The research advances of the South Asian High – one of the most important members

of the Asian Monsoon system

The research advances of the South Asian High – one of the most important members

of the Asian Monsoon system

Reporter: He Jinhai (hejhnew@jsmail.com.cn)

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

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The climatology (1948-2007) 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

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Winter A

The climatology (1948-2007) 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

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Summer

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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 (1948-2007) streamline on 150hPa from Jan to Dec

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The rapid westward progression of SAH from April to May is

actually the process of splitting and rebuilding.

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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

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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

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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 (1975-2005) streamline on 150hPa from the 22nd to 30th pentad (the red line is the ridge line)

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The SAH splitting & rebuilding processes can be divided

into 3 phases:

1. pre-splitting phase: 19th-22nd pentad;

2. splitting phase: 23rd-25th pentad;

3. rebuilding phase: 26th-27th pentad.

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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.

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pre-splitting phase

splitting phase

Rebuilding phase

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Barotropic modes Baroclinic modes

Left column: the height-longitude cross section of the wind (vectors), the ascending motion (shading, 10-2 pa-1) and the Q1 (contours, K day-1) along 90o-110oE in terms of the three different phases of the SAH splitting and rebuilding processRight column: the height-latitude cross section of the wind (vectors), the divergence (shading, 10-6 s-1) and the Q1 (contours, K day-1) along 5o-20oN

pre-splitting phase

splitting phase

Rebuilding phase

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)1(1

z

Qf

t z

z

)2(1

z

Qfv

z

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Sketch map of the SAH establishing processes on the ICP from April to May

Weak convection

Anticyclone on the West Pacific

SAH splitting

Convectionreinforcing

SAH rebuilding

Deepconvection

The northerly on the top

The southerlyon the bottom

ICPConvection

SouthAsia High

Phase I(19P-22P)

Phase II(23P-25P)

Phase III(26P-27P)

z

Qf

t z

z

1

z

Qfv

z

z

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28P

SCSM Onset

BOBSMOnset

Stationary ResponseNon-stationary Response13

How does the SAH move onto the Tibetan Plateau?(climatology 100hPa streamline field in June)

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SAH displaces onto the Tibetan Plateau on the 33rd pentad

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Outlines

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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.

pcR /

Inverse calculation (Yanai et al., 1992):

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PP

PTV

t

TCQ p

01

+ -

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.

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500hPa100hPa

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100hPa

Difference fields of circulations between intense and weak AHS years over the eastern plateau (intense years minus weak years)

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500hPa

Correlation between AHS over the eastern plateau and vorticity.The shaded areas are statistically significant at the 5% level.

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South Asian High (SAH) and West Pacific Subtropical High (WPSH) move in the horizontally-opposite directions in

terms of interannual variation

100hPa

100hPa

500hPa

500hPa

Composite geopotential height (gpm) in the intense and weak years of AHS over the eastern plateau

Intense years

Weak years

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Move toward each other

Back away

Outlines

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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

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Relationship between Ozone Low Center over TP

in summer and zonal oscillations of SAH

TOZ

July 16th,2006

Total Ozone (TOZ)Low Center

(shade)

Center of SAHat the level of 100hPa

geopotential height(contour)

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West mode East mode

Choosing typical cases(July, 2006)

Choosing typical cases(July, 2006)

July,23 to 30July,23 to 30

July,14 to 20July,14 to 20

West modeWest mode

East modeEast mode

Relationship between Ozone Low Center over TP in summer and zonal oscillations of SAH

Total Ozone(TOZ)

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West mode East mode

West mode East mode

SCO

TCO

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South Asian High (SAH)

West modeweak

East modestrong

Magnitude Weak Strong

Position Over the west of TP Over the east of TP

Areas Small Large

Relationship between the South Asian High and the Ozone (TOZ, TCO, SCO) Low Center

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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

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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.

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