Transcript VOCALS Update (Bretherton)

VOCALS Update
Chris Bretherton, Univ. of Washington
VOCALS THEME
To better understand and simulate how
marine boundary layer cloud systems
surrounding the Americas interact with the
coupled ocean-atmosphere-land system on
diurnal to interannual timescales.
VOCALS in CLIVAR
• Bob Weller will assume VOCALS leadership at this
meeting.
• VPM7 VOCALS participants:
US (Bretherton, Fairall, Mechoso, Weller)
Chile (Garreaud, Ruttland, Pizarro)
Uruguay (Terra – stranded in Uruguay)
Ecuador (Cornejo)
• VOCALS observational program overview
• VOCALS science advancing understanding/GCM
simulation of boundary layer clouds in the coupled
climate system.
• VOCALS radiator experiment
VOCALS Scientific Issues
• Time and space scales of CTBL-continent interaction.
• Regional S/I feedbacks between Sc clouds, surface
winds, upwelling, coastal currents and SST in E
Pacific.
• Feedbacks of Eastern Pacific cloud topped boundary
layer properties on overall tropical circulation and
ENSO.
• Climatic importance of aerosol-cloud interactions.
VOCALS STRATEGIES
•
Global and mesoscale model evaluation and
improvement (e.g parameterization development)
using multiscale data sets.
•
Model sensitivity studies to refine hypotheses and
target observations.
•
Science by synthesis/use of existing data sets,
enhancement through targeted instrument
procurement, algorithm evaluation and development,
and enhanced observation periods.
•
Co-ordination with oceanographic, aerosol, cloud
process communities, including CLIVAR cloud CPT,
CLOUDSAT, etc.
Ongoing VOCALS observational enhancements:
(1) 3.5 years of WHOI stratus buoy (20S 85W) data (Weller)
documents surface met, energy budget, subsurface cooling
by ocean eddies and waves. (SE end of TAO line also useful).
(2) U. Chile installed ceilometer and surface met at San Felix Is.
(maintenance/power continuity issues) (Ruttland/Garreaud).
(3) Buoy maintenance cruises for two weeks every Oct-Nov.
now have PACS-supported NOAA/ETL surface met./
cloud remote sensing (Fairall).
(4) Integrated satellite data:
Nascent JOSS VOCALS archive, starting with GOES data.
Minnis GOES products (selected periods).
(Weller)
San Felix Island
and buoy cloud
correlated with
southerly coastal
jet and clearing.
(Garreaud)
B
S
Clouds in PACS03 at buoy thin compared to the rest of the
cruise (and to EPIC 2001). Lots of aerosol variability
(Fairall/Zuidema)
A Patch of Open Cells (POC)
MODIS 250m visible imagery
100 km
MODIS effective cloud droplet radius – small in coastal pollution
larger in clean areas, excessive in broken cloud of POCs.
large (clean) in drizzle
POCs drizzle more
Figure by Kim Comstock/Rob Wood
Can we model apparent local aerosol-cloud-drizzle feedback?
Low-latitude cloud feedback Climate Process Team
Goal: Reduce uncertainty in lowlatitude cloud feedbacks on
climate sensitivity.
• In-depth diagnosis of cloud
feedbacks in models.
• Implement ‘best-practices’
parameterizations honed via
single-column methods, newest
observations.
• Start with boundary-layer clouds,
move to deep convective systems.
CPT organization
• Core group (C. Bretherton, M. Khairoutdinov, C. Lappen, B.
Mapes, J. Norris, R. Pincus, B. Stevens, K. Xu, M. Zhang):
Parameterization, diagnosis, observational hooks.
• Advisory group (B. Albrecht, A. Betts, C. Fairall, T. del Genio,
S. Ghan, G. McFarquhar, R. Mechoso, H. Pan, D. Randall, D.
Raymond, J. Teixeira, R. Weller)
• NCAR–Kiehl, Rasch, Collins; Liaison: hiring underway
GFDL-Klein, Held, Donner; Liaison: Zhao
GMAO-Bacmeister, Suarez.
• Not an exclusive effort - active coordination with
observational programs such as VOCALS, GCSS, European,
Canadian efforts, CFMIP.
ERBE
-SWCF
(W m-2)
NCAR
Annual mean
Control run
GFDL
GMAO
NCAR
GFDL
GMAO
SST+2
Bonygram
comparison
6-day EPIC buoy period soundings vs. global models
Forecast models and esp. GCMs underestimate ABL depth.
• Cloud is too shallow, thin (but surface drizzle still too high).
•
(Bretherton et al. 2004)
Initial conditions (30 levels) at 00Z 16 Oct. 2001
10 K inversion
ESE PBL winds
Forcings (from ECMWF analyses)
Homogenize above 600 mb
More subsidence during daytime
Ship-observed
SST = 291.8 K
Homogenize above 600 mb
U. Washington PBL/ShCu schemes in CAM3
• Grenier-Bretherton (2001 MWR) moist TKE/explicit
entrainment PBL scheme, modified so TKE diagnostic.
• Bretherton-McCaa-Grenier (2004 MWR) shallow cu scheme:
- Buoyancy sorting bulk entraining-detraining plume
- Cu-base mass flux M b  K exp(c2CIN / K )
- Plume momentum equation for overshooting entrainment
• Single column L30 tests using EPIC dataset (GCSS WG1?)
• L30 and L26 tests with T42 Eulerian core using a
preliminary version of CAM3.
6-day mean soundings
Drizzle suppression sensitivity test
Mechoso – UCLA AGCM
African topography also promotes Namibian Sc
Mechoso
VOCALS ‘radiator-fin’ experiment ca. Oct. 2007?
• Transect between WHOI buoy and coast
• Goals: Cloud/aerosol interactions, PBL diurnal cycle
mesoscale ocean structure
Diurnal subsidence wave
Cld microphys. gradient
Coastal jet
buoy
Ocn heat transport
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3-4 weeks
Surveyed in a radiator pattern by ship (ocn, cld obs)
Aircraft flights along transect
To realize this vision, major S American buy-in needed!