Coupled Model Simulations on the Effect of Large-scale Orography on Climate Akio KITOH Meteorological Research Institute, Tsukuba, JAPAN Kitoh (2004) J.Climate Kitoh (2007) Clim.Dyn 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

/plates.htm 65 Million years ago Past plates 30 Million years ago Clark et al 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

GCM Study on mountain and monsoon #AGCM perpetual July Hahn and Manabe 1975: Jul GFDL 270km L11 Kutzbach et al. 1989: Jan/Jul CCM R15 L9 #AGCM seasonal cycle Broccoli and Manabe 1992: GFDL R30 L9 NH midlatitude dry climates An et al. 2001: NCAR CCM3 4 stage Himalayan uplift Liu and Yin 2002: COLA AGCM 11cases: 0%, 10%, …, 100% #AGCM + slab ocean Kutzbach et al. 1993: CCM1 R15 L m slab ocean Kitoh 1997: MRI-II 4x5 L m slab ocean #AOGCM Kitoh 2002, Abe et al. 2003, 2004, 2005: MRI-CGCM1 (4x5) SST change Kitoh 2004, 2005, 2007: MRI-CGCM2 (T42)0% to 140% from AGCM to AOGCM

MRI CGCM2 AGCM AGCM –MRI/JMA98 –T42 (2.8x2.8), L30 (top at 0.4 hPa) –Longwave radiation - Shibata and Aoki (1989) –Shortwave radiation - Shibata and Uchiyama (1992) –Cumulus - Prognostic Arakawa-Schubert type –PBL - Mellor and Yamada level 2 (1974) –Land Surface - L3SiB or MRI/JMA_SiB OGCM OGCM –Resolution : 2.5 lat x lon, 23layers –Eddy mixing : Isopycnal mixing, GM –Seaice : Mellor and Kantha (1989) Coupling Coupling –Time interval : 24hours –With/without flux adjustment

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 year M14 (140%) M12 (120%) M10 (control) M8 (80%) M6 (60%) M4 (40%) M2 (20%) M0 (no mountain) Experiments Topography in Control (M10) Atmos: T42 (2.8x2.8) Ocean: 2.5 lon x 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

TaMin NM 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

precip Annual Precipitation M-NM NM M Precipitation increase in South Asia and East Asia

sws M-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% Winter (DJF) Precipitation

100%OBS 0% 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 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) JanJul 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 M M M M M M M M Numbers indicate spatial cc with obs 50N 10S Baiu appears with more than 60% orography Kitoh (2004) JC

Water budget: annual mean M-NM PrecipitationSoil 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-NM River water flux Precip - evapSea surface temperature

SST seasonal change in the N Arabian Sea DJF M0 JJA M10JJA M0 DJF M10

Koppen climate: Asia Köppen 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 OBSNMM 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 uplift

Mountain height (%) atm=cov /var, ocn=cov /var SST=NINO3.4 SST, Taux=Tau[150E-150W, 4S-4N] Air-sea coupling sensitivity Kitoh (2007) CD

Summary Systematic changes in SST and ENSO as well as precipitation pattern 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