**3. Meteorological tsunami in the world ocean**

The area where large meteorological tsunamis with the destructive damages were reported is marked in **Figure 2**. The colour palette in **Figure 2** indicates the phase speed of the ocean long wave *c* = (*gH*) 1/2, instead of the sea depth. Much of the events occurred in the mid-latitude, where the energy transport towards polar region is the most active throughout the meridional circulation. The wind speed of the mid-troposphere typically ranges 20–40 m/s along with the westerly jets, which is dominant to propagate the meso-β- or γ-scale atmospheric disturbance at sea level.

**Figure 2.** Map of the destructive meteorological tsunami events in the world. Colour shows the propagation speed of the ocean long wave *c* = (*gH*) 1/2 using the bathymetry of ETOPO5. Numbers indicate the location of event of the related references cited in this section.

**Figure 3.** Example of scenes on destructive meteorological tsunami [11, 12].

The Mediterranean Sea including Adriatic Sea is one of the hotspots of the meteorological tsunamis. One of the recent major events occurred on 23–27 June 2014 due to the internal gravity wave (IGW) of the mid- and low troposphere [10]. In that event, the wave height became as high as 2–3 m in the wide area of the sea. The atmospheric IGW propagated not only over the Mediterranean Sea but extended to the Black Sea. The east coast of the Adriatic Sea, Croatia (*šćiga* in local name) has many small islands and complicated shoreline shape with small bays (smaller than 10 km in axis length) and has suffered from severe events. The most severe event in June 1978 brought the maximum wave height as high as 6 m [11]. At least five destructive events with the inundation damage occurred other than 2014 event: in June 1978 at Vera Luka with 3-m wave height, in October 1984 at Ist Island with 4-m wave, in June 2003 over the middle Adriatic coast with approximately 3.5-m wave, in August 2007 at Ist Island with 4-m wave and in 2008 at Mali Lošinj [11]. The Balearic Island (*rissaga* or *resaca* in local name) is the area where large amplified waves hit as frequent as the Adriatic Sea. The large wave as high as 2 m hit that area once per 5–6 years. And 3–4-m waves hit once per 20–30 years. June 2006 event was the most severe one in recent decades: the wave as high as 4–5 m hit the the Ciudadella Harbour of the Menorca Island located in the east of the Balearic Islands [12]. An example of meteotsunami damages in those two areas is shown in **Figure 3**. Hundreds of fishing boats were destroyed by strong current, and hundreds of motorcars and number of residences were damaged by flood. Other coast at Sicily in Italy (*marrubio* in local name) and at Marta (*milghubo* in local name) also recorded wave height higher than 1 m in hitting the meteorological tsunamis [13].

Much of the large meteorological tsunami events had been reported over the coastal area of the northwest Europe, but not so frequent as compared to the Mediterranean Sea region. Since the shallow seafloor extended in the northwest Europe, it is easier for the wave to enhance by the Proudman resonance. Haslett et al. (2009) [14] summarized 9 events of the possible meteorological tsunamis over past 120 years in the United Kingdom. The recorded wave height ranged 4–9 m, caused mainly by squally thunderstorms. According to their paper, the sudden sea level rise within 5–10 min was reported. That time was too long to period of swell with the period around 10 s or little bit longer. The amplification effect in shoaling at the continental shelves of the Atlantic Ocean seemed to play an important role in the enhancement of the meteorological tsunamis. Much of the meteorological tsunami events were recorded in the South Wales and South England, where the channel opens to the west (Atlantic Ocean). The squall lines along with cold front in developed extratropical low sometimes bring the meteorological tsunamis in the southern North Sea [15] (*zeebeer* in Netherland, *seebär* in Germany) and Baltic Sea (*seebär* in Germany, or *sjösprång* in Swedish) [16]. The major recent event was brought by the cold front passed over the Netherland and Belgium on January 3, 2012. According to the weather information service webs in Netherland, sudden depression of the tide level was recorded by 1.66 m per 20 min at van Rijkswaterstaat [17], while the sudden rise of the tide level was recorded by 1.05 m per 20 min in Ijmuiden [18]. In the coastal area of the Finland, the latest major event brought the wave higher than 1.0 m (10–15 min in period) on July 29, 2010. The meteorological tsunami up to 1.5 m in wave height was also reported in May 15, 1924, caused by thunderstorm [19].

