Patterns of Asian Winter Climate Variability and Links to Arctic Sea Ice BINGYI WU AND JINGZHI SU Chinese Academy of Meteorological Sciences, Beijing, China ROSANNE D’ARRIGO Tree-Ring Laboratory, Lamont-Doherty Earth Observatory, Palisades, New York (Manuscript received 11 April 2014, in final form 17 June 2015) ABSTRACT This paper describes two dominant patterns of Asian winter climate variability: the Siberian high (SH) pattern and the Asia–Arctic (AA) pattern. The former depicts atmospheric variability closely associated with the intensity of the Siberian high, and the latter characterizes the teleconnection pattern of atmospheric variability between Asia and the Arctic, which is distinct from the Arctic Oscillation (AO). The AA pattern plays more important roles in regulating winter precipitation and the 850-hPa meridional wind component over East Asia than the SH pattern, which controls surface air temperature variability over East Asia. In the Arctic Ocean and its marginal seas, sea ice loss in both autumn and winter could bring the positive phase of the SH pattern or cause the negative phase of the AA pattern. The latter corresponds to a weakened East Asian winter monsoon (EAWM) and enhanced winter precipitation in the midlatitudes of the Asian continent and East Asia. For the SH pattern, sea ice loss in the prior autumn emerges in the Siberian marginal seas, and winter loss mainly occurs in the Barents Sea, Labrador Sea, and Davis Strait. For the AA pattern, sea ice loss in the prior autumn is observed in the Barents–Kara Seas, the western Laptev Sea, and the Beaufort Sea, and winter loss only occurs in some areas of the Barents Sea, the Labrador Sea, and Davis Strait. Sim- ulation experiments with observed sea ice forcing also support that Arctic sea ice loss may favor frequent occurrence of the negative phase of the AA pattern. The results also imply that the relationship between Arctic sea ice loss and winter atmospheric variability over East Asia is unstable, which is a challenge for predicting the EAWM based on Arctic sea ice loss. 1. Introduction During boreal winter, the strongest continental anti- cyclone on Earth, known as the Siberian high (SH), covers the Asian continent. Intense cooling of the air’s surface layer and sinking motion induced by the mid- and upper-level convergence contribute to an en- hancement of the SH (Ding and Krishnamurti 1987; Ding 1990). The SH strongly affects weather and climate over Asia and parts of Europe. Outbreaks of cold polar air westward from the SH pressure cell cause occasional severe cold spells over areas of Europe. An example is the winter of 2011/12, when more than 700 people died due to extreme cold con- ditions. The SH is an important part of the East Asian winter monsoon (EAWM) system. The EAWM is a highly significant feature of Asia’s winter circulation, closely associated with the development and south- ward propagation of cold surges over East Asia (Chang and Lau 1980; Ding 1990; Jhun and Lee 2004; Wu et al. 2006). Recent studies have shown a strengthening trend in the SH over the past two decades (Jeong et al. 2011; Wu et al. 2011). The corresponding winter surface air tem- perature (SAT) exhibits a negative trend over the Asian continent (Cohen et al. 2009, 2012; Wu et al. 2011). Some regions of Eurasia have recently experienced ex- ceptionally cold winters, such as in 2007/08, 2009/10, 2010/11, 2011/12, and 2012/13 (Fig. 1). It appears that cold winters have become more frequent over East Asia. It has been found that lower Arctic sea ice values from Corresponding author address: Bingyi Wu, Chinese Academy of Meteorological Sciences, No. 46, Zhong-Guan-Cun South Avenue, Haidian District, Beijing 100081, China. E-mail: [email protected]Denotes Open Access content. 1SEPTEMBER 2015 WU ET AL. 6841 DOI: 10.1175/JCLI-D-14-00274.1 Ó 2015 American Meteorological Society Unauthenticated | Downloaded 12/08/21 01:12 AM UTC
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Patterns of Asian Winter Climate Variability and Links to Arctic Sea Ice
BINGYI WU AND JINGZHI SU
Chinese Academy of Meteorological Sciences, Beijing, China
ROSANNE D’ARRIGO
Tree-Ring Laboratory, Lamont-Doherty Earth Observatory, Palisades, New York
(Manuscript received 11 April 2014, in final form 17 June 2015)
ABSTRACT
This paper describes two dominant patterns of Asian winter climate variability: the Siberian high (SH)
pattern and the Asia–Arctic (AA) pattern. The former depicts atmospheric variability closely associated with
the intensity of the Siberian high, and the latter characterizes the teleconnection pattern of atmospheric
variability between Asia and the Arctic, which is distinct from the Arctic Oscillation (AO). The AA pattern
plays more important roles in regulating winter precipitation and the 850-hPa meridional wind component
over East Asia than the SH pattern, which controls surface air temperature variability over East Asia.
