Modeling of present-day monsoon and ENSO

Akio KITOH

Meteorological Research Institute, Japan Meteorological Agency

1: Climate model

2: Simulation of monsoon

3: Simulation of ENSO

Definition of MonsoonDefinition of Monsoon

Originated from ancient Arabian word ‘Originated from ancient Arabian word ‘mausimmausim’ which ’ which means means a seasona season. It was first used by Arab sailors to . It was first used by Arab sailors to describe the seasonal winds that blow across the describe the seasonal winds that blow across the Arabian Sea. Arabian Sea.

Original definition based on Ramage (1972) is most Original definition based on Ramage (1972) is most often applied to the seasonal reversals of the wind often applied to the seasonal reversals of the wind direction. direction.

The zone of maximum rain The zone of maximum rain shifts from around 10shifts from around 10°°S in S in winter to north of 10winter to north of 10°°N in N in summer. The maximum summer. The maximum northward shift in rainbelt is northward shift in rainbelt is over the Asia-Pacific .over the Asia-Pacific .The red box denotes The red box denotes monsoonal regions as defined monsoonal regions as defined by Ramage.by Ramage.The rainbelt over this region The rainbelt over this region is in fact a part of the is in fact a part of the planetary scale TCZ and planetary scale TCZ and occurs due to its variation occurs due to its variation with the season.with the season.

Origin of monsoonOrigin of monsoon

A.A. Traditionally, Asian Traditionally, Asian monsoon is viewed as a monsoon is viewed as a gigantic land-sea breeze gigantic land-sea breeze system driven primarily by system driven primarily by land-ocean thermal land-ocean thermal contrast.contrast.

Differential surface Differential surface heating (land vs. ocean)heating (land vs. ocean)

Latent heat release in the Latent heat release in the atmosphereatmosphere

The Earth’s rotation The Earth’s rotation playing important rolesplaying important rolesB.B. Alternately, it is considered Alternately, it is considered

to be a part of the planetary to be a part of the planetary scale TCZ that essentially scale TCZ that essentially follows the seasonal march follows the seasonal march of the Sun.of the Sun.

Low pressure over the Asian continent forcing large-Low pressure over the Asian continent forcing large-scale convergence of moist air across surrounding scale convergence of moist air across surrounding oceansoceans. .

As monsoons have come to be better understood, the definition has As monsoons have come to be better understood, the definition has been broadened to include almost all of the phenomena associated been broadened to include almost all of the phenomena associated with the annual weather cycle over the affected regions: Seasonality with the annual weather cycle over the affected regions: Seasonality in wind and precipitation.in wind and precipitation.

Introduction: MonsoonIntroduction: MonsoonIntroduction: MonsoonIntroduction: Monsoon

⇧Regions experiencing a seasonal surface wind shift of at least 120° Regions experiencing a seasonal surface wind shift of at least 120° with a frequency of prevailing octant >40%with a frequency of prevailing octant >40%

⇧Asian summer monsoon Asian summer monsoon region: A part of the monsoon region: A part of the monsoon region including adjacent region including adjacent regions with predominant rainy regions with predominant rainy season occurring during boreal season occurring during boreal summer.summer.

⇧Two major components of Asian Two major components of Asian monsoon: South Asian and Southeast monsoon: South Asian and Southeast Asian monsoon: (1) Indo-China region Asian monsoon: (1) Indo-China region (between), (2) equatorial Indian (between), (2) equatorial Indian Ocean and (3) western North Pacific Ocean and (3) western North Pacific (adjacent). (adjacent).

