VOCALS UpdateChris Bretherton, Univ. of Washington

VOCALS VOCALS THEMETHEME

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

VOCALSVOCALS Scientific IssuesScientific 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 STRATEGIESVOCALS 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).

A Patch of Open Cells (POC)MODIS 250m visible imagery

100 km

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

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• 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 meanControl run

-SWCF(W m-2)

ERBE

NCAR

GFDL

GMAO

SST+2Bonygramcomparison

NCAR

GFDL

GMAO

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).

Initial conditions (30 levels) at 00Z 16 Oct.

10 K inversion

ESE PBL winds

Forcings (from ECMWF analyses)

Homogenize above 600 mb

Homogenize above 600 mb

Ship-observed

More subsidence during daytime

SST = 291.8 K

• 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.

U. Washington PBL/ShCu schemes in CAM3

2exp( / )bM K c CIN K

6-day mean soundings

Drizzle suppression sensitivity test

Mechoso – UCLA AGCM

African topography also promotes Namibian Sc

Mechoso

Diurnal subsidence wave

Cld microphys. gradient

Ocn heat transport

Coastal jet

• 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!

VOCALS ‘radiator-fin’ experiment ca. Oct. 2007?• Transect between WHOI buoy and coast• Goals: Cloud/aerosol interactions, PBL diurnal cycle

mesoscale ocean structure

buoy