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Impacts of two types of La Nin
˜a on the NAO during boreal winter
Wenjun Zhang •Lei Wang •Baoqiang Xiang •
Li Qi •Jinhai He
Received: 12 October 2013 / Accepted: 17 April 2014 / Published online: 4 May 2014
ÓThe Author(s) 2014. This article is published with open access at Springerlink.com
Abstract The present work identifies two types of La
Nin
˜a based on the spatial distribution of sea surface tem-
perature (SST) anomaly. In contrast to the eastern Pacific
(EP) La Nin
˜a event, a new type of La Nin
˜a (central Pacific,
or CP La Nin
˜a) is featured by the SST cooling center over
the CP. These two types of La Nin
˜a exhibit a fundamental
difference in SST anomaly evolution: the EP La Nin
˜a
shows a westward propagation feature while the CP La
Nin
˜a exhibits a standing feature over the CP. The two types
of La Nin
˜a can give rise to a significantly different tele-
connection around the globe. As a response to the EP La
Nin
˜a, the North Atlantic (NA)–Western European (WE)
region experiences the atmospheric anomaly resembling a
negative North Atlantic Oscillation (NAO) pattern
accompanied by a weakening Atlantic jet. It leads to a
cooler and drier than normal winter over Western Europe.
However, the CP La Nin
˜a has a roughly opposing impact
on the NA–WE climate. A positive NAO-like climate
anomaly is observed with a strengthening Atlantic jet, and
there appears a warmer and wetter than normal winter over
Western Europe. Modeling experiments indicate that the
above contrasting atmospheric anomalies are mainly
attributed to the different SST cooling patterns for the two
types of La Nin
˜a. Mixing up their signals would lead to
difficulty in seasonal prediction of regional climate. Since
the La Nin
˜a-related SST anomaly is clearly observed dur-
ing the developing autumn, the associated winter climate
anomalies over Western Europe could be predicted a sea-
son in advance.
Keywords Two types of La Nina Climate impacts
The North Atlantic and Western Europe
1 Introduction
The El Nin
˜o–Southern Oscillation (ENSO) represents a
periodic fluctuation between warm (El Nin
˜o) and cold
(La Nin
˜a) conditions in sea surface temperature (SST)
over the central to eastern tropical Pacific (Philander
1990; McPhaden et al. 2006). As one of the most
important coupled ocean–atmosphere phenomenon, the
ENSO has received extensive public attention because of
its profound global climate impacts (e.g., van Loon and
Madden 1981; Ropelewski and Halpert 1987,1996;
Trenberth and Caron 2000). By now, the linkage between
ENSO and the climate in the North Pacific and North
America has been well understood and is usually referred
to as the ‘‘Pacific–North America’’ (PNA) teleconnection
(e.g., Wallace and Gutzler 1981; Branston and Livezey
1987). However, climate responses to ENSO over the
North Atlantic (NA)–Western European (WE) sector are
controversial.
In the 1980s and early 1990s, early studies showed that
ENSO-related precipitation and temperature anomalies are
W. Zhang (&)L. Wang L. Qi J. He
Collaborative Innovation Center on Forecast and Evaluation of
Meteorological Disasters, Key Laboratory of Meteorological
Disaster of Ministry of Education, Nanjing University of
Information Science and Technology, Nanjing 210044, China
e-mail: zhangwj@nuist.edu.cn
W. Zhang
Key Laboratory of Numerical Modeling for Atmospheric
Sciences and Geophysical Fluid Dynamics, Institute of
Atmospheric Physics, Chinese Academy of Sciences,
Beijing 100029, China
B. Xiang
International Pacific Research Center, University of Hawaii
at Manoa, Honolulu, HI 96822, USA
123
Clim Dyn (2015) 44:1351–1366
DOI 10.1007/s00382-014-2155-z
almost absent over the NA–WE region (Ropelewski and
Halpert 1987; Halpert and Ropelewski 1992). The view-
point is supported by later studies that the climate signal of
ENSO over the NA–WE sector is difficult to be detected
because of the large inter-event variability (see an exten-
sive review by Bro
¨nnimann 2007). This non-stationary
behavior is possibly due to some modulating factors, such
as the complexity of ENSO itself (Greatbatch et al. 2004),
natural (or internal) variability in the extratropical circu-
lation (Kumar and Hoerling 1998), tropical volcanic
eruptions (Bro
¨nnimann et al. 2007a), and other climate
signals independent of ENSO (e.g., Mathieu et al. 2004;
Garfinkel and Hartmann 2010). Nevertheless, the argument
of the absence of ENSO signal over the NA–WE region
was challenged by numerous studies (e.g., Bro
¨nnimann
et al. 2007b; Ineson and Scaife 2009; Li and Lau 2012).
These studies argued that a significant ENSO signal is
found over the region of Europe despite the large inter-
event variability. A canonical El Nin
˜o response in late
winter is suggested to be accompanied by a negative North
Atlantic Oscillation (NAO)-like pattern with a colder and
drier than normal weather, and the La Nin
˜a has a largely
opposing impact (e.g., Gouirand and Moron 2003;
Bro
¨nnimann et al. 2007b). In comparison, the NA atmo-
spheric response to La Nin
˜a is found to be much more
stable than that due to El Nin
˜o during winter (Pozo-Va
´z-
quez et al. 2005). Since the NA atmosphere shows higher
predictability associated with the La Nin
˜a compared to the
El Nin
˜o, our focus of this study is on the NA–WE atmo-
spheric response associated with La Nin
˜a events.
Recent studies argued that a new type (or flavor) of El
Nin
˜o, in addition to the conventional El Nin
˜o, occurs more
frequently in the recent decades with its maximum center
over the central equatorial Pacific rather than the eastern
Pacific (EP) (Larkin and Harrison 2005; Ashok et al. 2007;
Kao and Yu 2009; Kug et al. 2009; Yeh et al. 2009; Ren
and Jin 2011; Wang and Wang 2013). In particular, the
new type of El Nin
˜o becomes the dominant mode after the
late 1990s (Xiang et al. 2013). For convenience, EP and CP
El Nin
˜os are referred to as the conventional and the new
type of El Nin
˜o herein, respectively. Many studies have
reported the importance of the CP El Nin
˜o in terms of its
distinctly different climate impacts from the EP El Nin
˜o
(Weng et al. 2007; Taschetto and England 2009; Feng et al.
2010; Feng and Li 2011,2013; Lee et al. 2010; Zhang et al.
2011,2012,2013; Xie et al. 2012; Yu et al. 2012; Afzaal
et al. 2013).
The La Nin
˜a diversity is also concerned in its impact on
extratropical atmosphere, such as over East Asia (e.g.,
Wang et al. 2012). At present, there appears a scientific
consensus on the occurrence of the new type of El Nin
˜o,
however, whether La Nin
˜a events can be separated into two
types remains open to debate. Some studies suggested that
the zonal location of the maximum SST anomaly center
does not show apparent change for individual La Nin
˜a
event (Kug et al. 2009; Kug and Ham 2011; Ren and Jin
2011). On the contrary, some other studies argued for the
existence of two types of La Nin
˜a (e.g., Cai and Cowan
2009; Shinoda et al. 2013). For example, the CP La Nin
˜ais
argued to be clearly distinguished from the EP La Nin
˜a
events in terms of ocean surface currents through analyzing
recent satellite data (Shinoda et al. 2013). So far, the fun-
damental dynamics is not well understood that is used to
explain differences in the generation and maintenance of
two types of ENSO. Given unclear dynamical mechanisms,
one possible way to distinguishing them is to investigate
the associated local circulation and extratropical telecon-
nections. The analyses performed in this paper show that
the winter atmospheric anomalies over the NA–WE region
are very different from each other for these two types of La
Nin
˜a. The result, on the one hand, will provide a possible
indirect evidence for the existence of different flavors of La
Nin
˜a. On the other hand, the necessity is emphasized to
separate the La Nin
˜a events into two types when analyzing
their associated extratropical climate impacts. Mixing up
their signals would increase difficulty in seasonal predic-
tion of the climate particularly over the NA–WE sector.
