TEMPORAL VARIATIONS OF ATMOSPHERIC TIDES OVER ATHENS, GREECE

The mean daily march of pressure (hourly values) for each month of the 96 year period 1894-1989 in Athens, Greece is studied using Fourier analysis. The annual variation of the harmonic parameters (amplitude, time of maximum, x and y-components) is examined. The globally excited 2nd and 3rd harmonics show in general the same behaviour as in other places of the Earth. Similar features show the corresponding parameters of the daily solar radiation march. The first harmonic displays some local characteristics. The long period fluctuations study revealed statistically significant trends in most parameters of the 2nd harmonic, most strikingly the 0.5 h shift in the time of its maximum during the 20th century. Power spectrum analysis showed the existence of a biennial oscillation in B1, the x-component of the first harmonic, but this oscillation is mainly confined to the second half of the entire period. A periodicity of about 6 years which could be associated to the Southern Oscillation was also found in B1 while in A1, the y-component, a periodicity close to the 11-year solar cycle and another one close to the nutation of the Earth's axis are present. The lunar tides are too small to be detected by the same methods. However the semilunar tide was revealed to be 10-20 times smaller than the semisolar.