Evidence of the 5-day period oscillations in the geoptential field

The geopotential height data for the standard isobaric levels for seventeen stations in the tropics are analysed cross-spectrally to trace the propagation of the planetary scale pressure waves. A spectral peak at the 4.6-day periodicity is available at most of the stations in the 850 mb and 700 mb levels and the associated phases correspond to the wavenumber one progression. At the higher levels, the spectral peak is not very prominent—most likely due to the poor signal to noise ratio, the phase progression is also not clearly seen. The inter-level cross-spectra show strong barotropy of the geopotential height fluctuations, the amplitude of which in terms of pressure is nearly constant up to 300 mb and works out to be about 1.5 mb.