The purpose of the study is to explore the different
teleconnection patterns and their associated climate
anomalies over the NA–WE sector for the two types of La
Nin
˜a. In the remainder of the paper, Sect. 2describes data,
methodology, and model experiments. Section 3illustrates
SST anomaly patterns for the two types of La Nin
˜a and its
associated atmospheric responses over the tropical Pacific.
Section 4presents atmospheric responses over the NA–WE
region. In Sect. 5, we explore possible mechanisms for the
climate impacts on influencing the NA–WE climate asso-
ciated with the two types of La Nin
˜a. Section 6discusses
asymmetry in influences of ENSO on the NA–WE climate.
The major conclusions are summarized in Sect. 7.
2 Data and methodology
2.1 Observations
The monthly SST datasets (1951–2009) used in this study
are the global sea ice and SST analyses from the Hadley
Centre (HadISST1) provided by the Met Office Hadley
Centre (Rayner et al. 2003). Atmospheric circulations were
examined based on the National Centers for Environmental
Prediction/National Center for Atmospheric Research
(NCEP/NCAR) reanalysis data (Kalnay et al. 1996). The
precipitation data are taken from the Climate Prediction
Center Merged Analysis of Precipitation (CMAP)
(1979–2009) (Xie and Arkin 1996) and the Global
1352 W. Zhang et al.
123
Precipitation Climatology Centre (GPCC) (1951–2009)
(Rudolf et al. 2005). The surface temperature anomalies
over WE are investigated using the Climate Research Unit
(CRU) air temperature anomalies version 4 (CRUTEM4)
(1951–2009) (Jones et al. 2012). Anomalies for all vari-
ables were conducted as the deviation from the 30-year
climatological mean (1961–1990). The 1971–2000 average
can also be defined as the climate mean, which does not
influence qualitative results. The average over the entire
period (1979–2009) is taken as the climate mean for the
CMAP precipitation because the data are available after
1979. In order to remove possible influence associated with
the long-term trend, all anomalies are linearly detrended
over the period 1951–2009, except for the CMAP data over
the period 1979–2009. The non-detrended data are also
examined and the results are almost the same. Composite
and regression analyses are employed to investigate dif-
ferences in climatic impact associated with the two types of
La Nin
˜a, using Student’s two-tailed significance test.
2.2 Definition of two types of La Nin
˜a events
Unlike contrasting SST anomaly patterns associated with
the two types of El Nin
˜o, Ren and Jin (2011) suggested that
the La Nin
˜a events seem to be difficult to be clearly sep-
arated into two types based on their index. Based on the
DJF (December–February) mean ENSO and ENSO Mod-
oki indices (Ashok et al. 2007), half of events selected are
the same in the two types of La Nin
˜a (Tedeschi et al. 2012).
It is also expected that the two types of La Nin
˜a events
cannot be well distinguished based on the index defined by
Kao and Yu (2009), since the current indices of the two-
type ENSO show high consistency (Ren and Jin 2013).
Considering the fact that the present ENSO indices cannot
effectively distinguish the two types of La Nin
˜a events, we
therefore identify the selection by an analysis of the spatial
distribution of SST anomaly patterns. First, 17 La Nin
˜a
winters are defined by the Climate Prediction Center (CPC)
over the period 1951–2009 based on a threshold of
-0.5 °C for winter (DJF) mean Nin
˜o3.4 (5°S–5°N, 120°–
170°W) SST anomaly. Then we identify seven EP La Nin
˜a
winters (1954/55, 1955/56, 1964/65, 1971/72, 1984/85,
1995/96, and 2005/06) and seven CP La Nin
˜a winters
(1973/74, 1974/75, 1975/76, 1983/84, 1988/89, 1998/99,
and 2000/01). The winters, having larger SST anomaly in
the EP (CP) east (west) of 150°W during the developing
and mature phases of La Nin
˜a, are classified into the EP
(CP) La Nin
˜a winters. The longitude of 150°W is selected
because it is a boundary of Nin
˜o3 (5°S–5°N, 150°–90°W)
and Nin
˜o4 (5°S–5°N, 160°E–150°W) areas, which are
usually used to define the two-type ENSO events (e.g., Kim
et al. 2009; Kug et al. 2009). Other three years (1970/71,
1999/00, and 2007/08) are defined as the mixed type of La
Nin
˜a, because the large cooling SST anomaly covers both
the EP and CP during the mature phase. Their character-
istics will be further discussed in Sect. 3. The year listed
here corresponds to year(0)/year(1). The developing year
of the La Nin
˜a event and the following year is designated
as year(0) and year(1), respectively. A typical ENSO tends
to develop during the spring season and lasts for roughly a
year. However, long-lasting La Nin
˜a events are often
observed, such as the events for 1954–56 and 1973–76
selected in this study. After excluding these events, the
qualitative difference influencing conclusions is not
detected.
2.3 Simulations
All model simulations are performed using the National
Center for Atmospheric Research (NCAR) Community
Atmospheric Model Version 5 (CAM5) (Neale et al. 2010).
CAM5 has been updated in many physical processes
compared to the previous version. The version has a finite
volume dynamic core with resolution of 1.9°longi-
tude 92.5°latitude and 30 vertical levels. In the control
run (CNTRL), CAM5 is driven by climatological (seasonal
varying) SST and the results were derived as a reference
state. A series of sensitive experiments listed in Table 1
were performed to compare the climate impacts of different
SST anomaly patterns associated with the two types of La
Nin
˜a. In the first simulation (EP cooling, EP_COOL), the
cold SST anomaly during the EP La Nin
˜a winter is
imposed on the monthly climatological SST from October
to February in the tropical Pacific (30°S–30°N, 120°E–
90°W). All anomalies outside of the region are set to zero.
The second experiment (CP cooling, CP_COOL) designed
is the same as the EP_COOL experiment, expect that the
SST anomaly is the composition during the CP La Nin
˜a
winter. The third experiment (CP warming, CP_WARM) is
Table 1 List of SST perturbation experiments conducted in this
study
Expt Description of SST perturbation
EP_COOL Cooling anomalies associated with EP La Nin
˜a
events imposed in the tropical Pacific (30°S–30°N,
120°E–90°W)
CP_COOL As in EP_COOL but for the CP La Nin
˜a events
CP_WARM As in CP_COOL but for warming anomalies in the
tropical Pacific (30°S–30°N, 120°E–120°W)
CP_CW CP_COOL cooling and CP_WARM warming
anomalies imposed together
AT_COOL As in CP_COOL but for cooling anomalies in the
northern tropical Atlantic Ocean (10°S–25°N, 0°–
80°W)
CPAT_COOL CP_COOL and AT_COOL cooling anomalies
imposed together
Impacts of two types of La Nin
˜a 1353
123
also the same as the EP_COOL and CP_COOL experi-
ments, but the warming SST anomaly during the CP La
Nin
˜a winter is added to the seasonally varying monthly
climatological SST over the western tropical Pacific. In this
experiment, we consider the possible impacts of the
warming SST anomaly, since the positive SST anomaly
appears significantly over the western tropical Pacific
during the CP La Nin
˜a winter. In the fourth experiment (CP
cooling and warming, CP_CW), we conduct sensitivity
simulations where the CP_COOL and CP_WARM forcings
are imposed together to inspect the combined contribution
of the warming and cooling SST anomaly over the tropical
Pacific during the CP La Nin
˜a winter. We also study pos-
sible effects of the cooling SST anomalies in the northern
tropical Atlantic Ocean during the CP La Nin
˜a winter in the
fifth experiment (Atlantic cooling, AT_COOL), since the
significant cooling SST anomalies occur there. In the last
experiment (CP and Atlantic cooling, CPAT_COOL), the
CP_COOL and AT_COOL forcings are both imposed to
examine their combined impacts on atmosphere. All sim-
ulations are integrated for 15 years and the last 10 years’
integration was considered to exclude influence of the
initial condition and the internal variability.
