Toward understanding

the MJO through the MERRA

data-assimilating model

Brian Mapes, U. Miami

Stefan Tulich, CIRES

Julio Bacmeister, GSFC

and

37 years of studying the MJO: Progress in description, but still no widely accepted theory

Madden and Julian 1972 Benedict and Randall 2007

37 years of studying the MJO: Progress in description, but still no widely accepted theory

Madden and Julian 1972 Benedict and Randall 2007

Outline1. Previous GCM studies of moisture

preconditioning & the MJO

2. Using novel MERRA data-assimilating model to study this and other MJO science issues

3. Structure of the MJO in MERRA Not new, but shows model biases

“Analysis tendencies” provide a new aspect to the problem

4. Future work: Model improvement as a path towards understanding

One of the first GCM moisture preconditioning experiments

• Tokioka et al. (1988): The equatorial 30-60 oscillation and the Arakawa-Schubert cumulus parameterization (J. Meteor. Soc. Japan)

Control No non-entraining plumes

One of the first GCM moisture preconditioning experiments

• Tokioka et al. (1988): The equatorial 30-60 oscillation and the Arakawa-Schubert cumulus parameterization (J. Meteor. Soc. Japan)

Control No non-entraining plumes

This modification also improves the MJO in the CAM 3.1

Maloney (2009)

This modification also improves the MJO in the CAM 3.1

Maloney (2009)

Still the model is not perfect

Even worse when looking at rainfall variance

Maloney (2009)

Improvements are also model dependent

Lee et al. (2009; in press)

How do we proceed further?

• Standard approach: Tinker with the model physics, run long time integration, diagnose model performance/feedbacks, repeat – Drawback: Time-consuming, tedious, feedbacks may

impact other aspects of the simulation in unintended ways

• Our alternative: Assimilation-based science to study the MJO in global models (illustration of concept here)

MERRA

• Modern Era Reanalysis for Research and Applications (GEOS-5 based)

• NASA’s new atm. reanalysis, 1979-present

• Still running (3 streams), ~90% available

• Attractive features:

- nowOpenDAP access (you needn’t download)

- many budget terms, not just state variables

- “analysis tendencies” available

time

analyzed variable

Z at discrete

times

free model solution: Żana= 0 (biased, unsynchronized, may lack oscillation altogether)

initialized free model

ΔZ/Δt = Żmodel + Żana

ΔZ/Δt = (Żdyn + Żphys) + Żana

use piecewise constant Żana(t) to make above equations exactly true in each time interval*

Modeling system integrates:

*through clever predictor-corrector time integration

Learning from analysis tendencies

(ΔZ/Δt)obs = (Żdyn + Żphys) + Żana

• If state is accurate (including flow & gradients), then (ΔZ/Δt)obs and advective terms Żdyn will be accurate

• and thus

Żana ≅ -(error in Żphys)

Choosing MJO cases

good(COARE)

MJO amplitude index

MERRA data available when I started

MERRA stream 2

bestavail

MERRA stream 3

Satellite OLR 15N-15S& MJO-filtered (contours) – used as reference lines below

Filtered OLR courtesy G. Kiladis eastward wavenumbers 0-9, 30-96 days

I averaged this over 15N-15S

15N-15S

GIBBS image archive

MJO phase definition

05

excluded

IO WP

Objective MJO phase categories

PHASE

10 phases relative to Benedict and Randall (2007)

9 8 7 6 5 4 3 2 1 0 ‘back (W)’ ‘front (E)’

5 = filtered OLR min.

Benedict & Randall 2007

MERRA rainrate compared to SSMI (SSMI over water only)

MERRA

SSMI

0

x 10-4 mm/s

too rainy phase 1-2

MERRA’s rain:

convective:

anvil:

large-scale cloud:

premature rain in phase 2 is mainly convective

deep Mc

Phase dependent mass flux

9 8 7 6 5 4 3 2 1 0 ‘back’ (W) ‘front (E)’

5 = filtered OLR min.

Model seems to be choking on the shallow-to-deep transition (even

with Tokioka modification)

Impact? Look at analysis tendencies

Phase dependent part of qv analysis tendency

1990 1992-3

Blame the convection scheme!

• seems to act too deep too soon in the early stages of the MJO.

• Analysis qv tendency has to compensate with moistening

Future work: Improving the model as path towards understanding

• Convection parameterization seems to be too insensitive to low- and mid-level moisture (even with Tokioka modification)

• Question: can we somehow further tighten/adjust the Tokioka limiter to reduce model errors?

Strategy: perform short assimilation runs; does Żana get smaller?

If so, something scientific learned from this technical activity.

Future work: Use analysis tendencies to develop a better forecast tool?

Consider MJO index of Wheeler and Hendon (2004):

Future work: Use analysis tendencies to develop a better forecast tool?

Idea: First, composite model analysis tendencies in this phase space

Future work: Use analysis tendencies to develop a better forecast tool?

Idea: First, composite model analysis tendencies in this phase space

Next, perform multi-day forecasts with these composite tendencies added during runtime.

Forecast improved?