CHANGES IN EAST ASIAN WINTER ATMOSPHERIC CIRCULATION
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CHANGES IN CHANGES IN EAST ASIAN WINTER EAST ASIAN WINTER ATMOSPHERIC CIRCULATION ATMOSPHERIC CIRCULATION WU, M C WU, M C YEUNG, K H LEUNG, Y K YEUNG, K H LEUNG, Y K
description
CHANGES IN EAST ASIAN WINTER ATMOSPHERIC CIRCULATION. WU, M C YEUNG, K H LEUNG, Y K. We attempt to find out. If there has been any change in the East Asian winter ( December-February ) atmospheric circulation in the last several decades ( 1958-2005 )? - PowerPoint PPT Presentation
Transcript of CHANGES IN EAST ASIAN WINTER ATMOSPHERIC CIRCULATION
CHANGES IN CHANGES IN EAST ASIAN WINTER EAST ASIAN WINTER
ATMOSPHERIC CIRCULATIONATMOSPHERIC CIRCULATION
WU, M CWU, M C YEUNG, K H LEUNG, Y K YEUNG, K H LEUNG, Y K
We attempt to find outWe attempt to find out• If there has been any change in the East Asian
winter (December-February) atmospheric circulation in the last several decades (1958-2005)?
– Trends of the characteristics of its major components?• their possible influences to Hong Kong’s winter temperature
– Changes in the interrelationships among the components?
– Influences of some dominate climate patterns, namely the Arctic Oscillation (AO) and the Pacific Decadal Oscillation (PDO)?
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1958 1963 1968 1973 1978 1983 1988 1993 1998 2003
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Overall Changes in Northern Hemisphere (NH) winterOverall Changes in Northern Hemisphere (NH) winter
Linear trend (1958-2005)
therefore a weakening of the East Asian winter monsoon
there should also be some changes in the circulation against the background of global warming
Weakening of N-S SLP gradient
+ ve- ve
Aloft (200 hPa)Aloft (200 hPa) Mid-troposphere (500 hPa)Mid-troposphere (500 hPa)
Lower troposphere (surface, 1000 hPa)Lower troposphere (surface, 1000 hPa)
8 major components8 major components
JETJETEMTEMTWMIWMIALPIALPISMHSMHEAWEAWSH_ISH_ISH_WSH_WSH_RSH_REATEATIndex:
Trends in the components?Trends in the components?
To compare the trends of different indicesConvert the trends to a common scale expressed in terms of a fraction of the standard deviation
Trend/stdev
0.47
0.53
0.22
0.34
0.31
0.33
0.35
0.23
0.51
•Mann-Kendall test is used to test the significance of trend in the time series of these indices
Significant trends (at 5% level) are found in the indices of the 7 components in the lower and mid-troposphere a remarkable change in the East Asian winter atmospheric circulation
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The most prominent trend in lower troposphere is the weakening of the Siberia-Mongolia high whereas in mid-troposphere, it is the eastwards shift of the East Asian trough
No significant trend is noted in the strength of the subtropical jet aloft
Index Change corresponding to the trend
Lower troposphere
WMI Weaker monsoon surge
SMH Weaker Siberia-Mongolia High
ALPI Deepening of the Aleutian low
EMT Weakening of the Equatorial monsoon trough
Mid- troposphere
SH_I Stronger subtropical high
SH_R Subtropical high shift northwards
SH_W Subtropical high shift westwards
EAW Zonal flow dominate in Eurasia sector
EAT East Asian trough shift eastwards
Aloft JET No significant trend
•Magnitude of trend is obtained by Sen’s slope
Trend (/decade)
1.67
1.32
0.64
1.72
3.65
0.44
6.06
0.04
1.28
Trend/stdev
0.47
0.53
0.22
0.34
0.31
0.33
0.35
0.23
0.51
1025
1030
1035
1040
1045
1959
1962
1965
1968
1971
1974
1977
1980
1983
1986
1989
1992
1995
1998
2001
2004
Strength of the Siberia-Mongolia High
135
140
145
150
155
1959
1962
1965
1968
1971
1974
1977
1980
1983
1986
1989
1992
1995
1998
2001
2004
Longitudinal position of the East Asian Trough
Str
engt
h (h
Pa)
Long
itude
(o E
)
Time series of SMH and EATTime series of SMH and EAT
Decrease in strength
Shift eastward
The influences of the Aleutian low and the equatorial monsoon trough are apparently slight as the difference in HK's winter temperature for large and small values of ALPI and of EMT are statistically not significant
