Transcript CAM-UW update Christopher S. Bretherton and Sungsu Park Dept. of Atmospheric Sciences, Univ.

CAM-UW update
Christopher S. Bretherton and Sungsu Park
Dept. of Atmospheric Sciences, Univ. of Washington, Seattle
Compare CAM-UW (UW moist turb+ShCu, 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.
RESTOA
LWCF
27.1
SWCF
49.2
CAM3-fv
-0.2
30.6
-55.1
CAM-UW (S026)
-0.3
31.2
-57.1
Nodeep (S027)
3.0
34.2
-56.5
CERES
CAM3-fv
CAM-UW
CAM-UW-nodeep
ERA40
SE Pacific
cross-section
SON climo
No
stratofogulus in
CAM3-UW
CAM3
CAM-UW
CAM3-fv
CAM-UW
CAM-UW-nodeep
CAM3-fv
CAM3-UW
CAM3-UW-nodeep
CAM3-fv
CAM-UW
CAM-UW-nodeep
DJF low cloud
DJF SAT and surface LWCF
CAM3-fv
CAM-UW
CAM-UW-nodeep
RMS error table (all gridpoints, 4 seasons)
Field
Data
Sea Level Pressure
Ocean Surface Stress
Surf. Air Temp (land)
Rainfall
Trop. Land Rainfall
Net LW (TOA)
Net SW (TOA)
U (300 hPa)
T (lat-p xsect)
RH (lat-p xsect)
Climate Bias Index
ERA40
ERS
L-W
Xie-Arkin
Xie-Arkin
CERES
CERES
ERA40
ERA40
ERA40
RMSE ratio vs. CAM3.0
3.3.45fvctrl S026 S027
1.01
1.33
1.08
0.96
1.02
0.83
1.11
1.14
1.14
1.12
1.09
1.04
1.06
1.02
1.12
1.19
1.20
1.00
1.06
0.99
0.98
0.93
1.15
0.85
0.93
0.96
0.98
0.84
0.89
1.02
1.02
1.08
1.00
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 Sungsu’s talk
tomorrow!), not affected by deep convection scheme.
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.
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 Ri>0.19
Goals: Compare HR, LR PBL depth, surface downward heat flux.
Hi-res results
CAM3 – deeper PBL
CAMUW – shallower PBL
8-9 hr mean
9 hour q time-heights
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.
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
SCAM RICO results
• CAM3 –develops
spurious inversion
because Cu goes
too deep.
• CAM3 and CAMUW both have
reasonable mean
rainfall rates
34-36 hour profiles
LES
Cumulus profiles
LES
• CAM3 shallow
Cu fraction too
large and topheavy, with
excess LWP and
numerical
oscillations.
• CAMUW better
overall.
• LES shows
rainfall highest at
2 km, not Cu
base (life cycle).
Condensate
from ShCu
scheme
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.
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.