Transcript MERRA reanalysis lessons

MERRA reanalysis budget
lessons about GCM errors in the
W. Atlantic / IAS region
Brian Mapes
Univ. of Miami
MERRA reanalysis
MERRA = Modern Era (from 1979) Reanalysis
for Research and Applications
Uses GEOS-5 GCM (formerly NSIPP)
½ x 2/3 deg resolution
3D state estimation process
Budgets balance exactly
albeit with “analysis tendencies”
built by Incremental Analysis Updating (IAU)
MERRA’s
variables
Z [T,u,v,qv]
satisfy:
ΔZ/Δt = Żmodel
+ Żana
ΔZ/Δt = (Żdyn + Żphys) + Żana
Oops -- missed by EZ! Adjust
Żana by -2EZ/Δt and try again
from t-Δt/2
EZ
EZ oops
some
analyzed
values
Z
at some point
Cost: 1.5x free model run
Żana(t) saved as a data set
time (6h increments)
Learning from analysis tendencies
✔
✔
(ΔZ/Δt)obs = (Żdyn + Żphys) + Żana
• If state is kept accurate (LS flow & gradients),
then (ΔZ/Δt)obs and advective terms Żdyn will be
accurate
• and thus
Żana ≅ -(error in Żphys)
Vertically integrated qv tendencies:
• mst = moist physics (convection + LS condens.)
• ana = analysis tendency
(~ –phys. error)
• Summer climatologies:
Moist physics (conv. + LS) <0
a
of water vapor
Analysis is moistening this area,
presumably because physics is an
excessive sink (raining too much)
Precipitation bias
rainy bias in all reanalyses
rainy bias in all reanalyses
Dynamical side: U analysis tendencies
overlaid with {u,v} vectors
1000mb
700
850
500
U analysis tendencies
overlaid with {u,v} vectors
850
1000mb
60-90W
Zonal mean
500
700
60-90W
Zonal mean
Analysis tends. on mass and wind fields:
fighting the model’s excessive baroclinic vortex
Cyclonic
analysis torque:
Lower thickness
wanted for
thermal wind
balance
Anticyclonic
analysis torque
Higher thickness
wanted
Analysis tends. on mass and wind fields:
fighting model’s excessive baroclinic vortex
Cyclonic
analysis torque:
Anticyclonic
analysis torque
Way too much: analysis opposes mean
deep convective heating
(with this model’s peculiar characteristic profile)
open
contours:
model
physics
heating
GEOS-5 model’s peculiar heating profile
in tropical deep convection
dT/dt_mst in TOGA COARE
15 day time section at a grid point
Strange cooling
spike at 700:
misplaced
melting (should
be 550 mb)
largest value on
globe: >3 m/s
per day u
deceleration by
analysis
tendency
(obs fighting
model)
warm SST season (later than summer)
Conclusions
• Analysis tendencies ~ -model systematic errors
– Obs chronically nudging model a certain way
• MERRA W. Atl. has too much deep convection
– excessive precip relative to GPCP/CMAP
– excessive qv sink (fought by pos. qv anal. tendency)
– excessive baroclinic vorticity couplet 600mb/200mb
– includes largest u200 analysis tendency on the planet
– seasonality: late summer (warm SST season)
– T’ errors in thermal wind balanced sense w/ above
– Just excessive strength: opposes mean moist Q
– profile is distinctive, erroneous: melting at 700 mb instead of 550
• Familiar: shallow v. deep convection problem
Thank you
http://www.ncdc.noaa.gov/gibbs/image/GOE-12/WV/2006-07-14-15