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. H L D C H D C Tibet L
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