MERRA reanalysis budget lessons about GCM errors in the

W. Atlantic / IAS region

Brian MapesUniv. 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 resolution3D state estimation process

Budgets balance exactly albeit with “analysis tendencies” built by Incremental Analysis Updating (IAU)

some analyzed

values

Z at some point

time (6h increments)

ΔZ/Δt = Żmodel + Żana

ΔZ/Δt = (Żdyn + Żphys) + Żana

MERRA’s variables Z [T,u,v,qv]satisfy: Oops -- missed by EZ! Adjust

Żana by -2EZ/Δt and try again from t-Δt/2

EZ oops

Cost: 1.5x free model runŻana(t) saved as a data set

EZ

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:

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 tendenciesoverlaid with {u,v} vectors

1000mb 850

700 500

U analysis tendenciesoverlaid with {u,v} vectors

1000mb 850

700 500

60-90WZonal mean

60-90WZonal mean

60-90WZonal mean

60-90WZonal mean

Analysis tends. on mass and wind fields: fighting the model’s excessive baroclinic vortex

Cyclonic analysis torque:

Anticyclonicanalysis torque

Lower thickness wanted for

thermal wind balance

Lower thickness wanted for

thermal wind balance

Higher thickness wanted

Higher thickness wanted

Analysis tends. on mass and wind fields: fighting model’s excessive baroclinic vortex

Cyclonic analysis torque:

Anticyclonicanalysis 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

Strange cooling spike at 700:

misplaced melting (should

be 550 mb)

Strange cooling spike at 700:

misplaced melting (should

be 550 mb)

dT/dt_mst in TOGA COARE15 day time section at a grid point

largest value on globe: >3 m/s

per day u deceleration by

analysis tendency

(obs fighting model)

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