Transcript Wakabayashi and Kawamura [2004]

A 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.
Introduction: Climate over North East Asia is
Elevation and 68 stations
Altai
Precipitation distribution
in summer (July)
Sayanskiy
Hangayn
Tian Shan
Tibet
Precipitation
seasonal
variation
Govi
Taklamakan
・Precipitation is concentrated
in summer season(~70%)
・Low-precipitation is in deserts
・High-precipitation is to the
north (rain-belt) over Mountain
regions
Climate change of precipitation over North-East Asia is seen
increasing
JJA
JUL
drought
Bars；
station data
Lines；
CMAP data
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]
We found a precipitation north-south seesaw pattern from
EOF analysis as a climate change over North-East Asia
EOF1 of July Prec.
Correlation with upper atmosphere
・A seesaw pattern between NorthEast Asia and Siberia can be seen.
・Correlation shows Rossby wave
patterns over Northern Eurasia
and over the Asian jet.
Iwao and Takahashi, 2006, GRL
Purpose 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
There are many works about Rossby waves
over Eurasia in summer
1: Rossby waves over Northern Eurasia
e.g.,Wakabayashi 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]
…
Here, 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
An 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
-> It might be connected to 2 wave trains over Siberia and the Asian jet
Longer Data
and Method
・Precipitation：NCDC 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)
How 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
K60N～6-8
K40N～8-10
EOF analysis for the low-frequency variation of v:meridional
wind (30-150E, 40 60N, 300hPa, JJA1961-2002) is applied
VEOFs 1 and 2 are found and used for analyses
λ60N～ 80°
→ k=4.5
→ K=6.4
λ40N～ 60°
→ k=6
→ K=8.5
・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
Distributions of VEOFs to the seesaw pattern
JJA (1961-2001)
7 high-precipitation 7 high-precipitation
years in Mongolia years in Siberia
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
Time evolution of composite fields
VMG-case
Z, WAF 300 hPa
-8 day
-4day
・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
Z300, Prcp
0 day
Wave Activity Flux：Takaya and Nakamura [2001]
Basic field = JJA climatology (1961-2002)
Color: 95% significant
To 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
Related vertical structures are like those
Height(lines) and
Temperature(color) anomalies
60N
Siberia
Mongolia
40N
VMG -2day
D. and Va (90-120E)
Mongolia
Siberia
Conv.
Div.
latitude-height section
longitude-height section
・Slight and large westward tilts
in the upper and lower
troposphere, respectively
・Meridional circulation is
between North-East Asia
and Siberia
Budget Analyses had
been done
200hPa Vorticity
budget shows
advection
〜 streaching
C
D
[10-6/s・day]
500hPa
Heat budget
Vertical advection
〜 heating
[K/day]
850hPa
Vorticity budget
frictional
〜 streaching
D
C
[10-6/s・day]
Water vapor budget is
estimated
Integrated qU (vector)
and the divergence (color)
VMG -2day
qU, condensation heating (color),
and U divergence (contour)
Mongolia
[mm/day]
cooling
・North-East Asia:
Condensation of water vapor from south
・Siberia:
Water vapor flux is divergence
Siberia
heating
[10-3W/kg]
Precipitation over north-east Asia is related to traveling cyclones
Then, 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.
Tracks 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.
Summary
・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 NorthEast Asia for low-precipitation summers.
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Tibet
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