3.1 The El Niño event1 ending in boreal spring 2016 …...3. Analysis of specific events 3.1 The El...
Transcript of 3.1 The El Niño event1 ending in boreal spring 2016 …...3. Analysis of specific events 3.1 The El...
3. Analysis of specific events
3.1 The El Niño event1 ending in boreal spring
2016 and its effects
The characteristics of the El Niño event that
occurred from boreal summer (June – August) 2014 to
spring (March – May) 2016 are described in Section
3.1.1, and various related effects observed from boreal
winter (December – February) 2015/2016 to autumn
(September – November) 2016 are outlined in Section
3.1.2.
3.1.1 2014/15/16 El Niño event2
(1) Overview
The El Niño event starting in summer (June –
August) 2014 and ending in spring (March – May)
2016 covered eight seasons, making it the longest
since 19493
. The monthly mean sea surface
temperature (SST) deviation from the climatological
reference4
over the El Niño monitoring region
(NINO.3 in Fig. 3.1-1) was +3.0°C in the mature stage
of November – December 2015, which was the
third-highest on record after the +3.6°C of the
1987/98 event and the +3.3°C of the 1982/83 event.
The amplitudes of SST variations in the
monitoring regions of the tropical Indian Ocean
(IOBW5) and the tropical western Pacific Ocean (Fig.
3.1-1), which are important climate effect indicators
for El Niño events, were also as large as those of the
1 JMA judges that an El Niño has begun when the
five-month running mean sea surface temperature (SST)
deviation for NINO.3 remains at +0.5°C or more for six
months. El Niño periods are expressed in seasonal units. 2 Previous El Niño events are identified by their relevant
periods (the full four-number expression for the first year
and the final two numbers for subsequent years). By way of
example, the 1997/98 El Niño event ran from boreal spring
1997 to spring 1998. 3 The second-longest El Niño events after that of
2014/15/16 (eight seasons) were those of 1968/69/70,
1986/87/88, 1982/83 and 1991/92 (six seasons each). 4 SST climatological references are monthly averages of
the latest sliding 30- year period for NINO.3, and are
defined as linear extrapolations with respect to the latest
30-year period for NINO.WEST and IOBW in order to
remove the effects of significant long-term warming trends
observed in these regions. 5 Indian Ocean Basin-Wide
1997/98 El Niño event as seen in NINO.3 SST
variations.
Lower-than-normal temperatures were observed in
western Japan throughout the boreal summers of 2014
and 2015, and higher-than-normal temperatures were
observed in eastern Japan during boreal winter
2015/2016. These characteristics were consistent with
common patterns observed in past El Niño events. The
global average surface temperature anomaly in 1998
was the highest since records began in 1891, and this
record was again broken in each year of the
2014/15/16 El Niño event. The formation of 2016’s
first typhoon was also later than normal as similarly
observed in the El Niño termination years of 1973,
1983 and 1998, when record-high NINO.3 SSTs were
recorded.
These climatic characteristics also relate to the
descending (ascending) nature of SST anomalies in
NINO.WEST (IOBW) regions in concurrence with
(subsequent to) the rise in NINO.3 SST anomalies.
The lifetime of the 2014/15/16 El Niño event in the
course of life is described below.
(2) SST deviation from climatological reference in
individual monitoring regions
Fig. 3.1-2 shows a time-series representation of
NINO.3 SST deviation from its climatological
reference in past El Niño events. The termination year
for each event is set as Year0, and NINO.3 SST
deviations are shown from January of Year−2 (two
years before Year0) to January of Year+1 (the year
after Year0). The black solid line indicates values for
the 2014/15/16 El Niño event, and the dotted black
line indicates the average of the 13 previous events.
These deviations are referred to as NINO.3dev below.
In the average of the 13 previous events,
NINO.3dev is +0.5°C or above for boreal spring in
Year−1, which results in the onset of an El Niño event
that reaches its mature stage around November –
December of Year−1. The value falls below +0.5°C
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around spring of Year0, resulting in the termination of
the event.
The 2014/15/16 El Niño event began in 2014
(Year−2), which was the year before its mature stage.
NINO.3dev varied between +0.2 and +1.0°C, and did
not show the signs of development commonly seen in
past El Niño events. Meanwhile, five-month running
averages of NINO.3dev remained at or above +0.5°C
from June 2014 onward and between +0.5 and +0.6°C
for eight of the ten months through to March 2015,
thereby meeting the criteria for the definition of an El
Niño event from boreal summer 2014 onward.
After spring 2015 (Year−1), NINO.3dev increased
at double the rate for the average of the previous 13
events, reaching its positive maximum of +3.0°C (the
third-highest of the past events) in December 2015.
The peak values of the four strongest El Niño events
occurring in 1972/73, 1982/83, 1997/98 and
2014/15/16 considerably exceeded the peak of the
average value of +1.7°C. These stand out from the
corresponding values for the 10 other events, which
were equal to or below the average.
NINO.3dev decreased rapidly from January 2016
(Year0) onward and approached the average of +0.1°C
in May, bringing about the end of the El Niño event.
The value subsequently remained near the average
(between −0.3 and −0.6°C) from July to November.
Fig. 3.1-3 is the same as Fig. 3.1-2 except for the
NINO.WEST region. NINO.WEST SST deviations
from the climatological reference are referred to as
NINO.WESTdev below.
NINO.WESTdev for the average of the 13
previous events (shown by the dotted black line)
turned negative around the summer of Year−1
immediately after the start of the averaged El Niño
event, and exhibited two negative peaks around
September of Year−1 and February of Year0. The
negative values eased around boreal spring of Year0
as the event ended, and turned positive in the summer
of Year0. During the El Niño event, distinctly
negative NINO.WESTdev values continued from
February 2015 (Year−1), in contrast to the average
value for the same season. Three negative peaks
distinctly below the average were observed in March,
in July – October 2015 and in February 2016 (Year0).
Despite the prolonged nature of these below-average
values, the negatives eased in boreal spring 2016
(Year0) along with the average and turned positive in
summer 2016 after the end of the El Niño event.
Fig. 3.1-4 is the same as Fig. 3.1-2, but for the
IOBW region. IOBW SST deviations from the
climatological reference are referred to as IOBWdev
below.
In the average of the previous 13 events,
IOBWdev tended to increase in association with
elevated NINO.3dev values around spring of Year−1
when the averaged El Niño event began. Values
reached their positive peak around January – April of
Year0 a few months after the mature stage of the El
Niño event (coinciding with the NINO.3dev peak)
around December of Year−1. In the Pacific Ocean,
positive NINO.3dev values eased in boreal spring of
Year0 resulting in the termination of El the Niño event,
while positive IOBWdev values persisted in the
Indian Ocean until boreal summer. This is an
important factor in considering the climate over the
western North Pacific during boreal summer (Xie et
al., 2009; Du et al., 2011).
