Model Ens Initialization Interval

Reforecast period

Source

SubX(NCEP-GEFS, NASA-GEOS5, ESRL-FIM, Navy-ESPC, RSMAS-CCSM4, NCAR-CESM1)

3~20 5~7 days 1999-2016 SubX

ECMWF Cy43R3 11 2/week 1997-2016 S2S

UKMO/KMA GloSea5 3 7 days 1991-2010 S2S

- RMM index (Wheeler and Hendon, 2004)

- ERAI, NOAA CDR OLR, GPCP precipitation (1979~2017) → “OBS”

- NH winter (Oct-March)

SubX and S2S reforecasts

MJO Propagation Processes and Mean Biases in the SubX and S2S Reforecasts

Hyemi Kim (SBU), Matthew A. Janiga (NRL) and Kathy Pegion (GMU)(JGR-Atmos, under review)

SubX, 07/10/2019

MJO Prediction

• Ensemble mean• All events: RMM amplitude >0

RMM Prediction Skill

→ Comparable skill range to S2S models (Vitart 2017, Lim et al. 2018)

• Slower Propagation Speed

Faster

Slower

Phase Bias

MJO propagation speed

• All MJO phases• Initially strong MJO

(RMM amp>1)

• Weaker amplitude (Quick decay of MJO signal)

Stronger

Weaker

Amplitude Bias

MJO amplitude

• All MJO phases• Initially strong MJO

(RMM amp>1)

• Weaker amplitude at Phase 1~4

→ Quick decay of signal when MJO starts from the Indian Ocean and propagates through the Maritime Continent

MJO amplitude by phase

Maritime Continent MJO prediction barrier

OBS: OLR & 850hPa wind anomalies

* MJO event selection- Initially Strong MJOs (RMM amp>1.0)- OBS: 246 events

MJO Propagation

Initial Phase 1 & 2

Forecast DAY 01

* MJO event selection- Initial Phase 1 & 2- Initially Strong MJOs- ( ): Number of events- Ensemble mean

OLR & 850hPa Wind ano

MJO Propagation

* MJO detours the Maritime Continent southward during boreal winter(e.g., Lau and Chen 1985, D. Kim et al. 2017)

Forecast DAY 10Forecast DAY 10

OLR & 850hPa Wind ano

MJO Propagation

MJO propagation skill

PCC(τ) (40-200E, 20S-20N)

DAY 10:

Q: What process impacts the fast decay of the MJO propagation signal?

Pattern Correlation Coefficient (PCC)

Bretherton et al. (2004)

Precipitable water, <q> (mm)

Pre

cip

itat

ion

(m

m d

ay-1

)

Daily mean Precipitation vs. PW (Tropical Ocean)

• Tropical deep convection occurs preferentially over the area of high column moisture

• Once the moisture (precipitable water) exceeds some threshold value, precipitation increases rapidly.

• MJO is distinguished from other waves by the strong moisture-convection coupling.

MJO: Moisture-Convection Coupling

“Moisture mode” theory for MJO

𝝏 𝒒

𝝏𝒕= − 𝑽 ∙ 𝜵𝒒 − 𝜔

𝜕𝑞

𝜕𝑝+ … .

• Growth, decay, and propagation of MJO convection are explained by those of anomalous moisture (or MSE).

• Colum-integrated moisture budget:

* Yu and Neelin (1994), Sobel et al. (2001), Raymond and Fuchs (2008), Raymond et al. (2009), Maloney (2009), Sobel and Maloney (2012, 2013), Jiang et al. (2015, 2017), Adames and Kim (2016)

− 𝑽′ ∙ 𝜵ഥ𝑸MJO wind Mean moisture

→ Advection of seasonal mean moisture( ത𝑄) by anomalous MJO circulation (V’) controls the MJO eastward propagation

Active MJOSuppressed

MJO

Winter mean moisture (Q850)

Observation

MJO Moisture advection MJO propagation

− 𝑽′ ∙ 𝜵ഥ𝑸

Moisture Advection

Day 01 Day 10

Eastward Propagation Process

OBS

Multi-model mean:Weaker

10 days meanMoisture advection (−𝑉′ ∙ 𝛻 ത𝑄)

Eastward Propagation Process

Mean State Bias: Q850

OBS

Bias (MMM-OBS)

Dry bias in the lower-

troposphere

Drier Wetter

Winter mean moisture (Q850)

(Less steep meridional Q gradient)

Mean State Bias: Q850

More rain

Drier Wetter

Precipitation (mm/day)

Mean State Bias: Precipitation

OBS

Bias (MMM-OBS)

Mean State Bias: Precipitation

Precipitation distribution

• Precip. days/Total days • 4-weeks average• [60E-180E, 15S-15N] • Control simulation • Land area excluded

→Models have too frequent light rain (drizzle)

Light Moderate Heavy

Precipitation rate (Tropical Oceans)

Moisture-Precipitation Relationship

→ Convection starts too early and occurs too frequently in the low moisture regime

Specific Humidity vs. Precipitation (Tropical Oceans)

→ Deep convection is not sufficiently inhibited when tropospheric moisture is low, which is likely due to the representation of entrainment.

Summary

• Common biases in SubX and S2S reforecasts:

- Convection starts too early in the low moisture regime

- Light precipitation occurs too frequently

→ Excess of surface precipitation & Drier lower troposphere

→Weaken the moisture advection process − 𝑉′ ∙ 𝛻 ത𝑄

→Weaken the MJO eastward propagation signal

→ Limit MJO prediction skill

Convection starts too early Dry bias MJO prediction skill