MJO sensitivities on aquaplanet
as simulated by SP-CAM
Marat Khairoutdinov
School of Marine and Atmospheric Sciences
Stony Brook University
Long Island, NY
Simulated sub seasonal tropical variability
OLR
OLR spectrum
SPCAM MMF
GCMMMF
with curtains
Observations
NOAA
Standard
CAMGCM
2.00
2.50
period (days)
frequency (cpd)
50
25
3.33
12
5.00
Kelvin
10.0
30 days
zonal wavenumber
MJO 30 days
ER
zonal wavenumber
westward
eastward
Precipitation
spectrum
MMF
GPCP
30 days
zonal wavenumber
CAM
2.00
period (days)
frequency (cpd)
2.50
3.33
5.00
10.0
30 days
30 days
30 days
MJO on Aquaplanet/Water World
Why Aquaplanet? Simplicity!
• no polar ice, no land/soil/terrain complications
• heat and vapor fluxes over water - we know how
• zonally symmetric (zonal means direction of latitude circle)
• perpetual equinox - no seasons
• Mean climate resembles the Earth’s
• Still has MJO and main equatorial waves
Sea Surface Temperature (prescribed)
Eq
Slightly asymmetric
about the equator
Simulated tropical variability on Aquaplanet looks similar
to subseasonal tropical variability on Earth
OLR
westward
eastward
Kelvin
waves
Rossby
waves
MJO
MJO forms ‘wave packets’ on Aquaplanet
384-day sample
0
100
200
Text
Lag (days)
days
Aquaplanet MJO-filtered OLR
~70 days
300
Correlation Coefficient
W/m2
W/m2
on Earth too
NOAA OLR
(Satellite observations, not a model)
Strong El Nino year
Sensitivity to Aquaplanet Sea Surface Temperature
OLR
Control - 2K
Control
Control + 2K
MJO-mode
Precipitation
Positive SST
perturbation
causes stronger MJO
and Kelvin modes,
but weaker Rossby
mode.
Rising CO2
Warmer
Tropical SST
mm/day
mm/day
mm/day
More extreme
rain associated
with MJO in the
future?
Sensitivity to Zonally Homogenized
Surface fluxes and Radiative Heating
•
Zonal Homogenization: Compute surface fluxes and radiation heating rates as
usual but apply them zonally averaged (no WISHE, no anomaly damping).
Control
Hom. Sfc Fluxes
Hom. Sfc Fluxes & Rad.
OLR
SST
• Homogenization shifts MJO towards
warmer SSTs and concentrates MJO
into narrower band;
• Zonal variation of surface fluxes and
radiative heating doesn’t seem to be
essential for maintaining simulated
MJO;
MJO OLR Var.
Control
SFC
SFC+RAD
Sensitivity to Zonally Homogenized
Water Vapor
•
Zonal Homogenization: Nudge (relax) water vapor to zonally averaged values
over diurnal time scale;
OLR
Control
• The existence of
Hom. all levels
Hom. above 850mb
Hom. above 400mb
mid-to-low troposphere (but above PBL) water-vapor anomalies
is the key for the existence of simulated MJO.
• The anomalies are associated with the shallow and congestus cloud activity hence, representation of those cloud types in GCMs is the key for MJO simulation
Conclusions
• Simulated tropical variability on Aquaplanet looks similar to subseasonal tropical variability
on Earth;
• On aquaplanet, MJO forms westward propagating packets - SuperMJO ?; (how about Earth?)
• +2K SST perturbation experiments suggest that warmer SSTs can cause stronger MJO and
stronger Kelving waves, but weaker Eq. Rossby waves;
• Zonal variation of surface fluxes and radiative heating may not be essential for maintaining
simulated MJO;
• The existence of mid-to-low troposphere (but above PBL) water-vapor anomalies is the key
for the existence of simulated MJO.