3 SST anomaly pattern and its associated atmospheric
response over the tropical Pacific
Figure 1displays the seasonal evolution of the equatorial
(5°S–5°N) SST anomaly for the above mentioned three
types of La Nin
˜a. The evolution of the EP La Nin
˜ais
similar to the conventional La Nin
˜a event (Fig. 1a) with its
SST anomaly developing in the far EP and reaching its
largest amplitude during November(0) and December(0).
The evolution of the maximum centers indicated by
marked crosses shows that the EP La Nin
˜a–SST anomaly
propagates westward at a certain speed. During the
developing and mature phase, the EP La Nin
˜a is manifested
by larger cooling SST anomaly mainly confined in the
eastern equatorial Pacific east of 150°W. In contrast to the
EP La Nin
˜a, the CP La Nin
˜a exhibits a fundamental dif-
ference in the SST anomaly structure and its evolution
(Fig. 1b). Firstly, its action center is shifted westward into
the central equatorial Pacific. Secondly, the SST anomaly
almost does not propagate for the CP La Nin
˜a, representing
a standing feature. The CP La Nin
˜a seems to be mainly
associated with the local air–sea interaction that develops
and decays in situ over the CP. As the CP La Nin
˜a
develops, its SST anomaly also extends eastward and
westward from the CP. Contrasting features of SST
anomaly evolution associated with the EP and CP La Nin
˜a
suggest that their underlying dynamics should be different,
which provides a possible evidence for the existence of
different types of La Nin
˜a. Such discussion has been given,
for example, previous studies argued that the thermocline
dynamics, as the most important dynamics for traditional
(or EP) ENSO, seems to play a less important role on the
CP ENSO (e.g., Kao and Yu 2009). For the mixed type of
La Nin
˜a (Fig. 1c), the SST anomaly center starts in the EP,
and shifts slightly eastward in the developing phase. Dur-
ing the mature phase, the SST anomaly center propagates
rapidly from the EP to the CP. The large negative SST
anomaly stretches across the EP and CP during the mixed
type of La Nin
˜a winter, mixing the SST anomalies asso-
ciated with the EP and CP La Nin
˜a (not shown).
To further investigate the phase locking of La Nin
˜a, we
use Nin
˜o3, Nin
˜o4, and Nin
˜o3.4 SST anomaly to denote the
EP, CP, and mixed type, respectively. As shown in Fig. 2,
the EP and CP La Nin
˜a events exhibit an approximate
feature during the developing phase. Both types of events
reach the maximum around December(0) with almost the
same intensity. After December(0), the CP La Nin
˜a enters a
slower decay phase than the EP La Nin
˜a. For the mixed
type of La Nin
˜a, it is characterized by much larger
amplitude and the delayed occurrence of the mature phase
by a month compared to the EP and CP La Nin
˜a. Again, the
mixed type of La Nin
˜a exhibits its distinct feature and it
seems necessary to classify them into a single group. Since
the action center of the mixed-type La Nin
˜a covers the EP
and CP as shown in Fig. 1, it may mix signals of the EP
and CP La Nin
˜a in terms of the extratropical atmospheric
response. In this paper, the contrasting climate impacts of
the EP and CP La Nin
˜a over the NA–WE sector are our
focus, so the mixed type of La Nin
˜a will not be discussed in
the remainder of the paper.
Figure 3shows the composite SST and surface wind
anomalies during EP and CP La Nin
˜a winters. During
boreal winter, the SST anomaly for the EP La Nin
˜a covers
the CP and EP with the maximum center occurring in the
EP. Almost no significant warming SST anomaly is found
over other domain of the tropical Pacific. As a Rossby
wave response (Gill 1980) to the cooling SST anomaly, a
pair of anticyclone anomalies resides at each side of the
central equatorial Pacific accompanying by easterly wind
anomaly at the equator. In contrast, the cooling center of
SST anomaly associated with the CP La Nin
˜a is displaced
westward into the central equatorial Pacific west of 150°W
with a weak SST anomaly in the far eastern equatorial
Pacific. As shown in Fig. 3, the amplitude of the CP La
Nin
˜a appears to be stronger than that of the EP La Nin
˜a,
with significant warming SST anomaly occurring in the
northwestern and southwestern tropical Pacific. The
weaker amplitude of the EP La Nin
˜a is possibly associated
with the faster decaying rate in its SST anomaly (Fig. 2). In
comparison with the surface wind response to the EP La
Nin
˜a, the pair of anticyclone anomalies occurring at both
1354 W. Zhang et al.
123
sides of the equator also shifts relatively westward into the
western tropical Pacific (Fig. 3b). It is notable that westerly
anomaly occurring over the far eastern equatorial Pacific
that is not observed in the EP La Nin
˜a composition could
inhibit the cooling upwelling and thus weaken the SST
anomaly there.
The tropical convection anomalies associated with the
two types of La Nin
˜a are expected to be distinct due to their
differing SST anomaly patterns (Fig. 4). Because precipi-
tation data over the tropical ocean are available since the
late 1970s, the divergence of water vapor (integrated from
surface to 300 hPa) is examined here to roughly reflect the
precipitation anomaly based on the balance equation of the
atmospheric water vapor (Yanai et al. 1973). Correspond-
ing to the EP La Nin
˜a, the associated convective anomaly
center emerges mainly over the CP to the west of the
negative SST anomaly center (Fig. 4a). Enhanced precip-
itation indicated by the convergence of water vapor appears
to the south and the north of the positive center and over
the Philippine Sea. During the CP La Nin
˜a winter, the
center of the negative precipitation is also located over the
central tropical Pacific but shifted slightly westward com-
pared to that during the EP La Nin
˜a winter (Fig. 4b). The
intensity of precipitation response to the CP La Nin
˜ais
obviously stronger than that to the EP La Nin
˜a, which is
associated with the stronger SST anomaly for the CP La
Nin
˜a. Another possible reason is related to the different
location of SST anomaly. Compared to the EP, the con-
vection over the CP is much more sensitive to the SST
anomaly because of a higher background SST (e.g., Kug
et al. 2009). As such, the SST anomaly for the CP La Nin
˜a
can induce stronger atmospheric response than that for the
(a) (b) (c)
Fig. 1 Time-longitude diagram of SST anomaly (°C) composites in
the equatorial Pacific (5°S–5°N) for aEP La Nin
˜a, bCP La Nin
˜a, and
cmixed La Nin
˜a. The ordinate presents an 11-month period from July
of year 0 to May of year 1. Contour lines indicate values that are
significant at the 95 % confidence level. Red crosses mark the
longitudes of the maximum SST anomalies which are smoothed
spatially using a 3-point running mean
Fig. 2 Composite monthly evolution of the Nin
˜o3 SST anomalies
(°C) for the EP La Nin
˜a(red curve), the Nin
˜o4 SST anomalies for the
CP La Nin
˜a(blue curve), and Nin
˜o3.4 SST anomalies for the mixed
La Nin
˜a(black curve). The abscissa indicates a 13-month period from
July of year 0 to July of year 1
Impacts of two types of La Nin
˜a 1355
123
EP La Nin
˜a. Another difference in the moist convergence
anomaly is that a more precipitation belt elongates north-
eastward from the Philippine Sea to the CP during the CP
La Nin
˜a episode. The CMAP precipitation is also examined
to investigate the convection anomalies for these two types
of La Nin
˜a compositions after 1979 and their difference is
similar to that indicated by the divergence of water vapor
except for the region of the northwestern tropical Pacific
(Fig. 4).
