1. VOCALS Chris Bretherton, Univ. of Washington

2. 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.

3. 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:

4. 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.

5. 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.
00LT
06LT
12LT
18LT
06LT
Garreaud and Munoz (2004) – 21 day regional MM5 simulation

6. 3. Strong aerosol/drizzle/cloud fraction feedbacks in SE Pacific
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) 19 20 21 22
GOES VIS 0545 LT
C-band 0200 LT
Longitude (ºW)
1.5
1.0
0.5
Height (km) 00 02 04 06
October 19 (Local Time)
MMCR
Here’s an example of some of the data we obtained. On the right is a GOES visible satellite image taken at 545 am local time on October 19th. You can see some unbroken as well as some broken Sc. The ship position is marked with the red circle. The yellow line shows the approximate advection over the previous 6 hours. This time period corresponds to the MMCR time-height section shown here (midnight to 6 am). From the satellite image we see that during this time broken Sc were passing over the ship (that is, clouds and holes). In the MMCR image we confirm this. We also see that there was significant drizzle falling out of some of these clouds. To get a better idea of what the heavily-drizzling cells passing over the ship looked like, we turn to the scanning C-band radar data.
This image was obtained at 2 am local time. It shows reflectivity from the vertically-averaged cloud layer (remember these are very thin clouds) with the same color scale as the MMCR. The ship is in the center, and the data extends to a 30 km radius. There are some very strong drizzle cells passing over the ship.
In each image, we can see a large degree of mesoscale variability, and both radars show us this is associated with a significant amount of drizzle.
Lets go to another example…
Drizzle echoes
EPIC2001 Sc cruise

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

8. 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.

9. 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.

10. 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.

11. DYCOMS-II RICO TAO-EPIC EPIC2001-Sc Galapagos I. Lima Arica WHOI buoy
San Felix I.

12. 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

13. (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

14. 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)

15. 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 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.

16. 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

17. Modeling, empirical, and satellite studies
VOCALS Timeline
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

18. 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)