VOCALSChris 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

• VOCALS is a developing process study within VAMOS, informally led by C. Bretherton.

• WG meetings at VPM3-6 (Spring 2000-2003).• Active participants:

US (Albrecht, Bretherton, Fairall, Mechoso, Miller, Stevens, Weller) Chile (Garreaud, Ruttland) Uruguay (Terra) Peru (Lagos) Ecuador (Cornejo)

• Draft plan: www.atmos.washington.edu/~breth.

Why VOCALS?

1. SE Pacific stratocumulus affect circulation/SST over entire Pacific basin by radiatively cooling both atmosphere and ocean, but are still inadequately simulated in CGCMs.

2. Climate-scale impacts of interactions between clouds and S American continent need more exploration, e.g. a recently discovered daytime subsidence wave initiated by Andean slope heating that propagates 1500 km offshore over the SE Pacific stratocumulus region, lowering inversion and enhancing daytime cloud thinning.

18LT06LT

Garreaud and Munoz (2004) – 21 day regional MM5 simulation

12LT06LT00LT

3. Strong aerosol/drizzle/cloud fraction feedbacks in SE Pacific. Aerosols much lower away from coast. Clean stratocumulus are drizzly, more cellular, with lower cloud fraction (example below).

60

km

Lati

tud

e (

ºS)

19

20

21

22

GOES VIS 0545 LTC-band 0200 LT 87 86 85 84 8360 km Longitude

(ºW)1.5

1.0

0.5Heig

ht

(km

)

00

02

04

06October 19 (Local Time)

MMCR

00

06

Drizzle echoes

EPIC2001 Sc cruise

MODIS effective cloud droplet radius – large (clean) in drizzle small in coastal pollution

Results of EPIC 2001 Sc cruise(Bretherton et al. 2004, BAMS, accepted)

• Strong diurnal cycle of cloud in this region.• Boundary layer deeper than predicted by most

GCMs.• Nocturnal drizzle important, but (unlike in GCMs)

mostly evaporates between cloud base and surface.• Drizzly days have low aerosol, pronounced cellular

structure in clouds.

The VOCALS plan is based on the 3 science motivations and these EPIC results.

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.

Arica

Lima

San Felix I.

WHOI buoy

Galapagos I.

DYCOMS-II

TAO-EPIC

EPIC2001-Sc

RICO

Ongoing VOCALS observations:(1)2.5 years of data from the WHOI stratus buoy (20S 85W) documents surface energy budget, subsurface cooling by ocean eddies and waves. (SE end of TAO line also useful).

Weller

(2) U. Chile installed ceilometer and surface met at San Felix Is.

LCL (surface met)

Cloud base (ceilometer)

Shows daytime rise of LCL, cld. base, with synoptic variations

Well-mixed

Decoupled

Mostly clear

Garreaud

VOCALS ThrustsVOCALS Thrusts• Continuing diagnostic, model sensitivity,

parameterization studies of SE/NE Pac stratocumulus and variability based on past field studies, satellite/model products, and in-situ observational enhancements.

• Contribution to RICO (Jan 2005, shallow Cu)

• Add ocean diagnostic study component based on ARGO/ODA, cruises, WHOI buoy aimed at better understanding of ocean upwelling/lateral heat transport processes and their reln. to atmospheric variability.

• Global atm./coupled, mesoscale atm., and regional ocean modeling.

• ‘Radiator fin’ coupled O-A-L expt. (Oct 2006)

• Augment San Felix Island instrumentation with wind profiler, radiation, microwave LWP, and aerosol sampler.

• NOAA/ETL sfc/remote sensing instrumentation on Pacific buoy maintenance cruises (funded, starting with Oct. 2003 cruise), and at RICO.

• Develop VOCALS data set through distributed satellite/model/in situ data archive at JOSS. Archive ECMWF and NCEP hi-res column data at WHOI buoy, SFI in co-ordination with CEOP (some funding).

• Work with cloud-climate sensitivity CPT to feed into coupled model development.

VOCALS short-term implementation

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

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

mesoscale ocean structure

buoy

VOCALS TimelineVOCALS Timeline

Modeling, Modeling, empirical, empirical,

and and satellite satellite studiesstudies

2003-2010 diagnostic/modeling work 2003 ETL-enhanced cruises SFI profiler VOCALS data archive2005/01 RICO2005 Cloudsat2007/10 Radiator expt.

Other active VOCALS science issues

• Role of Andes and Amazonia (flow blocking, deep convection) in influencing Sc.

• Comparison of WHOI buoy and TAO-EPIC ocean energy budgets with GCMs.

• Interest in coastal oceanography of region, including O-A interactions thru trapped coastal (e.g. Kelvin) waves.

• ENSO feedbacks with SE and NE Pacific clouds

• Shallow cumulus dynamics/microphysics – Sc to Cu transition (McCaa and Bretherton 2004; Wang et al. 2004)