4 Atmospheric responses over NA and WE
The contrast in the tropical atmosphere anomalies, in
association with different SST anomaly patterns of the two
types of La Nin
˜a, may result in large differences in the
extratropical circulation and thus regional climate. In this
paper, we focus on the climate response over the NA–WE
sector, in particular on their potential impacts on the NAO
associated with these two types of La Nin
˜a since it is the
dominant climate variability mode over the NA–WE sector.
In general, ENSO events reach their peaks during late
autumn and winter, however, the associated climate impacts
over the NA and WE region are found to be significant
during late winter (Gouirand and Moron 2003; Knippertz
et al. 2003; Bro
¨nnimann et al. 2007b). To illustrate the
seasonality of the ENSO signal, the NAO index is defined as
the difference in the normalized monthly sea level pressure
(SLP) regionally zonal-averaged over the NA–WE sector
from 80°Wto30°E between 35°N and 65°N (Li and Wang
2003). This simple NAO index is demonstrated to well
describe the spatial–temporal characteristics associated
with NAO (Li and Wang 2003). For the EP La Nin
˜a, the
NAO index appears to be at a normal state in ND(0)
(Fig. 5). During the JFM(1) period, a negative value cor-
responds to a negative NAO-like pattern indicative of a high
pressure anomaly in the mid-latitude and a low pressure
anomaly in the subtropics. This configuration is reversed
from AM(1). For the CP La Nin
˜a, the atmospheric response
in N(0) is characterized by a weak negative NAO-like
pattern. The revised sign of the NAO index in following
3 months is manifested by a positive NAO-like pattern,
demonstrating a low pressure anomaly to the north and a
high pressure anomaly to the south (Fig. 5). As shown in
Fig. 5, an opposite sign of the atmospheric response is
observed in winter for the two types of La Nin
˜a, and the
difference is most evident in JF(1). To detect the robust
signal, we shall hereafter define ‘‘winter’’ as the JF period
when investigating the atmospheric responses over the NA–
WE sector to the two types of La Nin
˜a. The ‘‘winter’’ can
also be defined by D(0)JF(1), and even D(0)JFM(1) or
JFM(1), and the qualitative conclusion is unchanged.
One prominent teleconnection associated with ENSO
events has been referred to as the PNA pattern
(a)
(b)
Fig. 3 Composites of SST
anomalies (shading and
contours in °C) and surface
wind anomalies (vectors in m/s)
during DJF for aEP La Nin
˜a,
and bCP La Nin
˜a. The SST
anomalies that are not
significant at the 95 % level are
not shown. Contour interval is
0.5 °C and zero contours are
omitted. Only values above
0.6 m/s are shown for surface
wind anomalies
1356 W. Zhang et al.
123
accompanied by an intensified Aleutian low during ENSO
warm phase. Corresponding to the ENSO cold phase, a
positive SLP anomaly covers the North Pacific indicating
a weakened Aleutian Low during both types of La Nin
˜a
events (Fig. 6a, b). Compared to the EP La Nin
˜a
composite, the significantly positive SLP anomaly is
slightly shifted southeastward for the CP La Nin
˜a com-
posite. However, their differences in SLP are pronounced
over the NA–WE sector. During winter for the EP La
Nin
˜a, a significantly high pressure anomaly to the north
and a significantly low pressure anomaly to the south
elongate zonally from the central North Atlantic to Eur-
ope (Fig. 6a). This SLP anomaly response resembles the
negative NAO-like pattern. Nevertheless, the signal of the
CP La Nin
˜a is roughly opposite to that of the EP La
Nin
˜a. A significant low (high) pressure anomaly to the
north (south) extends zonally from the western to eastern
NA (Fig. 6b), which corresponds to a positive NAO-like
pattern.
As indicated by the composite geopotential height at
300 hPa (Fig. 6c, d), the similar anomaly pattern in the
lower troposphere can also be detected in the upper tro-
posphere over the North Pacific and NA–WE regions. The
barotropic features are shown in the atmospheric response
to the two types of La Nin
˜a over the mid-latitude regions.
The result is consistent with the previous study (Ting
1996), in which it is pointed out that the tropical heating
(a)
(b)
Fig. 4 Composites of vertically
integrated moisture divergence
(shading and black contours in
mm/day) and CMAP
precipitation (pink contours in
mm/day) during DJF for aEP
La Nin
˜a, and bCP La Nin
˜a.
Shading presents values
exceeding the 90 and 95 %
confidence level. Black and pink
contour intervals are 1 and
2 mm/day, respectively. Zero
contours are omitted
Fig. 5 Composite monthly evolution of the NAO index for EP La
Nin
˜a(solid line) and CP La Nin
˜a(dashed line). The abscissa indicates
a 7-month period from November of year 0 to May of year 1
Impacts of two types of La Nin
˜a 1357
123
can cause a barotropic response in the atmospheric circu-
lation over the extratropics.
It is suggested that the subtropical jet is of importance in
bridging the ENSO and NAO teleconnection (Graf and
Zanchettin 2012). Here, the composite zonal wind anom-
alies at 200 hPa are displayed to investigate the change in
jet stream for the two types of La Nin
˜a (Fig. 7). In asso-
ciation with the EP La Nin
˜a, the zonal wind anomalies at
200 hPa over the North Pacific exhibit a tripolar structure
and tilt slightly southeastward (Fig. 7a). In the mid-latitude
of the North Pacific, significantly negative anomalies
suggest a weakening East Asia subtropical jet. These
anomalies elongate zonally from the western Pacific and
stay west of 60°W. Almost opposite anomaly structure in
200 hPa zonal wind emerges over the NA. The Atlantic jet
is significantly weakened indicated by a negative anomaly
in zonal wind at 200 hPa (Fig. 7a), corresponding to a
negative NAO-like atmospheric response (Fig. 6a, c).
During the CP La Nin
˜a, a similarly tripolar structure in
200 hPa zonal wind anomalies appears over the North
Pacific, however, the location is displaced equatorward.
The anomalies elongate zonally from the North Pacific and
extend far eastward to the NA. The Atlantic jet is
significantly strengthened and extends farther eastward
reaching WE, which corresponds to the positive NAO-like
atmospheric anomalies as shown in Fig. 6b, d. It can be
seen that the two types of La Nin
˜a could lead to a roughly
opposing response in the Atlantic jet, consistent with an
opposing NAO-like pattern over the NA (Figs. 5,6).
Many studies have demonstrated that the NAO con-
tributes significantly to surface temperature and precipita-
tion over the WE during winter (see the review of Jones
et al. 2003). The approximately opposing atmospheric
responses to the two types of La Nin
˜a over the NA may
result in diametric climate anomalies over WE. As
expected, the anomalies in surface air temperature and
precipitation show very different patterns (Fig. 8). During
the EP La Nin
˜a winter, the weakened Atlantic jet associ-
ated with the negative NAO phase tends to transport
unusually cold and dry air to WE. Thus a winter occurs
over WE that is colder than normal, where the anomalous
surface air temperature can reach -2°C (Fig. 8). Simul-
taneously, the precipitation is reduced in most regions of
WE, whereas the southwestern region including Spain and
Portugal receives excessive precipitation, which is likely
associated with the strengthened zonal wind to the south of
(a) (c)
(b) (d)
Fig. 6 Composites of JF SLP anomalies (hPa) for aEP La Nin
˜a and
bCP La Nin
˜a, and JF geopotential height anomalies (m) at 300 hPa
for cEP La Nin
˜a and dCP La Nin
˜a. Shading indicates values
exceeding the 90 and 95 % confidence level. Contour intervals in (a,
b) and (c,d) are 2 hPa and 30 m, respectively
1358 W. Zhang et al.
123
(a)
(b)
Fig. 7 Composites of JF zonal
wind anomalies (m/s) at
200 hPa for aEP La Nin
˜a and
bCP La Nin
˜a. Shading indicates
values exceeding the 90 and
95 % confidence level. Contour
intervals are 2 m/s
(a) (c)
(b) (d)
Fig. 8 Composites of JF surface air temperature anomalies (contours
in °C) for aEP La Nin
˜a and bCP La Nin
˜a, and JF GPCC precipitation
anomalies (contours in mm/day) for cEP La Nin
˜a and dCP La Nin
˜a.