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the trend of the index would likely to bring a warmer winter to HKwith the exception of the intensifying Aleutian low, the trends of all indices are found to be consistent with a warmer winter in Hong Kong
IndexDifference (o
C)Change corresponding to the trend
WMI 1.48* Weaker monsoon surge
SMH 1.49* Weaker Siberia-Mongolia High
ALPI -0.13 Deepening of the Aleutian low
EMT 0.66 Weakening of the Equatorial monsoon trough
SH_I 1.04* Stronger subtropical high
SH_R 1.47* Subtropical high shift northwards
SH_W 1.14* Subtropical high shift westwards
EAW 1.26* Zonal flow dominate in Eurasia sector
EAT 0.81* East Asian trough shift eastwards
Change in Hong Kong’s winter temperature Change in Hong Kong’s winter temperature accompanied with the trendsaccompanied with the trends
The change in HK should be similar to that in southern China*:the difference is significant at the 5% level.The significance of the difference is tested using the KS testthe difference in HK’s winter temperature between the 10 highest values and 10 lowest values of an index, from which the expected change in HK’s winter temperature accompanied with the trend of the index will be inferred
• Temporal variation in the relationship (correlation) between any two indices in the mid-troposphere
• Moving correlation analysis with a 29-year sliding window is used – Spearman’s rank correlation
Any change in covariability?Any change in covariability?
Mid- troposphere
SH_I Subtropical high intensity
SH_R Subtropical high ridge line position
SH_W Subtropical high western position
EAW Mid-latitude westerlies
EAT Longitudinal position of the East Asian trough
Lower latitudes
Mid-latitude
reflect if there any change in the covariability between lower latitudes and mid-latitude circulation
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1973 1975 1977 1979 1981 1983 1985 1987 1989 1991
EAW vs SH_I (intensity) Cor
rela
tion
coef
ficie
nt
Correlation in the period (1959-1988)
0
0.2
0.4
0.6
1973 1975 1977 1979 1981 1983 1985 1987 1989 1991
EAW vs SH_R (ridge-line position)
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-0.4
-0.2
0
1973 1975 1977 1979 1981 1983 1985 1987 1989 1991
EAW vs SH_W (western position)
Moving correlation analysisMoving correlation analysis
SignificantSignificant
InsignificantInsignificant
SignificantSignificant
InsignificantInsignificant
SignificantSignificant
InsignificantInsignificant
Correlation in the period (1958-1987)
1% significant level
5% significant level
(between the westerlies and subtropical high intensity)(between the westerlies and western position)(between the westerlies and the ridge position)
• The degree of correlations between the Westerlies and the three subtropical high indices are declining
• Indicates a decreasing covariability between lower latitudes circulation and mid-latitude circulation
• On the other hand the interrelationships among the subtropical high indices are ratherl robust– for example,
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1973 1974 1975 1976 1977 1978 1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991
Moving correlation analysisMoving correlation analysis(between the intensity & western position of subtropical high)(between the intensity & western position of subtropical high)
1 % significant level
5 % significant level
Therefore,
Decline in correlation from significant to insigificant
Significant correlation
Schematic diagram showing the interrelationships among the components
of the winter atmospheric circulation in mid-troposphere
Another indication of the change in the East Asian winter atmospheric circulation
in the last several decades
Another indication of the change in the East Asian winter atmospheric circulation
in the last several decades
Lower Lower latitudeslatitudescirculationcirculation
Question• Could the decline in covariability observed
be related to global warming in terms of the rising trend of NH winter temperature?
