Met Office SCM and CRM results Adrian Lock

Met Office SCM and CRM results Adrian Lock, Met Office, UK © Crown copyright Met Office

Met Office LEM/CRM set-up • Use 2 D “LES” with Dx=50 m, Dz=20 m in 6. 4 km domain (top at 8 km) • Started with Dx=100 m, Dz=50 m in 12. 8 km domain and higher resolution very similar • Otherwise LEM set-up as for GCSS-RICO • Run for 30 days (takes ~1 day to run) • Run Control and +2 K for points 6, 11, 12 © Crown copyright Met Office

Met Office SCM set-up • Run parallel simulations in the Met Office SCM • based on runs by Charmaine Franklin at CSIRO • Run for 100 days • Confession: • I’ve used the development version of the climate model, Had. GEM 3, instead of the proposed AR 5 model Had. GEM 2 • Test sensitivity to resolution • L 38 (~300 m at 1 km, as used in Had. GEM 2) • L 63 (~160 m at 1 km, as used in Had. GEM 3) © Crown copyright Met Office

S 6 profiles after 30 days 5 day mean in SCM (3 hour mean in CRM) Ctl +2 K Humidity (g/kg) Massflux Cloud fraction • SCM gives significantly deeper cumulus than CRM (4 km cf 2 km) but reasonable cloud cover profile and massflux • SCM gives drier (warmer) BL © Crown copyright Met Office

S 6 time series Unsmoothed © Crown copyright Met Office

S 6 time series 2 day means • SCM cloud cover matches CRM, especially at L 63 • Too much precipitation in SCM (cumulus too deep) • No sign of any cloud feedback in SCM or CRM © Crown copyright Met Office

S 11 profiles after 30 days 5 day mean in SCM (3 hour mean in CRM) Ctl +2 K Humidity (g/kg) Massflux Cloud fraction • SCM again gives deeper BL than CRM • SCM gives greater cloud cover underneath the inversion © Crown copyright Met Office

S 11 time series Unsmoothed © Crown copyright Met Office

S 11 time series 2 day means • Cloud cover much higher in SCM than CRM; L 38 very noisy • Too much precipitation again in SCM • SCM has positive feedback, ~independent of resolution • No feedback in CRM © Crown copyright Met Office

S 12 profiles after 30 days 5 day mean in SCM (3 hour mean in CRM) Ctl +2 K Humidity (g/kg) Cloud fraction • CRM boundary layer very shallow and cloud free • SCM similar to s 11 © Crown copyright Met Office

S 12 time series 2 day means • CRM: no cloud, so no feedback • SCM has positive feedback at L 63, negative at L 38 © Crown copyright Met Office

Cloud feedback mechanisms for S 11 See Mark Webb’s talk • Lower-tropospheric stability (LTS) • Theta difference between 3 km and surface • Control LTS = 22. 75 K • +2 K LTS= 23. 8 K • So S 11 shows increase in LTS, similar to GCMs • Does LTS implies increase in cloud = negative feedback? • CTEI parameter, based on inversion jumps: • Control = (11. 0 -15. 0) / (-15. 0) = - 4. 0 /-15. 0 = 0. 27 • +2 K = (11. 25 -16. 6) / (-16. 5) = -5. 25/-16. 5 = 0. 32 • So S 11 shows increase in , similar to GCMs • LES (Lock, 2009) suggest increase implies reduction in cloud cover, at least for Sc over Cu, = positive feedback © Crown copyright Met Office

Lock (2009): factors influencing cloud area at the inversion for shallow cumulus © Crown copyright Met Office

Summary • Lack of stratocumulus in CRM at s 11, s 12 is a concern • I’ll try 3 D on our new supercomputer when I get back • SCM has a tendency to give deeper boundary layers than the CRM • SCM reasonably resolution independent, except for s 12 • Climate change impact on LTS and kappa appears consistent with that seen in GCMs © Crown copyright Met Office

Summary SW feedback S 6 S 11 S 12 CRM 0 0 No cloud SCM L 38 0 10 -70 SCM L 63 0 10 70 (Wm-2) © Crown copyright Met Office

Questions? © Crown copyright Met Office