A precipitation seesaw mode between northeast Asia and

Siberia in summer associated with Rossby waves over the

Eurasian continent

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 isIntroduction: Climate over North East Asia isElevation and 68 stations Precipitation distribution

in summer (July)

SayanskiyAltai

Hangayn

Tian Shan

Tibet

Precipitation seasonal variation

GoviTaklamakan

・ 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

JUL

JJA

increasing droughtBars ；station data Lines ；CMAP data

・ 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]

Iwao and Takahashi, 2006, GRL

We found a precipitation north-south seesaw pattern from EOF analysis as a climate change over North-East AsiaWe 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 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

Purpose of present topics: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

1: Rossby waves over Northern Eurasiae.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 jete.g.,Krishnan and Sugi [2001] Enomoto et al [2003] Wakabayashi and Kawamura [2004] Sato and Takahashi [2006] Iwasaki and Nii [2006] …

There are many works about Rossby waves over Eurasia in summer

Here, we will take a combination of two teleconnection patterns related to summer Japan climateHere, 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

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

An east-west seasaw mode over Siberia is obtained

Longer Data and MethodLonger 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?

Local maxima of K can be wave-guides [Hoskins and Ambrizzi, 1993]

0 0

K (global) 300 JJA

K40N ～ 8-10

K60N ～ 6-8

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 analysesVEOFs 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

7 high-precipitation years in Siberia

7 high-precipitation years in Mongolia

JJA (1961-2001)

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

VMG

VSB

Time evolution of composite fieldsZ, WAF 300 hPa

-4day

-8 day

VMG-case

Z300, Prcp

0 day

Wave Activity Flux ： Takaya and Nakamura [2001]Basic field = JJA climatology (1961-2002)

・ 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

Color: 95% significant

To see Origin of the Rossby wave: To see Origin of the Rossby wave: Low-pass filtered height variances at 300 hPa for JJA

・ Wave source might be corresponding to frequent blocking around England in summer

from Pelly and Hoskins, 2003, JAS

shows Blocking episode frequency for JJA(red line) between Jun 1996 and May 2001

Conv. Div.

Related vertical structures are like those

D. and Va (90-120E)VMG -2day

60N

40N

Height(lines) and Temperature(color) anomalies

・ Slight and large westward tilts in the upper and lower troposphere, respectively・ Meridional circulation is between North-East Asia and Siberia

Siberia

Mongolia SiberiaMongolia

longitude-height section

latitude-height section

Budget Analyses had been doneBudget Analyses had been done

C

D

D

C

[10-6/s ・day]

[K/day]

[10-6/s ・day]

200hPa Vorticity budget shows

500hPaHeat budget

850hPaVorticity budget

advection 〜 streaching

Vertical advection 〜 heating

frictional 〜 streaching

Water vapor budget is estimated VMG -2day

[mm/day] [10-3W/kg]

・ North-East Asia: Condensation of water vapor from south・ Siberia: Water vapor flux is divergence

SiberiaMongolia

Integrated qU (vector)and the divergence (color)

qU, condensation heating (color),and U divergence (contour)

heatingcooling

Precipitation over north-east Asia is related to traveling cyclonesThen, tracking analyses of cyclones are donePrecipitation over north-east Asia is related to traveling cyclonesThen, tracking analyses of cyclones are done

● generation points for tracksShown 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

Local minimum points of 500hPa heights

Track

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

High-prcp. (8-years)

・ Cyclones pass over Mongolia frequently for high-precipitation summers

Difference

Low-prcp. (8-years)

・ The frequency of the traveling cyclones is suppressed over North-East Asia for low-precipitation summers.

SummarySummary

・ 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.

H L

L H

C

D

C

D

Tibet