The purpose of detrending is to ensure that one looks at the relationship between temperature and the index, not just the time variation of the index in view of the increase in temperature with time under global warming
Series ASeries B
29 years selected as colder group
(Group C)
29 years selected as colder group
(Group C)
29 years selected
as warmer group (Group W)
29 years selected
as warmer group (Group W)
Correlation between series A and B
for Group C
Correlation between series A and B
for Group C
Correlation between series A and B
for Group W
Correlation between series A and B
for Group W
Detrend ALL time series (NH winter temperature, EAW, SH_I, etc)Detrend ALL time series (NH winter temperature, EAW, SH_I, etc)
rank according to the detrended NH winter temperaturerank according to the detrended NH winter temperature
increase in the detrended NH winter temperature
Winter temperatureyear 1985,1972, 1969…… .. 1963
warmestcoldest
Runs-test suggests this sequence is random (p-value= 0.38) in terms of YEAR
e.g. EAWe.g. SH_I
Indices Correlation for group C Correlation for group W
EAW vs SH_I 0.47* 0.07EAW vs SH_R 0.29 0.26EAW vs SH_W -0.50* -0.12
Comparison of the correlations Comparison of the correlations between between Group CGroup C and and Group WGroup W
* Correlation significant at 1% level.
With a warmer NH winter, a decline in the correlation between the Westerlies and the subtropical high indices is suggested(most clear for the intensity and western position of the subtropical high)
Decline in correlation
Distribution of correlationDistribution of correlation
10,000 correlation10,000 correlation
Consider the covariability between the Westerlies (EAW) and the Subtro
pical high intensity (SH_I)as an example
How significant the relation betweeHow significant the relation between NH winter temperature and the cn NH winter temperature and the c
hange in covariabiltiy is?hange in covariabiltiy is?Detrend time series of
EAW and SH_IDetrend time series of
EAW and SH_I
Correlation for the 29 pairs
Correlation for the 29 pairs
Repeat 10,000 times
Repeat 10,000 times
Randomly select 29 pairs of EAW and SH_IRandomly select 29
pairs of EAW and SH_I
0.0
2.5
5.0
7.5
10.0
0.00
00.
025
0.05
00.
075
0.10
00.
125
0.15
00.
175
0.20
00.
225
0.25
00.
275
0.30
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325
0.35
00.
375
0.40
00.
425
0.45
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475
0.50
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525
0.55
00.
575
0.60
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625
0.65
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675
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Indices Correlation for group C Correlation for group W
EAW vs SH_I 0.47* 0.07
Rank correlation between detrended EAW and SH_I
% (
ou
t o
f 10
,000
sam
ple
s)Distribution of correlationDistribution of correlation
<3.1%<5.4%
the relationship between the covariability and NH winter temperature could be rather pronounced
the relationship between the covariability and NH winter temperature could be rather pronounced
Influences by some dominant Influences by some dominant modes of oscillation?modes of oscillation?
• PDO, AO
• Cumulative summation (CUSUM)– defined as the accumulating sum of
anomalies (from the overall mean) of all preceding values.
