984 (Chinese J Geophys ) 49 tropical regions leading to the formation of the Asian summer monsoon over India the BOB and the SCS The extension of the

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1 CHINESE JOURNAL OF GEOPHYSICS Vol 49 No 4 Jul (4) : Liang X Y Liu Y M Wu G X Roles of tropical and subtropical land- sea distribution and the Qinghai- Xizang Plateau in the formation of the Asian summer monsoon Chinese J Geophys (in Chinese) (4) : : ; (2006) P Roles of tropical and subtropical land- sea distribution and the Qinghai- Xizang Plateau in the formation of the Asian summer monsoon LIANG Xiao2Yun 1 2 LIU Yi2Min 1 WU Guo2Xiong 1 1 State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics ( LASG) Institute of Atmospheric Physics Chinese Academy of Sciences Beijing China 2 National Climate Center Beijing China Abstract Roles of tropical land- sea distribution and the Qinghai- Xizang Plateau in the formation of the Asian monsoon are examined through a series of idealized numerical experiments Results show that the existence and geometric shape of land- sea distribution crucially affect the Asian summer monsoon In an aqua-planet case no monsoon is observed In an experiment in which only the subtropical Eurasian landmass exists while the South Asian and African tropical lands are missing there is a weak summer monsoon over its southeastern corner but no evident cross-equatorial flow in summer and no summer monsoon over India the Bay of Bengal (BOB) or the South China Sea ( SCS) The existence of tropical lands such as the Indochina Peninsula the Indian Peninsula and the African continent induces cross- equatorial flows and strong low- level southwesterlies over the (ZKCX22SW2210) ( ) 1974 E2mail : iap ac cn

2 984 (Chinese J Geophys ) 49 tropical regions leading to the formation of the Asian summer monsoon over India the BOB and the SCS The extension of the subtropical continent into the tropics greatly enhances the summer convective rainfall over the subtropical land The Qinghai- Xizang Plateau works the East Asian monsoon as an amplifier makes it strengthen and develop northward However the South Asian monsoon becomes weak and shrinks southward under effects of the Qinghai- Xizang Plateau Keywords Tropic and subtropic Land- sea distribution Qinghai2Xizang Plateau Asian summer monsoon Numerical simulation Bay of Bengal summer monsoon South China Sea summer monsoon Indian summer monsoon 1 [1719 ] [1 ] Flohn [2 ] [3 ] Hahn and Manabe [4 ] ( ) [5 ] ; [6 ] 2 (BOB) [710 ] ( IAPΠ LASG) - - ( GOALS) [11 ] [20 21] [12 ] ( SAMIL2R42L9) [13 ] [22] [20 21] GOALS [23] [14 ] [15 16 ] 1

3 4 : Table 1 Experimental designs (AQ) T E HLNMT : 0 120E 20 N90 N (HLNMT) HLMT :HLNMT (8715E 3215N) (HLMT) 0 m m : (T - IC) T - IC :0 120E 20N90N ;95E105E 10S20N T - IN :0 120E 20N90N ;75E85E 5N20N (T - IN) T - AF :0 120E 20N90N ;0 50E 35S20N 0 m (T - AF) ENMT : ( T ) 0 120E 20N90N ; 95E105E 10S20N ; 75E85E 5N20N ; 0 ( ENMT) 50E 35S20N 0 m EMT :ENMT (8715E 3215N) ( EMT) m Hardly ( [25 T - IC T - IN T - AF 120 ) ] HLNMT E 120 AQ (1) (1) AMIP [24 ] GOALS ? HLNMT [26 ]

986 (Chinese J Geophys ) 49 1 (AQ) 7 1 ( 120 ) (7-1 ) ( 2 mmπd) Fig 1 Deflection of surface wind direction (shaded areas have differences larger than 120 ) and precipitation differences (contour

experiment (a) January (b) July The precipitation of shaded areas is larger than 2 mmπd the areas encircled by red curves in (b) denote where the difference of wind direction between January and July

