Yasushi MOCHIZUKI Tokyo Climate Center Japan Meteorological Agency 12 May 2015 FOCRAII 1 Unseasonable weather conditions in East Asia in summer 2014 Outline of this presentation Overview ID: 434525
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Slide1
Unseasonable weather conditions in East Asia in summer 2014
Yasushi MOCHIZUKITokyo Climate CenterJapan Meteorological Agency
12 May 2015, FOCRAIISlide2
1
Unseasonable weather conditions in East Asia in summer 2014
Outline of this presentation…
Overview
of East Asian summer monsoon
in 2014
Unseasonable weather conditions in East Asia in summer
2014
East Asia, especially western Japan, experienced
record-high precipitation and record-low sunshine durations. Two typhoons moved northward at low speed.Synoptic-scale fronts were situated around the mainland of Japan.The pronounced southward meandering of the subtropical jet stream to the west of Japan.Persistent moist air flow into western Japan to southeastern China.Suppressed cumulus convection over the Asian monsoon region in association with the tropical intra-seasonal oscillation is considered to have contributed to the southward shift and meandering of the jet stream.
Brief
introduction about climatic conditions and atmospheric
characteristicsSlide3
2
Unseasonable weather conditions in East Asia in summer 2014
Overview of East Asian summer
monsoon in 2014
（℃
）
（
％
）
northern Japan, northeastern China,
southeastern China and southeastern Mongoliawestern Japan, eastern china and northern MongoliaWarmer than normal
Colder than normal
W
etter than normal
Drier than normal
northern Japan, western Japan,
and eastern
China
northeastern China, western and
central
parts of Mongolia
Temperature anomalies
Precipitation ratio against normal
Fig.1
3-month mean temperature anomalies and precipitation ratios against normal for summer (JJA) 2014
† Data based on CLIMAT ReportSlide4
3
Unseasonable weather conditions in East Asia in summer 2014
Characteristic Atmospheric Circulation for summer
2014
SST anomalies
L
H
200-hPa stream function anomalies
OLR anomalies
850-hPa stream function anomalies
Fig.2 O
ceanic
conditions,
convective
activities and atmospheric circulations
for summer (JJA) 2014
† Data used for this investigation is JRA-55, OLR( provided by NOAA) and COBE-SST.
(W/m
2
)
(
℃
)
(1x10
6
m
2
/s)
(1x10
6
m
2
/s)Slide5
An
extraordinary session held at the JMA on 3 Sep. 2014
The TCC
Advisory Panel on Extreme Climatic
Events
issued a statement on primary factors causing the cloudy and rainy conditions observed in Japan in August 20144
Unseasonable weather conditions in East Asia in summer 2014
Unseasonable weather conditions in Japan in August 2014
TCC Advisory
Panel
on
Extreme Climatic Events
In August 2014, western Japan experienced record-high precipitation and record-low sunshine durations. From 30 July to 26 August, heavy rainfall events were observed throughout the country
.
Press Release
300
1
70
130
100
70
40
20
Precipitation Ratio(%)
August 2014
Ogasawara
Islands
Okinawa/
Amami
RegionSlide6
5
7/29
Unseasonable weather conditions in East Asia in summer 2014
Two typhoons in late July to early August
Tropical Cyclone Tracks
7/29
8/4
T1411
Halong
T1412
Nakri
In
this period,
the
subtropical jet stream was shifted northward of its normal position around
East Asia. As a result, Typhoon Nakri didn’t
turn eastward after approaching
Japan and Typhoon Halong moved
slowly northward in the area to the south of western
Japan, that made landfall over the western Japan.
7/28
8/15
200-hPa zonal wind speed
7/21
～
8/10
Weaker than normal zonal wind around Japan to eastern
China
Fig.3 Tropical cyclone tracks on T1411(Halong) and T1412(Nakri), data from RSMC-Tokyo
Fig.4 21-days mean zonal wind speed anomalies at 200-hPa (shade) and observed (contour) for 21 July – 10 August 2014
(m/s)Slide7
6
Unseasonable weather conditions in East Asia in summer 2014
front
Persistent fronts around Japan
After two typhoon passing over western Japan, around mid- to late August, synoptic-scale fronts were persistently situated around the mainland of Japan, likely in relation to the pronounced southward meandering of the subtropical jet stream to the west of Japan.
