Coupled Model Simulations on the Effect of Large-scale Orography

on Climate

Akio KITOHMeteorological Research Institute, Tsukuba, JAPAN

Kitoh (2004) J.Climate

Kitoh (2007) Clim.Dyn.

2007.7.25　 Celebrating the Monsoon, Bangalore

Significance of GCM experiments on the effect of orography

• Mechanisms that regulate our climate- land-ocean distribution

- mountain height

- seasonal cycle

- atmosphere-ocean interaction

• Understanding future climate change- reason of the changes in monsoon and ENSO

• Tectonics and climate- paleoclimate

- deep sea / lake drilling

http://www.ig.utexas.edu/research/projects/plates/plates.htm

65 Million years ago

Past plates

30 Million years ago

Clark et al. 2004

Changes in river routing

Tibetan Plateau uplift

Kutzbach et al. (1993) J.Geology

Effects of mountains on climate

Summer heating and monsoon circulation

Winter spin dynamics in mid-latitude westerlies, and low-level blocking

Upslope/downslope winds and rainfall patterns

Temperature

All mountains in the world are varied uniformly between 0% and 140%.

Land-sea distribution and vegetation are the same for all experiments.

MRI-CGCM2. No flux adjustment.

0 10 20 30 40 50 year

M14 (140%)

M12 (120%)

M10 (control)

M8 (80%)

M6 (60%)

M4 (40%)

M2 (20%)

M0 (no mountain)

ExperimentsTopography in Control (M10)

Atmos: T42 (2.8x2.8)

Ocean: 2.5 lon x 0.5-2.0 lat

Coupled Atmosphere-Ocean GCM

→ lapse-rate effect adjustment of 6.5 K/km

Annual mean 2m temperature (M-NM)

+ inland area - coastal area / ocean

Large temperature drop

← due to lapse rate effect

SST also changes

TaMinNM

M

M-NM

2m Temperature in the Coldest Month

Continental winter temperature is lower in mountain case

TaMax

Inland summer temperature rises by mountains

NM

M

M-NM

2m Temperature in the Warmest Month

TaRange

Large annual range of temperature by mountains except in South Asia

M-NM

NM

M

Annual Range of 2m Temperature

Month of Maximum 2m Temperature

Mountain advances the timing of the hottest month over some area over land, partly due to cooling by monsoon penetration

M-NM

NM

M

precipAnnual Precipitation

M-NM

NM

M

Precipitation increase in South Asia and East Asia

swsM-NM

NM

M

Soil Moisture in the Top Layer

Soil moisture changes are mainly due to precipitation changes

Monsoon: DJF minus JJA

Precipitation (color) and surface winds (vector)

モンスーンNM(0%)

20%

M(100%)40%

80%

60% 120%

140%

Monsoon emerges by land-sea contrast without orography

It moves inland with orography

100% OBS

0%

20

40

60

80

120

140

Summer (JJA) Precipitation

Precipitation area moves inland by mountain uplift

Baiu appears with more than 60% orography

→ 　 Tibetan Plateau is important for East Asian climate

June 850 hPa winds

100%

No M

20

40

80

120

140

60

Obs

Westerly summer monsoon flow over the North Indian Ocean becomes strong by mountain uplift

Location changes due to intensified North Pacific subtropical high

500 hPa Zonal winds (westerly jet)

U500 (January) U500 (July)

U500 (80E-100E ave)

Jan Jul

lat

month

Jet axis jumps from south to north of the Tibetan Plateau in early summer

500 hPa zonal wind (80E-100E ave)

No M

20%

M (100%)40%

80%

60% 120%

140%

OBS

Jet locates north of 40N throughout the year with lo orography

With mountain uplift, jet locates south of the Tibetan plateau in winter

Cold source effect of wintertime orography

120E-140E Precipitation obs

M4 0.75

M0 0.71

M8 0.81

M12 0.74

M2 0.74

M10 0.79

M6 0.79

M14 0.66

Numbers indicate spatial cc with obs

50N

10S

Baiu appears with more than 60% orography

Kitoh (2004) JC

Water budget: annual mean M-NMPrecipitation Soil moisture

RunoffEvaporation

Sea surface salinity

SSS decreases in the Asian marginal seas by mountain uplift

SSS increases in the Arabian Sea

Water budget: annual mean M-NMRiver water flux

Precip - evap Sea surface temperature

SST seasonal change in the N Arabian Sea

DJF M0

JJA M10JJA M0

DJF M10

Koppen climate: AsiaKöppen climate

Note the difference in arid climate (desert BW, steppe BS)

No M

20%

M (100%)40%

80%

60% 120%

140%

Kitoh (2005) JGSJ

Köppen climate type: China

“• BW” “BS” dominates in 0% 〜 40% cases; too dry

“• Cw” “Cf” appears from 60% case as precip increases

“• Cs” appears in 80% 〜 120% cases due to larger winter precip

OBS

100%0%

Köppen climate type: India

• “BW” “BS” “Aw” as precip increases

• “BS” in the interior part of peninsular India does not appear in the model due to coarse resolution

OBS

100%0%

Rainfall Index IMR: India, land

10N-30N, 60E-100E

SEAM: Southeast Asia

5N-25N, 100E-130E

EAM: East Asia

25N-35N, 120E-140E

CGCM

AGCM

CGCM

AGCM

CGCM

AGCM

Summer monsoon precipitation is not linear to mountain height, depending on its location and whether air-sea interaction is included or not (CGCM vs AGCM)

Kitoh (2004) JC

ENSO OBS NMM

SST

Wind 850

Precip

Sea surface temperature

Surface winds

Pacific trade winds become stronger associated with strengthened subtropical high with mountain uplift

When mountain is low, a warm water pool is located over the central Pacific; it shifts westward with uplift

SST gradient reverses over the Indian Ocean

uplift

Kitoh (2007) CD

El Nino Modulation

In M0, large amplitude and regular El Nino

El Nino becomes weaker, shorter period and less periodic with mountain uplift

In M0, the SST pattern is nearly symmetric about the equator

The spatial pattern (e.g. meridional width) changes with uplift

SST/SOI time series 　　　 SST pattern 　　　 power spectrum

7 yr

4 yr

large amp

small amp

Kitoh (2007) CD

uplif

t

Summary • Systematic changes in SST and ENSO as well as precipitation patter

n and circulation fields (Asian monsoon) appeared with progressive mountain uplift.

• In the summertime, precipitation area moved inland of Asian continent with mountain uplift, while the Pacific subtropical anticyclone and associated trade winds became stronger.

• The model has reproduced a reasonable Meiyu/Baiu rain band at the 60% case and higher.

• Desert area decreases with mountain uplift.

• When the mountain height is low, a warm pool is located over the central Pacific; it shifts westward with mountain uplift.

• El Nino is strong, frequency is long and most periodic in the no mountain run. They become weaker, shorter and less periodic when the mountain height increases.

ENSO-Monsoon relationship

From CLIVAR homepage

Drought conditions over India accompany warm ENSO events and vice versa

Model ENSO-monsoon relationship is fairly robust in lag=0 except for the no-mountain (M0) case

Temporal structure is different between low-mountain and high-mountain cases