Fig. 3.1-1 Locations of El Niño monitoring region,
western tropical Pacific region, and tropical Pacific
region
NINO.3 indicates El Niño monitoring region (5°S – 5°N,
150°W – 90°W), NINO.WEST indicates the western
tropical Pacific region (equator – 15°N, 130°E – 150°E),
and IOBW indicates the tropical Indian ocean (20°S – 20°N,
40°E – 100°E).
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Fig. 3.1-2 NINO.3 SST deviations from climatological
references for past El Niño events
Time-series representation of NINO.3 SST deviations from
climatological references for January in past El Niño
events. The termination year for each event is set to Year0,
and NINO.3 SST deviations are plotted from January of
Year−2 (i.e., two years before Year0) to January of Year+1
(i.e., the year after Year0). The solid black line represents
the 2014/15/16 El Niño event, and the dotted black line
represents the average of 13 previous events. The Year0 for
each El Niño event is listed to the upper left of the figure.
Fig. 3.1-3 Same as Fig. 3.1-2 except for NINO.WEST
SST deviations
Fig. 3.1-4 Same as Fig. 3.1-2, but for IOBW SST
deviations
During the 2014/15/16 El Niño event, IOBWdev
remained near zero after the onset of the event from
boreal summer 2014 (Year−2) to around February
2015 (Year−1) before turning positive in spring 2015
(Year−1) in association with the rapid development of
the event, and continued to rise before and after the
event’s mature stage (corresponding to the peak of
NINO.3dev). Three months after the peak of
NINO.3dev, IOBWdev peaked at +0.72°C in March
2016 (Year0). This IOBWdev was the second highest
on record after the +0.74°C value of January 1998
(Year0), and was twice as high as the average. Values
rapidly decreased thereafter, and the positive values
mostly eased in June 2016 (Year0) a month after the
disappearance of positive NINO.3dev values. As
mentioned above, the considerably above-average
positive IOBWdev values observed during the
2014/15/16 El Niño event continued, but disappeared
earlier than average. During boreal summer 2016
(Year0), values were near zero and turned negative in
autumn.
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(3) Atmospheric and oceanic temporal changes
To clarify the characteristics of air-sea interaction
in the onset, development and termination of the
2014/15/16 El Niño event, time-longitude sections for
areas along the equator (0.5°S – 0.5°N) over the
Indian and Pacific Oceans for SST anomalies and for
depth averaged temperature anomalies from the ocean
surface to 300 m are shown in Fig. 3.1-5, and
time-longitude sections for areas near the equator (5°S
– 5°N) for velocity potential anomalies in the upper
troposphere (200 hPa) and for zonal wind anomalies
in the lower troposphere (850 hPa) are shown in Fig.
3.1-6. Fig. 3.1-7 also shows three-month (seasonal)
average latitude-longitude sections covering 14
seasons from boreal spring 2013 to summer 2016 for
outgoing long radiation (OLR) and related anomalies
and SSTs with related anomalies, along with
longitude-depth sections at the equator for the
uppermost 300-m subsurface temperatures and related
anomalies.
Most typical El Niño events, such as that
described in Rasmusson and Carpenter (1982), emerge
in boreal spring or summer and develop during
summer and autumn, passing through the mature stage
from late autumn to early winter and terminating in
winter or spring the year after onset6. Although the
2014/15/16 El Niño event continued for eight seasons
from boreal summer 2014 to spring 2016, it did not
start early or end late and was almost twice as long as
typical El Niño events. Consequently, the
phenomenon is viewed as having been separated into
units of around a year from spring to spring,
representing a cycle of development and decay. Its
characteristics are described below for (a) spring 2014
– spring 2015, (b) spring 2015 – spring 2016, and (c)
spring 2016 onward.
6 Five exceptional periods of past El Niño events were
boreal spring 1953 – autumn 1953, autumn 1968 – winter
1969/1970, autumn 1986 – winter 1987/1988, spring 1982 –
summer 1983 and spring 1991 – summer 1992, whose
start/end points were unusual.
(a) Boreal spring 2014 – spring 2015
Strong lower-troposphere westerly wind bursts
over the western equatorial Pacific in mid-to-late
January 2014 preceded the onset of the 2014/15/16 El
Niño event. These bursts are illustrated in Fig. 3.1-6
(right) as strong westerly anomalies7 of 9 m/s or more.
Westerly bursts were again observed in late February
and early March. Warm Kelvin waves below the ocean
surface resulting from these bursts migrated eastward
through the central equatorial Pacific from March to
April 2014 to the eastern part (Fig. 3.1-5, right).
Eastward migration of weak warm Kelvin waves
was subsequently observed, and increased subsurface
water temperature anomalies in the uppermost 300 m
were seen in the central and eastern equatorial Pacific
from April to July 2014 (Fig. 3.1-5, right; spring
(MAM) 2014, Fig. 3.1-7, right). In accordance with
this increase, SST anomalies in the eastern equatorial
Pacific increased from May to July 2014 (Fig. 3.1-5,
left; summer (JJA) 2014, Fig. 3.1-7, center), and
positive anomalies of +1.5°C emerged in the eastern
part in June 2014, resulting in the onset of the
2014/15/16 El Niño event.
The area of above-normal convective activity
observed near Indonesia (100 – 140°E) until boreal
winter 2013/2014 moved to the western equatorial
Pacific in boreal spring 2014, resulting in
below-normal convective activity over Indonesia and
above-normal convective activity over the western
and central equatorial Pacific. However, the
subsequent east-west contrast of convective activity
7 A westerly burst is an event in which westerly winds with
speeds exceeding 5 m/s or so are observed for around 10
days in the lower troposphere over the western equatorial
Pacific when easterly trade winds blow under normal
conditions. Although several definitions of the term have
been utilized in previous research, here it refers to westerly
wind anomalies of 9 m/s or more. Easterly wind speeds in
the lower troposphere (trade winds) average around 4 – 6
m/s near the date line over the equatorial Pacific, with
strength on the eastern side and weakness on the western
side of the date line. For strong westerly wind anomalies of
9 m/s or more, westerly winds blow in the central equatorial
Pacific, resulting in the disappearance of trade winds.
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between Indonesia and the central equatorial Pacific
was unclear, and above-normal values in the western
equatorial part did not persist (winter (DJF) 2014 –
summer (JJA) 2014, Fig. 3.1-7, left; Fig. 3.1-6, right).