Shading indicates values exceeding the 90 and 95 % confidence level.
Contour intervals in (a,b) and (c,d) are 0.5 °C and 0.2 mm/day,
respectively
Impacts of two types of La Nin
˜a 1359
123
the Atlantic jet (Fig. 7a). In comparison, WE experiences a
warmer than normal winter during the CP La Nin
˜a winter.
This is because that the enhanced Atlantic jet across the
NA related to the positive NAO phase tends to transport
relatively warm and moist air to WE. The precipitation
anomalies are characterized by a dipolar structure with
increasing (decreasing) over northern (southern) WE. As
demonstrated in Fig. 8, WE experiences a very different
climate anomalies corresponding to the two different types
of La Nin
˜a. Therefore, it is necessary to consider the two
types of La Nin
˜a events when understanding their climate
impacts.
5 Mechanisms for the contrasting impacts
over NA–WE of two types of La Nin
˜a
According to the observed analyses above, different SST
anomaly patterns during the two types of La Nin
˜a are
possibly responsible for the approximately opposing NAO-
like atmospheric anomalies. To verify it, four experiments
were designed and performed, which has been described in
Sect. 2. Figure 9shows the SLP responses to the
EP_COOL, CP_COOL, CP_WARM, and CP_CW forcings
relative to the CNTRL run. In the EP_COOL simulations,
the imposed tropical SST cooling induces a weakened
Aleutian Low and a negative NAO-like atmospheric
anomaly indicated by a high SLP anomaly to the north and
a low SLP anomaly to the south of the North Atlantic
(Fig. 9a). These anomalies closely resemble the observed
EP La Nin
˜a composition (Fig. 6a). Under the CP_COOL
forcing, a positive SLP anomaly appears over the North
Pacific and a positive NAO-like atmospheric response
occurs over the North Atlantic (Fig. 9b). These features
agree well with the observed anomaly patterns during the
CP La Nin
˜a winter (Fig. 6b). Similarly anomalous patterns
are also simulated in the upper troposphere over the North
Pacific and North Atlantic (Fig. 10a, b). Consistent with
the observations, different cooling SST anomaly patterns
for the two types of La Nin
˜a can cause similar responses of
the Aleutian Low, but they trigger roughly opposing NAO-
like atmospheric responses.
Previous studies (e.g., Li et al. 2006) have discussed
importance of the western Pacific warming. Here, the
CP_WARM experiment is conducted to inspect possible
impacts of the western Pacific warming on the North
Atlantic atmosphere. As shown in Figs. 9c and 10c, cir-
cumglobal wave train is displayed, suggesting that the
CP_WARM has a minor impact on the positive NAO-like
atmospheric response for the CP La Nin
˜a. We also consider
(a) (c)
(b) (d)
Fig. 9 The ensemble mean JF SLP response (hPa) to aEP_COOL, bCP_COOL, cCP_WARM, and dCP_CW forcings. Contour intervals are
2 hPa
1360 W. Zhang et al.
123
the impacts of both cooling and warming SST anomalies
over the tropical Pacific in the CP_CW simulation. Their
responses appear to be a mixture of the CP_COOL and
CP_WARM responses (Figs. 9d, 10d), which are largely
the same as those of the CP_COOL forcing.
In addition, many studies reported that the tropical
Pacific heating have effects on the tropical Atlantic SST
anomaly (Wolter 1987; Curtis and Hastenrath 1995; Gal-
lego et al. 2001; Alexander et al. 2002; Huang et al. 2002),
which is argued to affect the North Atlantic atmosphere
(e.g., Watanabe and Kimoto 1999; Robertson et al. 2000).
Therefore, the tropical Atlantic SST may serve as a
mediator to link the tropical Pacific SST anomaly and the
NA atmosphere. In order to examine the possible effects of
the tropical Atlantic SST, Fig. 3also presents the SST and
surface wind anomalies over the Atlantic during the two
types of La Nin
˜a winters. For the EP La Nin
˜a, almost no
significant SST anomalies are observed over the tropical
Atlantic but the SST warming over the eastern NA is robust
(Fig. 3a). The warm SST anomaly is arguably due to the
cyclonic circulation and the associated easterly wind
anomalies, which could weaken the strong background
westerlies and thus the local evaporation. In contrast to the
EP La Nin
˜a, there appear significantly cold SST anomalies
over the northern tropical Atlantic and warming SST
anomalies over the western NA during the CP La Nin
˜a
winters (Fig. 3b). In accordance with the SST anomaly
pattern, an unusually anticyclonic circulation occurs over
the NA. Over the western mid-latitude Atlantic, the
anomalous southeasterlies can possibly pile up the surface
warm water and lead to increase in the SST there (Fig. 3b).
The SST cooling in the tropical Atlantic could also be
regarded to be a consequence due to the strengthened
easterlies and thus evaporation through wind–evaporation–
SST feedback.
Here, another series of experiments (AT_COOL) are
performed to inspect the possible effect of the cooling SST
anomaly over the northern tropical Atlantic during the CP
La Nin
˜a winter. Figure 11a, c show the atmospheric
responses at the lower and upper troposphere in the
AT_COOL simulations relative to the control run. The
AT_COOL forcing can trigger positive NAO-like atmo-
spheric anomalies, suggesting that the cooling SST
anomaly at the northern tropical Atlantic Ocean has con-
tribution to the NA atmospheric anomaly during the CP La
Nin
˜a event. However, the Aleutian Low is strengthened
under the forcing of the AT SST anomaly, implying the
dominant forcing effect from the tropical Pacific rather
than the local SST. Furthermore, we conducted another
experiment (CPAT_COOL), in which the CP_COOL and
AT_COOL forcings are imposed together. As shown in
Fig. 11b, d, the Aleutian Low is weakened and positive
NAO-like atmospheric anomalies occur under the
CPAT_COOL forcing. The atmospheric responses
(a)
(b)
(c)
(d)
Fig. 10 The ensemble mean JF
geopotential height response
(m) at 300 hPa (hPa) to
aEP_COOL, bCP_COOL,
cCP_WARM, and dCP_CW
forcings. Contour intervals are
20 m
Impacts of two types of La Nin
˜a 1361
123
resemble closely those of the CP_COOL and CP_CW
forcings, but with a slight improvement in the NA–WE
region compared to the observed pattern (Figs. 6b, d, 9b, d,
10b, d, 11b, d). It can be seen that the AT_COOL forcing
has some contribution on the local atmospheric anomalies.
