On the varieties offorced and spontaneously generated

tropical precipitation patterns:some expectations and results

Yoshi-Yuki Hayashi Yukiko Yamada

Yoshiyuki Takahashi Masaki IshiwatariMayumi Yoshioka

Wataru OhfuchiTakeaki Sampe

Kensuke Nakajima

1)Hokkaido University, 2)University of Tokyo, 3)Kyushu Universtiy, 4)ESC/JAMSTEC

shosuke@gfd-dennou.org2005-04-20

Reading, U.K.

Contents

• equatorial disturbances– From Hayashi & Sumi 1986 + Numaguti & Hayas

hi 1991• Classical image: wave-CISK, WISHE

– eastward vs. westward• advection or wave

– planeary scale modulation?

• steady response to SST anomaly– Hosaka et al 1998 vs. Hoskins & Neele 2000

equatorial disturbances

Hayashi and Sumi 1986Numaguti and Hayashi 1991a,b

•aqua planet condition•the first global NWP model of Japan Met. Agency run at the Univ. of Tokyo•T42L12•cumulus parameterization

• Kuo (Hayashi & Sumi 1986)• Kuo and Adjustment (Numaguti & Hayashi 1991a, b)

Hayashi & Sumi 1986 JMSJ 64 451

20 years ago …

• super (cloud) clusters:

eastward moving feature with a scale of a few grids• wave number one modulation (30 day oscillation):

inhomogeneous distribution of super clusters• double ITCZ

Hayashi and Sumi 1986

Hayashi & Sumi 1986 JMSJ 64 451

super cloud clusters: spurious or real• since their scale is at the edge of the model resolution, they were, at the beginning, regarded as computational noise. • Nakazawa 1986, equatorial OLR x-t diagram with the time resolution higher than those plotted before, gives some reality; many eastward features are identified within one active ISV phase

Nakazawa 1986 JMSJ 64 777

super cloud clusters in the model: Kelvin wave-CISK

Numaguti & Hayashi 1991 JMSJ 69 541

•Kuo scheme is regarded to be wave-CISK friendly•Composite structure resembles those expected for Kelvin wave-CISK

wave number one modulation (30 day oscillation): WISHE, frictional convergence?

with wind feedback

Kuo

Adj

ustm

ent

no wind feedback (zonal mean 　　　 　 )

•An experiment without surface wind feedback (longitudinally uniform evaporation) show little evidence of wave number one modulation

• However, Lee et al (2003) argues that frictional convergence is important.

Numaguti & Hayashi 1991 JMSJ 69 563

equatorial wave (no feedback)• equatorial wave-CISK with an asymmetric feedback where heating occurs only when low level vertical wind is positive tends to present only Kelvin coherent (non dispersive) wave packet. (Lau and Peng 1987)

linear CISK feedbackpositive only CISK feedback

Kelvin and westward gravity wave packetKelvin wave with single upward region

http://www.gfd-dennou.org/arch/ape/wavecisk

A simple way of thinking from old days: near the grid scale

• Hence, super cloud clusters may be regarded as a realization of

Kelvin wave-CISK.• Size of super cloud clusters is larger than covering several cloud

clusters.• according to the prediction of growth rate of wave-CISK theory,

it must be the smallest size in the range where dynamics of

convective cloud system (mesoscale dynamics) does not interfare.

• Because of the limitation of model resolution and representation of

moist process, grid scale convection in a model can represent as • super cloud clusters (Kelvin wave-CISK) propagating eastward• convective system advected westward mainly by the background

wind (cloud clusters)

A model may represent both or either of them. • A higher resolution model may represent envelope eastward

super cloud cluster and internal cloud clusters.

A simple way of thinking from old days: near the grid scale

AGU for APE cumulus comparison (T39L48)

eml ias

kuo-sc kuo

Adjust non

Takayabu (1998), Wheeler and Kiladis (1999)

• signals corresponding to westward gravity waves are identified.• So do some models

AGU for APE cumulus comparison (T39L48)

eml ias

kuo-sc kuo

Adjust non

AGU for APE cumulus comparison (T39L48) Qobs

eml ias

kuo-sc kuo

Adjust non

• Three types of grid scale precipitation

1. basically westward propagating + some eastward

2. basically eastward propagating modulated by westward moving envelop

3. both eastward and westward convective areas are similar

appearance

AGU for APE cumulus comparison (T39L48) Qobs

AGU for APE cumulus comparison (T39L48) Qobs

eml ias

kuo-sc kuo

Adjust non

AGUforAPE(eml) CSIRO GSFC

K1JAPAN LASG MGO

NCAR UKMOn48 UKMOn96

model comparison

AGUforAPE(eml) CSIRO GSFC

K1JAPAN LASG MGO

NCAR UKMOn48 UKMOn96

model comparison

radiative cooling weighted in the upper layer

radiative coolingweighted in the lower layer

• westward gravity waves seem to be also coupled with convection.

