NANJING UNIVERSITY OF INFORMATION SICENCE & TECHNOLOGY The research advances of the South Asian High – one of the most important members of the Asian Monsoon system Reporter: He Jinhai Nanjing University of Information Science & Technology (NUIST) Contributor: Chen Longxun, Liu yi, Wang Yuenan, Liu Boqi, Xu Kang, Shu Si July 2010

Outlines  Introduction  The splitting and rebuilding process of the South Asian High (SAH) from April to May  Relationship between the Atmospheric Heat Source (AHS) over the eastern plateau and the SAH during summer  Relationship between the Ozone and the SAH zonal oscillation (a case study)  Summary and discussion 2

The climatology ( ) streamline (top and middle) and moisture transport integrated from 1000hPa to 300hPa (bottom, vector, units: kg·m -1 ·s -1, the magnitude greater than 150 is shaded) in January 3 Winter A

The climatology ( ) streamline (top and middle) and moisture transport integrated from 1000hPa to 300hPa (bottom, vector, units: kg·m -1 ·s -1, the magnitude greater than 150 is shaded) in July 4 Summer A

5 1.SAH seasonal migration and its possible mechanism 1.1 Characteristics (1) The annual cycle characteristics (Zhu F. K., 1980; He J. H. et al., 2003) (2) The northward propagation of the SAH ridge line (Luo S. W., et al., 1982) (3) The winter mode and summer mode of the SAH (Qian Y. F., et al., 2002) (4) The splitting and rebuilding process of the SAH from April to May (He J. H. et al., 2006; Wang L. J. et al., 2007; Liu B. Q. et al., 2009) 1.2 Possible mechanisms (1)The heating effect of the Tibetan Plateau (Ye D. Z. et al., 1974; Krishnamurti et al., 1973; Huang R. H., 1985; Ding Y. H. et al., 1984; Wu A. M. et al., 1997; Zhao P. et al., 2001) (2) The “heat preference” of the SAH (Ye D. Z. et al., 1957; Qian Y. F. et al., 2002; Zhang J. J. et al., 1984; Zheng Q. L., et al., 1993; Jian M. Q. et al., 2001) (3) The complete form of vertical vorticity equation and the themal adaptation theory (Wu G. X. et al., 2003, 2008; Liu Y. M., et al., 2004) Introduction

The evolution of the climatology ( ) streamline on 150hPa from Jan to Dec A A A A A A A A A A A A The rapid westward progression of SAH from April to May is actually the process of splitting and rebuilding. 6

7 2. SAH zonal oscillation and its possible mechanism (1)The west mode (Tibetan Mode) and the east mode (Iranian Mode) of the SAH (Tao S. Y. et al., 1964; Luo S. W. et al., 1982; Li W. L. et al., 1991; Zhang Q., et al., 2002) (2) Possible mechanism (a) Thermal influence (Liu F. M., et al., 1981; Zhang Q. et al., 1999, 2002) (b) Interaction among different circulation systems (Sun G. W., et al., 1977; Zhu B. Z. et al., 1981; Lu L. H. et al., 1985) (c) Zonal asymmetric instability theory (Liu Y. M. et al., 2003) Introduction

8 3. SAH interannual variability and its relationship with the rainfall in China (1)The relationship between the SAH interannual variability and the SSTA (Zhang Q., et al., 2000; Tan J. et al., 2005; Li C. Y., et al., 2001; Yang H. et al., 2005) (2) The connection between the SAH and the flood-and-drought distribution in China (Chen L. X. et al., 1980; Zhang Q. Y. et al., 2006; Lu J. Z. et al., 1982; Zhu Q. G. et al., 1985; Guo Q. Y., 1985; Sha W. Y., 1985; Xu X. D. et al., 1992; Wang A. Y. et al., 1993; Zhang Y. C. et al., 2002) (3) The relationship between the SAH and the rainy band propagation in China (Zhang J. Y. et al., 1987; Zhu F. K. et al., 1987; Liu M. et al., 2007; Qian Y. F. et al., 2002; Zhang Q. Y. et al., 2003) (4) The linkage between the SAH and the Subtropical High (Tao S. Y. et al., 1964; Zhang Q. et al., 2002) Introduction

Outlines 9  Introduction  The splitting and rebuilding process of the South Asian High (SAH) from Apr to May  Relationship between the Atmospheric Heat Source (AHS) over the eastern plateau and the SAH during summer  Relationship between the Ozone and the SAH zonal oscillation (a case study)  Summary and discussion

The climatology ( ) streamline on 150hPa from the 22 nd to 30 th pentad (the red line is the ridge line) A A A A A A A A A A A A The SAH splitting & rebuilding processes can be divided into 3 phases: 1. pre-splitting phase: 19 th -22 nd pentad; 2. splitting phase: 23 rd -25 th pentad; 3. rebuilding phase: 26 th -27 th pentad. 10

Spatial distribution of barotropic (baroclinic) modes in Figs.a-c (d-f) for the phased stream fields relating to the SAH splitting and rebuilding processes, with pre-splitting in a, d, splitting phase in b, e and rebuilding phase in c, f. The shading represents baroclinic vorticity in d-f. 11 pre-splitting phase splitting phase Rebuilding phase A A AA A A A A A A Barotropic modesBaroclinic modes

