CAM6/CESM2 development simulations Cécile Hannay, Rich Neale, Pete Bogenschutz, Julio Bacmeister, Andrew Gettelman, and Joe Tribbia

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1 CAM6/CESM2 development simulations Cécile Hannay, Rich Neale, Pete Bogenschutz, Julio Bacmeister, Andrew Gettelman, and Joe Tribbia Thanks to: David Bailey, Cheryl Craig, Gokhan Danabasoglu, Brian Eaton, Jim Edwards, Marika Holland, Jean-Francois Lamarque, David Lawrence, Keith Lindsay, Keith Oleson, Bill Sacks, John Truesdale, Mariana Vertenstein, and gazillions of others.

2 At a glance CESM 2: Development simulations Huge team effort started in Mid November co-chair meetings/week Feb 2016: Mini Breck 34 experiments ( cases ) years of simulations + diagnostics June 2016: Breckenridge workshop 94 experiments ( cases ) years of simulations + diagnostics 271 T And also Many standalone simulations in individual working groups

3 AMWG homework Following mini-breck, we identified biases to be targeted Taylor score lower than in LENS Cold SSTs => Adjust tuning to reduce SWCF Underestimated Amazon precipitation => ZM changes Insufficient Tropical Sub-Seasonal Variability => ZM changes Weak Surface winds => Beljaars and ridge scheme (TMS off) Strong indirect effects => New autoconversion Excessive humidity (RHliq > 105%) => Fix in CLUBB Poor polar stratospheric clouds => New ice microphysics How did we do on our homework?

4 CESM 2: Development simulations In this talk, we will compare: LENS: Large Ensemble CESM1.5: Mini Breck - Feb 206 (This is 28 or 36) CESM2.0 - : Now June 2016 (This is 79). Are you lost in translation?

5 Taylor Diagram LENS Now Mini-Breck Significant improvement in Taylor score since mini-breck Current simulation is better than LENS

6 Sea Surface Temperature (SST) bias (ANN) LENS Bias = -0.24K RMSE = 0.91 Mini-Breck Bias = -0.62K RMSE = 1.12 Now Bias = -0.58K RMSE = 1.19

7 Sea Surface Temperature (SST) bias (ANN) LENS Bias = -0.24K RMSE = 0.91 Mini Breck Bias = -0.62K RMSE = 1.12 Now Bias = -0.58K RMSE = 1.19 Not much improvement in SST bias. Cold bias in Labrador sea (covered by sea-ice).

8 LENS (yrs ) Sea ice thickness (ANN) Mini-Breck (yrs 75-99) Now (yrs 72-91) Sea-ice thicker over Central Arctic Ice-covered Labrador sea

9 Sea ice thickness in Labrador sea New atm+ocn+lnd (79) Now Cause for changes still uncertain, but appears related to coupling of new ocean and new atmosphere New atm+ocn (66) New atm + ocn (64) New atm only (63) New ocn Only (MP3) Run from Feb (36) Courtesy Marika Holland Mini-Breck

10 Precipitation bias versus GPCP (ANN) LENS Bias = 0.37 RMSE = 1.13 (mm/day) Mini-Breck Bias = 0.19 RMSE = 1.12 (mm/day) Now Bias = 0.19 RMSE = 0.91 (mm/day)

11 Precipitation bias versus GPCP (ANN) LENS Bias = 0.37 RMSE = 1.13 (mm/day) Mini-Breck Bias = 0.19 RMSE = 1.12 (mm/day) Now Bias = 0.19 RMSE = 0.91 (mm/day) Improved precip bias Better precip over Amazon

12 Improvement in land precipitation Color code Green means better Red means worse Between Mini Breck and Now: 20% reduction in RMSE Courtesy Dave Lawrence

13 Equatorial Waves (rainfall) Wavenumber frequency decomposition of precipitation (10S-10N), annual mean Obs Now Kelvin Improved Kelvin waves MJO LENS Mini-breck Lack of Kelvin waves Courtesy Rich Neale

14 Sea-level pressure versus MERRA (ANN) LENS Bias = 0.29 RMSE = 1.61 (mbar) Mini Breck Bias = 0.09 RMSE = 3.02 (mbar) Now Bias = 0.28 RMSE = 1.76 (mbar)

15 Sea-level pressure versus MERRA (ANN) LENS Bias = 0.29 RMSE = 1.61 (mbar) Mini-Breck Bias = 0.09 RMSE = 3.02 (mbar) Now Bias = 0.28 RMSE = 1.76 (mbar) Improved SLP in Southern Ocean

16 Change in surface winds (ANN) Weak surface winds in LENS and in mini-breck simulation New beljaars/ridge scheme increase surface winds Increase of the surface winds between mini-breck and Now

17 Greenland and Antartica surface winds Mini-Breck Now Obs Greenland Antarctica Courtesy Lenaerts/Lipscomb

18 Aerosol effect Direct (W/m2) Indirect (W/m2) IPCC values -0.5 [-0.9 to -0.1] -0.7 [-1.8 to -0.3] LENS Mini Breck Now Mini-Breck: indirect effect too strong Now: New autoconversion reduced it 20 th Century warming Mini-Breck: not enough warming over 20 th C Now: No 20 th century simulation yet Expecting impact of reducing indirect effect

19 How did we do on our homework? Following mini-breck, we identified biases to be targeted Taylor score lower than in LENS => Improved Cold SSTs => Not improved (degraded Labrador sea) Underestimated Amazon precipitation => Improved Insufficient Tropical Sub-Seasonal Variability => Improved Weak Surface winds => Improved Strong indirect effects => Improved Excessive humidity (RHliq > 105%) in CLUBB => Improved Poor representation of polar stratospheric clouds => Improved Remaining issues in current simulations Ice too thick over central Arctic and ice-covered labrador sea

20 This has been 8 months of intense work We had good days We had bad days We always find the cause of the problem