In the Arctic Ocean and its marginal seas, sea ice loss in both autumn and winter could bring the positive
phase of the SH pattern or cause the negative phase of the AA pattern. The latter corresponds to a weakened
East Asian winter monsoon (EAWM) and enhanced winter precipitation in the midlatitudes of the Asian
continent and East Asia. For the SH pattern, sea ice loss in the prior autumn emerges in the Siberian marginal
seas, andwinter lossmainly occurs in theBarents Sea, Labrador Sea, andDavis Strait. For theAApattern, sea
ice loss in the prior autumn is observed in the Barents–Kara Seas, the western Laptev Sea, and the Beaufort
Sea, and winter loss only occurs in some areas of the Barents Sea, the Labrador Sea, and Davis Strait. Sim-
ulation experiments with observed sea ice forcing also support that Arctic sea ice loss may favor frequent
occurrence of the negative phase of the AA pattern. The results also imply that the relationship between
Arctic sea ice loss and winter atmospheric variability over East Asia is unstable, which is a challenge for
predicting the EAWM based on Arctic sea ice loss.
1. Introduction
During boreal winter, the strongest continental anti-
cyclone on Earth, known as the Siberian high (SH),
covers the Asian continent. Intense cooling of the air’s
surface layer and sinking motion induced by the mid-
and upper-level convergence contribute to an en-
hancement of the SH (Ding and Krishnamurti 1987;
Ding 1990). The SH strongly affects weather and
climate over Asia and parts of Europe. Outbreaks
of cold polar air westward from the SH pressure
cell cause occasional severe cold spells over areas of
Europe. An example is the winter of 2011/12, when
more than 700 people died due to extreme cold con-
ditions. The SH is an important part of the East Asian
winter monsoon (EAWM) system. The EAWM is a
highly significant feature of Asia’s winter circulation,
closely associated with the development and south-
ward propagation of cold surges over East Asia
(Chang and Lau 1980; Ding 1990; Jhun and Lee 2004;
Wu et al. 2006).
Recent studies have shown a strengthening trend in
the SH over the past two decades (Jeong et al. 2011; Wu
et al. 2011). The corresponding winter surface air tem-
perature (SAT) exhibits a negative trend over the Asian
continent (Cohen et al. 2009, 2012; Wu et al. 2011).
Some regions of Eurasia have recently experienced ex-
ceptionally cold winters, such as in 2007/08, 2009/10,
2010/11, 2011/12, and 2012/13 (Fig. 1). It appears that
cold winters have becomemore frequent over East Asia.
It has been found that lower Arctic sea ice values from
Corresponding author address: Bingyi Wu, Chinese Academy of
ated with the SH, supported by the correlation between
the PC1 and the detrended SHI (r 5 0.95; see Fig. 3).