A series of modelling experiments discussed above
suggest that the two types of La Nin
˜a have different
impacts on the NA–WE atmosphere through the atmo-
spheric teleconnection. The tropical Atlantic SST anoma-
lies associated with the CP La Nin
˜a also have effects on
NA atmospheric anomalies. Although the simulated
experiments suggest that the contrasting atmospheric
anomalies in the NA are mainly attributed to different
cooling SST anomaly patterns for the two types of La Nin
˜a,
dynamical mechanism addressing how the tropical SST
influences the NA–WE atmosphere is still an open ques-
tion. The atmosphere over the North Pacific is usually
argued to be linked to the tropical Pacific heating and the
NA–WE atmosphere anomalies (e.g., Wu and Hsieh 2004;
Li and Lau 2012). The North Pacific anomalies could
modify local mean flow and standing waves, which pos-
sibly propagate downstream to the North Atlantic and leads
to different NAO-like atmospheric responses. There
exhibits a nonlinear relationship between the atmospheric
anomalies over the North Pacific and NA. For example,
Castanheira and Graf (2003) demonstrated that a signifi-
cantly negative correlation could be detected between the
SLP over the North Pacific and the NA only when the polar
vortex is strong enough. Recently, the subtropical jet is also
emphasized to act as an ‘‘atmospheric bridge’’ to connect
the tropical Pacific heating and NA–WE atmospheric
anomalies (Graf and Zanchettin 2012). Further studies are
required to understand the mechanisms behind the con-
trasting atmospheric anomalies over the Atlantic Ocean
with these two types of La Nin
˜a.
6 Discussion: Asymmetry in influences of ENSO
on climate over the NA–WE sector
An investigation discussed above shows that the two types
of La Nin
˜a have roughly opposing impacts on the atmo-
sphere over the NA–WE sector. A significantly negative
(positive) NAO-like pattern is observed during the EP (CP)
La Nin
˜a winters. The previous study (Graf and Zanchettin
2012) have compared the climate impacts associated with
the EP and CP El Nin
˜o events and suggested that the two
types of El Nin
˜o lead to distinctly different atmospheric
responses over the NA–WE region. It is found that a sig-
nificantly negative NAO-like pattern occurs over the
(a)
(b)
(c)
(d)
Fig. 11 The ensemble mean JF SLP response to aAT_COOL and bCPAT_COOL forcings. Contour intervals are 2 hPa. The ensemble mean JF
geopotential height response (m) at 300 hPa (hPa) to cAT_COOL and dCPAT_COOL forcings. Contour intervals are 20 m
1362 W. Zhang et al.
123
NA–WE region during the CP El Nin
˜o winter, whereas no
apparent signal is found there during the EP El Nin
˜o
winter.
To clearly inspect the symmetry between the warm and
cold phases of ENSO, Fig. 12a, b display the relationship
between NAO and the two types of ENSO, respectively.
Following the study of Graf and Zanchettin (2012), EP El
Nin
˜o events identified are 1951, 1957, 1965, 1972, 1976,
and 1997; and CP El Nin
˜o events selected are 1968, 1977,
1986, 1994, 2002, and 2009. Some El Nin
˜o events are
excluded in their definition because concurrent volcanic
eruptions also have an important impact on the mid-latitude
climate (Graf and Zanchettin 2012). The SST anomaly over
the Nin
˜o3 region is used to denote the EP ENSO events
since the dominant SST anomaly is confined to the eastern
equatorial Pacific. Similarly, we referred to the Nin
˜o4
index as the CP ENSO events considering their SST
anomaly occurring mainly over the central equatorial
Pacific.
As shown in Fig. 12a, a negative NAO index appears in
most of the EP La Nin
˜a winters. Their composite NAO
index reaches -2.1, which is statistically significant at the
95 % confidence level. However, four out of six EP El
Nin
˜o events are in favor of occurrence of a negative NAO-
like pattern, and another two events correspond to a posi-
tive NAO-like pattern (Fig. 12a). Their composite result
shows a weak negative NAO index, which is not significant
at the 95 % confidence level. It is consistent with the
previous study (Graf and Zanchettin 2012) suggesting that
the atmospheric response to the EP El Nin
˜o over the NA–
WE region seems to be originated by chance. As a con-
sequence, the EP El Nin
˜o effect on NAO seems to be
asymmetric to the EP La Nin
˜a effect during winter.
Unlike the EP ENSO events, the CP ENSO events
exhibit linearity in their climate impacts over the NA–WE
sector (Fig. 12b). Six out of seven CP La Nin
˜a events tend
to result into a positive NAO-like atmospheric anomaly,
whereas five out of six CP El Nin
˜o events are in favor of
occurrence of a negative NAO index. Their compositions
are both significant at the 95 % confidence level, indicating
that the NA–WE atmospheric anomalies during the CP
ENSO winters are most likely not due to chance. It can be
seen that the NA–WE atmospheric response to the CP SST
anomaly is very different from that to the EP SST anomaly.
Figure 13 displays the relationship between the NAO index
and tropical SST anomaly indicated by the linear correla-
tion. As shown in Fig. 13, the NAO index is significantly
correlated with the CP SST anomaly near 150°–180°W. It
(a) (b)
Fig. 12 a Scatter plot of the
DJF Nino3 index and JF
(January–February) NAO index
for EP El Nin
˜o(red triangle)
and EP La Nin
˜a(blue triangle).
Red and blue solid circles are
the composites of EP El Nin
˜o
and EP La Nin
˜a, respectively.
bSame as (a), but for CP El
Nin
˜o and CP La Nin
˜a
Fig. 13 DJF SST anomaly
(contours in °C) regressed upon
JF NAO index from 1950/1951
to 2009/2010. Light (dark)
shading indicates regression
exceeding the 90 % (95 %)
confidence level. Contour
intervals are 0.1 °C
Impacts of two types of La Nin
˜a 1363
123
suggests that a positive SST anomaly over the CP is usually
accompanied by a negative NAO-like atmospheric anom-
aly, and vice versa. However, there is no significant cor-
relation between the NAO index and the EP SST anomaly.
Only the linear part of the relationship can be examined in
correlation analysis. The signal of the EP La Nin
˜a over the
NA–WE region is easily overlooked using a correlation
analysis. It is a possible reason that the traditional (or EP)
ENSO signal is difficult to be detected in the North Atlantic
and its adjacent land. Other methods such as composition
need to be used to detect the nonlinear relationship.
However, the physical mechanisms are not clear for the
asymmetry and deserve study in future.
7 Conclusions
Similar to the El Nin
˜o phenomena discussed previously,
this study has shown that the La Nin
˜a should be classified
into two types (i.e., the EP and CP La Nin
˜a) considering
their distinctly different climate impacts. The EP La Nin
˜a
is characterized by the cooling SST anomaly center con-
fined to the EP east of 150°W and relatively weak SST
anomaly observed over the CP. By contrast, the SST
anomaly center associated with the CP La Nin
˜a is shifted
westward into the CP west of 150°W and small cooling
SST anomaly is found over the EP. The two types of La
Nin
˜a exhibit very different features in the SST anomaly
evolution. For the EP La Nin
˜a, the SST anomaly starts in
the EP and propagates westward during the developing and
mature phase, while the CP La Nin
˜a shows a standing
feature with its SST anomaly developing and decaying
in situ over the CP. These differences in zonal location of
SST anomaly and their evolutions suggest the possibility in
different underlying dynamics.
Although the two types of La Nin
˜a can produce a similar
response in the atmosphere over the north Pacific, distinctly
different teleconnection patterns are found over the NA–
WE sector. For the EP La Nin
˜a, the NA–WE region
experiences the climate anomalies resembling a negative
NAO pattern accompanied by a weakening Atlantic jet.
This weakening jet tends to inhibit a strong transportation
of warm and moist air from the Atlantic sea and cause a
cooler and drier than normal winter over the WE region.
However, roughly opposing atmospheric anomalies appear
over the NA–WE sector during the CP La Nin
˜a winter,
which seems like a positive NAO phase with strengthening
Atlantic jet. The strong jet tends to bring more warm and
moist air from the sea to the WE area and results into a
warmer and wetter than normal winter there. A series of
modeling experiments indicate that the contrasting NAO-
like patterns are mainly attributed to different cooling SST
patterns for two types of La Nin
˜a. The analyses provided
here have shown that it is necessary to separate the La Nin
˜a
(a)
(b)
Fig. 14 Composites of SST
anomalies (shading and
contours in °C) during autumn
(SON) for aEP La Nin
˜a, and
bCP La Nin
˜a. The SST
anomalies that are not
significant at the 95 % level are
not shown. Contour intervals
are 0.5 °C and zero contours are
omitted
1364 W. Zhang et al.
123
into two types considering their different SST anomaly
location and evolution, and especially, very different cli-
mate impacts over the extratropics.
