VOCALS 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 VOCALS is a developing process study within VAMOS, informally led by C. Bretherton. WG meetings at VPM3-6 (Spring ). Active participants: US (Albrecht, Bretherton, Fairall, Mechoso, Miller, Stevens, Weller) Chile (Garreaud, Ruttland) Uruguay (Terra) Peru (Lagos) Ecuador (Cornejo) Draft plan:

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. 18LT 06LT 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 Latitude (ºS) GOES VIS 0545 LT C-band 0200 LT km Longitude (ºW) Height (km) October 19 (Local Time) MMCR 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.

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.

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 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 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 Timeline Modeling, empirical, and satellite studies diagnostic/modeling work 2003 ETL-enhanced cruises SFI profiler VOCALS data archive 2005/01 RICO 2005 Cloudsat 2007/10 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)