• aid to locate, in a qualitative sense, the change points in a time series
• to see whether changes tend to match up across indices
1959 1962 1965 1968 1971 1974 1977 1980 1983 1986 1989 1992 1995 1998 2001 2004
PDOPDO
19761976
1959 1962 1965 1968 1971 1974 1977 1980 1983 1986 1989 1992 1995 1998 2001 2004
AOAO
19881988
CUSUM charts for PDO & AOCUSUM charts for PDO & AO
PDO change phase by mid-1970s
AO change phase by mid- to late1980s
1959 1962 1965 1968 1971 1974 1977 1980 1983 1986 1989 1992 1995 1998 2001 2004
Nino 3.4 SSTNino 3.4 SST
ENSO varies according to the background of PDO
1959 1962 1965 1968 1971 1974 1977 1980 1983 1986 1989 1992 1995 1998 2001 2004
Western-positionWestern-position
IntensityIntensity Ridge-line positionRidge-line position
CUSUM charts for Subtropical HighCUSUM charts for Subtropical High
Changes coincide with the climatic shift in the PDO in the mid-1970s can be located
1959 1962 1965 1968 1971 1974 1977 1980 1983 1986 1989 1992 1995 1998 2001 2004 1959 1962 1965 1968 1971 1974 1977 1980 1983 1986 1989 1992 1995 1998 2001 2004
1959 1962 1965 1968 1971 1974 1977 1980 1983 1986 1989 1992 1995 1998 2001 2004
East Asian East Asian Trough position Trough position (EAT)(EAT)
Eurasian Westerlies Eurasian Westerlies (EAW) (EAW)
CUSUM charts for mid-latitude’s componentsCUSUM charts for mid-latitude’s components
Changes are noted in the westerlies and trough position by mid- to late 1980s
AO
~concurrent with the phase change in AO
• Changes in the East Asian winter atmospheric circulation (in terms of the changes in EAW, EAT, SH_I etc) could also be a manifestation of some natural climate variability (if AO and PDO as natural oscillation)
• Subtropical high is more strongly influenced by PDO
• Components in mid-latitude are likely to be influenced by AO
ThereforeTherefore
ConclusionConclusion
Changes in the East Asian winteChanges in the East Asian winter atmospheric circulation are apr atmospheric circulation are ap
parentparent
Thank You
謝謝
Conclusion
• Trends are noted in the components studied except the strength of the subtropical jet aloft– indicates an apparent change in the atmospheric circu
lation pattern – with the exception of the intensifying Aleutian low, all t
rends found are consistent with a rising winter temperatures in HK and southern China
• The covariability between the lower latitudes circulation and the mid-latitude circulation is declining which is another indication of the climatic change in the East Asian winter atmospheric circulation
Indices’ definition and Data sources
Discussion• The possibility of anthropogenic forcing of
the observed changes cannot be ruled out because natural climate oscillations could have been affected
• Difficult to distinguish between natural variability and change due to anthropogenic forcing
anthropogenic forcing
anthropogenic forcing
natural climate oscillations
natural climate oscillations
observed changes
observed changes
1959 1962 1965 1968 1971 1974 1977 1980 1983 1986 1989 1992 1995 1998 2001 2004
EATEAT
EAWEAW
1959 1962 1965 1968 1971 1974 1977 1980 1983 1986 1989 1992 1995 1998 2001 2004
NH winter tempNH winter temp
19851985
1959 1962 1965 1968 1971 1974 1977 1980 1983 1986 1989 1992 1995 1998 2001 2004
HK winter tempHK winter temp
CUSUM
Changes can be seen in the time series of the winter temperature of NH and winter temperature of Hong Kong in the mid- to late 1980s.
