Influence of the Indian Ocean Warm Pool Variability on the Spring Precipitation in China

杨宇星 黄菲中国海洋大学

1.Introduction

2.Data and methodology

Contents

3.Analysis and discussion

4.Summary

1.Introduction

The present study of influence of warm pool on precipitation focuses on summer precipitation: Huang and Sun(1994),Weng et al(1996), Li and Zhou(1999), Chen et al(2003),Zhang et al(2003), Jian et al(2004).

About spring rainfall, Li et al (1998,2000) studied the relationship between north Pacific SST and spring precipitation.

we are interested in spring precipitation. And there are not many papers to discuss the relationship between the warm pool and spring precipitation directly.

2.Data and methodology

SST from SODA ,1°*1°,1951~1998 SKT from NCEP/NCAR , 2.5°*2.5°,1951~1998 Wind field data, Specific humidity, geopotential high fi

eld data from NCEP/NCAR, 2.5°*2.5°,1951~1998 The rainfall data of 160 stations from National Meteorol

ogical Center of China

The main study methods include correlation analysis, composite analysis and etc.

3. Analysis and discussion

Warm Pool (28.5℃) （ August—red ， March—blue ， mean—green ）

80.00 90.00 100.00 110.00 120.00 130.00

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Influence of the IOWP variability on spring precipitation over China

Fig. Distributions of correlation between the IOWP area index in spring and spring precipitation, respectively. The dots indicate positive coefficients, dark dots are over 95% confidence level; the triangles indicate negative coefficients, dark triangles are over 95% confidence level.

The difference between the standardized spring rainfall anomaly composite for the spring IOWP warm events and that for the cold events (warm minus cold events). Shaded areas represent the confidence levels over 95%.

Warm events (cold events): the rainfall in the southwest of China becomes less (more); in the east and north, more (less)

Warm events ：1958 ， 1964 ，1969 ， 1970 ，1983 ， 1987 ，1988 ， 1991 ，1998(spring)Cold events ：1951 ， 1955 ，1956 ， 1965 ，1971 ， 1972 ，1974 ， 1975 ，1976 (spring)

g/kgm/s

3.1 Influence of the IOWP variability on spring transport of moist and warm air vapor in China

The climate averaged transport of the moisture flux (u*q ， v*q, vectors) in low levels (1000-850hpa) and divergence field (contours) in spring, the arrowheads indicate the two transport paths, the contour values are 10000 times of divergence

The partial negative correlation (remove the linear influence of nino3) between the IOWP and the wind field(1000-850hPa), the differences of the moisture flux (u*q ，v*q, vectors) and its divergence field (contours) in spring between the IOWP cold events and warm events (cold minus warm).

The average positions of the spring IOWP. Thick line represents the 28.5C isotherm in the cold years, and thin line shows the same isotherm in the warm years.

3.1.1 Influence of the contrast between the land and sea in IOWP area variability on vapor transport

The difference of STA between the IOWP cold and warm events (cold minus warm). The shaded areas signify confidence levels over 90% by the significance test. The heavy shaded area over the Tibetan Plateau denotes the topography over 2200m above sea level.

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seasea WC landland WC

landsea WW landsea CC then

if

〈

Warm events ： 1953/54 ， 1963/64 ， 1972/73 ，1977/78 ， 1978/79 ， 1982/83 ， 1987/88 ， 1989/90 ， 1990/91 ， 199

7/98 ；Cold events ： 1952/53 ，1955/56 ， 1956/57 ， 1964/65 ， 1970/71 ， 1971/72 ， 1973/74 ， 1975/76 ， 1981/82 ， 1992

/93 ， 1996/97 。

3.1.2 The Influence of pre-winter IOWP on vapor transport

The difference of the spring moisture flux (u*q ， v*q, vectors) and divergence field (contours) at low level (1000-850hPa) between the previous winter IOWP cold events and warm events (cold minus warm).( confidence levels over 90% ).

3.2 West Pacific Tropical High Influence on vapor transport

Fig. The average position of WNPSH and wind field (vector) at spring IOWP warm (red) and cold (green) phases. The solid line indicate 1510 gpm contour at 850 hPa, the dashed line indicate the zero contour of zonal wind denoting the ridge position of WNPSH. The heavy shaded area over the Tibetan Plateau denotes the topography

4 Summary

The relationship between spring IOWP and the spring precipitation is shown by the chart:

There exists a seesaw-like correlation between the IOWP and the spring rainfall in China.

The cold (warm) phase of spring IOWP

The contrast between the sea and land decrease (increase)

The position of WNPSH eastward and northward (westward and southward)

West-south vapor Transport of strengthen (weaken)

The wind vector northwest of WNPSH northward （ southwo-rd ）

The spring rainfall in southwest of China increase (decrease) and decrease (weaken) in the north part of China

the vapor conver-gence at southe-ast of Tibet Plateau strengthen (weaken)

Future work

Further study the possible reasons of the relationship between the IOWP and spring precipitation in the north area in china

Further study the Influence of West Pacific Tropical High on spring precipitation

Thank you ！