200-hPa zonal wind and its axis
normal
2014
Fig.5
15-days mean zonal wind speed at 200-hPa (shade) and its normal (contour) for 11-25 August 2014
Fig.6
15-days mean equivalent potential temperature at 850hPa (contour) and its anomaly (shade) for 11-25 August 2014
(m/s)
(K)
850-hPa equivalent potential temperatureSlide8
Unseasonable weather conditions in East Asia in summer 2014
Anti-cyclonic circulation anomalies in the lower troposphere
In mid- to late August
, the Pacific High was
enhanced
to the southeast of
Japan. At the same time, anti-cyclonic
circulation anomalies in the
lower-troposphere are seen over the South China Sea. These two factor contributed to the persistent moist air flow into western
Japan to southeastern China.
Fig.7 15-days mean stream function at 850-hPa (contour) and its anomalies (shade) for 11-25 August 2014
Fig.8
15-days mean water vapor flux anomalies at 925hPa (vector) and specific
humidity
anomalies (shade) for 11-25 August 2014
moist air flow
H
925-hPa water vapor flux
specific humidity
850-hPa
stream
function
7
(1x10
6
m
2
/s)
(kg/kg)
the Pacific High was enhanced to the southeast of JapanSlide9
Unseasonable weather conditions in East Asia in summer 2014
Phase propagation associated with intra-seasonal oscillation
（
W/m
2
）
In mid- to late August
, the
convective activities around the Philippines are suppressed, it is likely corresponding to the BSISO phase 2-3.
OLR anomalies
BSISO regressed OLR and 850-hPa wind
Fig.9
15-days mean OLR anomalies for 11-25 August 2014
Fig.10
BSISO regressed OLR and 850-hPa wind
Fig.11 Area averaged OLR anomalies.
The line color is corresponding to the rectangles shown in Fig.9
（
W/m
2
）
8
daily
normal
Inactive convective activities around the Philippines in mid- to late AugustSlide10
Unseasonable weather conditions in East Asia in summer 2014
Attribution experiment by Linear Baroclinic Model (LBM)
C
C
D
D
D
In the LBM analysis, the convergence/divergence pattern emerged by the given heat anomalies only in the tropics are similar to that of observation.
Fig.12 the given heat anomalies (upper left), the observed OLR (upper right), response in χ200 (bottom left) and
observed
χ200(bottom right), the experiments are conducted for period 1-29 August.
Observed OLR
Observed
χ200
Forcing ( observed heat anomalies)
Response in
χ200
9
D
Diabatic
heating only on the tropics are givenSlide11
Unseasonable weather conditions in East Asia in summer 2014
L
L
H
H
L
L
L
L
H
H
L
L
In the LBM analysis, the circulation pattern driven by the given heat anomalies only in the tropics are similar to that of observation.
Attribution experiment by Linear Baroclinic Model (LBM)
Observed
ψ
200
Response in
ψ200
Observed
ψ
85
0
Response in
ψ
850
Fig.13 the
response in ψ200
(upper left), the observed
ψ200
(upper right), response in
ψ850
(bottom left) and
observed
ψ850(bottom right).
10Slide12
Unseasonable weather conditions in East Asia in summer 2014
Conclusion – schematic
figure –
Enhanced
Pacific High
I
nactive convection
The subtropical jet stream meandered southward of its normal position to the west of Japan, and vice versa, northward to the east of Japan, and shifted southward of its normal position near the nation’s mainland.
S
ubtropical jet stream
The subtropical jet stream shifted southward of its normal position and meandered in association with inactive convection over large parts of Asian summer monsoon region.
Convective activity was enhanced over the eastern Pacific and eastern Indian Ocean in association with positive SST anomalies, contributing to the suppressing of convective activity around the Philippines and positive pressure anomalies were seen at the lower troposphere.
The North Pacific High was stronger than normal to the southeast of Japan, and its westward expansion was weaker than normal.
2014
inflow of moist air
Front line
Typhoon
Enhanced convective activity
（
Eastern Pacific
）
Normal position
Enhanced convective activity
11Slide13
Thank you for your attention.
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