The deformation of the Earth due to surface loading by storm surges and atmospheric pressure
PublisherUniversity of Liverpool
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Models have been developed for computing the loading deformation of the Earth due to storm surges and atmospheric pressure variations. It shown that atmospheric pressure loading and storm surge loading, can cause surface deformations up to several millimeters and changes in the gravity accelerations of a few microGal. The loading effects associated with storm surge events vary faster (within hours) compared with those related with atmospheric pressure fluctuations (within 2-5 days); furthermore non-tidal ocean loading is generally larger (especially at high latitudes) but affects relatively small areas at a time (about 500 km of extension), while pressure variations generally affect very broad areas and the largest deformations are usually registered during the winter periods and mainly derive from an area within 2000 km from the observation point. The regions situated in the south east of England and along the Dutch- German-Danish coastlines exhibit the largest deformation effects associated with non-tidal ocean loading (up to -30 mm of radial displacement, 10 mm in the tangential north-west direction and gravity changes of about 8J.LGal during particularly large storm surge events). The effect decreases gradually inland with values of almost -10 mm in the vertical deformation, 1-2 mm in the horizontal and gravity variations of 2-3 pGal at distances of 150 km from the coast. Atmospheric pressure loading and storm surge loading have almost the same magnitude but opposite signs in the northern regions of the British Isles in such extreme meteorological conditions. For stations situated well inland in Europe, atmospheric pressure loading is responsible for most of the deformation induced. Storm surge and atmospheric pressure loading effects are particularly different when they are associated with winter seasons characterized by opposite NAO indices. When the NAO index is positive (negative) the vertical displacements produced by non-tidal loading are negative (positive) in sign as a consequent sinking (rising) of the areas investigated and the associated gravity variations are positive (negative). The work described in this thesis is mainly concerned with developing models for better understanding the atmospheric pressure and storm surge loading deformations in the UK and north west Europe. However, as a final part of this work, comparisons are made with available geodetic observations in this area. The comparison between the gravity measurements performed by an SG at the geophysical station of Membach (Belgium) and the predicted gravity variations induced by non-tidal ocean loading represents a useful validation of our model. On the other hand even if the signal due to the loading deformation induced by atmospheric pressure and storm surges is present in the GPS coordinates and there is some evidence that sub-daily GPS results in particular exhibit a pattern that is similar to the modelled deformation, the observed time series are too noisy at the 5-10 mm level and the comparison with modelled results are generally not conclusive.