Download AO - UGAMP

East Asian climate and Arctic/Antarctic Oscillations
Daoyi Gong ([email protected])
State Key Laboratory of Earth Surface Processes and Resource Ecology
Beijing Normal University
AO and East Asian climate
(a) East Asian winter monsoon
(b) East Asian summer monsoon
(b) Weather extremes/climate disasters
Climate meanings:
Basic/fundamental state of free atmosphere: westerly flow
What cause AO/AAO variability:
… downward propagation of stratosphere anomalies
… eddy-mean flow interaction, e.g., EP flux theory
… stationary wave-mean flow interaction
… troposphere thermal or dynamical forcing. e.g., Autumn
snow in Siberian -> negative AO.
Changes of air temperature at 925 hPa level in association
with a one unit of AO. Areas significant at 0.05 level are shaded
and the high correlation center with |r|>0.6 indicated by darker
shading. Contour intervals: 0.5C. Zero lines are omitted for clarity.
ERA40 data
Changes of regional atmospheric circulation in association with a -1 unit of AO.
Contours: 500hPa height, solid lines: positive anomalies, dashed lines are negative,
unit is gpm.
Vectors: horizontal wind at 850hPa level, maximum values are 2.4m/s. Shadings: air
temperature at 925hPa, light shading: -0.5 to -1C; darker shading: cooler than lower 1C
ERA40 data, DJF
Correlations among indices (DJF, 1880-2001)
AO
Sib. High
Trough
T_China
AO
Sib. High
Trough
T_China
/
-0.60
-0.58
+0.42
/
-0.88
-0.71
/
+0.64
/
Time-series of AO (a), Siberian High (b), East Asian Trough (c), and temperature in East
China (d) since late 19th century
• Winterphase
influence
on inter-annual to decadal time scale
Negative
AO:
Strong Siberian High due to
• AO influence on summer monsoon and monsoonal rainfall
(a) cooler Euasian continent in mid-high latitude,
(b) enhanced downward air motion by convergence in
• AO modulation
variability and extremes
upper
level with on
thehigh-frequency
enhanced trough
in temperature
…Strong winter monsoon
…Cooler East Asia.
Reg.<May
AO,
JJA rainfall>
May
AO and JJA
Rainfall
60N
Data:
5x5 degree,
global land
(Hulme 1992)
40N
Grey squares:
Data availability
>95% during
1900-98
20N
Shading:
>95% c.l.
100E
120E
140E
160E
Changes in summer precipitation (mm) corresponding to a one
standard deviation of the May AO index.
100
200
Pressure (hPa)
300
400
500
600
700
800
900
1000
60
50
40
30
20
10
EQ
Cross section of the zonal mean zonal wind (u), meridional
wind (v) and vertical motion (ω) over East Asia (110ºE-150º
E) regressed onto the May AO index.
Spring NDVI
Summer U200
The first paired modes of singular value decomposition (SVD)
analysis between spring normalized difference of vegetation
index (NDVI) anomaly and summer zonal wind at 200 hPa (U200)
anomaly
(a) First-paired mode for NDVI
(b) First-paired mode for U200.
Units are arbitrary. Contour interval is 0.02 and the 0 value line is omitted for clarity.
Mao et al., 2008
Cross section of the summer zonal mean zonal wind (u),
meridional wind (v) and vertical motion (ω) over East Asia (100E120E) regressed onto the spring NDVI-PC1.
The u is shown as the contours with interval of 1 m/s. Regions above 95% confidence level are
shaded. The covariance of v and ω are shown as vectors. Values are m/s for u and v, and hPa/s
for ω. The values of largest vectors are 0.40 m/s for v and 1.3× 10-2 hPa/s for ω.
Dust storms
Sea ice severity
AO and spring dust storm frequency in northern China (shown
only the inter-annual components). Their Spearman correlation
is –0.304.
Outline…
• Winter influence on inter-annual to decadal time scale
• AO influence on summer monsoon and monsoonal rainfall
• AO modulation on high-frequency variability and extremes
in temperature
Contour lines are regression of the synoptic variance of daily 850hPa heights
upon dust storm frequency (F_D). Contour intervals: 0.5m. Zero contours are
omitted for clarity. Shading areas are significant at the 95% level. Horizontal
wind changes at 500 hPa level Maximum wind vectors are 1.8m/s.
Ice severity index
AO
Time-series of Sea ice severity in Bohai Sea and AO.
DJF.
AO x -1
normalized.
Jinzhou station, north Bohai Sea
 2 1
> +1.2σ, 7 winters
< -1.2σ, 6 winters
 -12 days
Less freezing days, where T < -4C
AAO and East Asian summer monsoon
(a) Correlation between the
April–May AAO and June–
August precipitation in China
for the period 1951–2001.
r = +0.49
(b) Normalized time
series of spring AAO and
summer precipitation in
Yangtze River valley.
Nan and Li 2003, GRL
…Cross-equatorial air flow in Indian Ocean
…Cross-equatorial air flow in western Pacific
…Troposphere Rossby waves ?
…through influencing regional SST/Precipitation ?
A
A
A: anticyclone
Water transport below 700hPa, wind vector at 850 hPa.
