Ocean Assimilation System (SAM2): Sea surface temperature Temperature and salinity profiles Sea level anomaly from satellite altimeters 3DVar Ice analysis: SSM/I, SSM/IS, CIS charts, Radarsat image analyses ASCAT, AVHRR, AMSR2 coming this fall Purpose: Boundary conditions for regional systems Initialize seasonal forecasts Emergency response Global coupled forecasting Smith et al., QJRMS, 2015

4 Blending with 3DVAR ice analyses Impact on ice thicknesses Smith et al., QJRMS, 2015 Require multicategory blending for CICE Method 1: Rescale distribution (RED) Method 2: Rescale Fcst Tendency (RFT) Use of RFT results in a smaller impact on total ice volume Thought experiment (excessive melt) Total conc. Initial: 100% Trial: 50% Analysis: 100% RED: 100% RFT: 100% 0.00 thin thick

5 GODAE Oceanview Class4 realtime sea ice intercomparison 4 -day forecasts RMS error Mean ice concentration Common set of obs shared in real-time Groups calculate model equivalents for all lead times Use AMSR2 with NasaTeam2 retrieval Quality control applied to observations to reject obs affected by surface melt SST>4 C or Tair>0 C Participating Groups Mercator (PSY4) UK Metoffice (FOAM) Env Canada (GIOPS) NERSC (new addition! Not shown) Page 5 November-8-17 Courtesy Andy Ryan, UK Metoffice

6 GODAE Oceanview Class 4 Sea ice concentration (AMSR-2) intercomparison 5 day lead Scores calculated using contingency table metrics: Proportion correct total: PCT=(a+d)/n Proportion correct Ice: PCI=a/(a+c) Proportion correct Water: PCW=d/(b+d) Range [0,1]; 1 is perfect score Timeseries of sea ice intercomparison growing, available for external use as part of YOPP NERSC is now contributing Other groups have expressed interest in joining GOFS, DMI, Data to be distributed through YOPP Data Portal: Yopp.met.no Page 6 November-8-17 PCI PCT Conc > 0.25 Forecast Ice Forecast Water Northern Hemisphere 2017 AMSR2 Ice Hit ice (a) Miss (c) AMSR2 Water False Alarm (b) Hit water (d) PCW RMSE Courtesy: Jinshan Xu, DFO

7 Global Coupled Medium-range Deterministic Forecasts Coupled NWP system running in operations at CCMEP since July 2016 (Operational Nov. 1st, 2017!). GDPS coupled to GIOPS Global, fully-coupled A-I-O, 25 km(a)-1/4deg(io), 10 day forecast (2/day) Horizontal resolution increase of atmosphere to 15 km in 2018 Available on GeoMet and RPNWMS: E.g. MSC datamart dd.weather.gc.ca Atm: GRIB2, GEM NEMO CICE Ocean/Ice: Netcdf4 Page 7 November-8-17 Smith et al., MWR, 2018

8 Impact of a dynamic ice cover on coupled forecasts over the Beaufort Sea Sea level pressure 1035 mb 965 mb (CPL-UNCPL) Page 8 Forecast from global coupled model (GEM-NEMO-CICE; 33km-15km resolution) R. Muncaster, F. Roy, J.-M. Belanger

9 Impact of a dynamic ice cover on coupled forecasts over the Beaufort Sea Coastal polynya formation sensitive to: Atmosphere-ice and ice-ocean stresses, ice thicknesses, landfast ice parameterization, uncertainty in atmospheric forecasts Sea level pressure 1035 mb 965 mb Difference in ice fraction (CPL-UNCPL) Difference in 2m temperature Page 9 Forecast from global coupled model (GEM-NEMO-CICE; 33km-15km resolution) R. Muncaster, F. Roy, J.-M. Belanger

10 32 day Ensemble GIOPS Forecasts (EnsGIOPS) Running in real-time (every Thursday) since June 2016 forced by GEPS Forced by Global Ensemble Prediction System (50km) EnKF Atmospheric analysis, daily 15d forecasts, 32d forecast 1/week Persistence anomaly for SST with diagnostically adjusted sea ice cover 21 members with perturbed analyses and different model physics Finalizing development of Coupled GEPS-GIOPS system No perturbations to GIOPS analyses or forecasts yet 21 day forecast Canadian Ice Service Regional Analysis Page 10

11 How do ensemble forecasts forced by GEPS (50km) compare to GIOPS forecasts forced by GDPS (25km)? Example 10 day forecast issued as compared to GIOPS ice analyses Similar errors Page 11 GIOPS errors slightly larger?

12 Verification against IMS analyses IMS Ice IMS Water 10-day forecasts over full Arctic domain from Aug to Sep 2017 Forecast Ice Forecast Water Hit ice Miss False Alarm Hit water Proportion Correct Total Proportion Correct Ice Proportion Correct Water Ensembles provide slight improvement Gain related to increase in ice cover Ensemble mean GIOPS Page 12 *14-day filter applied to PCT timeseries

13 Canadian Arctic Prediction System (CAPS) An ECCC contribution for YOPP High-resolution coupled atmosphere-ice-ocean prediction system In support of : Weather prediction for northern Canada EC METAREAs Services Marine emergency response Coupled atmosphere-ice-ocean model GEM (3.0 km) Improved microphysics NEMO-CICE (3-8 km) Tides, landfast ice Improved ice-ocean assim 48 h forecasts (2/day) Available at: GEM 3.0 km RIOPS

14 Pan-Arctic Coupled Atmosphere-Ice-Ocean Canadian Arctic Prediction System (CAPS) Forecasts A contribution to the Year of Polar Prediction ( ) Accepted for experimental implementation Nested within 25km global coupled NWP system Two-way exchange of fluxes at every timestep Captures small-scale features CAPS Flow through fjords Impact of leads in seariops ice GEM Sfc Air Temperature and winds NEMO CICE 3.0 km Smith et al., MWR, 2018 Sfc Air Temperature Sea ice concentration

15 Impact of atmospheric resolution on winds Difference between daily 2.5km and 15km 48hr forecasts for August 2012 Page 15 November-8-17 Chris Subich

16 Future work Coming this year Coupling with 3km atmospheric model RIOPS Ocean data assimilation system Coupled GEPS-GIOPS monthly ensemble forecasting system (including 20- yr reforecasts) Challenges How to generate perturbations in ice analyses and forecasts to adequately sample uncertainty (stochastic physics vs differing parameterizations) Assessment of sources of error (model physics vs atmospheric uncertainty?) Treatment of biases (exaggerated melt)

17 Adapting to user needs. Did anyone check the sea ice forecast this morning? M km 2! Courtesy Corinne Bourgault-Brunelle