Asian Summer MonsoonAsian Summer Monsoon South Asian MonsoonSouth Asian Monsoon Southeast Asian Southeast Asian MonsoonMonsoon

Climate ModelClimate Model

Observed SST, Precip, Wind (JJA) Simulation MRI

Simulation MRIObserved SST, Precip, Wind (DJF)

最暖月

Koppen climateKoppen climate

Koppen climate

Simulation of MonsoonSimulation of Monsoon

JJAS Mean: Rainfall & 850 hPa Wind FieldJJAS Mean: Rainfall & 850 hPa Wind Field

MRI/JMAMRI/JMA

Realistic FeaturesRealistic Features Rainbelts over parts Rainbelts over parts

of India, Indo-China, of India, Indo-China, South China Sea South China Sea through Philippine through Philippine SeaSea

Zonal rainbelt from Zonal rainbelt from Indonesian region to Indonesian region to mid-Pacificmid-Pacific

The rainbelt The rainbelt associated with associated with Meiyu-Baiu front.Meiyu-Baiu front.

DeficiencyDeficiency Southward shift of Southward shift of

rainbelt over Bay of rainbelt over Bay of BengalBengal

Deficit of rainfall Deficit of rainfall over the equatorover the equator

MRI/JMAMRI/JMACRDCRD

•Onset to around 10N in late Onset to around 10N in late May/early June. May/early June. •The equatorial rainbelt is active The equatorial rainbelt is active throughout the year and the throughout the year and the continental rainbelt is centered continental rainbelt is centered around 15N and extends beyond around 15N and extends beyond 25N.25N.

Seasonal Variation of pentad mean precipitation over IndiaSeasonal Variation of pentad mean precipitation over India

Onset occurs around late May as a Onset occurs around late May as a quick transitionquick transitionPersistent heavy rainfall throughout Persistent heavy rainfall throughout the season the season longer duration of longer duration of monsoonmonsoonThe oceanic rainbelt is weaker, the The oceanic rainbelt is weaker, the northward extent of continental northward extent of continental rainbelt is limited within 20Nrainbelt is limited within 20NThe two rainbelts are connected by The two rainbelts are connected by very weak intraseasonal northward very weak intraseasonal northward propagations.propagations.

MRI/JMAMRI/JMACRDCRD

Over 120E-140EOver 120E-140E Observation shows disappearance of dry region over the Philippine Observation shows disappearance of dry region over the Philippine Sea in early May and a northward shift of rainbelt from 20N in May to Sea in early May and a northward shift of rainbelt from 20N in May to 35N in July. 35N in July. This northward shift and late June Baiu rainfall peak are well This northward shift and late June Baiu rainfall peak are well reproduced by the model. reproduced by the model. The model simulates revival of rainbelt in late August/September with The model simulates revival of rainbelt in late August/September with a slightly early peak.a slightly early peak.

CRDCRD MRI/JMAMRI/JMA

Mean Evolution of Monsoon: Strength of monsoon & extent of domainMean Evolution of Monsoon: Strength of monsoon & extent of domain

Monsoon annual Monsoon annual rangerange difference difference between maximum between maximum May-Sep. pentad May-Sep. pentad mean rainfall & Jan. mean rainfall & Jan. mean rainfall mean rainfall ((""maximum of relative maximum of relative climatological pentad climatological pentad mean rainfallmean rainfall""). ).

Contour 4 Contour 4 mm/day delineates mm/day delineates monsoon domain. monsoon domain.

Simulation is Simulation is close to close to observation.observation.

Kang et al. (2002)

The Monsoon Domains observed and simulated by 10 AGCMs. (Kang et al., 2002, CD)

CLIVAR/GCM Monsoon Intercomparison Project: COLA, DNM, GEOS, GFDL, IAP, IITM, MRI, NCAR, SNU, SUNY/GLA

Smoothed annual cycle defined as the sum of annual Smoothed annual cycle defined as the sum of annual mean plus first 12 harmonics of the climatological mean plus first 12 harmonics of the climatological

pentad mean rainfallpentad mean rainfall..

Onset of Monsoon on Indian Landmass Onset of Monsoon on Indian Landmass Onset of Monsoon on Indian Landmass Onset of Monsoon on Indian Landmass

Mean Onset DateMean Onset Date

• • Gradual northwestward progression of monsoon Gradual northwestward progression of monsoon from Bay of Bengal. from Bay of Bengal.

