BAMOS Sep 2020
13
Figure 2 . Location of the sea level stations and the offshore mooring TR50 . Track of the tropical low 14U is also shown .
Figure 3 . Time series of ( a ) observed water level at Hillarys Boat Harbour ; ( b ) high pass filtered water level ; and , ( c ) atmospheric pressure from the UWA station .
All three of the conditions described above depend on the coastal topography and bathymetry as the speed of the shallow water waves is dependent on the water depths .
Analysis of 13 tide gauges around Australia over the 5‐year period 2009 – 2014 identified 214 meteotsunami events with 80 events having wave heights ( peak to trough ) > 0.4 m ( Pattiaratchi et al ., 2015 ). Maximum wave height of 1.5 m was recorded at Cape Cuvier ( WA ) over this period . There were no events recorded at the northern ( tropical ) stations from Port Hedland ( WA ) to Cape Ferguson ( Qld ) most likely due to lack of propagating pressure systems . South‐west Australia ( between Geraldton and Esperance ) recorded the highest number of events and these were associated with thunderstorms and tropical cyclones during the summer months and passage of cold fronts in winter . A meteotsunami associated with a
combination of a cold front and an extra‐tropical cyclone resulted in the highest water level recorded in Fremantle over a 110‐year record ( Pattiaratchi and Wijeratne , 2014 ).
As an example , a meteotsunami recorded at Hillary ’ s Boat Harbour ( Figure 2 ) on 14 December 2018 indicated a maximum wave height of 0.61 m that was higher than the tidal range ( Figures 3a , b ). This meteotsunami was in response to a propagating pressure jump of 3.4 hPa over a 15 minute period associated with a thunderstorm ( Figure 3c ). The rainfall radar during the event ( Figure 4 ) indicated the rapid formation of the thunderstorm offshore that propagated from north‐west to south‐east offshore Fremantle with a speed of 18.5 ms -1 . This indicates that Proudman resonance would occur in water depths close to 35 m , which is the depth of the inner continental shelf in this region .
Figure 4 . Time lapse imagery of rainfall radar from the Perth region on 14 December 2018 ( times in UTC ): ( a ) 12:00 ; ( b ) 12:30 ; ( c ) 13:00 ; ( d ) 14:00 Source : Images obtained through the Bureau of Meteorology ..