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
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
Why are the SSTs so low in the SEP?
AGCM with
mixed layer
ocean model
(50 m depth)
contours
qv at 925 hPa
SSTANDES – SSTAQUA
Takahashi
and Battisti (2007)
Andes vs no Andes (but flat land), fixed
SST
ANDES
no ANDES
1. Stratocumulus
cover increases
without SST change
(thus clouds are not
simply a feedback
on SST)
2. Andes vs
aquaplanet  Andes
vs flat land
From Richter and Mechoso (2006)
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
Smelter locations
MODIS
Cloud Droplet
Concentration
(SON 2001-2004)
0
100
200
300
Cloud droplet concentration [cm-3]
400
Microphysical synoptic variability
Cloud fraction (MODIS)
Composite
strong weak
SE Pacific
high
pressure
Rhea
George
Stability (NCEP)
Cold/warm advection (NCEP)
Cloud effective radius (MODIS)
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
VOCALS-REx Platforms and
Sampling
Oct-Nov
2008
Aircraft:
NSF C-130
CIRPAS Twin
Otter
DoE G-1
UK BAe-146
Ships:
NOAA Ronald H
Brown
UNOLS
Wecoma
Jose Olaya
Land sites
VOCALS Timeline
IUGG Perugia
Planning
Phase
REx and
Modeling
Workshops
2003
- 2006
Field site
surveys
2007
PI
Proposal
submission
VOCALS
REx
2008
VOCALS
Conference
2009
2010
Field and modeling
synthesis/analysis
Mean SST departure from zonal mean
GFDL
Clouds in
climate
models
- change in low
cloud amount for
2CO2
CCM
model number
from Stephens (2005)
CGCM Problems: NOAA CFS
Model
CFS Errors
• The CFS model has significant
errors in the SEP
• There is a meridional shift in
ITCZ (top), a warm SST bias
(middle) and insufficient
stratocumulus cloud cover,
(bottom)
• These errors adversely affect the
skill of CFS climate forecasts
(ENSO).
What model developments
are required to alleviate
Prec
SST
CLD
source: IPCC 2007
ISCCP inferred St/Sc amount
Aerosol, cloud, drizzle and POCs