A Possible Impact Way of the Stratosphere on Troposphere

LI Chongyin, PAN JingLASG, Institute of Atmospheric Physics

ASM-STELhasa, July 21-23, 2010

I. IntroductionInteraction between the stratosphere andtroposphere (a hypothesis)

Mid-Lati.Low-Lati. High-lati.

Tropopausebreak

Planetary waveStrong convection

Stratosphere impact on the troposphere at high latitude

-----The Cosmic Rays ---- Clouds

Marsh and Svensmark (2000)

-----The circulation at high latitudes

How about the impact of polar vortex on the AO ?

As an example, in this study we will discuss :

AO in troposphere

Stratospherepolar vortex

Mei-yu anomalies

Mei-yu (Bai-u) ---- An important phenomenon

(system) of Asian summer monsoon activity

Mei-yu front

The Mei-yu has a great social and economic

importance in China, its anomaly often causes t

he flood or drought over the Yangtze River Val

ley in summer.

It is an important problem to study Mei-yu

and its variability in China

II. The Used Data

The 121yr Mei-yu dataset (1885 – 2005) is from

National Climate Center of CMA, which describes t

he precipitation, duration, start date and end date o

f Mei-yu season; It is constructed by averaging data

at 5 stations: Shanghai, Nanjing, Wuhu, Jiujiang an

d Wuhan.

The atmospheric circulation data (1948–2006) a

re from the NCEP (reanalysis).

III. The AO and Mei-yu

1. The correlation between the Mei-yu

precipitation and AO ;

2. The AO in March and Atmospheric circulation in summer

AO (Arctic Oscillation) Thompson and Wallace （ 2000 ） found that the SLP field in the high l

atitude has variation out-of-phase to that in the middle latitude and this patt

ern is symmetric longitudinally. It was named the Arctic Oscillation, or the

Northern Annular Mode (NAM).

Is there a relationship between the Mei-yu variation and the AO?

1960 1965 1970 1975 1980 1985 1990 1995 2000

-2

0

2

Normalized AO index in March (dashed) and mei-yu precipitation (solid) from 1958 to 2002

Correlation coefficients between monthly AO indices and mei-yu precipitation from 1958 to 2002.

(* indicates the 95% significance level)

Months Correlation coefficientsJan. -0.01

Feb. 0.07

Mar. -0.31*

Apr. -0.04May -0.16Jun. -0.05

Jul. 0.03

Agu. -0.01

There is remarkable correlation between the Mei-yu precipitation in summer and AO index in last March

Correlation between the Mei-yu and SLP/geopotential height i

n March

SLP

SLP 500hPa

500hPa

The Mei-yu is closely related to the AO mode in March

Correlation between the AO index and SLP/geopotential heig

ht in March

Correlation between the Mei-yu and zonal mean geopotential height in March（ 1958－ 2002）

AO mode

95 ％ (significance)99 ％

Summertime 200-850hPa thickness regressed on March AO index. (Units: gpm, dark and light shadings indi

cate 99% and 95% significance levels)

Why the AO in March can affect on summer mei-yu?

The regression 850hPa wind in summer using the AO index (positive) in March

Latitudinal-height section of the averaged wind field between (110º － 150ºE ) in summer regressed on March A

O index. (Vertical speed is multified by 10 )

AO anomaly in march could cause summer circulation anomalies in East Asia, which is favorable (unfavorable) to the Mei-yu rainfall.

IV. Stratospheric Polar Vortexin Feb. and the AO in Mar.

1. Their relationship;

2. The downward propagating of anomalies in the stratosphere

Distribution of correlation coefficients between March AO index and latitudinal averaged height in February.

(Dark and light shadings is 99% and 95% significance levels)

Correlation coefficients between AO index in March and 30hPa height field in the previous September (a), October (b), November (c),

December (d), January (e) and February (f).

Sep. Nov.

Feb.Dec.

The SLP and 500hPa height in March regressed on 1st PC and 3rd PC of 30hPa height in February,

shadings is 99% and 95% significance levels

-+

NAM-like

-

-

-

-

E-P flux in February regressed on 1st (a) and 3rd (b) PC of 30hPa geopotential height in February.

(Dark and light shadings indicate 95% and 90% significance levels)

AO index in March has evident correlation with the stratospheric polar vortex in February. There is downward wave activityfrom the stratosphere and will affect

the troposphere circulation in the high latitude (AO).

V. Conclusions

2. The stratospheric atmosphere circulation in February is closely related to the AO in March. It may affect the AO through the downward propagating of wave activity anomalies.

1. It is shown that the mei-yu precipitation may be influenced by the stratospheric polar vortex anomaly through the Arctic Oscillation (AO) in troposphere.

3. The anomalous AO in March may in turn exert an impact on summertime circulation in East Asia, which is closely related to thermal condition of the tropospheric atmosphere in summer over East Asia. The changed thermal condition and the circulation over East Asia can then lead to anomalous convergence (divergence) over the Yangtze River Valley, and anomaly of Mei-yu precipitation.

Schematic diagram

Polar vortex anomaly in the Stratosphere in Feb.

AO anomalyin March

Summer circulation Anomaly over East Asia

Mei-yu anomaly

in summer

?downward propagating

of wave activity

ThankThank

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