In June – July 2014, easterly wind anomalies were
observed in the central and eastern Pacific, and in July
– August eastward migration of equatorial cold Kelvin
waves was observed in the ocean subsurface along
with negative SSTs (Fig. 3.1-5). Displacement of
above-normal convection area to the central equatorial
Pacific as commonly observed in past El Niño events
was not clearly seen, but above-normal convective
activity was occasionally observed to the west of the
date line, and westerly wind anomalies were seen over
the western equatorial Pacific in July and September
2014 (Fig. 3.1-6). These effects stimulated two weak
warm Kelvin waves that reached the eastern
equatorial Pacific in October and December 2014, and
positive SST anomalies persisted in the eastern and
central Pacific (Fig. 3.1-5; Autumn (SON) 2014, Fig.
3.1-7, center)
Fig. 3.1-5 Time-longitude sections for SST anomalies (left), and subsurface temperature anomalies averaged from
ocean surface to the depth of 300 m (right) along the equator (0.5°S – 0.5°N)
The data are from November 2013 to October 2016.
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Fig. 3.1-6 Time-longitude sections of velocity potential anomalies in the upper troposphere (200 hPa) (left) and zonal
wind anomalies in the lower troposphere (850 hPa) (right) along equatorial regions (5°N – 5°S)
Negative velocity potential anomalies (left) indicate stronger-than-normal divergence (i.e., above-normal convective
activity), and positive values indicate weaker-than-normal divergence (i.e., below-normal convective activity). Positive
zonal wind anomalies (right) represent westerly anomalies, and negative values indicate easterly anomalies. The data cover
the period from November 2013 to October 2016.
In November and December 2014, above-normal
convective activity was observed near Indonesia, and
easterly wind anomalies were seen in the western
equatorial Pacific (Fig. 3.1-6; winter (DJF) 2015, Fig.
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3.1-7, left). Cold Kelvin waves stimulated by easterly
wind anomalies reached the eastern equatorial Pacific
in January – March 2015, and the SST anomalies there
turned negative (Fig. 3.1-5; winter (DJF) 2015, Fig.
3.1-7, center).
Thus, from boreal spring 2014 to spring 2015, the
El Niño event continued with no clear air-sea
interaction (i.e., no sign of development), and neither
developed nor decayed. During this period, SSTs were
considerably higher than in average years over the
entire tropical region in the North Pacific and over the
entire tropical Indian Ocean, which contributed to the
record-high global average SST recorded in 2014. At
the same time, SSTs remained below normal over the
central and eastern tropical Pacific in the Southern
Hemisphere in contrast to the above-normal SSTs
commonly observed in the same area during the
development process in past El Niño events.
(b) Boreal spring 2015 – spring 2016
From boreal spring 2015 onward, the El Niño
event developed with continued above-normal
convective activity over the western equatorial Pacific
along with westerly wind anomalies from around
January 2015 and the onset of westerly wind burst
activity in late March (Fig. 3.1-6). Ocean subsurface
warm Kelvin waves excited by this activity reached
the eastern equatorial Pacific in April – May, and
ocean subsurface temperature anomalies subsequently
turned positive in the central – eastern equatorial
Pacific (Fig. 3.1-5, right; spring (MAM) 2015, Fig.
3.1-7, right). SST anomalies then rose near the
western coast of South America in the eastern
equatorial Pacific, and in this area positive anomalies
expanded gradually westward in boreal summer –
autumn 2015 (Fig. 3.1-5, left; spring (MAM) 2015 –
Autumn (SON) 2015, Fig. 3.1-7, center).
Meanwhile, the relative maximum positive SST
anomaly was observed near the date line in the
equatorial Pacific. Before the development of the El
Niño event, the relative maximum was to the west of
the date line until early boreal spring 2015, and slowly
migrated eastward during boreal spring and summer
2015 in accordance with the development of the event,
joining positive anomalies expanding westward from
the eastern Pacific in boreal summer and autumn (Fig.
3.1-5, left).
This eastward migration of the relative maximum
SST anomaly near the date line indicates displacement
of water at temperatures of 28°C or more (referred to
as warm pools) extending from the ocean surface to a
depth of 100 m in the western equatorial Pacific (Fig.
3.1-7, right). In the course of eastward warm-pool
expansion from boreal winter 2014/2015 to autumn
2015, ocean subsurface water temperatures of 30°C or
above and relative maximum water temperature
anomalies migrated eastward. SST variations
corresponded to those of the ocean subsurface (Fig.
3.1-7, center).
Ocean subsurface variations closely corresponded
to those of atmospheric circulation. In May, June –
July, August and October 2015, four westerly bursts
occurred in areas shifting from west to east of the date
line with warm-pool eastward migration (Fig. 3.1-6,
right). In boreal spring 2015, above-normal
convective activity areas were centered west of the
date line and expanded to the central and eastern
equatorial Pacific. The center of this activity
gradually moved eastward and reached the central
equatorial Pacific east of the date line during the
mature stage of the El Niño event. Convective activity
near Indonesia turned below normal with the
displacement of the above-normal area. The clear
contrast of convective activity with the above-normal
levels near the date line persisted until boreal spring
2016 when the El Niño event ended (Fig. 3.1-6, left;
spring (MAM) 2015 – spring (MAM) 2016, Fig. 3.1-7,
left).
The positive SST anomalies in the central and
eastern equatorial Pacific peaked in November –
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December 2015 before gradually easing from the
eastern part (Fig. 3.1-5, left). In January 2016, another
westerly wind burst was observed over the central
equatorial Pacific, and ocean subsurface warm Kelvin
waves stimulated by this burst arrived at the eastern
equatorial Pacific in January – February 2016. No
remarkable warm Kelvin waves were subsequently
observed. Ocean subsurface cold waters in the
western equatorial Pacific migrated eastward in
March and April, and ocean subsurface water
temperature anomalies in the uppermost 300 m turned
negative over most of equatorial Pacific from the
western part to the eastern part in April (Fig. 3.1-5,
right; spring (MAM) 2016, Fig. 3.1-7, right). As a
result, the thermocline8 was shallower than normal
over most of the equatorial Pacific, and negative SST
anomalies expanded westward from the eastern
equatorial Pacific where the thermocline was at its
shallowest. In boreal spring 2016 , the El Niño event
ended with the easing of positive SST anomalies over
the central and eastern equatorial Pacific (Fig. 3.1-5,
left; spring (MAM) 2016, Fig. 3.1-7, center).
(c) Boreal summer 2016
In boreal summer 2016, the relative minimum
negative ocean subsurface temperature anomaly
moved to the central equatorial Pacific (Fig. 3.1-5,
right; summer (JJA) 2016, Fig. 3.1-7, right), and SSTs
turned below normal from the central to eastern
equatorial Pacific (Fig. 3.1-5, left; summer (JJA) 2016,
Fig. 3.1-7, center). Meanwhile, ocean subsurface
temperature anomalies turned positive and SSTs rose
above normal over most of the western tropical
Pacific, where SST areas of 30°C or more prevailed.