This systematic atmospheric circulation anomaly is
herein termed the SH pattern. The 850-hPa meridional
wind anomalies, however, do not exceed the level of
statistical significance over eastern China south of 308N(Fig. 2d). Strengthened northerlies are seen over the
area from Lake Baikal extending southeastward to the
northwestern Pacific. When accompanied by a strength-
ened SH, weak southerly anomalies emerge over parts
of southern China. The SH pattern mainly reflects large-
scale meridional circulation anomalies over the middle
and high latitudes.
The same analysis process was carried out over three
different domains: 1) 308–708N, 508–1308E, 2) 308–808N,
508–1308E, and 3) 208–708N, 608–1308E. The leading
EOFs over the three domains respectively account for
46%, 46%, and 44% of the variance. Corresponding
winter SLP, 500-hPa height, SAT, and 850-hPa meridi-
onal wind anomalies, derived from linear regressions on
their PC1s, closely resemble those shown in Figs. 2a–d (not
shown). Their PC1s are significantly correlated with the
detrended SHI, with correlations of 0.90, 0.75, and 0.81,
respectively (Fig. 3).
For EOF2, the amplitudes of both positive SLP and
500-hPa height anomalies are weaker than those for
EOF1 (Figs. 4a,b). Positive SLP anomalies appear over
most of the Asian continent south of 508N, with
moderate negative anomalies in the north. Negative
SLP and 500-hPa height anomalies mainly appear in
the Arctic and northern North Pacific, making this
pattern distinct from the positive phase of the AO. In
fact, the correlation between EOF2 and the detrended
AO is 0.28 (0.44) for winters of 1979/80–2008/09 (win-
ters of 1979/80–2012/13). Positive SAT anomalies are
observed in the middle and high latitudes of the Asian
continent, with negative SAT anomalies to the south
(Fig. 4c). Such a spatial distribution of SAT anomalies
is dynamically consistent with that for the SLP anom-
alies. Significant anomalies in 850-hPa meridional
winds are observed in East Asia, particularly in eastern
and northeastern China (Fig. 4d).
The second EOFs over the three domains (308–708N,
508–1308E; 308–808N, 508–1308E; and 208–708N, 608–1308E) respectively account for 22%, 23%, and 22% of
the variance. Anomalies in detrended winter SLP,
500-hPa height, SAT, and 850-hPa meridional winds,
derived from linear regressions on their PC2s, closely
resemble those shown in Figs. 4a–d for the domain 308–808N, 508–1308E, but with anomalies of opposing sign for
the other domains (not shown). For two domains (308–708N, 508–1308Eand 208–708N, 608–1308E), the PC2 time
series are out of phase with that for 308–708N, 808–1208E(Fig. 5); their correlations are 20.95 and 20.90, re-
spectively. Over the domains 308–708N, 808–1208E and
308–808N, 508–1308E, the PC2 time series are in phase
(Fig. 5; their correlation is 0.84). Although the domains
are different for EOF analysis, the atmospheric circu-
lation anomalies associated with EOF2s exhibit similar
FIG. 3. Normalized time series of the detrended winter SHI (red line) and the PC1s of EOF
analyses of detrended winter mean SLP variability over four different domains: 308–708N, 808–1208E (green); 308–708N, 508–1308E (blue); 308–808N, 508–1308E (black); and 208–708N, 608–1308E (purple).
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features over Asia and the Arctic. Thus, this systematic
circulation anomaly is herein termed the Asia–Arctic
(AA) pattern. The AA pattern predominantly exhibits
large-scale zonal circulation anomalies, differing from
the SHpattern. Because the intensity of the SH is closely
related to the EAWM variability (Jhun and Lee 2004;
Wu et al. 2006), the extracted leading SLP pattern
should characterize SH variability as accurately as pos-
sible. If we selected a domain that covers more area of
the Arctic Ocean, the correlation between the leading
SLP pattern and the detrended SHI would decline.
