Low-Latitude Cloud Feedbacks Climate Process Team (CPT)
Overall Goal: Increase our understanding of tropical
and subtropical cloud feedbacks on climate sensitivity, and reduce the large
uncertainty in GCM simulations of these feedbacks
Motivation
Cloud feedbacks on natural climate variations and anthropogenic climate
change continue to be a leading source of uncertainty in climate predictions. In
low latitudes, most clouds are generated by physical processes such as cumulus
convection or boundary-layer eddies which involve turbulent circulations of very
small length scales (meters to a few km) not resolvable by the grid of a typical
numerical model used for global climate prediction, which typically has cells
exceeding 100 km in each horizontal dimension and 20-60 vertical levels. These
processes must be represented in the model as parameterizations which represent
the effects of the small scale motions on heating, moistening, condensed water,
etc. based only on the large-scale variables prognosed by the model, such as
temperature, moisture, and winds. Formulation of parameterizations for
'moist' processes involving clouds has been a long-standing challenge since the
development of global climate models in the 1960s. However, modern satellite and
in-situ observations, coupled with cloud-resolving models that can explicitly
simulate the turbulent circulations that generate most low-latitude clouds over
a domain of limited size, and computers that allow us to globally simulate with
finer and finer numerical mesh sizes, provide hope for making more rapid
progress on moist-process parameterization and on reducing uncertainties in
cloud feedbacks on climate projections.
Specific Tasks
- Diagnose in detail the reasons for different trends of NCAR vs. GFDL
low-latitude cloud distribution with 2xCO2, in which we see low-lying clouds
tending to increase in the NCAR (CCSM) climate model but decrease in the GFDL
model.
- Constrain relevant cloud feedbacks using current and historical data, esp.
the low cloud feedbacks relevant to (1).
- Improve relevant GCM parameterizations using best available physics,
focussing especially on cloud microphysics, shallow and deep cumulus
convection, and cloud-topped PBLs.
For a fuller description of the CPT concept, the three current
CPTs and their goals, see:
- Bretherton,
C. S., R. Ferrari, and S. Legg, 2004: Climate Process Teams: A new
approach to improving climate models. U.S. CLIVAR Variations,
Vol. 2, No. 1, 1-6.
- Bretherton, C. S., 2006:
The Climate Process Team on Low-Latitude Cloud Feedbacks on Climate
Sensitivity. U.S. CLIVAR Variations, Vol. 4, No. 1, 7-12 (Link is to
whole issue, so you can also read about progress of the two ocean CPTs if you
are curious.)
-
Powerpoint highlights of Clouds
CPT given at ARM Spring Meeting, Mar. 2006 (abbreviated version given at CCSM
AMWG, Mar. 2006).
Peer-reviewed publications
-
Bony, S., and coauthors, 2006: How well do we understand climate change
feedback processes? J. Climate, 19, 3445-3482.
Full text copy.
-
Held, I. M.,
M. Chao, and B. Wyman, 2006: Radiative-convective equilibrium with GCM column physics.
J. Atmos Sci., submitted.
-
Kiehl, J. T.,
C. A. Shields, J. J. Hack, and W. D. Collins, 2006: The climate sensitivity of the
Community Climate System Model: CCSM3. J. Climate, 19,
2584-2596.
Full text copy.
-
Lappen, C. L. and D. A. Randall, 2005: Using
idealized coherent structures to parameterize momentum fluxes in a PBL
mass-flux model. J. Atmos Sci., 62, 2829–2846.
Full text copy.
-
Pincus, R. P., R. Hemler, and S. A. Klein, 2006: Using
stochastically-generated subcolumns to represent cloud structure in a
large-scale mode. Mon. Wea. Rev.,
accepted.
-
Wyant, M. C., C. S. Bretherton, J. T. Bacmeister, J. T. Kiehl, I. M. Held, M.
Zhao, S. A. Klein, and B. A. Soden, 2006: A comparison of tropical cloud
properties and responses in GCMs using mid-tropospheric vertical velocity.
Climate Dyn., 27, 261-279.
Full text copy.
-
Wyant, M.
C., M. Khairoutdinov, and C. S. Bretherton, 2006: Climate sensitivity and
cloud response of a GCM with a superparameterization. Geophys. Res. Lett.,
33, L06714, doi:10.1029/2005GL025464.
Full
text copy.
-
Zhang, M., and H. Soon,
2006: Deceleration of the atmospheric Walker circulation
in the last fifty years. Geophys. Res. Lett., 33, L12701,
doi:10.1029/2006GL025942.
Full text copy.
Organization
Lead PI: Christopher S. Bretherton, University of Washington
Participating Modeling Centers (and public CPT web sites):
Center |
Lead PI |
CPT Liaison Scientist |
Other participants |
GFDL |
Isaac Held |
Ming Zhao |
Leo Donner, Brian Soden |
NCAR |
Jeff Kiehl |
Cecile Hannay |
Bill Collins, Phil Rasch, Jim Hack |
GMAO (NASA) |
Julio Bacmeister |
|
Max Suarez |
Core PIs (and public CPT web sites) outside modeling centers and their CPT group members.
CPT PI |
Institution |
Group members |
Task area |
Chris Bretherton |
U. Washington |
Matt Wyant |
PBL, cumulus parameterization; GCM cloud diagnostics |
Marat Khairoutdinov |
Colo. St. U. |
|
'Superparameterization' and CRM simulations |
Cara-lyn Lappen |
Colo. St. U. |
|
Unified turbulence/cumulus param.; SCAM in GCSS |
Brian Mapes |
U. Miami |
|
Deep convective cloud diagnosis/parameterization. |
Joel Norris |
Scripps |
|
Use of historical cloud observations |
Robert Pincus |
NOAA/CDC |
Crispian Batstone |
Subgrid microphysical/radiative modeling |
Bjorn Stevens |
UCLA |
Brian Meideiros |
Idealized planets and bulk modeling of cloud-topped PBL |
Kuan-Man Xu |
NASA |
Takmeng Wong |
New CERES satellite products |
Minghua Zhang |
Stony Brook U. |
|
GCM cloud/convection diagnosis and validation |
Advisory panel
- CPT workshops:
-
- Introductory all-hands meeting. 20-21 November 2003, NCAR
- 7 July 2004 mini-meeting, Santa Fe CCSM:
- All-hands Meeting II. 21-22 October 2004, Seattle
- Agenda
(including CPT password-protected links to presentations).
All-hands Meeting III. 29-30 November 2005, GFDL
- Agenda
(including CPT password-protected links to presentations).
- Selected background
readings on cloud feedbacks
- Column lat/lons for
special study.
- Internal CPT web page (password required)
Chris Bretherton <breth@atmos.washington.edu>