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 Precipitation distribution in summer (July) Sayanskiy Altai 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 JUL JJA increasing drought Bars ； station data Lines ； CMAP data ・ Data show Increasing trend from the 1980s to the 1990s ・ also show Drought for → 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 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: ・ 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 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] … 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 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 Method ・ Precipitation ： NCDC data → summertime mean （ JJA) , 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 ] 00 K (global) 300 JJA K 40N ～ 8-10 K 60N ～ 6-8 EOF analysis for the low-frequency variation of v:meridional wind (30-150E, 40 60N, 300hPa, JJA ) is applied

VEOFs 1 and 2 are found and used for analyses λ 60N ～ 80° → k=4.5 → K=6.4 λ 40N ～ 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 ( ) 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 fields Z, WAF 300 hPa -4day -8 day VMG-case Z300, Prcp 0 day Wave Activity Flux ： Takaya and Nakamura [2001] Basic field = JJA climatology ( ) ・ 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: 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 done C D D C [10 -6 /s ・ day] [K/day] [10 -6 /s ・ day] 200hPa Vorticity budget shows 500hPa Heat budget 850hPa Vorticity budget advection 〜 streaching Vertical advection 〜 heating frictional 〜 streaching

Water vapor budget is estimated VMG -2day [mm/day][10 -3 W/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 cyclones Then, tracking analyses of cyclones are done ● 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 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.

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 ・ 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. HL LH C D C D Tibet