Western-position vs IntensityWestern-position vs Intensity
Western-position vs Ridge-line positionWestern-position vs Ridge-line position Intensity vs Ridge-line positionIntensity vs Ridge-line position
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-0.8
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0
1973 1974 1975 1976 1977 1978 1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991
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1973 1974 1975 1976 1977 1978 1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991
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1
1973 1974 1975 1976 1977 1978 1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991
Why SH_I, SH_R and SH_W(they are different features of the SH and do have different influences on the weather)
e.g.,
TC track,
rainbelt (south China vs central China)
Trend vs Interrelationship (correlation)
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EAW vs SH_WIndices Correlation for group C Correlation for group W
EAW vs SH_W -0.50* -0.12
CUSUM for detrended time series
1959 1962 1965 1968 1971 1974 1977 1980 1983 1986 1989 1992 1995 1998 2001 2004 1959 1962 1965 1968 1971 1974 1977 1980 1983 1986 1989 1992 1995 1998 2001 2004
1959 1962 1965 1968 1971 1974 1977 1980 1983 1986 1989 1992 1995 1998 2001 2004 1959 1962 1965 1968 1971 1974 1977 1980 1983 1986 1989 1992 1995 1998 2001 2004
AO PDO
SH_WEAW, EAT
1959
1982
2005
1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 43 45 47
Distribution of years
Ranking (from coldest to warmest NH winter temperature after detrending)
year
• Changes in some components of the East Asian winter atmospheric circulation have been suggested to be related to global warming based on the results of coupled GCMs simulations.
• These include for examples, the weakening of the Siberia-Mongolia high [BRANDEFLT, 2006], the deepening of Aleutian low [HU et al, 2000] and the weakening of the East Asian winter monsoon [HORI et al, 2006].
The two-sample KS test is one of the most useful and general nonparametric methods for comparing two samples, as it is sensitive to differences in both location and shape of the empirical cumulative distribution functions of the two samples
For a single sample of data, the Kolmogorov-Smirnov test is used to test whether or not the sample of data is consistent with a specified distribution function. When there are two samples of data, it is used to test whether or not these two samples may reasonably be assumed to come from the same distribution
Rank correlation (pearson correlation)
Hong Kong vs 28 stations in SC
1959-2005 = 0.916 (0.936)
1959-2001 = 0.909 (0.933)
1959 1962 1965 1968 1971 1974 1977 1980 1983 1986 1989 1992 1995 1998 2001 2004
PDOPDO
19761976
1959 1962 1965 1968 1971 1974 1977 1980 1983 1986 1989 1992 1995 1998 2001 2004
AOAO
19881988
1959 1962 1965 1968 1971 1974 1977 1980 1983 1986 1989 1992 1995 1998 2001 2004
NH winter tempNH winter temp
19851985
1959 1962 1965 1968 1971 1974 1977 1980 1983 1986 1989 1992 1995 1998 2001 2004
Western-positionWestern-position
1959 1962 1965 1968 1971 1974 1977 1980 1983 1986 1989 1992 1995 1998 2001 2004
IntensityIntensity
1959 1962 1965 1968 1971 1974 1977 1980 1983 1986 1989 1992 1995 1998 2001 2004
Ridge-line positionRidge-line position
Sub-tropical high SH
CUSUM Charts (2)
Mid-1970sPDO
The relationship between the Pacific Decadal Oscillation (PDO) and the Arctic Oscillation (AO) on decadal timescale in the extended winter (November-March) is investigated in this study. The results indicate that AO plays an important role in the low frequency variability of PDO. When AO leads PDO by 7-8 years, the lagging correlation between them becomes the strongest with correlation coefficient 0.77. The leading decadal variability of AO provides a valuably precursory signal for predicting the variability of PDO. The results of regression and lagging correlation reveal the possible mechanism for the AO-PDO coupling: A strong AO would lead to an enhanced Aleutian Low that is linked to PDO by ocean-atmosphere interaction in the North Pacific, and vice versa.
(1) Intensity index (SH_I): The sum of the code of geopotential height 588 dagpm (that is 588 dagpm as 1, 589 as 2, 590 as 3, and so on). Region considered is (110-180oE)
(2) Western position index (SH_W): The western most longitude of the contour of 588 dagpm in the region 90-180oE.
(3) Ridge-line index (SH_R): The mean latitude of the ridge-line of 588 dagpm contour in the region 110-150oE. It is calculated by averaging the values of latitude of the ridge-line at longitudes 110oE, 115oE, 120oE, 125oE, 130oE, 135oE, 140oE, 145oE and 150oE.
