A Possible Impact Way of the Stratosphere on Troposphere LI Chongyin, PAN Jing LASG, Institute of Atmospheric Physics ASM-STE Lhasa, July 21-23, 2010

I. Introduction Interaction between the stratosphere and troposphere (a hypothesis) Mid-Lati. Low-Lati. High-lati. Tropopause break Planetary wave Strong 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 Stratosphere polar 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 the flood or drought over the Yangtze River Valley 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 the precipitation, duration, start date and end date of Mei-yu season; It is constructed by averaging data at 5 stations: Shanghai, Nanjing, Wuhu, Jiujiang and Wuhan. The atmospheric circulation data (1948–2006) are 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 latitude has variation out-of-phase to that in the middle latitude and this pattern 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? 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 (* indicates the 95% significance level) Months Correlation coefficients Jan Feb Mar * Apr May Jun Jul Agu 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 in March SLP 500hPa The Mei-yu is closely related to the AO mode in March Correlation between the AO index and SLP/geopotential height in March

Correlation between the Mei-yu and zonal mean geopotential height in March （ 1958 － 2002 ） AO mode 95 ％ (significance)99 ％

Summertime hPa thickness regressed on March AO index. (Units: gpm, dark and light shadings indicate 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 AO 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 Vortex in 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 activity from 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 anomaly in March Summer circulation Anomaly over East Asia Mei-yu anomaly in summer ? downward propagating of wave activity

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