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

49

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).

50

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.

51

(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.

52

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.

53

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.

54

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 –

55

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)).

56

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.

58

Fig. 3.1-7 Continued (boreal winter (December – February) 2014/2015 – summer (June – August) 2016)

59

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

60

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