EAMEX East Asian Monsoon Experiment: 1. Summer Rainstorm Experiment 2. Winter Rainfall Experiment Tsing-Chang Chen Department of Geological and Atmospheric Sciences Iowa State University U.S.A 1 1. Pilot Studies of the Summer Rainstorm Experiment 1) Importance of Rainstorms 2) Rainstorm Genesis Mechanism 3) Rainstorm Forecastability by NCEP GFS 4) Intraseasonal Variation 5) Interannual Variation 2 Climatology GMS IR A 1998 SCSMEX case ? JMA-sfc ? 3 Rainfall cycle PTaiwan Taiwan rainfall 5/15-6/15 mmd-1 ⋅season-1 Break Active Revival Rainstorm TC (Chen et al. 2004) (Wang and Chen 2007) 4 Historical perspectives: a. TAMEX (The Taiwan Area Mesoscale Experiment; Spring 1987) TAMEX Network Kuo and Chen (1990; BAMS) 5 MCS occurrence frequency • prefrontal squall lines • mesoscale convective systems Kuo and Chen (1990; BAMS) 6 Historical perspectives: b. SCSMEX (South China Sea Monsoon Experiment; May-June 1998) Network (SCSMEX formal announcement 1997) 7 (1998 May-Jun) (Lau et al. 2000; BAMS) 8 2) Rainstorm Genesis Mechanism ∆(V,|V|) [6/1-6/15]–[5/16-5/31] L 200mb 200mb H H H L L 400mb 400mb H H H H L L 600mb H H L 850mb H L L H H 600mb L L L 850mb H L L H 9 a. Genesis mechanism Charney-Stern baroclinic instability African easterly waves 10 b. Diurnal variation Genesis location/timing of rainstorm 6Z, 12Z → Afternoon/Evening 0Z, 18Z → Midnight/Morning 11 c. Structure & downscale development MTSAT / GFS May, 2006 12 Distribution of genesis location Max(ζ) (MJ, 2005~2006) 25°N 20°N 15°N 13 21Z 6/12/05 V(600mb), IR L 30° 30°N 20° 20°N 10° 10°N 110°E 18Z 6/12/05 14 d. topographic effect Case: May, 2006 V(700mb),Rf V(925mb),Rf rainfall intensification (V,-V⋅∇h) (925mb) 15 e. Dissipation process merged mid-latitude cyclone dissipated L L H H H H L L H H H 16 N-S cross section merged midlatitude cyclone dissipated weak low-level westerlies 17 3) Rainstorm Forecastability by GFS Case 2 (R7; June 11-15, 2005) Analysis Forecast (actual trajectory) (actual trajectory) 18 , IR Analysis Case June 11-15, 2005 Forecast from 00Z 6/12/05 19 GFS forecast performance (MJ, 2005-2006) km (x-direction) For the mid-tropospheric perturbation: (actual – forecasted) 240 200 Error of position RMS of dx between real & forecast trough locations depicted in v(600mb) 160 120 80 1 standard deviation 40 t=0 ms-1 8 6 24 48 72 96 hr Error of propagation speed 4 2 0 1 standard deviation determined by trough location at 600mb -2 t= 0 24 48 72 Average duration to reach Taiwan 96 hr 20 2. Pilot Studies of the Winter Rainfall Experiment 1) Importance of Winter Rainfall 2) Impact of Cold Surge on Winter Monsoon Rainfall a. Tropical Southeast Asia b. East Asia c. Midlatitude d. Indochina 21 Winter climatology of East/Southeast Asia CMAP / ERA-40 1979-2002 A B C 22 Historic perspective 1) AMTEX [Air Mass Transformation Experiment (1975/76)] (Lenschow 1972) 23 The air-sea heat flux open cell ocean ocean closed cell (Sheu and Agee 1971) ocean ocean 24 The AMTEX storm SLP Feb 1975 L H L H L L H H L H H H L Chen et al. (1985; MWR) L H 25 2) Winter Monsoon Experiment (Greenfield and Krishnamurti 1979) WMONEX (1978/79) 26 L H L L H H 27 (Lau and Lau 1984) (Lau and Chang 1987) 28 2) Impact of Cold Surge on Winter Monsoon Rainfall Multiple-scale process Tropics-midlatitude interaction (different perspective) Regional hydrological cycle 29 Cold-surge vortex Occurrence frequency Genesis location Trajectory 30 Rainfall contribution of cold surge vortices 74% 31 Rainfall variability in tropical Southeast Asia is caused by a multiple-scale interaction among: • ENSO • MJO (30-60 day mode) • Cold surge (12-24 day mode) • Synoptic disturbance: cold-surge vortices 32 Taiwan low – no front Example Taiwan low – Taiwan front Taiwan low – redevelopment of South China front 33 Impact on Taiwan Contribution of rainfall from different types of perturbation Rainfall rate Rainy day 34 Interannual variation – Cold surge ( Chen et al. 2004; JCLI) 35 North Pacific Short-Wave Train during the Extreme Phase of ENSO ( Chen 2002; JCLI) 36 37 Clim Cold Warm 38 ( Chen 2002; JCLI) Field Experiment of EAMEX 1. Summer Rainstorm Experiment 2. Winter Rainfall Experiment Tsing-Chang Chen Department of Geological and Atmospheric Sciences Iowa State University U.S.A 39 1. Summer Rainstorm Experiment Observation/ Initialization Science plan Multiple-scale interaction Tropical-midlatitude interaction 9Z 5/28/06 Downstream Amplification Upstream Genesis Regional hydrological cycle NWP/Simulation 40 Summer Monsoon Rainstorm Experiment 0 | ▓ 41 2. Winter Rainfall Experiment Observation/ Initialization Science Plan V(925mb), pS L L H H Multiple-scale interaction VIS Tropics-midlatitude interaction Regional hydrological cycle NWP/Simulation 42 Winter Rainfall Experiment 0 | ▓ 43 3. Time Table (with international projects) WR Exp. RS Exp. 2006 2007 pilot exp. 2006 2007 build-up phase IPY (International Polar Year) 2008 IOP post-EAMEX analysis phase 2009 2010 post-EAMEX analysis phase 2008 2009 2007 2008 2009 2010 2006 2007 2008 2009 2010 2007 2008 2009 2010 2007 2008 2009 AIPO China-Japan Weather Disaster Reduction Project AMY IOP 2010 2006 MAHASRI CEOP-II 2009 2008 2008 2011 44