**1. Introduction**

Meteorological tsunami (or meteotsunami) is a kind of ocean long wave with the tsunami frequency bands from several minutes to 2 h driven by atmospheric forcing such as the disturbance of sea level pressure, wind, and others [1, 2]. The sea level rises (or depresses) inside

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

of the negative (positive) pressure anomalies. The sea level also rises accordingly with the horizontal convergence of the wind stress, for example, around the front or the coastal area. Such basic mechanism to set the wave up is similar as the storm surge. But the period of the storm surge is as long as tidal motion (approximately half or 1 day), while that of meteorological tsunami is generally much shorter than tidal motion. The intensity of the sea level deformation by severe storm is typically as large as several 10 cm or higher than 1 m including wind stress. But the intensity itself of the forcing to meteorological tsunami is much smaller than that related to storm surge: an order of several centimetres in typical cases. The multiple mechanism of the resonance at the sea interface enlarges the amplitude of the ocean long waves, and the wave will possibly become higher than 3 m with flooding and destruction of the dikes. The primitive mechanisms on meteorological tsunami are founded by geophysicists in the earlier and middle twentieth century [2–4]. In recent decades, however, the integration of the scientific findings throughout severe case studies and the advances in field observation, numerical modelling and data assimilation have revealed the significance of the multiscale mechanisms on atmospheric and oceanographic processes.

In the present chapter, we briefly introduce resonant mechanisms as propagating meteorological tsunamis. Next, we show the area where destructive meteorological tsunamis have been reported. After that, we present the various kinds of the weather conditions resulting in meteorological tsunamis. **Figure 1** indicates the typical scale of meteorological phenomena and oceanographic motion. The temporal scale of meteorological tsunami typically matches the meso-β-scale motion in the atmosphere such as squall line, internal gravity wave, gravitational flow and so on. However, the genesis of those motion is influenced by both smaller- and largerscale motions. The organization of turbulent plume will generate the cumulus convection, and cluster of the convective cells will form the meso-β-scale system.

**Figure 1.** Scale of the various meteorological phenomena, and oceanographic motions.

The larger-scale motion provides the atmospheric instability structure by mixing dry air and moist air mass, that is, thermodynamic inhomogeneity. Hence, we first present the mesoscale phenomena resulting in meteorological tsunami, and then we discuss the meteorological phenomena including the large-scale motion (synoptic or continental scale). After that, we discuss and conclude the predictability of the meteorological tsunami with the current technologies on field observation, numerical modelling and data assimilation.
