Abstract

Abstract. The dynamic ocean topography (DOT) of the polar seas can be described by satellite altimetry sea surface height observations combined with geoid information as well as by ocean models. The altimetry observations are characterized by an irregular sampling and seasonal sea ice coverage complicating reliable DOT estimations. Models display various spatiotemporal resolutions but are limited to their computational and mathematical context and introduced forcing models. In the present paper, ALES+ retracked altimetry ranges and derived along-track DOT heights of ESA's Envisat and water heights of the Finite Element Sea Ice-Ocean Model (FESOM) are compared to investigate similarities and discrepancies. The goal of the present paper is to identify to what extent pattern and variability of the northern Nordic seas derived from measurements and model agree with each other, respectively. The study period covers the years 2003–2009. An assessment analysis regarding seasonal DOT variabilities shows good agreement and confirms the dominant impact of the annual signal in both datasets. A comparison based on estimated regional annual signal components shows 2–3 times stronger amplitudes of the observations but good agreement of the phase. Reducing both datasets by constant offsets and the annual signal reveals small regional residuals and highly correlated DOT time series (Pearson linear correlation coefficient of at least 0.67). The highest correlations can be found in areas that are ice-free and affected by ocean currents. However, differences are visible in sea-ice-covered shelf regions. Furthermore, remaining constant artificial elevations in the observational data can be attributed to an insufficient representation of the used geoid. In general, the comparison results in good agreement between simulated and altimetry-based descriptions of the DOT in the northern Nordic seas.

Highlights

  • Observing the dynamic ocean topography (DOT) enables the investigation of important oceanic variables

  • The analysis reveals some systematic discrepancies. These can be explained by three different error sources: they partly originate from modeling errors of Finite Element Sea Ice-Ocean Model (FESOM), partly from measurement uncertainties of altimetry and partly from errors of the geoid used for computing the altimetry DOT

  • High-frequency altimetry-derived DOT is compared with water elevations of FESOM in order to identify their similarities and discrepancies as well as their respective benefits

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Summary

Introduction

Observing the dynamic ocean topography (DOT) enables the investigation of important oceanic variables. Knowledge about Arctic water mass distribution and ocean transport variability is essential to understand and quantify changes in the global overturning circulation system (e.g., Johannessen et al, 2014; Morison et al, 2012). These relationships have led to studies and expeditions since the early 20th century, e.g., by Helland-Hansen and Nansen (1909) investigating northern polar circulation. The launch of the European Space Agency’s (ESA) Earth observation satellite ERS-1 in 1991 constituted the starting point of regular observed DOT information in the higher latitudes that covers more than 25 years This was followed by regularly improving radar altimetry as well as significant progress

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