HARMONICAL ANALYSIS OF SEA LEVEL DATA AT VARNA TIDE GAUGE

Abstract

This article outlines time series analysis of sea level data from Varna tide gauge stations, to solve for short and long term sea level variations. The period of observations span to 1928 � 2022. Monthly sea level data were processed using a linear regression model includes mean sea level, trend, annual, semiannual and decadal variations. Analysis of monthly sea level data for period 1928-2022 clearly indicates annual and decadal variations of mean sea level. Hourly sea level data of radar tide gauge include the period May 2013 - December 2022. The period is enough for separation the influence of long from short term tidal constituents. To analyzing of hourly sea level data, a harmonic analysis with least squares was used to resolve the amplitudes and phases of the tidal components. Harmonic analysis described observed data like series presented by sum of components whit a previously known frequencies stable in time. More than sixty statistically significant short term tidal constituents are obtained. Observation of the mean sea level is an important not only from an changing climate point of view, it also plays an key role in geodesy and geophysics. The results obtained for the annual and semi-annual tides from the regression analysis of monthly sea level and the harmonic analysis of hourly sea level data are compared.