To be sure, a lowered atmospheric pressure system (a tropical cyclone or a concentric baric low) overlies a water cushion, the so-called baric wave, moving together with the pressure system at the sea surface. The wave’s height depends on the pressure decrease in the centre of the system. A pressure drop of Δp = 1 hPa results in a static sea level rise of ΔHs = 1 cm at the stationary low ( Figure 9a, Formula 1). When the low moves over the sea surface, the latter becomes dynamically deformed

(ΔHd). The sea level deformation associated with the baric wave shows positive wave elevations in the centre and negative elevations on the flanks of the deformation ( Figure 9b, Formula 2). During the passage of a deep low, the sea level rise may be 2–4 times higher than the rise produced by static conditions. The fluid GSK2656157 level deformation moves according to the laws of forced long wave propagation. When the wave propagation velocity is close

to that of a baric system passage, the wave amplitude will reach large values under the dynamic parameters of the system. As a result of the progressive movement of a baric low, the ratio of low progression (VL) to the free wave characteristics becomes important: equation(3) c=gHm,where Hm – average sea depth, Besides, an additional disturbance taking the form of diverging trans-verse waves is propagated PCI-32765 perpendicularly to the passage trajectory of the baric system. The waves look like those generated by a ship’s movement. The amplitude of these additional disturbances should be expected to be lower than that of the basic sea level deformation caused by the baric wave. In addition to the major forced wave, i.e. the wave propagating at the speed of the baric system, there can be additional free long

waves associated with the rapid change in the baric low velocity or direction. Thus, storm-generated surges and falls of sea level are a net effect of wind action and a baric wave resulting from the baric field characteristics. Wind and a baric wave can produce the same effect, i.e. both factors cause the sea level on the coast to rise or fall; they can also Farnesyltransferase produce opposite effects, when one factor raises the sea level and the other lowers it. The effects of a baric wave may be several times greater than those of the wind action. When the storm (baric wave, wind) abates, the sea level – knocked out of balance – will undergo free damped oscillations until equilibrium is restored (seiche-like variations). Owing to the complexity of the phenomenon, any sea level forecast during a storm surge will be problematic. An additional difficulty is that sea level changes are greatly affected by local conditions on the coast and the seafloor relief in the inshore zone and in a port. Therefore, it is necessary that the sea surface deformation factor by the rapidly moving baric low be included in future models developed to forecast storm surges and falls.