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Met Office SCM and CRM results
Adrian Lock, Met Office, UK
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Met Office LEM/CRM set-up
• Use 2D “LES” with Dx=50m, Dz=20m in 6.4km domain (top at 8km)
• Started with Dx=100m, Dz=50m in 12.8km 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 +2K for points 6, 11, 12
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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, HadGEM3, instead of the proposed AR5 model HadGEM2
• Test sensitivity to resolution
• L38 (~300m at 1km, as used in HadGEM2)
• L63 (~160m at 1km, as used in HadGEM3)
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S6 profiles after 30 days 5 day mean in SCM (3 hour mean in CRM)
• SCM gives significantly deeper cumulus than CRM (4km cf 2km) but reasonable cloud cover profile and massflux
• SCM gives drier (warmer) BL
Cloud fractionMassfluxHumidity (g/kg)
Ctl+2K
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S6 time seriesUnsmoothed
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S6 time series2 day means
• SCM cloud cover matches CRM, especially at L63
• Too much precipitation in SCM (cumulus too deep)
• No sign of any cloud feedback in SCM or CRM
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S11 profiles after 30 days 5 day mean in SCM (3 hour mean in CRM)
Cloud fractionMassfluxHumidity (g/kg)
Ctl+2K
• SCM again gives deeper BL than CRM
• SCM gives greater cloud cover underneath the inversion
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S11 time seriesUnsmoothed
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S11 time series2 day means
• Cloud cover much higher in SCM than CRM; L38 very noisy
• Too much precipitation again in SCM
• SCM has positive feedback, ~independent of resolution
• No feedback in CRM
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S12 profiles after 30 days 5 day mean in SCM (3 hour mean in CRM)
Cloud fraction
Ctl+2K
• CRM boundary layer very shallow and cloud free
• SCM similar to s11
Humidity (g/kg)
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S12 time series2 day means
• CRM: no cloud, so no feedback
• SCM has positive feedback at L63, negative at L38
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Cloud feedback mechanisms for S11See Mark Webb’s talk
• Lower-tropospheric stability (LTS)
• Theta difference between 3km and surface
• Control LTS = 22.75K
• +2K LTS= 23.8K
• So S11 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
• +2K = (11.25-16.6) / (-16.5) = -5.25/-16.5 = 0.32
• So S11 shows increase in , similar to GCMs
• LES (Lock, 2009) suggest increase implies reduction in cloud cover, at least for Sc over Cu, = positive feedback
tp
tp
tp
e
qcL
qcL
qcL
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Lock (2009): factors influencing cloud area at the inversion for shallow cumulus
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Summary
• Lack of stratocumulus in CRM at s11, s12 is a concern
• I’ll try 3D 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 s12
• Climate change impact on LTS and kappa appears consistent with that seen in GCMs
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Summary
SW feedback
(Wm-2)
S6 S11 S12
CRM 0 0 No cloud
SCM L38 0 10 -70
SCM L63 0 10 70
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Questions?