SSTs turned remarkably above normal from the
eastern Indian Ocean near Indonesia to the
northeastern coast of Australia.
8 The ocean subsurface layer with its steep vertical
temperature gradient indicated in 15 – 25°C temperature
layers with tight contours (Figure 3.1-7, right).
The area of above-normal convective activity
periodically varied in association with intra-seasonal
oscillations from May to July 2016, and the
positive/negative status of zonal wind anomalies in
the lower troposphere changed periodically over the
equatorial Pacific. Meanwhile, westerly wind
anomalies in the lower troposphere persisted over the
Indian Ocean (Fig. 3.1-6). From around August 2016,
easterly wind anomalies were continually observed in
the lower troposphere over the equatorial Pacific. The
seasonally averaged OLR showed common
characteristics of past El Niño events in boreal spring
2016, with convective activity being below normal
near Indonesia and above normal near the date line
over the equatorial Pacific. However, in boreal
summer 2016, the area of above-normal convective
activity near the date line disappeared, and convective
activity fell below normal over most of the equatorial
Pacific from western to eastern parts. Meanwhile,
convective activity was above normal over the eastern
Indian Ocean from boreal spring 2016, and the area of
above-normal activity extended over the eastern
Indian Ocean and Indonesia (summer (JJA), Fig. 3.1-7,
left).
The 2014/15/16 El Niño event is described above
in the context of year units running from spring to
spring, representing the period from before the onset
until after the end of the event. The atmospheric and
oceanic processes observed in the period from boreal
spring 2015 to spring 2016 (described in (b))
correspond to the stages of a typical El Niño event
from development to decay as described in
Rasmusson and Carpenter (1982), and are in contrast
to the period from spring 2014 – spring 2015
(described in (a)).
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References
Du, Y., L. Yang. and S.-P. Xie, 2011: Tropical Indian Ocean
Influence on Northwest Pacific Tropical Cyclones in
Summer following Strong El Niño. J. Climate, 24,
315-322.
Rasmusson, E. M. and T. H. Carpenter, 1982: Variations in
Tropical Sear Surface Temperature and Surface
Wind Fields Associated with the Southern
Oscillation/El Niño. Mon. Wea. Rev., 110, 354-384.
Xie, S.-P., K. Hu, J. Hafner, H. Tokinaga, Y. Du, G. Huang,
and T. Sampe, 2009: Indian Ocean Capacitor Effect
on Indo-Western Pacific Climate during the Summer
following El Niño. J. Climate, 22, 730–747.
57
Fig. 3.1-7 Seasonally averaged latitude-longitude sections for outgoing longwave radiation (OLR) (left) and SST
(center), and longitude-depth sections for ocean subsurface temperature along the equatorial Pacific (right) along
with their anomalies (boreal spring (March – May) 2013 – autumn (September – November) 2014)
Blue and black contours indicate observed values, and shading with white contours indicates anomalies from the normal
(i.e., the 1981 – 2010 average). Contour intervals are 20 W/m2 (OLR), 10 W/m2 (OLR anomalies), 1°C (SST and ocean
subsurface temperature) and 0.5°C (SST anomalies and ocean subsurface temperature anomalies). Contours for OLR are
shown for values of 250 W/m2 or less, with lower values indicating greater convective activity. Green shading indicates
regions of above-normal convective activity, and brown shading indicates regions of below-normal convective activity.
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Fig. 3.1-7 Continued (boreal winter (December – February) 2014/2015 – summer (June – August) 2016)
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3.1.2 Influences of the El Niño event on the global
climate
As described in the previous subsection, the El
Niño event peaked in winter 2015/2016 and ended in
spring 2016. SSTs in the Indian Ocean trailed the
event by a couple of months and remained above
normal toward spring/summer 2016. Influences from
the resulting SST anomalies were extensively felt
across the globe, with effects including dry conditions
in Southeast Asia, extremely heavy precipitation
along the Yangtze river basin, delayed formation of
the first typhoon of the season in the western North
Pacific, and far higher-than-normal temperatures over
Japan in the first half of winter 2015/2016.
(1) Development of the El Niño event and
associated atmospheric circulation
Atmospheric circulation anomalies associated
with the event are briefly described here for the period
from May to October 2015 (the Asian summer
monsoon season) during the development phase and
before the peak, and for the period from April to June
(around the onset of the Asian summer monsoon),
when SST anomalies in the Indian Ocean peaked in
the wake of the event. Also shown are results from
statistical analysis of atmospheric circulation
observed during the past El Niño events and high-SST
events in the Indian Ocean.
Fig. 3.1-8 shows changes in the NINO.3 index and
the IOBW index, which are defined as SST departures
from the climatological mean based on the latest
sliding 30-year period averaged over the eastern
equatorial Pacific and the tropical Indian Ocean,
Fig. 3.1-9 3-month mean SST anomalies
From top to bottom: boreal spring, summer, autumn 2015,
winter 2015/2016 and spring 2016. Anomalies are
represented with respect to the 1981 – 2010 average.
Fig. 3.1-8 NINO.3 and IOBW index fluctuations
Thin lines indicate monthly values and thick lines indicate
the five-month moving average. These indices are defined
as SST anomalies averaged over the areas shown in the
bottom panel.
Jun. to Aug. 2015
Sep. to Nov. 2015
Dec. 2015 to Feb. 2016
Mar. to May 2016
Mar. to May 2015
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respectively. The NINO.3 index turned positive
around spring 2014 and began to increase rapidly in
spring 2015. Values began to decline after peaking in
winter 2015/2016, returned to near-normal in spring
2016 and turned negative in summer 2016. The IOBW
index surged on the heels of NINO.3, peaking in
spring 2016 before declining throughout summer. Fig.
3.1-9 indicates seasonal mean SST anomalies
observed from spring 2015 to spring 2016.
Fig. 3.1-10 shows stream function anomalies at
850 hPa composited over the three-month periods of
May to July (early Asian summer monsoon), August
to October (late Asian summer monsoon) and
December to February (boreal winter) of El Niño
years from 1958 – 2012 based on JRA-55 (Kobayashi
et al., 2015). The figures show that, during Asian
summer monsoon periods, equatorial symmetric
cyclonic and anticyclonic circulation anomalies tend
to develop in the Pacific and in the area from the
Indian Ocean to the Maritime Continent, respectively,
in response to convection anomalies associated with
El Niño events. This anomaly pattern leads to
weaker-than-normal southwesterlies and suppressed
monsoon precipitation over Southeast Asia. In winter,
anticyclonic circulation anomalies extend over and to
the east of Japan in association with a wave train
pattern in the upper troposphere (figure not shown),
indicating the mild winters experienced in Japan
during El Niño events.
