  In this paper, the method of Singular Spectrum Analysis (SSA) is applied for
investigation of the zenith troposphere delay time-series derived from VLBI
observations. With the help of this method we can analyze the structure of
time-series and separate the harmonic and irregular (trend) components.
Combined IVS time-series of zenith wet and total troposphere delays obtained in
IGG were used for analysis. For this study, several VLBI stations with the most
long time series of troposphere zenith delays were selected, also taking into
consideration the geographic region where the station is located. The
investigations were carried out using SSA mode. As a result, trends and
seasonal components (with annual and semiannual periods) were obtained for all
the stations. Using of SSA enabled us to determine nonlinear trends in zenith
delay, and also to study variations in the amplitude and the phase of the
seasonal components with time.