• • Monsoon establishes over the subcontinent by the Monsoon establishes over the subcontinent by the middle of July.middle of July.

After Rao (1976)After Rao (1976)

CRDCRD MRI/JMAMRI/JMA

Indian regionIndian region• • Northeastward Northeastward progression over AS progression over AS and the northwestward and the northwestward progression over the progression over the Bay of Bengal are well Bay of Bengal are well reproduced.reproduced. East AsiaEast Asia• • The model simulates The model simulates earlier monsoon onset earlier monsoon onset over southeast Asia. over southeast Asia. • • Onset over Indochina Onset over Indochina in early May, the mid-in early May, the mid-May onset over the SCS May onset over the SCS & later northward & later northward progression due to progression due to Meiyu/Baiu rainband Meiyu/Baiu rainband are all simulated, are all simulated, although the precise although the precise timings differ slightly.timings differ slightly.• • In northern China, In northern China, onset is earlier and onset is earlier and precipitation is heavier. precipitation is heavier.

Onset Pentad: the Julian pentad in which the relative Onset Pentad: the Julian pentad in which the relative climatological pentad mean rainfall rate exceeds 4 climatological pentad mean rainfall rate exceeds 4

mm/day.mm/day.

MRI/JMAMRI/JMACRDCRD

• • The peak pentad is The peak pentad is realistic over most of realistic over most of the Indian region, the Indian region, except for the late except for the late peak rainfall over peak rainfall over northwest India. northwest India.

• • Over most of the Over most of the west Pacific region west Pacific region model peak rainfall model peak rainfall timing realistictiming realistic

Mean Evolution of Monsoon: Peak Rainfall PentadMean Evolution of Monsoon: Peak Rainfall Pentad

CRDCRD MRI/JMAMRI/JMA

Simulation close to Simulation close to observation.observation.

Withdrawal Pentad: Withdrawal Pentad: the transitional the transitional pentad in which pentad in which rainfall drops rainfall drops below 4 mm/day.below 4 mm/day.

Mean Evolution of Monsoon: Monsoon withdrawalMean Evolution of Monsoon: Monsoon withdrawal

Observation Observation shows:shows: southward retreat of southward retreat of monsoon over India, monsoon over India, southeast Asia and southeast Asia and Western north Pacific Western north Pacific

northward retreat northward retreat over East Asia.over East Asia.

ENSO and ENSO-monsoon ENSO and ENSO-monsoon relationshiprelationship

ENSO and its effect on climate its effect on climate

ENSO 1997/98ENSO 1997/98 NOAA/PMEL

Rainfall anomalies during November 1997-April Rainfall anomalies during November 1997-April 19981998

BAMS (1999)

from M.Latif

from M.Latif

Monsoon - ENSO Monsoon - ENSO ConnectionsConnections

The three components of The three components of the monsoon system are the monsoon system are tied to the heated land, the tied to the heated land, the tropical warm pools and tropical warm pools and the cold winter ocean and the cold winter ocean and land areas. All of these land areas. All of these produce the strongest produce the strongest heating gradients on the heating gradients on the globe. There are three globe. There are three major circulation major circulation associated with the boreal associated with the boreal and austral summer and austral summer monsoons. These form a monsoons. These form a simplified but integrated simplified but integrated view of the Monsoon view of the Monsoon ENSO atmospheric ENSO atmospheric circulations in the Indo-circulations in the Indo-Pacific Region.Pacific Region.

with flux adjustment without flux adjustment

SST-EOF1

Surface air temperature

SST-EOF1 with vs without flux adjustmentSST-EOF1 with vs without flux adjustment

Control run: global SST EOF1 and regressionsSST-EOF1 and its regressions (MRI-CGCM2 control)SST-EOF1 and its regressions (MRI-CGCM2 control)

spectrum of SST-NINO3 （ Global Wavelet ）

Model tends to shift towards higher frequency than observedModel tends to shift towards higher frequency than observed