A composite map of stream function anomalies at
850 hPa for the three-month periods of April to June
in positive IOBW years based on JRA-55, as shown in
Fig. 3.1-11, indicates cyclonic circulation anomalies
north of the equator in the Indian Ocean and
Fig. 3.1-10 Composite map for stream function at 850
hPa during El Niño events
Three-month mean for (a) early Asian summer monsoon
(May to July), (b) late Asian summer monsoon (August to
October) and (c) boreal winter (December to February).
Anomalies are represented as deviations from the zonal
mean. Contours are at intervals of 0.5 x 106 m2/s. Shading
denotes statistical confidence.
Fig. 3.1-11 Composite map for stream function at 850
hPa during warm IOBW events
Three-month mean for April to June. Anomalies are
represented as deviation from the zonal mean. Contours are
at intervals of 0.5 x 106 m2/s. Shading denotes statistical
confidence.
(a)
(b)
(c)
61
equatorial symmetric anticyclonic circulation
anomalies over the area from Indochina to the western
North Pacific. These anticyclonic anomalies are likely
related to equatorial Kelvin waves, which propagate
from the Indian Ocean where SSTs remain above
normal in the aftermath of an El Niño event, toward
the western Pacific and induce Ekman divergence
north and south of the equator (Xie et al., 2009).
Anomalies of outgoing longwave radiation (OLR)
and stream function at 850 hPa for May to October
2015 are shown in Fig. 3.1-12 (a). The circulation
pattern of this period is characterized by cyclonic
circulation anomalies over the Pacific and
anticyclonic circulation anomalies centered over
Indochina, which is quite similar to the situation of
anomalies observed in past El Niño summers as
shown in Fig. 3.1-10 (a) and (b).
Anomalies of OLR and stream function at 850 hPa
for April to June 2016 (around the monsoon onset) are
shown in Fig. 3.1-12 (b). The anomaly pattern closely
resembles that for the positive IOBW shown in Fig.
3.1-11, with cyclonic circulation anomalies in the
Indian Ocean and anticyclonic anomalies and
suppressed convection over the area from Indochina
to the western tropical North Pacific.
(2) Influences on the global climate
Some pronounced influences on the global climate
from atmospheric circulation anomalies associated
with the El Niño event and positive SST anomalies in
the Indian Ocean are described below.
(a) Suppressed precipitation over Southeast Asia
Southeast Asia experienced below-normal
precipitation from spring 2015 to spring 2016, which
adversely affected water resource management and
agriculture. In addition to the worst drought
conditions for 90 years in Viet Nam (United Nations
Food and Agriculture Organization), a state of
Fig. 3.1-12 Anomalies of outgoing longwave radiation
(shading) and stream function at 850 hPa (contours)
(a) May to October 2015, and (b) April to June 2016. H and
L denote anticyclonic and cyclonic circulation anomalies,
respectively. Contours are at intervals of 0.5 x 106 m2/s.
Fig. 3.1-13 Cumulative precipitation averaged over
stations in Indochina
Observation stations are shown on the inset map. The red,
yellow and blue lines indicate cumulative precipitation for
12-month periods starting April 2015, April 2014 and April
2011, respectively. Grey lines indicate other years after
2000. All data are from SYNOP.
(a) May to Oct. 2015
(b) Apr. to Jun. 2016
W/m2
W/m2
62
emergency was declared for the Mekong Delta in
relation to damage caused by sea water running up the
water-deprived river (Unite Nations Country Team
Viet Nam). Wildfires were frequently reported in
Indonesia and Malaysia (United States National
Aeronautic and Space Administration).
Daily cumulative precipitation calculated from
Indochina observation station data is shown in Fig.
3.1-13 for the period from April 1 2015 to March 31
2016 along with the same period in recent years for
comparison. In 2015, precipitation remained below
normal from around May, and cumulative
precipitation for the 12-month period ending March
2016 was the lowest since 2000.
Precipitation totals for the 12 months from April
2015 to March 2016 were lower than 60% of the
normal for some stations in Borneo and 60 – 70% for
stations in Indochina (Fig. 3.1-14). Precipitation was
also below normal for the southern part of the
Philippines.
As mentioned previously, southwest summer
monsoon activity in Southeast Asia tends to be weak
during El Niño events. The anticyclonic anomalies in
the lower troposphere centered over Indochina, which
are considered to be responses to the weak monsoon
and similar to atmospheric characteristics seen in past
El Niño events (Fig. 3.1-12(a)), were a factor behind
below-normal precipitation from 2015 to 2016.
(b) Heavy precipitation in the Yangtze River basin
Areas along the middle and lower Yangtze River
experienced above-normal precipitation starting in
April 2016. Cumulative precipitation from April 1
averaged over the stations in the basin was the highest
since 1997 (Fig. 3.1-15). Amounts soared from late
June onward in particular, with the highest cumulative
30-day precipitation among the stations for June 21 to
July 20 exceeding 900 mm (Fig. 3.1-16). More than
200 fatalities were reported in relation to heavy
rainfall and landslides from late June to early July,
according to the government of China.
Such an extended period of extremely heavy
precipitation was caused by strong convergence of
moist air flow from the South China Sea over the
Yangtze River (Fig. 3.1-17). This was induced by
anticyclonic circulation anomalies over the western
tropical North Pacific associated with the high SSTs
in the Indian Ocean (Fig. 3.1-12 (b)).
This pattern of high SSTs in the Indian Ocean, the
anticyclonic circulation anomalies over the western
tropical North Pacific, moist air intrusion from the
Fig. 3.1-14 12-month precipitation anomalies for April
2015 to March 2016
Anomalies are based on CLIMAT reports and represented
as ratios against the normal.
Fig. 3.1-15 Cumulative precipitation averaged over
stations in the middle and lower Yangtze River basin
Observation stations are shown on the inset map. The red,
blue and green lines indicate cumulative precipitation for
the periods starting on April 1 of 2016, 1998 and 1999, and
grey lines indicate the same period for all other years since
1997. The dashed black line indicates the average over the
19 years from 1997 to 2015.
63
South China Sea and water vapor convergence over
southern China resembled the conditions seen in 1998
– another year when the Yangtze River basin was hit
by heavy precipitation.
Fig. 3.1-16 30-day precipitation in the middle and lower
Yangtze River basin
The map indicates 30-day precipitation for June 21 to July
20, 2016, when particularly heavy rainfall was recorded.
Red dots denote stations recording the three highest
precipitation amounts for the 30-day period (Anqing,
Wuhan and Macheng) and the highest amount for April 1 to
July 24 (Huangshan).
Fig. 3.1-17 Water vaper flux (arrows) and normalized
divergence (shading) anomalies at 850 hPa for April to June 2016
Warm and cool colors indicate divergence and convergence
anomalies, respectively.