http://www.gfd-dennou.org/arch/ape/agcm5/mradl/kuo-mradlA-xteq.html

Heating profile (CISKy condition) and wavesby a simple AGCM5.3 model (Kuo)

radiative cooling weighted in the upper layer

radiative coolingweighted in the lower layer

• westward gravity waves also coupled

http://www.gfd-dennou.org/arch/ape/agcm5/mradl/mradlA-xteq.html

Heating profile (CISKy condition) and wavesby a simple AGCM5.3 model (adjustment)

Planetary scale modulation

• Super cloud clusters vs. planetary scale modulation

• Eastward propagating low frequency large scale modulation does not

seem to appear very frequently

AGU for APE (T159L48, none) flatLarge scale modulation

Planetary scale modulation• Super cloud clusters vs. planetary scale modulation.

How do we recognize them?

• These may be considered as higher resolution version of super clusters, wave-CISK

like features, rather than a planetary scale modulation.

Planetary scale modulation• How about those?

K1JAPAN FRCGC

AGUforAPE T159 non flat

• This must be different from super cloud clusters

steady response to SST anomaly

• Neal & Hoskins 2001 ASL 　 (3keq)precipitation decrease both to the east and west

• Hosaka el al 1998 JMSJ precipitation increase to the east of SST anomaly

•AGCM5.3 GFD Dennou Club• by Numaguti from JMA NWP model• prototype of CCSR/NIES model

•SIMPLE•simple radaitive process

• three bands for dry atmosphere

• one band for water vaper•no cloud, no rain

•T42L16

•4K (3.6K on the grid) SST anomaly •Hosaka et al 1998 JMSJ 76 289

Set up of Hosaka et al. 1998

surface pressure response of Hosaka et al. 1998

•To the east wide extension of low pressure anomaly associated with Kelvin wave like response•To the west narrow extension of low pressure anomaly associated with Rossby wave like response, and high pressure anomaly

Hosaka et al 1998 JMSJ 76 289

•To the east

Precipitation decreases as (moist) downwelling Kelvin wave front arrives, and then

precipitation increases because of Ekman convergence toward the equatorial

low pressure associated with the Kelvin wave.•To the west

Precipitation continues to decrease after the arrival of

Rossby wave, since Ekman flow is diverging near the equator.

pressure precipitation

Initial development of SST response exemplified by 128 ensemble mean

•Toyoda et al 2000 Nagare Multi Mdeia http://www.nagare.or.jp/mm/99/toyoda/ •Nakajima et al 2004 JMSJ 82 1483

precipitation response to the east of SST anomaly

• Precipitation to the east of the SST anomaly increases because of

the Ekman convergence associated with the low pressure anomaly

caused by the warm Kelvin wave response extending from

the convection center (SST anomaly region).

• Hence, if the equatorial low pressure anomaly is week compared

to the off-equatorial latitudes,

precipitation may not increase.

• Equatorial surface pressure may not be low enough when

condensation heating is top heavy so that

second baroclinic mode is more intense.

Realistic models which include sophisticated moist processes

and radiation feedbacks cause top heavy profile

compared to simple AGCM5.3.

GSFCAGUforAPE

K1Japan LASG

NCAR UKMO96

model comparison: precipitation anomaly (3Keq)

AGUforAPE GSFC

K1Japan LASG

NCAR UKMO96

model comparison: surface pressure anomaly (3Keq)

AGU for APE cumulus comparison (T39L48) 3Keq

eml ias

kuo-sc kuo

Adjust non

AGU for APE cumulus comparison (T39L48) flat3Keq

eml ias

kuo-sc kuo

Adjust non

AGCM5.3 (simple model, T42L16)

3Keq

Qobs3Keq

flat3Keq

H1998

AGCM5.3 (simple model, T42L16)

3Keq

Qobs3Keq

flat3Keq

H1998

AGU for APE zonal mean precipitation (T39L48)

eml ias

kuo-sc kuo

Adjust non

AGUforAPE GSFC

K1Japan LASG

NCAR UKMO96

model comparison: zonal mean precipitation

Some confessions

• Aqua planet is not easy to understand.• It seems that I do not dislike wave-CISK as a crude theory of

instability caused by wave-wave interaction coupled by

condensation heating. • in other word, I do not have any good simple device to describe

what is going on in the model. • Hayashi and Sumi (1986) is not very robust, rather fragile.

• However, according to late Numaguti, you can tune most of the

parameterizations to reproduce eastward coherent motion of

grid scale activities. • But its tuning does not seem to be easy. • Integration period of those old GCM runs of Hayashi & Sumi (1986)

or Numaguti & Hayashi (1991) is too short to confirm robustness of

planetary scale modulatio.

Figures of AGUforAPE are available from http://www.gfd-dennou.org/arch/ape/