Left column: the height-longitude cross section of the wind (vectors), the ascending motion (shading, pa -1 ) and the Q 1 (contours, K day -1 ) along 90 o -110 o E in terms of the three different phases of the SAH splitting and rebuilding process Right column: the height-latitude cross section of the wind (vectors), the divergence (shading, s -1 ) and the Q 1 (contours, K day -1 ) along 5 o -20 o N pre-splitting phase splitting phase Rebuilding phase 12

Sketch map of the SAH establishing processes on the ICP from April to May Weak convection Anticyclone on the West Pacific SAH splitting Convection reinforcing SAH rebuilding Deep convection The northerly on the top The southerly on the bottom ICP Convection South Asia High Phase I (19P-22P) Phase II (23P-25P) Phase III (26P-27P) 28P SCSM Onset BOBSM Onset Stationary ResponseNon-stationary Response 13

How does the SAH move onto the Tibetan Plateau? (climatology 100hPa streamline field in June) A A A A A A SAH displaces onto the Tibetan Plateau on the 33 rd pentad 14

Outlines 15  Introduction  The splitting and rebuilding process of the South Asian High (SAH) from Apr to May  Relationship between the Atmospheric Heat Source (AHS) over the eastern plateau and the SAH during summer  Relationship between the Ozone and the SAH zonal oscillation (a case study)  Summary and discussion

Computational Method of the Atmospheric Heat Source (AHS) In which θ is potential temperature, ω is vertical velocity, V is horizontal velocity, R is constant of dry air, Cp is specific heat. Positive calculation needs the data of condensation heating, sensible heat and vertical transfer and radiation balance, but we pay primary attention to the variation of the total AHS. Therefore, inverse calculation is adopted to obtain the daily AHS in the entire troposphere. Inverse calculation ( Yanai et al., 1992 ): 16

+ - Correlation between AHS over the eastern plateau and AHS over other areas from 1971 to 2000 The shaded areas are statistically significant at the 5% level. The thick dashed line denotes the wavetrain. 17

500hPa100hPa A A C C Difference fields of circulations between intense and weak AHS years over the eastern plateau (intense years minus weak years) A A C C C 500hPa Correlation between AHS over the eastern plateau and vorticity. The shaded areas are statistically significant at the 5% level. 18

South Asian High (SAH) and West Pacific Subtropical High (WPSH) move in the horizontally-opposite directions in terms of interannual variation 100hPa 500hPa Composite geopotential height (gpm) in the intense and weak years of AHS over the eastern plateau Intense years Weak years 19 Move toward each other Back away

Outlines 20  Introduction  The splitting and rebuilding process of the South Asian High (SAH) from Apr to May  Relationship between the Atmospheric Heat Source (AHS) over the eastern plateau and the SAH during summer  Relationship between the Ozone and the SAH zonal oscillation (a case study)  Summary and discussion

Tropospheric Ozone Stratospheric Ozone TOZ SCO TCO Total Ozone Integrated from land surface to the top of atmosphere Tropospause of NCEP Vertical classification of Ozone 21

Relationship between Ozone Low Center over TP in summer and zonal oscillations of SAH TOZ July 16 th,2006 Total Ozone (TOZ) Low Center (shade) Center of SAH at the level of 100hPa geopotential height (contour) ？ 22

West mode East mode Choosing typical cases (July, 2006) Choosing typical cases (July, 2006) July,23 to 30 July,14 to 20 West mode East mode Relationship between Ozone Low Center over TP in summer and zonal oscillations of SAH Total Ozone (TOZ) 23

West mode East mode West mode East mode SCO TCO 24

South Asian High (SAH) West mode weak East mode strong Magnitude WeakStrong Position Over the west of TPOver the east of TP Areas SmallLarge Relationship between the South Asian High and the Ozone (TOZ, TCO, SCO) Low Center 25 Possible mechanism: When the SAH appears the east (west) mode, the air with less Ozone from low latitudes is transported into the middle troposphere over the east (west) of the TP by strong (weak) summer monsoon currents, the convergence and the ascending is also strong (weak), in turn the Ozone low center is strong (weak).

Outlines 26  Introduction  The splitting and rebuilding process of the South Asian High (SAH) from Apr to May  Relationship between the Atmospheric Heat Source (AHS) over the eastern plateau and the SAH during summer  Relationship between the Ozone and the SAH zonal oscillation (a case study)  Summary and discussion

Summary and discussion  The South Asian High (SAH) moves onto the Indo-China Peninsula via the splitting-rebuilding process. The process actually is a substitution that a high-level anticyclone (HLA) being generated and strengthened over the Peninsula and the original HLA getting relatively weakened over waters east of the Philippines. And the principal triggering factor is the changes in the South-Asian atmospheric diabatic heating regime.  SAH and West Pacific subtropical high move in the horizontally- opposite directions in terms of interannual variation, for which AHS over the eastern plateau seems to be thermodynamically responsible.  The oscillation of SAH in east- and west-directions maybe an important factor of the Ozone low center variation. 27