Consequently, the first two PCs of EOF analysis over
308–708N, 808–1208E can be regarded as indices that
depict the SH and AA patterns, respectively. It should
be pointed out that the SH and AA pattern well
represent the first two coupled patterns between winter
mean SLP over Eurasia (308–708N, 508–1308E) and any
meridional vertical cross section of zonal winds over the
Asian continent (extracted by the maximum covariance
analysis; not shown). Thus, neither of the SH and AA
patterns relies on the EOF method. They reflect differ-
ent dynamic regimes, namely large-scale meridional and
zonal circulation anomalies.
The regionally averaged winter 850-hPa meridional
wind over eastern China (308–408N, 1108–1208E) is sig-nificantly correlated with the AA pattern (r 5 20.56;
after removing linear trends, the correlation is 20.60,
at 0.01 significance level). In contrast to the AA pattern,
the SH pattern does not show a significant relationship
with the regionally averaged 850-hPa meridional wind
FIG. 4. As in Fig. 2, but regressed on the normalized PC2 of EOF analysis of detrendedwintermean SLP variability
over 308–708N, 808–1208E [outlined by green lines in (a)]. Contour intervals are 0.5 hPa in (a), 5 gpm in (b), 0.58C in
(c), and 0.3m s21 in (d).
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(r 5 20.20 after detrending). At the surface, however,
the regionally averaged meridional wind (at 10m) over
29.528–40.958N, 110.6258–1208E is significantly corre-
lated with the SH and AA patterns after detrending
at 20.51 and 20.57, respectively. This implies that
compared with the SH pattern, the AA pattern shows a
closer relationship with the EAWM.
To investigate dynamical connections to Arctic atmo-
sphere variability, we first selected positive and negative
phasewinters for which their standard deviations are.0.8
or,20.8, as shown in Table 1. We selected the latitude–
pressure vertical cross section at 1108E to show wave ac-
tivity fluxes (Fig. 6). In the middle and high troposphere
south of 758N, the wave activity fluxes show coherent
propagations southward to 458N, reflecting a dynamical
linkage between the Arctic and the midlatitudes of East
Asia (Fig. 6a). In the Arctic north of 758N, the wave ac-
tivity fluxes propagate northward over nearly the entire
troposphere. For the AA pattern, southward propagation
is mainly observed between 408 and 658N (Fig. 6b), in-
dicating that sub-Arctic atmospheric variability is directly
linked with that over the midlatitudes of East Asia via
atmospheric energy propagations. Over the Arctic, the
wave activity fluxes display northward propagations. At
500hPa, the wave activity fluxes originated from the
Barents–Kara Seas propagate southeastward to the high
latitudes of the Asian continent, and then propagate
northeastward to the Arctic Ocean (Fig. 6c). Another
branch propagates to the northwestern Pacific.
Figure 7 shows the latitude–pressure vertical cross
section of westerly anomalies associated with the SH
and AA patterns along 1108E. Relative to the negative
phase of the SH pattern, its positive phase corresponds
to a strengthened westerly jet in the higher troposphere
(Fig. 7a) (the center of the westerly jet at 1108E is
around 308N and 200hPa; not shown). Meanwhile, over
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FIG. 6. (a) Differences in detrended mean geopotential heights between the positive and
negative phases of the SH pattern along the latitude–pressure cross section at 1108E, super-imposed on meridional and vertical (multiplied by 0.05) wave activity flux (vectors; m2 s22) of
Takaya and Nakamura (2001); light blue and blue areas indicate geopotential height differ-
ences at 0.05 and 0.01 significance levels, respectively. (b) As in (a), but for differences in
detrended mean geopotential heights between the negative and positive phases of the AA
pattern. (c) Differences in detrended mean geopotential heights between the negative and
positive phases of the AA pattern at 500 hPa; contour intervals are 20 gpm; composite winter
cases for the SH and AA patterns are shown in Table 1 (nonboldface winters).
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Eurasia except for some areas of northern Eurasia and
the Tibetan Plateau where negative SAT anomalies are