Although ENSO events usually reach their mature phase in
winter, the associated strong SST anomaly pattern is clearly
observed during the preceding autumn. As sho wn in Fig. 2,the
La Nin
˜a events tend to intensively develop from August to
December and decay in the following months, which has also
been mentioned by previous studies (e.g., Larkin and Harrison
2001). Figure 14 displays the composite SST anomaly corre-
sponding to the two types of La Nin
˜a during the developing
autumn (September–November). The SST anomaly structure
and intensity in the autumn is similar to those in the winter,
indicating that the related SST anomaly signal in the mature
phase can be obviously observed in the autumn. If the SST
signal of La Nin
˜a is observed over the equatorial Pacific during
the autumn, we easily expect that the La Nin
˜aeventwould
persist into winter. It provides a potential predictability source
for predicting the NA–WE climate anomalies at least a season
in advance based on the strong cooling SST anomaly at the
equator.
Acknowledgments This work is supported by the National Basic
Research Program ‘‘973’’ (2012CB417403), the National Nature
Science Foundation of China (41005049), the Special Fund for Public
Welfare Industry (Meteorology) (GYHY201206016), and the Priority
Academic Program Development of Jiangsu Higher Education Insti-
tutions (PAPD). BX is supported by APEC Climate Center. BX also
acknowledges partial support from International Pacific Research
Center which is sponsored by the JAMSTEC, NASA and NOAA.
Open Access This article is distributed under the terms of the
Creative Commons Attribution License which permits any use, dis-
tribution, and reproduction in any medium, provided the original
author(s) and the source are credited.
References
Afzaal M, Li JP, Jin FF (2013) The asymmetric influence of the two
types of El Nin
˜o and La Nin
˜a on summer rainfall over Southeast
China. J Clim 26:4567–4582
Neale RB et al (2010) Description of the NCAR Community
Atmosphere Model (CAM 5.0), Tech Note NCAR/TN-
486?STR, Natl Cent for Atmos Res, Boulder, Colo June.
http://www.cesm.ucar.edu/models/cesm1.0/cam/docs/description/
cam5_desc.pdf
Alexander MA, Blade
´I, Newman M, Lanzante JR, Lau NC, Scott JD
(2002) The atmospheric bridge: the influence of the ENSO
teleconnections on air–sea interaction over the global oceans.
J Clim 15:2205–2231
Ashok K, Behera S, Rao AS, Weng HY, Yamagata T (2007) El Nin
˜o
Modoki and its possible teleconnection. J Geophys Res
112:C11007. doi:10.1029/2006JC003798
Branston A, Livezey RE (1987) Classification, seasonality, and
persistence of low-frequency circulation patterns. Mon Weather
Rev 115:1083–1126
Bro
¨nnimann S (2007) Impact of El Nin
˜o–Southern Oscillation on
European climate. Rev Geophys 45:RG3003. doi:10.1029/
2006RG000199
Bro
¨nnimann S, Ewen T, Griesser T, Jenne R (2007a) Multidecadal
signal of solar variability in the upper troposphere during the
20th century. Space Sci Rev 125:305–315
Bro
¨nnimann S, Xoplaki E, Casty C, Pauling A, Luterbacher J (2007b)
ENSO influence on Europe during the last centuries. Clim Dyn
28:181–197
Cai W, Cowan T (2009) La Nin
˜a Modoki impacts Australia autumn
rainfall variability. Geophys Res Lett 36:L12805. doi:10.1029/
2009GL037885
Castanheira JM, Graf HF (2003) North Pacific–North Atlantic
relationships under stratospheric control? J Geophys Res
108:4036. doi:10.1029/2002JD002754
Curtis S, Hastenrath S (1995) Forcing of anomalous sea-surface
temperature evolution in the tropical Atlantic during Pacific
warm events. J Geophys Res 100C:15835–15847
Feng J, Li JP (2011) Influence of El Nin
˜o Modoki on spring rainfall
over South China. J Geophys Res 116:D13102. doi:10.1029/
2010JD015160
Feng J, Li JP (2013) Contrasting impacts of two types of ENSO on the
boreal spring Hadley circulation. J Clim 26:4773–4789
Feng J, Wang L, Chen W, Fong SK, Leong KC (2010) Different
impacts of two types of Pacific Ocean warming on Southeast
Asia rainfall during boreal winter. J Geophys Res 115:D24122.
doi:10.1029/2010JD014761
Gallego D, Garcı
´a R, Herna
´ndez E, Gimeno L, Ribera P (2001) An
ENSO signal in the North Atlantic subtropical area. Geophys
Res Lett 28:2939–2942
Garfinkel CI, Hartmann DL (2010) Influence of the quasi-biennial
oscillation on the North Pacific and El Nin
˜o teleconnections.
J Geophys Res 115:D20116. doi:10.1029/2010JD014181
Gill AE (1980) Some simple solutions for heat-induced tropical
circulation. Q J R Meteorol Soc 106:447–462
Gouirand I, Moron V (2003) Variability of the impact of El Nin
˜o–Southern
Oscillation on sea-level pressure anomalies over the North Atlantic in
January to March (1874–1996). Int J Climatol 23:1549–1566
Graf HF, Zanchettin D (2012) Central Pacific El Nin
˜o, the ‘‘subtrop-
ical bridge’’, and Eurasian climate. J Geophys Res 117:D01102.
doi:10.1029/2011JD016493
Greatbatch RJ, Lu J, Peterson KA (2004) Nonstationary impact of
ENSO on Euro-Atlantic winter climate. Geophys Res Lett
31:L02208. doi:10.1029/2003GL018542
Halpert MS, Ropelewski CF (1992) Surface temperature patterns
associated with the Southern oscillation. J Clim 5:577–593
Huang BH, Schopf PS, Pan Z (2002) The ENSO effect on the tropical
Atlantic variability: a regional coupled model study. Geophys
Res Lett 29:2039. doi:10.1029/2002GLO14872
Ineson S, Scaife AA (2009) The role of the stratosphere in the
European climate response to El Nin
˜o. Nat Geosci 2:32–36
Jones, PD, Osborn TJ, Briffa KR (2003) Pressure-based measures of
the North Atlantic Oscillation (NAO): a comparison and an
assessment of changes in the strength of the NAO and in its
influence on surface climate parameters In: Hurrell JW et al (eds)
The North Atlantic Oscillation: climatic significance and envi-
ronmental impact. Geophys Monogr Ser, vol 134. AGU,
Washington, pp 51–62. doi:10.1029/134GM03
Jones PD, Lister DH, Osborn TJ, Harpham C, Salmon M, Morice CP
(2012) Hemispheric and large-scale land surface air temperature
variations: an extensive revision and an update to 2010.
J Geophys Res 117:D05127. doi:10.1029/2011JD017139
Kalnay E et al (1996) The NCEP/NCAR 40-year reanalysis project.
Bull Am Meteorol Soc 77:437–471
Kao HY, Yu JY (2009) Contrasting eastern-Pacific and central-Pacific
types of ENSO. J Clim 22:615–632
Kim HM, Webster P, Curry J (2009) Impact of shifting patterns of
Pacific Ocean warming on North Atlantic tropical cyclones.