4 986 (Chinese J Geophys ) 49 1 (AQ) 7 1 ( 120 ) (7-1 ) ( 2 mmπd) Fig 1 Deflection of surface wind direction (shaded areas have differences larger than 120 ) and precipitation differences (contour interval is 2 mmπd) between July and January for the AQ experiment 2 (mπs) ( mmπd) (a) 1 (b) 7 2 mmπd (b) Fig 2 Surface wind vector (mπs) and precipitation (shaded mmπd) for the HLNMT experiment (a) January (b) July The precipitation of shaded areas is larger than 2 mmπd the areas encircled by red curves in (b) denote where the difference of wind direction between January and July is larger than 120 degree yellow heavy dashed lines indicate the boundaries between land and sea 4 (a c e) ( WΠm 2 ) ( mπs) ; (b d f) ( WΠm 2 ) ( mπs) (a b) T - IC (c d) T - IN ; (e f) T - AF 1mΠs Fig 4 Latitude2time section of zonally averaged (tropical land longitude) diabatic heating (shaded WΠm 2 ) and surface meridional wind (mπs) for T - IC(a b) T - IN(c d) and T - AF(e f) experiments (a c e) Sensible heating and meridional wind ; (b d f) Latent heating and meridional wind Contour interval is 1 mπs

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6 988 (Chinese J Geophys ) 49 [28 (4b) ] (2a) : ( (LO) ( SE) 4a) (4b) 7 (CO) (D) (3b 3c) ( ) [27 ] LOSECOD : (2b) (30N ) (2a) (2b) 30 N (4b) 4 mmπd (2b) WΠm 2 (4c) (4d) (3e) 313 (3f) 40E 40E (4e) (3a) (4f) 40E (4a) 4 ( ) (3h 3i) 80E (4a)

7 4 : 989

8 990 (Chinese J Geophys ) 49 ( ENMT) (6d) (5a) chou [30 ] 50N (5b) T ( (6d 6e) EMT 3b 3e 3h) (3b 3e 3h) 5c ENMT HLNMT - (5c) 5b E [31 ] 314 6d 5b HLMT (6a) (6b) (6b) (6a) ( ) (6a) HLNMT (2b) [29 ] 115 E : (6c) (1) (2) ENMT EMT 6d 6e 5a 5b 4 (3)

9 4 : E [ 6 ] (6) : E 40E (4) E [12 ] (4) : ( References) Sinica (in Chinese) (4) : [13 ] [ 1 ] (4) : : Yeh T C Lo S W Chu P C The wind structure and heat balance in the lower troposphere over the Tibetan Plateau and its surrounding Acta Meteorol Sinica (in Chinese) : [ 2 ] Flohn H Contributions to a mteorology of Tibetan Highland Atm Sci Paper No 130 Colorado State Univ Ft Collons 1957 [ 3 ] : Ye D Z Gao Y X Meteorology of the Qinghai- Xizang Plateau (in Chinese) Beijing : Science Press [ 4 ] Hahn D G Manabe S The role of mountains in the south Asian monsoon circulation J Atmos Sci : [ 5 ] Xu H M He J H Dong M Numerical study of the effect of Indian (2) : 4151 Luo M X Zhang K S Numerical simulation of the roles of the atmospheric heat source and the topography in the formation of the Indian and the East Asian summer monsoon Sinica (in Chinese) (2) : 4151 Scientia Atmospherica Wu G X Zhang Y S Thermal and mechanical forcing of the Tibetan Plateau and the Asian monsoon onset Part : Situation of the onset Scientia Atmospherica Sinica (in Chinese) ( 6) : [ 7 ] (3) : Liu X D Influences of Qinghai- Xizang (Tibet) Plateau uplift on the atmospheric circulation global climate and environment changes Plateau Meteorology (in Chinese) (3) : [ 8 ] (5) : Liu X D Jiao YJ Sensitivity of the East Asian monsoon climate to the Tibetan Plateau uplift Scientia Atmospherica Sinica ( in Chinese) (5) : [ 9 ] Kitoh A Effects of large- scale mountain on surface climate A coupled ocean-atmosphere general circulation model study J Climate (4) : [10 ] Rajendran K Kitoh A Yukimoto S South and East Asian Summer Monsoon climate and variation in the MRI coupled model (MRI - CGCM2) J Climate (4) : [11 ] : 1988 Qian Y F Yan H Wang Q Q et al Numerical Simulation of the Effect of Topography in Planetary Atmosphere (in Chinese) Beijing : Science Press 1988 Qian Y Qian Y F The sensitivity experiments of influences of uplift of Tibetan Plateau on circulation in summer Acta Meteorologica Chen J H Chen L X The role of the land- sea distribution of the south of Asia in the formation of Asian summer monsoon Quarterly Journal of Applied Meteorology (in Chinese) (4) : [14 ] (4) : Ren XJ Qian Y F Numerical simulation experiments of the impacts of local sea-land thermodynamic contrasts on the SCS summer monsoon onset Journal of Tropical Meteorology (in Chinese) (4) : [15 ] (2) : peninsula on south Asian summer monsoon process Journal of