ENSO - Monsoon RelationshipENSO - Monsoon Relationship

The role of air-sea interaction: Remote SST Impact on ISMRThe role of air-sea interaction: Remote SST Impact on ISMRSignificant remote SST impact on Indian monsoon is the inverse relationship between ISMR and ENSOSignificant remote SST impact on Indian monsoon is the inverse relationship between ISMR and ENSO

Standardized indices of model ISMR, DMI (a measure of the monsoon strength in terms of the zonal wind Standardized indices of model ISMR, DMI (a measure of the monsoon strength in terms of the zonal wind shear between 850 and 200 hPa over 40E-110E, 5N-20N) and NINO3 SST (over 150W-90W,5S-5N) .shear between 850 and 200 hPa over 40E-110E, 5N-20N) and NINO3 SST (over 150W-90W,5S-5N) .

The correlation between ISMR and DMI is 0.69 because DMI is a measure of the large-scale monsoon The correlation between ISMR and DMI is 0.69 because DMI is a measure of the large-scale monsoon circulation and does not necessarily correspond to the regional rainfall variation represented by ISMR. circulation and does not necessarily correspond to the regional rainfall variation represented by ISMR.

The correlation between ISMR and NINO3 SST is -0.73 much larger than observed value of -0.46 (which The correlation between ISMR and NINO3 SST is -0.73 much larger than observed value of -0.46 (which suggests NINO3 SST is only one of the modulators of monsoon). The correlation between DMI and NINO3 suggests NINO3 SST is only one of the modulators of monsoon). The correlation between DMI and NINO3 SST is also high -0.86. Both correlations are negative consistent with the tendency for below (above) normal SST is also high -0.86. Both correlations are negative consistent with the tendency for below (above) normal monsoonmonsoon during ENSO years during ENSO years but imply a much stronger impact of NINO3 SST on ISMR in the model. but imply a much stronger impact of NINO3 SST on ISMR in the model.

Remote SST Impact on ISMRRemote SST Impact on ISMR

LCC from -2 years to +2 years of LCC from -2 years to +2 years of equatorial monthly SSTs against equatorial monthly SSTs against JJAS mean NINO3+4 (160E-JJAS mean NINO3+4 (160E-90W,7.5S-7.5N) SST. 90W,7.5S-7.5N) SST.

Observation Observation 1.1. High positive correlations for about High positive correlations for about

one and a half years beginning from one and a half years beginning from around Jan (0) to around July (+1) around Jan (0) to around July (+1) in the central and eastern equatorial in the central and eastern equatorial Pacific. Pacific.

2.2. Simultaneously, there are negative Simultaneously, there are negative correlations over the West Pacific correlations over the West Pacific and positive correlations over the and positive correlations over the Indian and Atlantic Oceans. Indian and Atlantic Oceans.

Model Model 1.1. A small amplitude QBO appears to A small amplitude QBO appears to

be dominant in the model. be dominant in the model. 2.2. Strong positive correlations (Strong positive correlations (~~0.75) 0.75)

extending over the whole of Indian extending over the whole of Indian Ocean during JJAS season at lag (0). Ocean during JJAS season at lag (0). indicates the strong connection indicates the strong connection between Pacific SST and equatorial between Pacific SST and equatorial Indian Ocean SST in the model. Indian Ocean SST in the model.

Remote SST Impact on ISMRRemote SST Impact on ISMR

LCC from -2 years to +2 years of equatorial LCC from -2 years to +2 years of equatorial monthly 850 hPa zonal wind against JJAS monthly 850 hPa zonal wind against JJAS mean NINO3+4 (160E-90W,7.5S-7.5N) SST. mean NINO3+4 (160E-90W,7.5S-7.5N) SST.