Science 325:77–80
Impacts of two types of La Nin
˜a 1365
123
Knippertz P, Ulbrich U, Marques F, Corte-Real J (2003) Decadal
changes in the link between El Nin
˜o and springtime North
Atlantic Oscillation and European–North African rainfall. Int J
Climatol 23:1293–1311
Kug JS, Ham YG (2011) Are there two types of La Nina? Geophys
Res Lett 38:L16704. doi:10.1029/2011GL048237
Kug JS, Jin FF, An SI (2009) Two types of El Nin
˜o events: cold
tongue El Nin
˜o and warm pool El Nin
˜o. J Clim 22:1499–1515
Kumar A, Hoerling MP (1998) Annual cycle of Pacific/North
American seasonal predictability associated with different
phases of ENSO. J Clim 11:3295–3308
Larkin NK, Harrison DE (2001) Tropical Pacific ENSO cold events,
1946–1995: SST, SLP, and surface wind composite anomalies.
J Clim 14:3904–3931
Larkin NK, Harrison DE (2005) On the definition of El Nin
˜o and
associated seasonal average U.S. weather anomalies. Geophys
Res Lett 32:L13705. doi:10.1029/2005GL022738
Lee SK, Wang C, Enfield DB (2010) On the impact of central Pacific
warming event on Atlantic tropical storm activity. Geophys Res
Lett 37:L17702. doi:10.1029/2010GL044459
Li Y, Lau NC (2012) Impact of ENSO in the atmospheric variability
over the North Atlantic in late winter—role of transient eddies.
J Clim 25:320–342
Li J, Wang J (2003) A new North Atlantic Oscillation index and its
variability. Adv Atmos Sci 20:661–676. doi:10.1007/BF026
90792
Li S, Hoerling M, Peng S, Weickmann K (2006) The annual response
to tropical Pacific SST forcing. J Clim 19:1802–1819
Mathieu PP, Sutton RT, Dong BW, Collins M (2004) Predictability of
winter climate over the North Atlantic European region during
ENSO events. J Clim 17:1953–1974
McPhaden MJ, Zebiak SE, Glantz MH (2006) ENSO as an integrating
concept in earth science. Science 314:1740–1745
Philander SG (1990) El Nin
˜o, La Nin
˜a, and the Southern Oscillation.
Academic, San Diego
Pozo-Va
´zquez D, Ga
´miz-Fortis SR, Tovar-Pescador J, Esteban-Parra
MJ, Castro-Dı
´ez Y (2005) North Atlantic winter SLP anomalies
based on the autumn ENSO state. J Clim 18:97–103
Rayner NA, Parker DE, Horton EB, Folland CK, Alexander LV,
Rowell DP, Kent EC, Kaplan A (2003) Global analyses of sea
surface temperature, sea ice, and night marine air temperature
since the late nineteenth century. J Geophys Res 108. doi:10.
1029/2002JD002670
Ren HL, Jin FF (2011) Nin
˜o indices for two types of ENSO. Geophys
Res Lett 38:L04704. doi:10.1029/2010GL046031
Ren HL, Jin FF (2013) Recharge oscillator mechanisms in two types
of ENSO. J Clim 26:6506–6523
Robertson AW, Mechoso CR, Kim YJ (2000) The influence of the
Atlantic sea surface temperature anomalies on the North Atlantic
Oscillation. J Clim 13:122–138
Ropelewski CF, Halpert MS (1987) Global and regional scale
precipitation patterns associated with the El Nin
˜o/Southern
Oscillation. Mon Weather Rev 115:1606–1626
Ropelewski CF, Halpert MS (1996) Quantifying Southern Oscilla-
tion–precipitation relationships. J Clim 9:1043–1059
Rudolf B, Beck C, Grieser J, Schneider U (2005) Global precipitation
analysis products. Global Precipitation Climatology Centre
(GPCC), DWD, Internet publication, 1–8
Shinoda T, Hurlburt HE, Metzger EJ (2013) Anomalous tropical
ocean circulation associated with La Nin
˜a Modoki. J Geophys
Res 116:C12001. doi:10.1029/2011JC007304
Taschetto AS, England MH (2009) El Nin
˜o Modoki impacts on
Australian rainfall. J Clim 22:3167–3174
Tedeschi RG, Cavalcanti IFA, Grimm AM (2012) Influences of two
types of ENSO on South American precipitation. Int J Climatol
33:1382–1400
Ting M (1996) Steady linear response to tropical heating in barotropic
and baroclinic models. J Atmos Sci 53:1698–1709
Trenberth KE, Caron JM (2000) The Southern Oscillation revisited:
sea level pressure, surface temperatures, and precipitation.
J Clim 13:4358–4365
van Loon H, Madden RA (1981) The Southern Oscillation. Part I:
global associations with pressure and temperature in northern
winter. Mon Weather Rev 109:1150–1162
Wallace JM, Gutzler DS (1981) Teleconnections in the geopotential
field during the Northern Hemisphere winter. Mon Weather Rev
109:784–812
Wang C, Wang X (2013) Classifying El Nin
˜o Modoki I and II by
different impacts on rainfall in Southern China and typhoon
tracks. J Clim 26:1322–1338
Wang X, Wang DX, Zhou W, Li CY (2012) Interdecadal modulation
of the influence of La Nin
˜a events on mei-yu rainfall over the
Yangtze River Valley. Adv Atmos Sci 29:157–168
Watanabe M, Kimoto M (1999) Tropical–extratropical connection in
the Atlantic atmosphere–ocean variability. Geophys Res Lett
26:2247–2250
Weng H, Ashok K, Behera SK, Rao AS, Yamagata T (2007) Impacts
of recent El Nin
˜o Modoki on dry/wet conditions in the Pacific
rim during boreal summer. Clim Dyn 29:113–129
Wolter K (1987) The Southern Oscillation in surface circulation and
climate over the tropical Atlantic, eastern Pacific, and Indian
Oceans as captured by cluster analysis. J Clim Appl Meteorol
26:540–558
Wu AM, Hsieh WW (2004) The nonlinear Northern Hemisphere
winter atmospheric response to ENSO. Geophys Res Lett
31:L02203. doi:10.1029/2003GLO18885
Xiang B, Wang B, Li T (2013) A new paradigm for predominance of
standing Central Pacific Warming after the late 1990s. Clim Dyn
41:327–340
Xie P, Arkin PA (1996) Analyses of global monthly precipitation
using gauge observations, satellite estimates, and numerical
model predictions. J Clim 9:840–858
Xie F, Li JP, Tian WS, Feng J, Huo Y (2012) Signals of El Nin
˜o
Modoki in the tropical tropopause layer and stratosphere. Atmos
Chem Phys 12:5259–5273
Yanai M, Esbensen S, Chu JH (1973) Determination of average bulk
properties of tropical cloud clusters from large-scale heat and
moisture budgets. J Atmos Sci 30:611–627
Yeh SW, Kug JS, Dewitte B, Kwon MH, Kirtman BP, Jin FF (2009)
El Nin
˜o in a changing climate. Nature 461:511–514
Yu JY, Zou Y, Kim S T, Lee T (2012) The changing impact of El
Nino on US winter temperatures. Geophys Res Lett 39:15702.
doi:10.1029/2012GL052483
Zhang WJ, Jin FF, Li JP, Ren HL (2011) Contrasting impacts of two-
type El Nin
˜o over the western North Pacific during boreal
autumn. J Meteorol Soc Jpn 89:563–569
Zhang WJ, Jin FF, Ren HL, Li JP, Zhao JX (2012) Differences in
teleconnection over the North Pacific and rainfall shift over the
USA associated with two types of El Nin
˜o during boreal autumn.
J Meteorol Soc Jpn 90:535–552
Zhang WJ, Jin FF, Zhao JX, Qi L, Ren HL (2013) The possible
influence of a non-convectional El Nin
˜o on the severe autumn
drought of 2009 in Southwest China. J Clim 26:8392–8405
1366 W. Zhang et al.
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