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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.

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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)

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
VOCALSScientific Issues
  • Time and space scales of CTBL-continent interaction.
  • Regional S/I feedbacks between Sc clouds, surface winds, upwelling, coastal currentsand 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.


  • 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:

  • 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).
pocs drizzle more
POCs drizzle more

Figure by Kim Comstock/Rob Wood


MODIS effective cloud droplet radius – small in coastal pollution

larger in clean areas, excessive in broken cloud of POCs.

large (clean) in drizzle

low latitude cloud feedback climate process team
Low-latitude cloud feedback Climate Process Team

Goal: Reduce uncertainty in low-latitude 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
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.
annual mean control run


Annual meanControl run


(W m-2)




6 day epic buoy period soundings vs global models
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).
forcings from ecmwf analyses
Forcings (from ECMWF analyses)

Homogenize above 600 mb

More subsidence during daytime


SST = 291.8 K

Homogenize above 600 mb

u washington pbl shcu schemes in cam3

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
  • - 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.

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


Ocn heat transport

  • 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!