VOCALS Chris Bretherton, Univ' of Washington

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VOCALSChris Bretherton, Univ. of Washington
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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.
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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.

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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.
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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.
18LT
12LT
06LT
00LT
06LT
Garreaud and Munoz (2004) 21 day regional MM5
simulation
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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).
Drizzle echoes
EPIC2001 Sc cruise
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MODIS effective cloud droplet radius large
(clean) in drizzle
small in coastal
pollution
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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.

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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.

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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.

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DYCOMS-II
RICO
Galapagos I.
TAO-EPIC
Lima
Arica
EPIC2001-Sc
WHOI buoy
San Felix I.
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• Ongoing VOCALS observations
• 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
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(2) U. Chile installed ceilometer and surface met
at San Felix Is.
Decoupled
Cloud base (ceilometer)
LCL (surface met)
Well-mixed
Mostly clear
Garreaud
Shows daytime rise of LCL, cld. base, with
synoptic variations
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VOCALS 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)

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VOCALS short-term implementation

• 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.

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• 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

• 3-4 weeks
• Surveyed in a radiator pattern by ship (ocn, cld
  obs)
• Aircraft flights along transect

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VOCALS Timeline

• 2003-2010
• diagnostic/modeling work 2003 ETL-enhanced
  cruises
• SFI profiler
• VOCALS data archive
• 2005/01 RICO
• 2005 Cloudsat
• 2007/10 Radiator expt.

Modeling, empirical, and satellite studies

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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)