Numerical simulation on the effects of latent heating and Taiwan topography on Typhoon Morakot (2009) 莫拉克颱風之數值模擬研究：颱風、地形、及降雨 指導教授：王重傑 博士 學生：陳郁涵

About Typhoon Morakot Affect Taiwan during 7-9 August 2009 The most serious typhoon-induced damages over southern Taiwan in 50 years. Maximum accumulated rainfall of 2884 mm, surpassing previous record of 1987 mm set by Typhoon Herb in 1996.

About Typhoon Morakot Morakot was embedded in the unusually strong large-scale monsoon gyre (Hong et al., 2010). Weak steering flow made it move slowly. With most rain to the south of typhoon center. the high topography of Taiwan enhanced uplifting and increased the rainfall significantly (Ge at el., 2010).

About Typhoon Morakot Why it moved so slowly? Three points are inseparable: ─ the track of typhoon (slow movement) ─ the asymmetric convection and latent heat release ─ topography of Taiwan that enhanced latent heating at fixed location Why it moved so slowly? ─ simply the steering flow? ─ the latent heating (LH) effect ???

Model and experiment designs Cloud-Resolving Storm Simulator (CReSS) (X,Y,Z)dim = 576 x 480 x 50 dx,dy,dz = 3km x 3km x 500m dzmin = 100 m from 8/6 0000 UTC to 8/10 0000 UTC (96 hrs)

extreme rainfall on 8/8 – 8/9 (from the NSC Scientific Report on Typhoon Morakot)

Result

Control v.s. JTWC best track ✽The two tracks are similar.

(24hr) accumulated rainfall CWB v.s. Model

accumulated rainfall TRMM PR v.s. Model

asymmetric rainfall structure

Sensitivity Experiment

Different water vapor amount

Different water vapor amount

[Control run] 100%terrain height 100%water vapor 100%terrain height 25% water vapor

At 8/8 2200 UTC [Control run] 100% terrain height 100% water vapor

100% Water vapor 50% Water vapor 25% Water vapor

Different terrain height of Taiwan

Different terrain height of Taiwan

[Control run] 100% terrain height 100% water vapor 0% terrain height 100% water vapor

“ The topography effect on the track is important when the scale of the topography is greater than the vortex Rmax. “ (Kuo et al., 2001) From west to east of Taiwan → 140 km Morakot’s Rmax → about 180 km Discernible impact of Taiwan topography on Morakot’s track, but smaller than that of reducing moisture content (latent heating effect)

100% terrain height 50% terrain height 0% terrain height

No cloud microphysics

The speed of Morakot km/hr

Conclusion heating effect was the another reason As well as the steering flow, latent heating effect was the another reason that caused Typhoon Morakot’s slow speed.

References Tsuboki, K. and Sakakibara, A. 2002: Large-scale parallel computing of Cloud Resolving Storm Simulator. High Performance Computing, 243-259. Tsuboki, K. and Sakakibara, A. 2007: Numerical Prediction of High-Impact Weather Systems –The Textbook for Seventeenth IHP Training Course in 2007. Hydrospheric Atmospheric Research Center, Nagoya, Japan, 281 pp. Kuo, H.-C., Williams, R.-T., Chen, J.-H., and Chen, Y.-L., 2001: Topographic effects on barotropic vortex motion: no mean flow. Journal of the Atmospheric Sciences, 58, 1310-1327. Ge, X., T. Li, S. Zhang, and M. Peng, 2010: What causes the extremely heavy rainfall in Taiwan during Typhoon Morakot (2009)? Atmos. Sci. Lett., 11, 46-50. Hong, C.-C., M.-Y. Lee, H.‐H. Hsu, and J.‐L. Kuo, 2010: Role of submonthly disturbance and 40–50 day ISO on the extreme rainfall event associated with Typhoon Morakot (2009) in Southern Taiwan. Geophy. Res. Lett., 37, 6pp. 周仲島, 李清勝, 鄭明典, 鳳雷, 于宜強, 2010: 莫拉克颱風綜觀環境與降雨特徵分析。莫拉克颱風科學報告, 1-26。

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