The VOCALS Regional Experiment
Aerosols, clouds, and precipitation in
southeast Pacific stratocumulus
Robert Wood
Atmospheric Sciences
University of Washington
Global sea-surface temperature
October 25th 2007
10
15
20
25
30
ISCCP inferred St/Sc amount
Twomey
Albrecht
Rich marine habitats, few continental ones…
SeaWIFS Ocean Color
Tarapacá, Atacama Desert
Net primary productivity of Humboldt current 3 tC ha-1 yr-1
Net primary productivity of boreal forests 2-8 tC ha-1yr-1
rainfall [mm]
Iquique annual precipitation 1899-2003
20oS
Longitudinal cross-section at 20oS
85oW
65oW
SST anomaly
from zonal mean
ERBE net cloud
forcing
A coupled problem
• Correct prediction of
stratus properties is
important for the correct
prediction of the climate
over the tropical warm
pool
– connections with ITCZ
through both ocean and
atmosphere
Yu and Mechoso 2001
Precip [mm day-1]
0 2 4 6
8 10 12 14
SST Biases in Coupled Models
• SST Biases in NCAR CCSM (Collins et al. 2006)
Ocean surface heat budget
Net heat input into ocean at center of stratus sheet > 50 W m-2
Must be corresponding cold water transport from somewhere
Annual Heat Fluxes 20oS, 85oW
W/m2
250
Net SW
200
Net LW
150
Sensible
100
Latent
Net Heat
50
0
-50
-100
-150
Bob Weller, WHOI
Mesoscale ocean eddies
• Mesoscale ocean eddies
form in coastal upwelling
regions and propagate
westward
• Their impact on the heat,
nutrient, and freshwater
budgets is poorly known
• They are not resolved in
coupled GCMS
Simulation from Penven et al. (2005)
Mesoscale ocean eddies
Height
SST
Eddies impact SST and can be observed using altimetry
courtesy Shang-Ping Xie, University of Hawaii
14-year animation of eddies identified
using satellite altimetry (courtesy Dudley
Chelton, OSU)
Clouds and cloud processes
ERBE
-SWCF
(W m-2)
NCAR
GFDL
Clouds in
Global
Models
GMAO
Annual mean
Control run
Atmospheric models
Why this Uncertainty?
resolution of ~5m
required to resolve
inversion!
~12K!
Free-tropospheric
T set by ITCZ
θe
2,000km
~1km
BL T set by local SST
Drizzle is important over the SEP
Mesoscale variability in stratocumulus
200 km
Pockets of
Open Cells
(POCs)
Mesoscale stratocumulus structure
• Cloud albedo
strongly
dependent upon
open/closed cells
Open Cells
Closed Cells
Satellite
Low albedo
• Strong
precipitation
associated with
open cell structure
100 km
High albedo
• Open cells form
in clear marine
environment –
potential
anthropogenic
impacts
Strong drizzle
Ship Radar
Weak drizzle
Drizzle and cloud droplet concentration
EPIC data, Bretherton et al. (2004)
POCs and Aerosols
• Strong
reductions in
accumulation
mode aerosol
concentration
• New nucleation
• Links between
aerosol
microphysics
and cloud
macrophysics?
Global cloud droplet concentration
(MODIS, annual mean 2001-2004)
Cloud
Microphysical
Variability
MODIS
Cloud Droplet
Concentration
(SON 2001-2004)
0
100
200
300
400
Cloud droplet concentration [cm-3]
Smelter locations
The VAMOS Ocean-Cloud-AtmosphereLand Study
Aim: to promote activities leading to improved understanding and model
predictions of the SEP coupled system on diurnal to interannual timescales
THE
VOCALS
STRATEGY
VOCALS Regional Experiment (REx)
VOCALS-Rex will collect datasets required to address a set
of issues that are organized into two broad themes:
• Aerosol-cloud-drizzle interactions in the marine
boundary layer (MBL) and the physicochemical and
spatiotemporal properties of aerosols
• Chemical and physical couplings between the upper
ocean, the land, and the atmosphere.
VOCALS-REx Platforms
NSF C-130
DoE ASP G-1
NOAA Ronald H Brown
CIRPAS Twin Otter
The aircraft
DoE ASP G-1
CIRPAS Twin Otter
NSF C-130
Chemistry and
aerosols, cloud
microphysics,
turbulence
Remote sensing
and cloud imaging
Chemistry and aerosols, cloud
microphysics, turbulence,
radar/lidar remote sensing
Radar remote
sensing,
microphysics,
turbulence
Aerosols, cloud
microphysics,
radiative
measurements
NERC Dornier 228
UK FAAM BAe-146
The Ships
IMARPE José Olaya
NOAA Ronald H Brown
VOCALS-REx Platforms and Sampling
Aircraft:
NSF C-130
CIRPAS Twin Otter
DoE G-1
UK BAe-146
NERC Do 228
Ships:
NOAA Ronald H
Brown
José Olaya
Land sites:
Iquique
Paposo
VOCALS-REx Cross-Section Sampling
Combined NOAA Ronald H Brown
and NSF C-130
Missions
- direct evaluation of GCM lower
tropospheric structure
Flight-plan for C-130
POC-Drift missions
Operations Bases
• Arica (Operations Center)
– C-130, G-1, UK 146, Do228
• Iquique
– CIRPAS Twin Otter, Sounding station
• Paposo
– Ground station for aerosol characterization