Abstract
Abstract. The sensitivity of the dynamics of the Mediterranean Sea to atmospheric pressure and free surface elevation formulation using NEMO (Nucleus for European Modelling of the Ocean) was evaluated. Four different experiments were carried out in the Mediterranean Sea using filtered or explicit free surface numerical schemes and accounting for the effect of atmospheric pressure in addition to wind and buoyancy fluxes. Model results were evaluated by coherency and power spectrum analysis with tide gauge data. We found that atmospheric pressure plays an important role for periods shorter than 100 days. The free surface formulation is important to obtain the correct ocean response for periods shorter than 30 days. At frequencies higher than 15 days−1 the Mediterranean basin's response to atmospheric pressure was not coherent and the performance of the model strongly depended on the specific area considered. A large-amplitude seasonal oscillation observed in the experiments using a filtered free surface was not evident in the corresponding explicit free surface formulation case, which was due to a phase shift between mass fluxes in the Gibraltar Strait and at the surface. The configuration with time splitting and atmospheric pressure always performed best; the differences were enhanced at very high frequencies.
Highlights
The Mediterranean Forecasting System (MFS, Pinardi and Flemming, 1989) started in the late 1980s, a time of growing interest in the operational framework of applied marine science
In this study we focus on the two different Nucleus for European Modelling of the Ocean (NEMO) methods to solve the surface elevation Eq (2), and on how these methods affect the reproduction of the atmospheric pressure induced dynamics
The sensitivity of the circulation response due to the atmospheric pressure effect is analysed as a function of the free surface elevation formulation in NEMO
Summary
The Mediterranean Forecasting System (MFS, Pinardi and Flemming, 1989) started in the late 1980s, a time of growing interest in the operational framework of applied marine science. Oceanic responses to atmospheric pressure forcing can depart from a pure inverse barometer effect under specific circumstances, especially in the presence of geometrical constraints (i.e. straits or channels) (Garrett and Majaess, 1984) as in the Mediterranean Sea (Le Traon and Gauzelin, 1997; Pasaric et al, 2000). The validity of this IB assumption depends on the timescales and space scales considered: the ocean response to atmospheric pressure generally differs from the IB for periods less than 3 days and at high latitudes.
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