CAM-UW update

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CAM-UW update
Christopher S. Bretherton and Sungsu Park
Dept. of Atmospheric Sciences, Univ. of
Washington, Seattle
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Compare CAM-UW (UW moist turbShCu, fv2x2.5, L30)
CAM-UW-nodeep (as above but no
ZM) (5yr) with CAM3-fv (2x2.5L26). These
runs are with CAM3.1, but we have now migrated
CAM-UW to CAM3_3_45 development branch with
little apparent change in climo.
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CAM3-fv
CAM-UW
CAM-UW-nodeep
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ERA40
CAM3
CAM-UW
SE Pacific cross-section SON climo No
stratofogulus in CAM3-UW
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CAM3-fv
CAM-UW
CAM-UW-nodeep
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CAM3-fv
CAM3-UW
CAM3-UW-nodeep
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CAM3-fv
CAM-UW
CAM-UW-nodeep
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DJF low cloud
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DJF SAT and surface LWCF
CAM3-fv
CAM-UW
CAM-UW-nodeep
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RMS error table (all gridpoints, 4 seasons)

• Field Data RMSE ratio vs. CAM3.0
• 3.3.45fvctrl S026 S027
• Sea Level Pressure ERA40 1.01 1.33 1.08
• Ocean Surface Stress ERS 0.96 1.02 0.83
• Surf. Air Temp (land) L-W 1.11 1.14 1.14
• Rainfall Xie-Arkin 1.12 1.09 1.04
• Trop. Land Rainfall Xie-Arkin 1.06 1.02 1.12
• Net LW (TOA) CERES 1.19 1.20 1.00
• Net SW (TOA) CERES 1.06 0.99 0.98
• U (300 hPa) ERA40 0.93 1.15 0.85
• T (lat-p xsect) ERA40 0.93 0.96 0.98
• RH (lat-p xsect) ERA40 0.84 0.89 1.02
• Climate Bias Index 1.02 1.08 1.00

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Synthesis so far

• CAM-UW bias patterns are very similar to CAM3
  overall, except for accentuated biases of SLP and
  jets.
• Biases in boundary layer SWCF in trade Cu regimes
  are highly correlated with precipitation biases.
• Removing ZM deep convection by using only the UW
  shallow Cu scheme for all convection has larger
  impact on tropical biases, improves SLP, wind
  stress and overall skill, though not as much as
  switching to the two new candidate deep
  convection schemes.
• Excessive high latitude winter low cloud/SAT in
  CAM3, even worse in CAM3-UW (but see Sungsus
  talk tomorrow!), not affected by deep convection
  scheme.

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SCAM GEWEX intercomparison results

• At UW and with C. Lappen of CSU, we have
  initiated SCAM3/SCAM-UW participation in
  international boundary-layer SCM/LES
  intercomparison studies.
• Here, we discuss interesting insights from
• GABLS-1 idealized stable boundary layer case
• How might PBL contribute to hi-lat cloud/TS
  biases?
• RICO precipitating shallow Cu (latest GCSS case)
• Exposes issues with cloud fraction, LWP, precip.

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GEWEX Atmospheric Boundary Layer Study (GABLS)

• Case 1 Idealized stable boundary layer (Beare et
  al, Cuxart et al 2006)
• - Stratified initial sounding, no moisture
• - Surface cooling of 0.25K/hr for 9 hrs
• - 8 m/s geostrophic wind, 1 cm surface roughness
• - Good consensus among LES simulations with Dz
  2 m.
• - Requires several mods to SCAM to set up.
• High res 10 m vertical resolution
• Low res L30 as used in CAM-UW, grid levels at
  60, 180, m,
• CAM3 K-profile diagnosed PBL depth, no Ri
  cutoff.
• CAM-UW K(Ri) from Galperin (1988) in stable PBL,
  cuts off if Rigt0.19
• Goals Compare HR, LR PBL depth, surface downward
  heat flux.

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9 hour q time-heights
Hi-res results CAM3 deeper PBL CAMUW
shallower PBL
8-9 hr mean
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Surface sensible heat flux parameterization
resolution

• Downward heat flux larger in CAM3 than in LES,
  CAM-UW.
• Only slight change for both params at L30 vs.
  hi-res, even though there is only one grid layer
  within the CAMUW PBL!
• Both params work respectably for this stable PBL
  case.

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GCSS-BLCWG RICO shallow cu intercomparison

• VanZanten, Siebesma et al. ongoing.
• Deep, weakly capped trade Cu with some showers
• Based on composite conditions for 16 Dec. 2004-5
  Jan. 2005
• Metrics
• - Radar rain rate 1 mm/d.
• - T, q profiles should be quasisteady given
  forcings.
• - LES simulations.
• SCAM results have ZM turned off to avoid spurious
  deep convection.

B. Stevens photo
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SCAM RICO results
34-36 hour profiles

• CAM3 develops spurious inversion because Cu goes
  too deep.
• CAM3 and CAM-UW both have reasonable mean
  rainfall rates

LES
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Cumulus profiles
LES
Condensate from ShCu scheme

• CAM3 shallow Cu fraction too large and top-heavy,
  with excess LWP and numerical oscillations.
• CAMUW better overall.
• LES shows rainfall highest at 2 km, not Cu base
  (life cycle).

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Summary

• The UW moist turbulence and shallow Cu schemes
  have a modest effect on CAM climatology, despite
  improving single-column performance in GCSS
  cases.
• Interactions with stratiform cloud and deep
  convection parameterizations have big impacts on
  PBL biases.
• Both current CAM and CAM-UW do a respectable job
  on the GABLS dry stable PBL case even at L30
  resolution, bracketing the LES truth.
• Tomorrow Sungsu will show you a disturbing but
  legitimate way to reduce Arctic low cloud/TS in
  CAM that dwarfs effects of changing PBL scheme.

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A curiosity - Leads and SHF through sea ice

• CAM includes a geographically and seasonally
  varying climatological open water fraction in
  sea-ice regions.
• Although small, this often produces upward
  sensible heat flux even in the highly stable
  winter PBL over the Arctic Ocean, making
  diagnosis of PBL type ambiguous, and has a 5-10 W
  m-2 effect in surface energy budget.