(c) Delayed formation of the season’s first typhoon
The first tropical cyclone (TC) of 2016 over the
western North Pacific basin formed on July 3, where a
TC is defined as a tropical low pressures system with
its maximum wind speed of 17.2 m/s or higher. This
was the second-latest since 1951, and slightly earlier
than the July 9 date recorded in 1998 (Table 3.1-1).
The top four records in Table 3.1-1 coincide with
typhoon seasons subsequent to winter when an El
Niño event reached its peak and the IOBW index
remained high (Fig. 3.1-18). During all these typhoon
seasons, pronounced anticyclonic circulation
anomalies developed in the lower troposphere and
convection activity was suppressed over the western
tropical North Pacific as per the pattern in Fig. 3.1-12
(b).
In summary, suppressed convective activity over
the western North Pacific in association with high
SSTs in the Indian Ocean in the wake of the El Niño
event was a factor in the delayed first TC formation of
2016.
Table 3.1-1 Top 10 years of delayed TC formation
Rank Year Time of first TC formation (UTC)
1 1998 06Z, July 9
2 2016 00Z, July 3
3 1973 18Z, July 1
4 1983 06Z, June 25
5 1952 18Z, June 9
6 1984 06Z, June 9
7 1964 06Z, May 15
8 2001 00Z, May 11
9 2006 12Z, May 9
10 2011 12Z, May 7
Fig. 3.1-18 IOBW index changes over the last 50 years
(d) Mild 2015/2016 winter in Japan
In winter 2015/2016, particularly early in the
season, significantly above-normal temperatures (Fig.
3.1-19) and below-normal snowfall were observed
64
across Japan. The monthly mean temperature for
December averaged over eastern Japan was the
highest since 1946. It was reported that the extremely
low snowfall amount adversely affected the winter
sports industry. Its influence extended to spring and
summer, when restrictions on river water usage were
put into effect because earlier-than-normal snow
disappearance led to low water reserves.
In the first half of winter 2015/2016, convective
activity was suppressed over the Maritime Continent
and anticyclonic circulation anomalies extended from
the South China Sea to the seas east of Japan (Fig.
3.1-20 (a)). This anomaly pattern closely resembled
the composite map in Fig. 3.1-10 (c), which depicts
circulation anomaly characteristics seen in past El
Niño events.
Meanwhile, negative sea level pressure anomalies
were seen across Eurasia, indicating a
weaker-than-normal Siberian High (Fig. 3.1-20 (b)).
The EU index, which is closely correlated with the
intensity of the Siberian High, remained in a negative
phase throughout most of December (Fig. 3.1-21 (a)).
The negative phase of the EU index (the reverse of the
anomaly pattern shown in Fig. 3.1-21 (b)) is
consistent with the weak Siberian High and a weak
cold air mass over the Eurasian continent.
The thermal balance over and around Japan shown
in Fig. 3.1-22 corroborates the above as factors
involved in Japan’s mild winter – that is, southerly
warm air advection associated with anticyclonic
anomalies to the east of the country (Fig. 3.1-22 (a))
and temperature anomaly advection associated with
the weak cold air mass over the continent (Fig. 3.1-22
(b)).
It can therefore be concluded that influences from
the El Niño event and the internal variability of the
high-latitude atmosphere (a negative EU phase) were
factors behind the higher-than-normal temperatures
recorded in Japan in the first half of winter 2015/2016.
Any possible relationship between the polarity of
ENSO and EU still needs to be clarified.
References
Du, Y., L. Yang. and S.-P. Xie, 2011: Tropical Indian Ocean
Influence on Northwest Pacific Tropical Cyclones in
Summer following Strong El Niño. J. Climate, 24,
315-322.
Kobayashi, S., Y. Ota, Y. Harada, A. Ebita, M. Moriya, H.
Onoda, K. Onogi, H. Kamahori, C. Kobayashi, H.
Endo, K. Miyaoka and K. Takahashi, 2015: The
JRA-55 Reanalysis: General Specifications and
Basic Characteristics. J. Meteorol. Soc. Japan, 93,
5-48.
Rasmusson, E. M. and T. H. Carpenter, 1982: Variations in
Tropical Sear Surface Temperature and Surface
Wind Fields Associated with the Southern
Oscillation/El Niño. Mon. Wea. Rev., 110, 354-384.
Xie, S.-P., K. Hu, J. Hafner, H. Tokinaga, Y. Du, G. Huang,
and T. Sampe, 2009: Indian Ocean Capacitor Effect
on Indo-Western Pacific Climate during the Summer
following El Niño. J. Climate, 22, 730 – 747.
Fig. 3.1-19 Five-day running mean of area-average
temperature anomalies for winter 2015/2016
65
Fig. 3.1-20 (a) Anomalies of OLR (shading) and stream
function at 850 hPa (contours) and (b) sea level pressure
anomalies for Dec. 2015 to Jan. 2016
Arrows in (a) indicate wave activity flux at 850 hPa in units
of m2/s2. Contours in (a) are at intervals of 10 x 106 m2/s
(thick) and 2.5 x 106 m2/s (thin).
Fig. 3.1-21 (a) Daily EU index for Nov. 2015 to Feb.
2016 (b) Geopotential height anomalies at 500 hPa
regressed onto EU indices (contours) and correlation
coefficients (shading) (c) Geopotential height at 500 hPa
(contours) and anomalies (shading) for Dec. 2015
(a)
(b)
(a)
(b)
(c)
66
Fig. 3.1-22 (a) Climatological temperature advection
associated with wind anomalies, and (b) temperature
anomaly advection associated with climatological winds
at 925 hPa (K/day) for Dec. 1 2015 to Jan. 10 2016
(a)
(b)
67
3.2 Extreme climate conditions in Japan in August
2016
Western Japan experienced hot summer conditions
in August 2016, especially in the middle of the month.
Meanwhile, primarily due to the approach of typhoons,
monthly precipitation was the highest on record on the
Pacific side of northern Japan. This section reports on
surface climate characteristics and atmospheric
circulation observed in August 2016.
3.2.1 Surface climate conditions, SSTs and typhoon
activity in and around Japan
(1) Surface climate conditions
Fig. 3.2-1 shows temperature, precipitation and
sunshine duration for Japan in August 2016 as
deviations from or ratios against the normal (i.e., the
1981 – 2010 average).
Monthly mean temperatures and sunshine
durations were generally above normal all over the
country. Western Japan experienced hot summer
conditions, especially in mid-August, with monthly
mean temperatures +0.9°C above the normal and the
second-highest 10-day mean temperature for
mid-August since 1961 (+1.6°C above the normal).
Monthly sunshine durations against the normal on the
Sea of Japan side and the Pacific side of western
Japan were 131% (the second-highest since 1946) and
126% (the third-highest since 1946), respectively.
