Figure 1: Composites of non-radiative diabatic heating (Q1 minus QR; K day-1) per unit of WH04 MJO amplitude, averaged over 10˚S-10˚N, 100-120˚E, for each WH04 MJO phase. Phases 3 and 4 (7 and 8) are the active (suppressed) phase. The lifecycle is shown twice.

Nicholas P. Klingaman | Steven J. Woolnough | Department of Meteorology, University of Reading

E-mail: n.p.klingaman@reading.ac.uk Web: www.met.rdg.ac.uk/~ss901165 Twitter: @nick_klingaman

Project web: http://www.ucar.edu/yotc/mjodiab.html Wiki: http://climate.ncas.ac.uk/pmwiki/MJO_Diabatic_Hindcast

Vertical structure and diabatic processes of the MJO : 20-day hindcasts

1. Introduction to the MJO

4. Assessments of model skill

Summary

References

• This intercomparison aims to understand how errors in vertical profiles of diabatic heating, moistening and momentum affect model representations of the MJO.

• Models typically exhibit greater (less) skill for Indian Ocean/W. Pacific (Maritime Continent) MJO phases.

• In suppressed phases, more (less) skilful models show shallow (deep) heating and more (less) low- and mid-level moistening from physics. Skilful models also gradually transition from low-level total moistening in suppressed phases to upper-level moistening in active phases.

5. Vertical profiles of diabatic heating and moistening

The Madden-Julian oscillation(MJO) is the leading mode of sub-seasonal (30-70 day) tropical variability. By modulating monsoons and influencing extra-tropical variability (e.g., the North Atlantic Oscillation; Cassou, 2008), the MJO provides a key source of weekly and monthly predictability. Despite the importance of the MJO, many general circulation models (GCMs) fail to represent its amplitude, period and equatorial eastward propagation (Lin et al., 2006). Biases in GCM vertical profiles of diabatic heating, as well as incorrect or weak feedbacks between heating and circulation, may be key sources of errors in the MJO (e.g., Li et al. 2009; Fu and Wang 2009). Increasing entrainment for deep convection in the Hadley Centre GCM improved the MJO; diabatic-heating profiles show a clearer transition from shallow to deep convection (Fig. 1).

2. Objectives and design of the intercomparison

A major international model intercomparison project is underway, which aims to link errors in MJO simulation to errors in vertical profiles of heat, moisture and momentum in the tropics. The goal is to develop an evaluation framework GCM developers can use to improve parameterisations. The “Vertical Structure and Diabatic Processes of the MJO” intercomparison project has three components: (1) 20-year AMIP-style simulations; (2) daily, two-day hindcasts of YoTC Cases E and F (Fig. 2), with timestep output of sub-grid tendencies; (3) daily, 20-day hindcasts of the same cases, providing three-hourly output.

Figure 2: The two MJO active events targeted by the 20-day (orange) hindcast components. Shown is TRMM precipitation (mm day-1), averaged 5˚S to 5˚N. 20-day hindcasts are initialised every day during the periods marked in blue.

The 20-day hindcast component of the project focuses on: • The predictability of

YoTC Cases E and F

• The model drift away from its initial state (analysed in the 2-day hindcast component) and towards its attractor (analysed in the 20-year component).

• How errors in vertical profiles of diabatic processes contribute to the drift and the lack of predictability.

Figure 3: Left: Bi-variate correlations of observed and forecast RMM indices. Right: Skill in RMM1 against skill in RMM2, where “skill” is the first lead time at which correlation < 0.75.

Cassou, C., 2008: Nature, 455, 523-527.

Fu, X. and B. Wang, 2009: J. Climate, 22, 3939-3959.

Gottschalck, J. et al., 2010: BAMS, 91, 1247-1258.

Li, C. et al., 2009: Clim. Dynam., 32, 167-187.

Lin, J.-L. et al., 2006: J. Climate, 19, 2665-2690.

Wheeler and Hendon, 2004: MWR, 132, 1917-1932.

YoTC Case F YoTC Case E

3. Participating modelling centres

HadGEM3 High (+50%) Entrainment HadGEM3 Default Entrainment

Modelling Centre Model Code

European Centre for Medium-range Weather Forecasts ECMWF IFS (Monthly system) EC

National Aeronautics and Space Administration NASA GEOS-5 NA

Colorado State University / Univ. of Washington SPCAM 3.0 SP

Columbia University NASA GISS Model E2 GI

University of Tokyo / JAMSTEC NICAM NI

University of Tokyo MIROC 5 MI

U.K. Met Office Hadley Centre MetUM GA3.0 MO

Naval Research Laboratory NRL NavGEM NR

Centre National de Recherches Meteorologiques CNRM Atmospheric GCM CN

Swedish Hydrological and Meteorological Institute EC-Earth 3 E3

National Center for Atmospheric Research NCAR CAM5 C5

UC San Diego / Lawrence Livermore National Laboratory CAM5 with modified microphysics CZ

Environment Canada CCCma CanAM4 CC

University of Miami Linear Inverse Model (statistical) LI

Several models achieve 20 days’ skill (bivariate correlation=0.7), while others are similar to persistence. Nearly all models display greater skill in RMM2 (the anti-correlation between the Indian Ocean and West Pacific) than in RMM1 (variability over the Maritime Continent).

6. Transition from shallow to deep convection

Models with greater predictability produce light rain rates (red lines) from shallow heating profiles (as at left), while models with lower predictability produce such rain rates from upright profiles and deep ascent (as at right). Models with greater predictability show net moistening from physics at low rain rates (red and yellow lines), while those with lower predictability have net drying. Figure 4: Total (top) heating and (bottom) moistening rates from sub-grid physics (no radiation), composited on quartiles of rain rate from each model, excluding rates less than 1 mm day-1, using all start dates and lead times. Data interpolated to 10x10 grid.

NASA GEOS5 MetUM GA3 CNRM Atmos

CNRM MetUM NASA

Figure 5: Colours are total moistening rate binned by gridpoint precipitation rate, using gridpoints in the Indian Ocean (10S-10N, 60-90E) and all start dates and lead times. Solid line shows contour of zero tendency from advection; dotted line shows contour of zero tendency from physics. Advection (physics) moistens to right (left) of line. Dashed line shows PDF of precipitation (right-hand axis).

ECMWF YoTC 3-24 hour forecasts NASA GEOS5

CNRM Atmos MetUM GA3.0

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