JJA. ERA40 data
Regression coefficients of the ERA40 SLP
upon the Sr-content time series during 1958–
1993. The unit is hPa per standard deviation
of Sr. Prior to analysis, the Niño3.4 SST
signals were excluded from Sr-content time
series.
Weekly cycles in atmosphere over China:
Polluted weather ?
Dao-Yi GONG1, Chang-Hoi HO2, Deliang CHEN3, Yun QIAN4, Yong-Sang CHOI2, and Jinwon KIM5
1 State Key Laboratory of Earth Surface Processes and Resource
Ecology, College of Resources Science & Technology, Beijing Normal University, 100875, China
2 School of Earth and Environmental Sciences, Seoul National University, Seoul 151-742, Korea
3 Earth Sciences Centre, Göteborg University, Guldhedsgatan 5A, Box 460, 405 30 Göteborg, Sweden
4 Atmospheric Science and Global Change Division, Pacific Northwest National Laboratory, WA 99352, USA
5 Department of Atmospheric and Oceanic Sciences, University of California, Los Angeles, California, USA
Gong et al., J.G.R., 2006; 2007
Anomalies of temperature from Sunday through Saturday.
29 stations, JJA, 2001-2006
Error bars are  1 standard error about the 29-sample mean.
Anomalous frequency of light rains from Sunday through Saturday.
P 5mm/day, 29 stations, JJA, 2001-2006
Error bars are  1 standard error about the 29-sample mean.
Globe: Cities with more than 100,000 people in 1997
China:
448 with population >0.5 million, 174 with population >1 million.
Most in East China. By 2003
Source: United Nations Statistics Division
PM10
PM10, JJA, 2001-2006. ‘’ : PM10 stations, ‘’:
R2 grids, ‘O’: radio-sounding temperature stations
Radio-sounding
Profile of temperature anomaly from Sunday
through Saturday in troposphere. Shown
here is the mean of 15 radiosonde
observations. Unit: C. 1100UTC.
T, R2
Profile of temperature anomaly from Sunday through
Saturday in troposphere. Shown here is the mean of 29 R2
grids. Unit: C.
Data sources: Durre et al., 2006. J. Climate, 19, 53-68
Anomaly of the daily mean vertical air velocity (ω) in the lower troposphere
between 925 and 850 hPa levels at 29 R2 grids during 2001-2005.
Radio-sounding
Anomaly of the horizontal wind velocity in lower troposphere between 925 and
850hPa levels, shown as the average from radiosonde observations. Error bars are 
1 standard error about the sample mean. 1100UTC, data availability >90%.
Data sources: Durre et al., 2006. J. Climate, 19, 53-68
Climate implication…
0.05 level
1956-2005. Whole China. JJA.
Climate implication…
Regional mean trends [<10mm/day]:
Linear trend of the number of light rain
days during the time period 1956-2005.
Unit: days/10yr.
JJA.
1956-05: -1.7days/10yr
[～20％]
1980-05: -2.4days/10yr,
0.01 level
Conclusion:
(1) There are significant, consistent weekly cycles in
meteorological variables in east China during summer ,
most likely connected to the weekly cycle of air pollution,
and a result of aerosol-atmosphere interaction.
(2) The significant decreasing of light rains is likely related to
the enhanced human activities, and suppressed by the
increasing air pollution.
(3) …modelling validation
Variability of the low-level cross-equatorial
jet of the western Indian Ocean since 1660 as
derived from the coral proxies
Dao-Yi Gong
( Beijing Normal University, China, [email protected])
Jürg Luterbacher
(University of Bern, Switzerland, [email protected])
Gong & Luterbacher, G. R. L., 2008
Trend in the 20th century: A puzzling fact
In association with climate warming
A notably enhancing trend in wind in
western Arabian Sea
(Anderson et al. 2002, Science, 596)
… and also suggested by some
simulations (Hu et al., 2000)
Data:
8 coral proxies
from Indian
Ocean Basin
Longest:
~1660AD
O Grids of COADS July wind speed data
→

ERA40 climate wind vectors of 850hPa level in June-July-August.
Mean meridional wind to define the cross-equatorial jet flow (i.e., V850).
Coral sites.
IFA: Ifaty (Zinke et al., 2004), SEY: Seychelles (Charles et al., 1997), NIN: Ningaloo (Kuhnert et al., 2000), PIR: Pirotan
(Chakraborty and Ramesh, 1998), REU: Réunion (Pfeiffer et al., 2004), BAL: Bali (Charles et al., 2003), XIS: Xisha (Sun et al., 2004), BUN: Bunaken
(Charles et al., 2003). Data from: http://www.ncdc.noaa.go/paleo [all are δ18O except XIS which is Sr]
Trend in the 20th century: A puzzling fact
Observed and simulated wind during the 20th century
COADS surface wind, July only
averaging from 8 grids
IPCC AR4, V850, JJA
Coupled models simulations for
20th century (20C3M) forced by
observed natural and
anthropogenic forcings.
Ensemble of 21 models
Only low-frequency shown.
Shading: 2SE of the ensemble
means.
Data source: Zhou T J
Conclusion:
Low-level Indian monsoon wind shows no enhancing tendency
as global temperature rises during the 20th century.
Thanks !