THE SECONDARY LOW AND HEAVY RAINFALL ASSOCIATED WITH TYPHOON MINDULLE (2004) Speaker : Deng-Shun Chen Advisor : Prof. Ming-Jen Yang Lee, C.-S., Y.-C. Liu and F.-C. Chien, 2008:The Secondary Low and Heavy Rainfall Associated with Typhoon Mindulle(2004). Mon. Wea Rev., 136,

The 7-2 Flood Was Caused by MINDULLE 2

College Entrance Examination 3

Outline 4  Case description  Model design and verification a) model settings b) verification of the simulation  The evolution of the primary and the secondary centers  Budget analyses during the formation of secondary low a) thermal budget b) vorticity budget  The roles of the secondary low  Discussion and conclusion

Case description 5

Synoptic Scale hPa 7/1 1200Z 500 hPa 7/2 1200Z

Mesoscale Surface Analyses Z 1 July surface0000Z 2 July surface

Visible Satellite 8

NCU Radar Observation Z & 0316Z 2 July

CWB Radar Reflectivity 10 20Z 1July02Z 2 July 12Z 2 July17Z 2 July

24-h Accumulation Rainfall (mm) 11 00Z 1 July – 00Z 2 July00Z 2 July – 00Z 3 July 00Z 3 July – 00Z 4 July

12 Model design and verification a) model setting b) verification of the simulation

Model MM5 Domain D1:45 km ; D2: 15 km ; D3: 5 km, two-way interaction Levels 31 levels, extend vertically up to100 hPa Microphysics Resiner Mixing – Phase ( Reisner et al. 1998) PBL Medium-Range Forecast (MRF) PBL (Hong et al.) Radiation Simple Cooling Radiation Scheme IC ECMWF/TOGA 。 X 。 resolution BC cumulus Grell cumulus parameterization (Grell et al. 1994) Model Setting 13

Reisner mixed-phase 14

Accumulation Rainfall (Sim. vs. Obs.) 15 SimulationObservation 00Z 2 July – 00Z 3 July

Geopotential Height at 925-hP and Reflectivity h34 h

The Evolution of Primary & Secondary Low (I) h20 h28 h

The Evolution of Primary & Secondary Low (I) h36 h42 h

Geopotential Height & Potential Vorticity 19 T T T T T C C C 500 hPa 17h19h21h 23h25h27h Primary center merged with secondary low

Horizontal Wind & Potential Temperature 20 6h12h At 2 km AGL

SLP & PV (I) 21 8 h12 h SLP : Sea Level Pressure, PV : Potential Vorticity

SLP & PV (II) h20 h

SLP & PV (III) h34 h

Potential vorticity at σ =0.9 (I) h after landfall

Potential vorticity at σ =0.9 (II) 25

26 Budget analyses during the formation of secondary low a) Thermal budget b) Vorticity budget

Thermal Budget 27 8h18h Condensational heating

Thermal Budget Result 28 Model 8 h Vertical advection Model 8 h Local change term Model 18 h Vertical advection Model 8 h Local change term

Potential Temperature & Trajectory 29

The Representation of Trajectory 30  Trajectory 1 The sinking motion resulted in adiabatic warming also is the early stage formation of the secondary low at low level.  Trajectory 2 The air parcels that transported vorticity to the low pressure region which assisted the development of the secondary low.

Vorticity Budget 31 Local ChangeLC Horizontal Advection HA Vertical AdvectionVA Divergence TermDT Tilting TermTT Residual TermRT

Vorticity Budget Result 32 Developing Mature Disappearing Developing Mature Disappearing

Distribution of LC, HA and DT h h LC HA DT

The Roles of the Secondary Low (I) 34  The interaction between the primary center and the secondary center Fujiwhara effect The reason why secondary low did not replace the original center

The Roles of the Secondary Low (II) 35  Impact of the secondary low and the typhoon circulation on rainfall I II I 28h34h

Conclusion (I) 36  Two processes resulted in the formation of a secondary low,1) downslop adiabatic warming,2) the shear vorticity that circled around the northern tip of the CMR.  The low level horizontal vorticity advection and then local convergence further concentrated the vorticit.  The vortex stretching and advection are dominant terms during the formation of the secondary low(Chang,1982)

Conclusion (II) 37  Mindulle can be treated as a ‘‘quasi-continuous track’’  Such results are somewhat different form the previous studies that show weaker typhoons having more chances to induce a secondary low. (Chang 1982)  The secondary low and the typhoon circulation played an important role in the heavy rainfall over the central and southern parts of the island west of the CMR.

Conclusion (III) 38  It is impossible to isolate the role of typhoon circulation and secondary low on the heavy rainfall.  The secondary low should play a role as a modification of environmental flow, which could result in the west-east convergence lines.

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