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The Meso-scale Features Associated with Typhoon Mindulle (2004) When It Was Affecting Taiwan

The Meso-scale Features Associated with Typhoon Mindulle (2004) When It Was Affecting Taiwan Cheng-shang Lee, Yi-chin Liu (NTU), Fang-ching Chien (NTNU). Daily Rainfall (mm). Operational fixes of Mindulle (CWB). July 1. July 2.

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The Meso-scale Features Associated with Typhoon Mindulle (2004) When It Was Affecting Taiwan

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  1. The Meso-scale Features Associated with Typhoon Mindulle (2004) When It Was Affecting Taiwan Cheng-shang Lee, Yi-chin Liu (NTU), Fang-ching Chien (NTNU)

  2. Daily Rainfall (mm) Operational fixes of Mindulle (CWB) July 1 July 2 Mindulle and the following southwesterlies brought 1,860 mm rainfall to Taiwan– locally called 7-2 flood.

  3. Rainfall on July 1 (max ~ 383 mm) -- mainly by the terrain slope lifting of typhoon circulation Rainfall on July 3 - 4 (max over 700 mm) (Chien et al. 2006) -- mainly by the southwesterly flow (occurred over CMR) Rainfall on July 2 (max ~ 787 mm) -- multiple factors (meso-scale features) are playing roles. Focus of this talk: Meso-scale processes occurred on July 2 - focus on the evolution of the secondary center Interaction between secondary center and main center. The influences of secondary center and typhoon circulation on the heavy rainfall.

  4. Surface analysis and visible satellite imageries 1500 UTC 1 July 2100 UTC 1 July A secondary low formed over Taiwan Strait - moved toward the ENE, made landfall and then dissipated.

  5. Composite radar reflectivity (CWB) 0702 0600 UTC 0702 0200 UTC Heavy rainfall ~highly related torainbands, which occurred to the south of the secondary center. 0702 1200 UTC 0702 1700 UTC

  6. Analysis based on MM5 model simulation MM5 model setup • Initial data: EC Advanced Data Set TC bogus at 12 h before initial time (Jien et al., 2003, 2005) • Simulation time: 0100~0300 UTC July, 2004 • D1: 160×160，45km D2: 154×154 ,15km D3: 133×133 , 5km • Physics options Cumulus: Grell PBL: MRF IMPHYS: Mixed-Phase • Objective analysis: little-r • FDDA

  7. Tracks of primary and secondary centers -model simulationvs. observation Primary center (0206) Secondary center (0123) Model simulates reasonably welltracks of primary and secondary centers.

  8. 500 739 701 Accumulated daily rainfall (July 2, 2004) Observation Simulation (24~48h) Model reproduces reasonably well the rainfall distribution.

  9. Evolution of primary (red) and secondary (blue) centers 12 h 20 h 28 h 3 h before landfall 5 h after landfall 13 h after landfall

  10. Evolution of primary (red) and secondary (blue) centers 32 h 36 h 42 h 2 h after moving off-shore 6 h after 12 h after

  11. Trajectories during the developing phase of the secondary low (backward trajectory: 18 hr  8 hr) Over CMR 2 1 2 1 Around CMR Two groups of air parcel trajectories P and Theta at 1.5 km AGL Subsidence warming produced the initial low pressure. Flow around the northern tip of CMR brought in shear vorticity for the further development of the secondary low.

  12. Vorticity averaged inside box A (include matured vortex) A 925 hPa vorticity (shaded)P msl and 10 m winds Height Stages of low-level vortex:developing – 12 ~ 20 hmature – 20 ~ 26 hmax vorticity ~ 2.5X10-4 s-1disappearing – 26 ~ 30 h time

  13. Vorticity budget LC HA VA DT TT RT The low level ( 950 ~ 800hPa ) HA ~ advection of shear vorticity from the north of the CMR The midlevel ( 800 ~ 500 hPa ) HA ~ vorticity of primary center moved across the CMR

  14. L Evolution of secondary center – a schematic diagram After landfall Before landfall L L

  15. For the secondary vortex at mature stageArea-averaged vorticity ~ 2.5X10-4 s-1 Rossby radius of deformation ~ 120 km (if c = 30 m/s).Heating would be efficient for secondary vortex to develop. Why the secondary vortex didn’t replace the primary center? 1.5 PVU at σ= 0.9 (27- 33 h) What has happened to the low-level primary center? The strong vorticity remnant associated with the primary center moved northward on the eastern side of the CMR. The primary center re-developed after it moved off shore. An unique feature of a northward- moving typhoon? (Similar for Ofelia, 1990)

  16. After primary center re-developed over the ocean ~ 7/2 0700 UTC 7/2 0900 UTC 7/2 1100 UTC 7/2 0500 UTC • Two centers rotated cyclonically wrt each other • landfall of secondary center (dissipated over land) A reasonable result for a typhoon with such track pattern. Shaded: PV at σ= 0.9, Contour: 900 hPa gpm

  17. Sensitivity test (no initial vortex) no typhoon and no secondary vortex 28 h 34 h Div at σ= 0.9 (strong conv shaded) 28 h 34 h Meso-scale circulation Terrain SW flow

  18. Summary Horizontal vorticity advection is important to the spin-up of the secondary vortex (Lin et al. 2006). It is difficulty for the secondary center to replace the primary center for a typhoon northward moving (along the east coast of Taiwan). Several factors are affecting the heavy rainfall on 2 July for Mindulle (2004) case: typhoon circulation, secondary center southwesterly flow, Taiwan topography. Thank you!

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