**Figure 2.** Map of the destructive meteorological tsunami events in the world. Colour shows the propagation speed of

The Mediterranean Sea including Adriatic Sea is one of the hotspots of the meteorological tsunamis. One of the recent major events occurred on 23–27 June 2014 due to the internal gravity wave (IGW) of the mid- and low troposphere [10]. In that event, the wave height became as high as 2–3 m in the wide area of the sea. The atmospheric IGW propagated not only over the Mediterranean Sea but extended to the Black Sea. The east coast of the Adriatic Sea, Croatia (*šćiga* in local name) has many small islands and complicated shoreline shape with small bays (smaller than 10 km in axis length) and has suffered from severe events. The most severe event in June 1978 brought the maximum wave height as high as 6 m [11]. At least five destructive events with the inundation damage occurred other than 2014 event: in June 1978 at Vera Luka

1/2 using the bathymetry of ETOPO5. Numbers indicate the location of event of the related

the ocean long wave *c* = (*gH*)

18 Tsunami

references cited in this section.

**Figure 3.** Example of scenes on destructive meteorological tsunami [11, 12].

The developed squall line system or the atmospheric gravity waves brought the meteorological tsunamis in the wide area of East Coast of the United States including the Florida Peninsula and Gulf of Mexico [20, 21]. On March 1995, the giant meteorological tsunami with a 3.3-m wave height hit along the east coast of the Gulf of Mexico, Florida, due to the atmospheric gravity waves propagated from the Texas-Louisiana thunderstorm [20]. The derecho developed at the inland area of the North US brought the meteorological tsunamis not only in the Atlantic Ocean but also in the Great Lakes [22]. The meteorological tsunami on the Great Lakes as large as 3 m in wave height recorded on by squall line passage in June 1954 even the lateral extent was not so wide (~250 km) as compared to the continental shelves in Atlantic Ocean [23]. The west coast of United States has complicated shoreline shapes, similar to the Adriatic Coasts. However, the wave amplitude for each event was not so large [24].

East Asia region is one of the major spots of meteorological tsunami. There are several characteristics that can enhance meteotsunami much easier than other coastal regions. The unstable layer in the middle troposphere can easily form because a couple of jets in the upper air get closed in the leeward of the Tibetan Plateau. The lifting of the wet moist air from lower latitude and the descending of the upper dry air from continental region makes the so-called wave-ducting layer often. A wide coastal continental shelf is extended from China to the Islands of Japan. The equivalent speed of the ocean long wave ranged 20–40 m/s except the Okinawa trough near the Kyushu Island, Japan. What is more, there are many small inlets having eigen periods ranging between several minutes and several hours. In March 1979, a giant meteorological tsunami (*abiki* in local name) hit on the Nagasaki Bay in Kyushu, Japan, by passing abrupt pressure jump of 5.9 hPa per 30 min. The tide gauge observed the maximum wave height of 2.78 m [25]. A large meteorological tsunami also caused by train of pressure wave with the amplitude of 0.5–2.0 hPa, with the wave length of 20–100 km [26, 27]. In the west Kyushu, most of meteorological tsunami are likely observed in the season between February and early April [28, 29]; however, the severe squall system such as Baiu front sometimes generates the strong downdraft to meteorological tsunamis [30]. On the west of the Korean Peninsula, maximum amplitude of 1.4–1.6 m recorded in March 2007 and May 2008 with the pressure jump of 2–5 hPa travelled over the Yellow Sea [31]. In the Bohai Sea of China, sea level oscillations with the amplitude higher than 1.0 m are often observed; however, the oscillation period was much longer (56–160 min) than that reported in other coasts (nearly 5–20 min). Such large amplified oscillation remained unclear as to what kind of the atmospheric sources induces such a long period wave [32]. The meteorological tsunami hit on the Kuril Island and the Kamchatka when the developing low approached the area from Hokkaido, Japan. In recent years, the wave height recorded was higher than 1.2 m in February 2010 [33].

Some destructive events have been introduced in recent papers, which occurred on the southern hemisphere. The west coast of Australia caused the meteorological tsunami resulting from squall line or frontal passage in the low pressure system. The wave height of 1.0 m was recorded in the frontal passage on June 12, 2012 [34]. Similar magnitude of meteorological tsunami was measured on the coast of New Zealand in April 2002 (*rissaga* in local name) [35]. A large flooding damage by meteorological tsunami 2.9-m wave height occurred on the west coast of South Africa on August 7, 1969. In that event, the flooding damage of housings and parked automobiles was brought within the area of 2 km along the shoreline and 100–200 m across the shoreline due to run-up of the wave [36].

It is possible that other coastal areas hit the meteorological tsunami if the multiple resonant conditions were satisfied. However, the recorded wave height were smaller than 1-m in those coastal areas. For example, Pattriaratki and Wijeratne (2015) [14] introduced smaller meteotsunamis in the tropical region such as Sri Lanka and India.
