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Atmospheric pressure wave inducing the meteotsunami in the East China Sea

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Thursday, 27 January 2011
Atmospheric pressure wave inducing the meteotsunami in the East China Sea
Kenji Tanaka, Kumamoto Univ., Kumamoto, Japan

In the west coast area of Kyushu Island, Japan, has been suffered from the meteotsunami (a large amplified seiche ), especially during winter and early spring season. Meteotsunami are long-period waves in the tsunami frequency band generated by a travelling atmospheric disturbance (Vilibić and Šepić, 2009). With high phase velocity and high amplitude, meteotsunami can be destructive in coastal areas.

On numerical experiment of meteotsunami, most of studies were assumed that the idealized single pressure wave. However, the horizontal distribution and evolution of the pressure wave bands have not been well discussed. Hence, this study is aimed to investigate the evolution and propagation of the atmospheric pressure wave bands over the East China Sea, using the WRF model.

I selected cases the four events: 1) 25 Feb 2009, 2) 1 Feb 2010, 3) 5 Mar 2010, and 4) 25 Mar 2010. Both of them related to the passing the extratropical cyclone over the targeted area with the stationary or cold front. Before the numerical simulation, the synoptic scale condition was investigated using JMA-GSM dataset and found that the subtropical jet slightly curved toward north on the east china sea. Below the jet, the dry air mass transported along with the southwesterly wind in the midtroposhere.

The design of the computation was as following. Three domain was set: the coarse domain covered the whole of East Asia region with the grid spacing of 50km; the intermediate domain covered whole Japan and Plain Area of the China with the grid spacing of 10km; and the East China Sea, the targeted area of the pressure wave analysis, with the grid spacing of 2.5km. The JMA-GSM data and NCEP SST data were used for initial and boundary condition. The time series of the surface meteorological variables were recorded for each time step (ever 15 seconds in Domain 3)

As the result, the band-shaped pressure perturbation occurred for both four cases over the west of the extratropical cyclone or the northwest of the stationary front. The horizontal scale of the each cell was 30-70km. The cell speed was 70-120 km/h, comparable to the phase speed of the ocean long wave. Such movement of the cell is dominated by the midtroposhere (700-400 hPa) wind around the top of the convection. Time series of the sea level pressure showed that the peak existed between the period of 10 minutes and 50 minutes after continuous wavelet analysis. The distribution of the bulk Richardson number including moisture physics showed that there existed unstable layer in the midtroposhere, evolved by the horizontal intrusion of the dry air mass along with the curvature of the wind stream in the midtroposphere.