Mesoscale Convective Systems in the Initiation of the MJO

Mesoscale Convective Systems in the Initiation of the MJO

Jian Yuan and Robert A. HouzeUniversity of Washington

CloudSat/CALIPSO Science Team Meeting Montreal, Quebec, Canada, 16 June 2011

The Madden-Julian Oscillation (MJO):

• Play important roles in weather and climate

• Current prediction skill, especially for the initial phase of MJO is very limited

• Cumulus parameterizations in GCMs is the primary limiting factor in MJO simulation and prediction.

(Zhang et al. 2010, DYNAMO)

(Courtesy of US CLIVAR MJO Working Group)

MJO initiation processes

Feedbacks between:

•Clouds•Radiative heating•Convection•Precipitation •Ocean

are a key to understanding the MJO.

Fundamental processes related to MCSs that are crucial to understand MJO:

•the diabatic heating structure•convective sensitivity to environmental moisture•cloud microphysics•convective organization

Courtesy of Zhang et al. 2009, DYNAMO After Stephens et al. 2004, “Humidistat Feedback”

MCSs including both raining and anvil components are identified using A-Train

instruments

Yuan and Houze 2010

MODIS TB11 + AMSR-E (Yuan and Houze 2010)

combined to find“cold centers” & “raining areas”

Use 260 K threshold

Locate 1st closed contour

Use 1 mm/h threshold for rain rate

Associate pixels with nearest cold center

Use 6 mm/h threshold for heavy rain

MCS Criteria (Yuan and Houze, 2010)

Systems whose largest raining cores have

• Area > 2000 km2

• Min TB11 ≤ 220 K

Must have one dominant core

• with intense cells, and• accounting for >70% rain area56% all tropical rain

MCSs are further divided to two groups :

1.Separated (40 % rain fall)

1.Connected (>=3 MCSs share the same rain feature, 16% rain fall)• Separated MCS: Frequently found over all

convective zones, especially continents

• Connected MCS: more organized convection, primarily found over warm ocean area

MODIS/AMSR-E/CloudSat

identifies MCSs obtains the global distribution of MCSs

investigates variability of MCSs in MJO

(EIO:-15-15oN;75-100oE; Composite of 8 phases; Wheeler and Hendon 2004)

More Connected MCSs observed in MJO

active phases

OLR

Deeper MCSs observed in pre-onset, initial and active phases

Low level Θe likely determines the Tb_min

(“hot tower” hypothesis)

Phase 1-3

Phase 5-7

Climatology of EIO:

•T150 hp ≈ 205 K

•Θe150 hp≈ 352.6 K

Moisture effects need to be better understood

Deeper MCSs

Deeper MCSs

Less MCSs; less

organized

More MCSs; more

organized

Summary and Conclusions

A-Train instruments make it possible to identify MCSs (raining + anvil components) globally

MJO pre-onset phase active phases over EIO:

Deeper MCSs & Warmer low level Θe (both)

Less More MCSs

Relatively Less More organized MCSs

Drier Moister middle troposphere

End

MJO activities viewed in OLR

MCSs Over the Whole Tropics: oceanic conditions favor larger systems

Smallest 25% (<12,000 km2)

Largest 25% (>40,000 km2)

“Superclusters”