Observation Observation Zonal wind anomalies propagates eastward Zonal wind anomalies propagates eastward

from IO to the WPfrom IO to the WP ModelModel Wind anomalies also propagate eastwards but Wind anomalies also propagate eastwards but

with a slightly faster speed. This difference in with a slightly faster speed. This difference in phase speed corresponds well with the phase speed corresponds well with the simulated QBO time scale. (In the equatorial simulated QBO time scale. (In the equatorial Pacific, simulated SST and the wind anomalies Pacific, simulated SST and the wind anomalies extended further westward with slightly extended further westward with slightly narrower meridional extend. Consequently, the narrower meridional extend. Consequently, the travel time of wind forced oceanic Rossby travel time of wind forced oceanic Rossby waves to reach the western boundary is shorter waves to reach the western boundary is shorter compared to observation. This acts as an compared to observation. This acts as an essential factor for the shorter time-scale of essential factor for the shorter time-scale of model ENSO). model ENSO).

During JJAS season at lag (0), the much higher During JJAS season at lag (0), the much higher negative correlations over the IO extends over negative correlations over the IO extends over the whole domain establishing the enhanced the whole domain establishing the enhanced impact of Pacific SST in the model. impact of Pacific SST in the model.

The dominance of QBO time scale of Pacific The dominance of QBO time scale of Pacific Warming and its stronger correlation with Warming and its stronger correlation with Indian monsoon can play a major role in Indian monsoon can play a major role in modifying the mean monsoon pattern during modifying the mean monsoon pattern during warm years. warm years.

The weakening of zonal wind component (e.g., due to remote impact of Pacific SST) leads to reduction in The weakening of zonal wind component (e.g., due to remote impact of Pacific SST) leads to reduction in evaporation over the IO which in turn result in reduced monsoon precipitation over India through reduced evaporation over the IO which in turn result in reduced monsoon precipitation over India through reduced moisture convergence. Associated with this reduced evaporation and precipitation, the land temperature tends to moisture convergence. Associated with this reduced evaporation and precipitation, the land temperature tends to increase over India. increase over India. In summary, positive equatorial East Pacific SST anomalies have a negative impact on the large scale Indian In summary, positive equatorial East Pacific SST anomalies have a negative impact on the large scale Indian summer monsoon (mostly on a biennial time scale in the model through the zonal shifting of the regions of summer monsoon (mostly on a biennial time scale in the model through the zonal shifting of the regions of maximum tropical precipitation and diabatic heating from convective precipitation processes).maximum tropical precipitation and diabatic heating from convective precipitation processes).

The role of air-sea interaction: Remote SST Impact on ISMRThe role of air-sea interaction: Remote SST Impact on ISMRLag (0) regression of model wind speed (at 10m), evaporation, precipitation and surface air temperature over India against Lag (0) regression of model wind speed (at 10m), evaporation, precipitation and surface air temperature over India against

NINO3 SST.NINO3 SST.

Reduced moisture convergence towards Reduced moisture convergence towards Indian monsoon regionIndian monsoon region

Weaker Indian Summer Weaker Indian Summer MonsoonMonsoon

Weaker equatorial IO Zonal WindWeaker equatorial IO Zonal WindTendency for Enhanced land temperature Tendency for Enhanced land temperature

over Indiaover India

Reduced Evaporation over Reduced Evaporation over equatorial IO & Indiaequatorial IO & India

Reduced ConvectionReduced ConvectionReduced PrecipitationReduced Precipitation

Positive equatorial East Pacific Positive equatorial East Pacific SST AnomalySST Anomaly

IMR and NINO3.4 SST from 1000-year runIMR and NINO3.4 SST from 1000-year run

MRI-CGCM2 1000-yr run

MRI-CGCM2 1000-yr run

IMR and NINO3.4 SSTIMR and NINO3.4 SST

Note a large interdecadal variability of ENSO-monsoon relationshipNote a large interdecadal variability of ENSO-monsoon relationship

MRI-CGCM2 1000-yr run

IMR and NINO3.4 SSTIMR and NINO3.4 SST

A weakening of ENSO-monsoon A weakening of ENSO-monsoon relationship is associated with relationship is associated with warmer Eurasian continent warmer Eurasian continent