72 (2001) group waves. Key words: Correlation coefficient for consecutive wave heights, mean run length (1993) (1996) (1998) (1999) (1993) (

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1 (2001) chtsai@mail.ntou.edu.tw hsiang@mail.ihmt.gov.tw (mean run length) Group waves and dangerous waves at the coast Tsai Cheng-Han Lin Yin-Chern Tseng Hsiang-Mao Abstract Many fishermen lost their lives to the dangerous waves occurred at the coast. This article attempts to clarify "What are these dangerous waves?" by interviewing survivors of the incidents and investigations of the sites where these waves occurred. It was found that these waves were huge waves occurred in high sea states during passages of Typhoons or in the severe monsoon weather. The common features of the sites are that they are breakwaters or rocky shores located in the depths of more than 10 meter. Their coastal bathymetry also has a steep slope. With these two conditions, the huge waves can advance directly onto the shore without breaking and without dissipating their energy. Furthermore, based on the wave data recorded during the September 1998 Typhoon Yani, at which time a fatal incident occurred on the Ho-Ping Island, Keelung. The data were collected just 500m offshore the incident site. This wave data showed significant increase of the correlation coefficient for consecutive wave heights and mean run length at the time of the fatal incidence. This means that there might be a correlation between these dangerous waves and

2 72 (2001) group waves. Key words: Correlation coefficient for consecutive wave heights, mean run length (1993) (1996) (1998) (1999) (1993) (1999)(1996) (1993) (1998) (1993)

3 : : : : :00 (Zane) 10 (1) 3 (2) ) :

4 74 (2001) :

76 (2001) 1 1 71-82 1998 9 29 1 500 33 (3) 18 H s 1/3 H max 3 1998 9 27 28 (4)

6 76 (2001) (3) 18 H s 1/3 H max (4) 996 hpa :00 17: H max (13:00

7 77 ) /29/ /29/ /29/ /28/ /28/ /27/ /27/ /26/ /26/ /25/ ( ) 8 Wave height (m) Hmax Hs 0 9/25/98 9/26/98 9/27/98 9/28/98 9/29/98 9/30/98 10/1/98 Time 5 H s H max :00-13:18 (Goda, 1970) N 1 (1/( N 1)) ( Hi H mean )( Hi + 1 H mean ) i = 1 γ = (1) N 2 (1/ N ) ( H H ) i = 1 i mean

8 78 (2001) L (mean run length) (1) H H mean L (wave burst) run L(run length) ( ) (7) 3 L Surface elevation (cm) :00 13:03 13:06 13:09 13:12 13:15 13:18 Time :00 ( ) 270cm 8 L : : : :00 2 (10) :00-12: :00 2.6

9 79 Threshold level Run length L 7 (run length) γ /25/98 9/26/98 9/27/98 9/28/98 9/29/98 9/30/98 10/1/ Mean run length /25/98 9/26/98 9/27/98 9/28/98 9/29/98 9/30/98 10/1/98 Time 8

10 80 (2001) Wave height (m) Hmax Hs 0 9/25/98 9/26/98 9/27/98 9/28/98 9/29/98 9/30/98 10/1/98 Time 9 H s H max γ /25/98 9/26/98 9/27/98 9/28/98 9/29/98 9/30/98 10/1/ Mean run length /25/98 9/26/98 9/27/98 9/28/98 9/29/98 9/30/98 10/1/98 Time 10

11 81 (run-up) (11) ( ) (Sorensen 1993)(1999) " 2-3 In phase 11 dangerous waves at the coast. Dangerous waves at the

12 82 (2001) coast freak waves (rouge waves) (Ochi 1998) freak waves (1998) freak waves (1999) km 1. (1993) (1998) II (1999) 5. Goda, Y., (1970) Numerical experiments on wave statistics with spectral simulation, Port and Harbour Research Institude, Report 9, No. 3, pp Sorensen, R. M., (1993) Basic Wave Mechanics: for coastal and ocean engineers, John Wiley & Sons, Inc., New York, pp Ochi, M. K., (1998) Ocean Waves, The Stochastic Approach, Cambridge University Press, Cambridge, UK, pp

~ a 3 h NCEP ~ 24 3 ~ ~ 8 9 ~ km m ~ 500 m 500 ~ 800 m 800 ~ m a 200

~ a 3 h NCEP ~ 24 3 ~ ~ 8 9 ~ km m ~ 500 m 500 ~ 800 m 800 ~ m a 200 31 1 2013 3 Journal of Arid Meteorology Vol. 31 No. 1 March 2013. J. 2013 31 1 62-69. doi 10. 11755 /j. issn. 1006-7639 2013-01 - 0062 211101 2000 ~ 2010 3 h 2. 5 2. 5 NCEP 2 5 ~ 7 02 11 05 ~ 08 2 ~ 8