The Eurasia westerlies index (Iw) is defined as:
where the zonal (Iz) and meridional (Im) indices represent the mid-latitude circulation conditions in the Eurasia sector (0-150oE, 45-65oN) and the ￣ denotes the average. Detailed definition of Iz and Im can be found in Zhang (1999). Basically, these indices measure zonal and meridional pressure (or geopotential height) gradient aloft, respectively. Positive I corresponds to the dominance of zonal flow pattern in Eurasia.
m
m
z
z
I
I
I
I
Northern Annular Mode (Arctic Oscillation) Available format:
HTML Table
The NAM (or Arctic Oscillation) is defined as the first EOF of NH (20-90N) winter SLP data (see below). It explains 23% of the extended winter mean (December-March) variance, and it is clearly dominated by the NAO structure in the Atlantic sector. Although there are some subtle differences from the regional pattern over the Atlantic and Arctic, the main difference is larger amplitude anomalies over the North Pacific of the same sign as those over the Atlantic. This feature gives the NAM a more annular (or zonally-symmetric) structure. For more information, see http://horizon.atmos.colostate.edu/ao/.
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15
16
17
18
19
20
1959
1960
1961
1962
1963
1964
1965
1966
1967
1968
1969
1970
1971
1972
1973
1974
1975
1976
1977
1978
1979
1980
1981
1982
1983
1984
1985
1986
1987
1988
1989
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
14
15
16
17
18
19
20
1959
1960
1961
1962
1963
1964
1965
1966
1967
1968
1969
1970
1971
1972
1973
1974
1975
1976
1977
1978
1979
1980
1981
1982
1983
1984
1985
1986
1987
1988
1989
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
1958/59-2004/05: +0.23/decade (significant at 5%)
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15
16
17
18
19
20
1959
1960
1961
1962
1963
1964
1965
1966
1967
1968
1969
1970
1971
1972
1973
1974
1975
1976
1977
1978
1979
1980
1981
1982
1983
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1985
1986
1987
1988
1989
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
1958/59-2004/05: +0.23/decade (significant at 5%)
1958/59-1985/86:+0.24/decade (not sig.)
1986/87-2004/05:-0.17/decade (not sig.)
Winter temperatures in Hong Kong
-2.5
-1.5
-0.5
0.5
1.5
2.5
1959
1960
1961
1962
1963
1964
1965
1966
1967
1968
1969
1970
1971
1972
1973
1974
1975
1976
1977
1978
1979
1980
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1988
1989
1990
1991
1992
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1997
1998
1999
2000
2001
2002
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2005
1986/87
Regime shifts in winter temperature in southern China(average of the 28 stations)
>0.8 oC
-2
-1
0
1
2
1959
1960
1961
1962
1963
1964
1965
1966
1967
1968
1969
1970
1971
1972
1973
1974
1975
1976
1977
1978
1979
1980
1981
1982
1983
1984
1985
1986
1987
1988
1989
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
-4
-2
0
2
4
-2
-1
0
1
2
1959
1960
1961
1962
1963
1964
1965
1966
1967
1968
1969
1970
1971
1972
1973
1974
1975
1976
1977
1978
1979
1980
1981
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1983
1984
1985
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1988
1989
1990
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1996
1997
1998
1999
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2005
-4
-2
0
2
4
AO (+ve phase)
AO (-ve phase)
Weaker winter monsoon
Stronger winter monsoon
EAWMI
WMI
late 1980s
Relationship between Arctic Oscillation and winter monsoon
1025
1030
1035
1040
10451959
1962
1965
1968
1971
1974
1977
1980
1983
1986
1989
1992
1995
1998
2001
2004
Strength of the Siberia-Mongolia High
135
140
145
150
155
1959
1962
1965
1968
1971
1974
1977
1980
1983
1986
1989
1992
1995
1998
2001
2004
Longitudinal position of the East Asian Trough
Change point
Trend magnitude
Result in trend