10 992 (Chinese J Geophys ) 49 Tropical Meteorology (in Chinese) (2) : [16 ] model for global climate studies J (3) : Xu H M He J H Wen M et al A numerical study of effects of the Indo- China Peninsula on the establishment and maintenance of the South China Sea summer monsoon Scientia Atmospherica Sinica (in Chinese) (3) : [17 ] M Murakami T BB simulations PCMDI Report No 60 September (1) : 3442 He J H Zhu Q G Murakami M T BB data-revealed features of Asian-Australian monsoon seasonal transition and Asian summer Beijing : Science Press 1978 monsoon establishment Journal of Tropical Meteorology ( in [26 ] : Chinese) (1) : [18 ] Liu Y M Diabatic Heating and Subtropical Anticyclones ( in (4) : He J H Xu H M Zhou B et al Large scale features of SCS summer monsoon onset and its possible mechanism Climatic and Environmental Research (in Chinese) (4) : Research Letter (5) 1201 doi : Π2002GL [19 ] [28 ] : ( ) (4) : (3) : Wu G X Liu Y M Thermal adaptation overshooting dispersion He J H Wen M Shi X H et al Splitting and eastward withdrawal of the subtropical high belt during the onset of the South China Sea summer monsoon and their possible mechanism J (Nat Sci ) (in Chinese) (3) : Nanjing Univ [20 ] LASG - - ( GOALSΠLASG) () : 1528 Wu G X Zhang X H Liu H et al LASGglobal ocean-atmosphereland system model and simulation Quarterly Journal of Applied Meteorology (in Chinese) (Suppl ) : 1528 [21 ] Zhang X H Shi G Y Liu H et al IAP Global Ocean-Atmosphere- Land System Model Beijing : Science Press 2000 [22 ] Xue Y K Sellers P J Kinter J J et al A simplified biosphere Climate : [23 ] Wu T W Liu P Wang Z et al The performance of atmospheric component model (R42L910) of GOALSΠLASG Adv Atmos Sci : [24 ] Taylor K E Williamson D Zwiers F The sea surface temperature and sea-ice concentration boundary conditions for AMIP [25 ] C S (1 ) : 1978 Ramage C S Monsoon Meteorology ( First edition) (in Chinese) Chinese) Beijing : China Higher Education Press [27 ] Wu G X Liu Y M Summer quardruplet heating pattern in the subtropics and the associated atmospheric circulation and subtropical anticyclone part Geophysic : thermal adaptation and overshooting Scientia Atmospherica Sinica (in Chinese) (4) : [29 ] Dirmeyer P A Land- sea geometry and its effect on monsoon circulations Journal of Geophysical Research ( D10) : [30 ] Chou C Land- sea heating contrast in an idealized Asian summer monsoon Climate Dynamics [31 ] Kuo H L Qian Y F Influence of the Tibetan Plateau on cumulative and diurnal changes of weather and climate in summer Mon Wea Rev (11) : ()

48 Chinese Journal of Atmospheric Sciences 29 Vol hpa, Flohn [2 ] 7 8 d W = F + (thermal anticyclonic cell), d a Q, (1) t ( ), F, Q, a,, W = P

48 Chinese Journal of Atmospheric Sciences 29 Vol hpa, Flohn [2 ] 7 8 d W = F + (thermal anticyclonic cell), d a Q, (1) t ( ), F, Q, a,, W = P 29 1 2005 1 Chinese Journal of Atmospheric Sciences Vol1 29, No1 1 Jan1 2005 1 1 2 1 1 1, 100029 2, 100085, 100629895 (2005) 0120047210 P641 A How the Heating over the Tibetan Plateau Affects the Asian