Abstract
Abstract. The exponential increase in the use of altimeter data in oceanographic studies in the past two decades has improved the knowledge of the processes that govern the interaction between the ocean and the atmosphere. One of these processes is the response of the ocean to atmospheric pressure variations, which has been deeply analysed in the past. That response is based on the isostatic assumption used to establish a standard correction for altimetric purposes, the Inverse Barometer Correction (IBC). As a general rule, the ocean goes up/down 1cm when the atmospheric pressure goes down/up 1mbar. However, in light of recent works in some oceanic regions, discrepancies arise when the real response is compared to the hypothetical one. It is important to quantify this discrepancy, in order to improve the accuracy of the correction, which is one of the most significant geophysical corrections applied to altimeter records. Some aspects of this response remain unclear, such as the real space-temporal scales where IBC can be applied, the influence of wind, non-isostatic atmospheric pressure-driven signals, and the effect of aliasing from high frequency signals. This paper is an attempt to gain insight into this phenomenon. The data used are the residuals obtained between sea surface heights from the ERS-2 altimeter and the outputs of a global barotropic ocean model. Significant departures from the hypothetical isostatic response in all data series (spatial and temporal domain) have been found, especially in the case of altimeter records. By applying the collinear track method, we observe that the estimated Atlantic Ocean response is quite similar to the one deduced from the isostatic assumption at all latitudinal bands. Nonetheless, the Indian and Pacific Oceans show important departures from the hypothetical value at low latitudes. Results obtained with the crossover track method show important deviations at low latitudes in the three basins. In order to understand why the Atlantic Ocean response is different from the one obtained in the other two, we can infer some explanations based on the interaction of seasonal and intraseasonal signals with the isostatic one. Key words. Meteorology and atmospheric dynamics (ocean-atmosphere interactions). Oceanography: physical (sea level variations; remote sensing, instruments and techniques)
Highlights
Sea level is one of the most important variables in ocean dynamic studies
With the aim to analyse the real response of the ocean to atmospheric pressure variations, we are going to use two different and independent sources of information: ERS-2 altimeter data, provided by the Centre ERS d’Archivage et de Traitment (CERSAT) (European Space Agency) and the outputs of a global Ocean Barotropic Model, developed by the Jet Propulsion Laboratory (JPL) (National Aeronautics and Space Administration)
The SLA data will be fitted to the DSP data through the simple linear regression equation: SLA(, λ, T ) = BF [DSP (, λ, T )] + ε where the regression coefficient BF may be understood as a barometric factor, and ε is the residual signal which is incoherent with the atmospheric pressure forcing
Summary
Sea level is one of the most important variables in ocean dynamic studies. In general, in sea level measurements there is some temporal and spatial variability, mainly due to fluctuations in surface wind stress, atmospheric pressure and surface heat fluxes in the atmosphere-ocean interface, as well as large-scale water mass transport (Gill and Niiler, 1973). One of the geophysical phenomena that we must eliminate from altimeter records is the ocean’s compensation for atmospheric pressure variations, the so-called Inverse Barometer Correction (hereafter referred to as IBC). This correction is based on the above mentioned Isostatic Assumption. With the aim to analyse the real response of the ocean to atmospheric pressure variations, we are going to use two different and independent sources of information: ERS-2 altimeter data, provided by the Centre ERS d’Archivage et de Traitment (CERSAT) (European Space Agency) and the outputs of a global Ocean Barotropic Model (hereafter referred to as OBM), developed by the Jet Propulsion Laboratory (JPL) (National Aeronautics and Space Administration).
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