VOCALS Update Chris Bretherton, Univ. of Washington
VOCALS THEME To better understand 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. • VPM 7 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 • 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.
Ongoing VOCALS observational enhancements: (1) 3. 5 years of WHOI stratus buoy (20 S 85 W) data (Weller) (2) documents surface met, energy budget, subsurface cooling (3) by ocean eddies and waves. (SE end of TAO line also usefu (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 250 m 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 lowlatitude 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. Mc. Farquhar, 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.
ERBE -SWCF (W m-2) NCAR Annual mean Control run GFDL GMAO
NCAR GFDL GMAO SST+2 Bonygram comparison
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 00 Z 16 Oct. 10 K inversion ESE PBL winds
Forcings (from ECMWF analyses) Homogenize above 600 mb More subsidence during daytime Ship-observed SST = 291. 8 K Homogenize above 600 mb
U. Washington PBL/Sh. Cu schemes in CAM 3 • Grenier-Bretherton (2001 MWR) moist TKE/explicit entrainment PBL scheme, modified so TKE diagnostic. • Bretherton-Mc. Caa-Grenier (2004 MWR) shallow cu scheme: - Buoyancy sorting bulk entraining-detraining plume - Cu-base mass flux - Plume momentum equation for overshooting entrainment • Single column L 30 tests using EPIC dataset (GCSS WG 1? ) • L 30 and L 26 tests with T 42 Eulerian core using a preliminary version of CAM 3.
6 -day mean soundings
Drizzle suppression sensitivity test
Mechoso – UCLA AGCM
African topography also promotes Namibian Sc Mechoso
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 To realize this vision, major S American buy-in needed!
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