Monthly precipitation amounts were below normal
on the Pacific side of western Japan and in
Okinawa/Amami. Meanwhile, due to rainfall from
typhoons, fronts and moist air inflow, values were
significantly above normal in northern Japan. The
total on the Pacific side of northern Japan was the
highest on record at 231% of the normal since 1946.
Fig. 3.2-1 Temperature anomalies, precipitation ratios
and sunshine duration ratios for August 2016
Fig. 3.2-2 10-day mean sea surface temperature (top)
and its anomaly (bottom) for 11 – 20 August 2016
Sea surface temperatures (unit: °C) are based on the
MGDSST dataset. The aqua rectangle indicates the northern
part of the East China Sea (30 – 35°N, 120 – 130°E).
68
(2) Sea surface temperature around Japan1
As with the hot conditions in western Japan, SSTs
in the northern part of the East China Sea were much
higher than normal in association with
greater-than-normal solar radiation and weak surface
winds. Areas with SSTs exceeding 31°C were seen in
mid-August (Fig. 3.2-2). The 10-day mean sea surface
temperature in the northern part of the East China Sea
in mid-August was the highest since 1982 at 29.9°C.
(3) Typhoon activity in the western North Pacific
Seven tropical cyclones (TCs) with maximum
wind speeds of 17.2 m/s or more formed over the
western North Pacific in August 2016 (Fig. 3.2-3).
Four of them (Chanthu (T07), Mindulle (T09),
Lionrock (T10) and Kompasu (T11)) made landfall on
Japan in rapid succession. This was the country’s
highest monthly landfall total since records began in
1951 (tying with August 1962 and September 1954).
Several TCs affected Hokkaido and other parts of
northern Japan. Chanthu (T07) made landfall around
Cape Erimo in Hokkaido on 17 August, Kompasu
(T11) made landfall on Kushiro City in Hokkaido on
21 August, and Mindulle (T09) made landfall on
Tateyama City in Chiba Prefecture on 22 August
before moving over mainland Japan and making
landfall again on the Hidaka district of Hokkaido on
August 23. This was the first year in which multiple
TCs made landfall on Hokkaido since 1951. Hokkaido
was also affected by Conson (T06), which passed the
region’s Nemuro Peninsula. Lionrock (T10) was the
first typhoon to make landfall on the Tohoku region
from the Pacific side since 1951.
1 Based on the Merged satellite and in-situ data Global
Daily Sea Surface Temperature (MGDSST; Kurihara et. al,
2006) of JMA. Climatological normal (i.e., the 1981-2010
average) are calculated from MGDSST and COBE-SST
(JMA, 2006) datasets.
Fig. 3.2-3 Tracks of tropical cyclones in August 2016
T05 – T11 are TC identification numbers. The solid lines
show the tracks of TCs with maximum wind speeds of 17.2
m/s or more, and the dashed lines show the tracks of
tropical depressions or extratropical cyclones.
3.2.2 Atmospheric conditions
(1) Hot summer conditions in western Japan
The active phase of the Madden-Julian Oscillation
(MJO) propagated eastward from the Maritime
Continent to the Pacific during the period from the
end of July to mid-August 2016 (not shown). The
time-latitude cross section for OLR anomalies
averaged over the 105 – 125°E area (Fig. 3.2-4)
indicates that an enhanced convection phase, which
started to propagate northward in mid-July (Boreal
Summer Intraseasonal Oscillation; BSISO), reached
the area around the Philippines in August. Convective
activity from this area to the sea east of the
Philippines was enhanced in association with MJO
and BSISO (especially in mid-August). This
enhancement was also probably due in part to
higher-than-normal sea surface temperatures over the
same area (Fig. 3.2-5).
Fig. 3.2-6 shows 200-hPa stream function
anomalies and divergent wind anomalies, along with
latitude-height cross section data for meridional
wind/vertical pressure velocity anomalies averaged
over the 110 – 130°E area for 8 to 17 August 2016. In
the upper troposphere, outward flow from the area
over the Philippines is clearly seen in association with
enhanced convective activity. The Tibetan High was
stronger than normal over its northeastern part, and
anticyclonic circulation anomalies were seen over
69
northeastern China. These two flows converged over
the area from eastern China to the East China Sea
(approx. 30 – 35˚N), and downward flows were seen
in the mid-troposphere. Fig. 3.2-7 shows vertical
temperature advection at 925 hPa. This advection and
greater-than-normal solar radiation were considered to
be factors behind the hot summer conditions observed
from eastern China to western Japan.
Fig. 3.2-4 Time-latitude cross section for OLR anomalies
averaged over the 105 – 125°E area
Fig. 3.2-5 Monthly mean sea surface temperature
anomalies for August 2016 (unit: °C)
Based on the MGDSST dataset
(a)
(b)
Fig. 3.2-6 (a) 200-hPa stream function anomalies
(shading; unit: 106 m2/s) and divergent wind anomalies
(vectors; unit: m/s) (b) Latitude-height cross section for
meridional wind/vertical pressure velocity anomalies
averaged over the 110 – 130°E area for 8 to 17 August
2016
The green rectangle in (a) indicates the area of 110 – 130°E
and 10 – 50°N, and the shading in (b) shows vertical
pressure velocity anomalies (unit: Pa/s). Positive (negative)
values denote downward (upward) flow anomalies. Vectors
for the meridional wind/vertical pressure velocity anomaly
are magnified x 100 vertically.
Fig. 3.2-7 Advection of normal temperatures due to
vertical pressure velocity anomalies at 925 hPa for 8 to
17 August 2016 (unit: K/day)
70
(2) Record precipitation in northern Japan
Fig. 3.2-8 (a) shows the 500-hPa height field for
August 2016. The westerly jet stream meandered over
a wide area of the Northern Hemisphere, and was
displaced northward of its normal position over and
around the Kamchatka Peninsula and southward over
Japan and the central Pacific. Blocking highs over
western Siberia (around 60˚E) were seen throughout
the month, and also developed over and around the
Kamchatka Peninsula from mid-August onward (Fig.
3.2-9). In the upper troposphere, propagation of
quasi-stationary Rossby wave packets along the
subtropical jet stream from the cyclonic circulation
anomalies located to the south of the blocking high
over western Siberia was seen, with anticyclonic
circulation anomalies over northern China and the
Kamchatka Peninsula (Fig. 3.2-8 (b)). Over and
around western Siberia and the Kamchatka Peninsula,
positive anomalies of 500-hPa height tendency
associated with eddy vorticity flux were seen in the
areas where anticyclonic circulation anomalies were
observed (Fig. 3.2-8 (c)). This suggests that
eddy-related feedback may have contributed to the
development and maintenance of these highs.
