Title: A precipitation seesaw mode between northeast Asia and Siberia in summer associated with Rossby wave
1A precipitation seesaw mode between northeast
Asia and Siberia in summer associated with Rossby
waves over the Eurasian continent
- K. Iwao and M. Takahashi
- CCSR, University of Tokyo
- Yatsushiro National College of Technology
This research was supported by Global
environment research fund G-2 about Mongolian
desertification.
2Introduction Climate over North East Asia is
Precipitation distribution in summer (July)
Elevation and 68 stations
Sayanskiy
Altai
Hangayn
Tian Shan
Govi
Tibet
Taklamakan
Precipitation seasonal variation
Precipitation is concentrated in summer
season(70) Low-precipitation is in
deserts High-precipitation is to the north
(rain-belt) over Mountain regions
3Climate change of precipitation over North-East
Asia is seen
increasing
drought
Bars station data Lines CMAP data
JJA
JUL
Iwao and Takahashi, 2006, GRL
Data show Increasing trend from the 1980s to
the 1990s also show Drought for 1999-2002 ?
Enormous damages to livestock Morinaga and
Shinoda, 2003 Increase of dust events
Kurosaki and Mikami, 2003
4We found a precipitation north-south seesaw
pattern from EOF analysis as a climate change
over North-East Asia
Correlation with upper atmosphere
EOF1 of July Prec.
A seesaw pattern between North- East Asia and
Siberia can be seen. Correlation shows Rossby
wave patterns over Northern Eurasia and
over the Asian jet.
Iwao and Takahashi, 2006, GRL
5Purpose of present topics
to clarify the seesaw pattern - We see
Rossby waves over Northern Eurasia and over
the Asian jet - The seesaw pattern is
interpreted dynamically by the wavy
structures - Origin of Rossby waves? -
Budget analyses are also done - View of
cyclone tracking difference analyses is discussed
6There are many works about Rossby waves over
Eurasia in summer
1 Rossby waves over Northern Eurasia e.g.,Wakabay
ashi and Kawamura 2004 Fukutomi et al.
2004 Nakamura and Fukamachi 2004
Sato and Takahashi 2004
Miyasaka and Kimoto 2005
2 Rossby waves over the Asian jet e.g.,Krishnan
and Sugi 2001
Enomoto et al 2003 Wakabayashi and
Kawamura 2004 Sato and Takahashi
2006 Iwasaki and Nii 2006
7Here, we will take a combination of two
teleconnection patterns related to summer Japan
climate
from Wakabayashi and Kawamura, JMSJ, 2004
over Northern Eurasia
over the Asian jet
Both wave patterns might be connected to a seasaw
pattern between Mongolia and Siberia
8An east-west seasaw mode over Siberia is obtained
by Fukutomi et al., JGR, 2004
east-west seasaw mode
high-pass 500hPa anomaly in East Siberia wet
climate is different from east and west Siberia
In their work, north-south seasaw pattern is also
seen in East Siberia wet phase -gt It might be
connected to 2 wave trains over Siberia and the
Asian jet
9Longer Data and Method
PrecipitationNCDC data ? summertime mean(JJA)
1961-2004, 39 stations Meteorological
fields ERA40 (6-hourly) data ? Low-frequency
anomaly data 10-day low-pass
(daily calendar mean)
10How climate mean fields for Rossby wave guides
are?
0
0
Local maxima of K can be wave-guides
Hoskins and Ambrizzi, 1993
K (global) 300 JJA
K60N6-8
K40N8-10
EOF analysis for the low-frequency variation of
vmeridional wind (30-150E, 40 60N, 300hPa,
JJA1961-2002) is applied
11VEOFs 1 and 2 are found and used for analyses
?60N 80 ? k4.5 ? K6.4
?40N 60 ? k6 ? K8.5
Zonal wave numbers are consistent with estimated
K The wave phases along two latitudes are
opposite in Eastern Eurasia and closer toward
the west VEOF2 is shifted eastward from VEOF1 by
1/4 wave length ? both modes can explain zonal
phase shift
12Distributions of VEOFs to the seesaw pattern
7 high-precipitation years in Siberia
7 high-precipitation years in Mongolia
JJA (1961-2001)
VMG
VSB
Composite for each phase events
exceed 1std. more than 5-days ?
VMG(VEOF-indicating Mongolia rainfall event) 36
VSB (VEOF-indicating Siberia rainfall
event) 35
13Time evolution of composite fields
VMG-case
Z, WAF 300 hPa
Eastward propagating Rossby waves branch off
the north-south direction North-south opposite
anomalies in Eastern Eurasia are due to the
difference of wave length
-8 day
-4day
Z300, Prcp
0 day
Wave Activity FluxTakaya and Nakamura
2001 Basic field JJA climatology (1961-2002)
Color 95 significant
14To see Origin of the Rossby wave
Low-pass filtered height variances at 300 hPa for
JJA
shows Blocking episode frequency for JJA(red
line) between Jun 1996 and May 2001
from Pelly and Hoskins, 2003, JAS
Wave source might be corresponding to frequent
blocking around England in summer
15Related vertical structures are like those
Height(lines) and Temperature(color) anomalies
VMG -2day
D. and Va (90-120E)
Siberia
60N
Mongolia
Siberia
Mongolia
40N
Conv.
Div.
latitude-height section
Slight and large westward tilts in the upper
and lower troposphere, respectively Meridional
circulation is between North-East Asia and
Siberia
longitude-height section
16Budget Analyses had been done
C
200hPa Vorticity budget shows
advection ? streaching
D
10-6/sday
500hPa Heat budget
Vertical advection ? heating
K/day
850hPa Vorticity budget
D
frictional ? streaching
C
10-6/sday
17Water vapor budget is estimated
VMG -2day
Integrated qU (vector) and the divergence (color)
qU, condensation heating (color), and U
divergence (contour)
Siberia
Mongolia
mm/day
10-3W/kg
heating
cooling
North-East Asia Condensation of water vapor
from south Siberia Water vapor flux is
divergence
18Precipitation over north-east Asia is related to
traveling cyclonesThen, tracking analyses of
cyclones are done
Local minimum points of 500hPa heights
Track
? generation points for tracks Shown tracks
are only ones which pass the squared region as an
example
Frequent tracks of cyclones from West
Siberia to northeast Mongolia Scarce tracks over
arid and semiarid regions Frequent
generation over north Mongolia and South
Siberia
Generation
The cyclones pass frequently over northeast
Mongolia due to traveling from the west and
generation over north Mongolia.
19Tracks for each case of the seesaw mode are
calculated
Tracks
Difference
High-prcp. (8-years)
Low-prcp. (8-years)
Cyclones pass over Mongolia frequently for
high-precipitation summers
The frequency of the traveling cyclones is
suppressed over North-East Asia for
low-precipitation summers.
20Summary
There is a precipitation seesaw mode between
North-East Asia and Siberia, which represents
an interannual variation of the summertime
precipitation over North-East Asia. Summertime
precipitation over North-East Asia increased from
the 1980s to the 1990s, and a severe drought
occurred for 1999-2002. The seesaw mode is
interpreted by stationary waves propagating
from the west over North-East Asia and
Siberia. The frequency of the traveling cyclones
is suppressed over North- East Asia for
low-precipitation summers.
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Tibet