Fig. 3.2-10 shows stream function anomalies,
wave activity flux and OLR anomalies in the upper
and lower troposphere for August 2016. Convective
activity was enhanced from the western North Pacific
to the area near the dateline around 20˚N. In response
to this enhancement (a Rossby wave response),
massive cyclonic circulation associated with a deep
monsoon trough was seen over a wide area from the
South China Sea to the south of Japan in the lower
troposphere. Convective activity over the seas to the
southeast of Japan (150 – 170˚E, 10 – 30˚N) in August
2016 was enhanced to record levels (Fig. 3.2-11).
Intrusions of high potential vorticity (PV) air
associated with the trough over the mid-latitude
central Pacific (the mid-Pacific trough) contributed to
the enhanced convective activity. Fig. 3.2-12 shows
how high PV air intruded equatorward in a southern or
southwestern direction over the central Pacific. Such
air also frequently intruded southward from the
mid-latitudes of the central Pacific (not shown), and
propagated westward over the subtropical Pacific (Fig.
3.2-13). Cyclonic circulation in the lower troposphere
was enhanced, and tropical depressions formed west
of the dateline. In this way, high PV migrating from
the mid-latitudes contributed to enhanced convective
activity and the formation of more tropical cyclones
than normal in the central Pacific.
The westerly jet stream meandered and southerly
winds prevailed over the sea to the east of Japan. The
Pacific High was displaced far eastward of its normal
position and extended toward the south of the
Kamchatka Peninsula in August 2016 in association
with a persistent wave train pattern in the upper
troposphere extending from Eurasia to the mid-Pacific
(Fig. 3.2-14). In the lower troposphere, propagation of
quasi-stationary Rossby wave packets from cyclonic
circulation anomalies over the sea to the south of
Japan was seen. This may have been related to the
expansion of the Pacific High toward the south of the
Kamchatka Peninsula (Fig. 3.2-10 (b)).
Tropical depressions forming over the sea to the
southeast of Japan were upgraded to named tropical
cyclones that moved northward over the sea to the
east of Japan and approached or hit the northern part
of the country. Lionrock (T10) followed a peculiar
path, first moving southwestward over the sea south
of the Kanto region and then making a U-turn over the
Pacific Ocean and moving northwestward in
association with the meandering westerly jet stream
(Fig. 3.2-3). This was the first typhoon to make
landfall on the Tohoku region from the Pacific side
since 1951. These TCs brought a series of heavy
precipitation events and serious damage to northern
Japan, especially on the Pacific side.
71
(a)
(b)
(c)
Fig. 3.2-8 (a) 500-hPa height (contours at intervals of 60
m) and anomalies (shading) (b) 300-hPa wave activity
flux (vectors; unit: m2/s2) and stream function anomalies
(contours at intervals of 2 × 106 m2/s) (c) 500-hPa height
tendency anomalies associated with eddy vorticity flux
(shading; unit: m/day) and 500-hPa height anomalies
(contours at intervals of 60 m) for August 2016
H and L in (b) represent anticyclonic and cyclonic
circulation anomalies, respectively. In (c), eddies are
defined as two- to eight-day band-pass-filtered fields.
Fig. 3.2-9 Time-longitude cross section showing
maximum geopotential height anomalies at 500 hPa in
the latitude bands between 40 and 80°N for June to
August 2016
(a)
(b)
Fig. 3.2-10 (a) 200-hPa and (b) 850-hPa stream function
anomalies (contours at intervals of (a) 3 × 106 m2/s and
(b) 1.5 × 106 m2/s) and wave activity flux (vectors; unit:
m2/s2) for August 2016
Shading indicates OLR anomalies (unit: W/m2). The green
rectangle in (b) indicates the area of 150 – 170°E and 10 –
30°N.
72
Fig. 3.2-11 Time-series representation of OLR (unit:
W/m2) averaged over the area to the southeast of Japan
(150 – 170°E, 10 – 30°N) for August from 1979 to 2016
Fig. 3.2-12 Monthly mean OLR (shading; unit: W/m2)
and potential vorticity on the 360-K isentropic surface
(contours at intervals of 1 PVU) for August 2016
Fig. 3.2-13 Time-longitude cross section for potential
vorticity on the 360-K isentropic surface averaged over
the 20-30°N area (shading; unit: PVU) and relative
vorticity at 850 hPa averaged over the 15 – 25°N area
(contours at intervals of 10-6/s; shown for 2×10-6/s or
more) for August 2016
The blue dots represent genesis points of tropical
depressions later upgraded to named TCs. “T16xx”
expresses TC identification numbers.
Fig. 3.2-14 Monthly mean sea level pressure (contours at
intervals of 4 hPa) and anomalies (shading) for August
2016
3.2.3 Summary
The atmospheric circulation conditions discussed
here are summarized in Fig. 3.2-15.
In the upper troposphere, propagation of
quasi-stationary Rossby wave packets from cyclonic
circulation anomalies located to the south of the
blocking high over western Siberia was seen. The
westerly jet stream meandered over a wide area,
ridges were seen over north China and the Kamchatka
Peninsula, and troughs were seen over Japan and the
central Pacific.
In association with intrusions of high PV air from
the trough over the mid-latitude central Pacific,
convective activity was enhanced from the area
southeast of Japan to the area near the dateline at
around 20˚N. In response to this enhancement (a
Rossby wave response), massive cyclonic circulation
was seen over the sea to the south of Japan in the
lower troposphere.
The Pacific High was displaced far eastward of its
normal position and extended toward the south of the
Kamchatka Peninsula. The blocking highs over and
around the Kamchatka Peninsula as well as the
propagation of quasi-stationary Rossby wave packets
from cyclonic circulation anomalies over the sea to
the south of Japan in the lower troposphere may have
contributed to this extension.
73
Tropical depressions forming over the sea to the
southeast of Japan were upgraded to named tropical
cyclones (TCs) that moved northward over the sea to
the east of Japan and brought a series of heavy
precipitation events and serious damage to northern
Japan.
In association with enhanced convective activity
over and around the Philippines and the
stronger-than-normal Tibetan High over northeastern
China, downward flows were seen from eastern China
to western Japan in the mid-troposphere. This vertical
advection and greater-than-normal solar radiation
brought hot summer conditions to western Japan.
Fig. 3.2-15 Characteristics of atmospheric circulation
associated with extreme climate conditions in Japan in
August 2016
References
JMA, 2006: Characteristics of Global Sea Surface
Temperature Data (COBE-SST), Monthly Report on
Climate System, Separated Volume No. 12.
Kurihara, Y., Sakurai, T., and Kuragano, T., 2006: Global
daily sea surface temperature analysis using data from
satellite microwave radiometer, satellite infrared
radiometer and in-situ observations (in Japanese),
Weather Service Bulletin, Vol. 73, S1 – S18.
74