Wavenumber-frequency spectra of large-scale disturbances in the atmosphere and sea surface temperature in the mid-latitudes of the North Atlantic

Atmospheric pressure, surface air temperature and sea surface temperature (SST) data of the 22-yearly observations carried out by Weather Ships in the North Atlantic were used to estimate wavenumber-frequency spectrum of large scale variability in the atmosphere and upper ocean. Meridional constituents of pressure and temperature waves with wavelengths of 6000 km and 4000 km respectively were detected by the method of maximum likelihood. Previous theoretical studies could explain the pressure spectra as a domination of quasi-stationary disturbances (external Rossby waves) which resonate, generated by orographic or thermal forcing of steady westerly winds in mid-latitudes. Short temperature waves detected by wavenumber spectral analysis are likely explained by the existence of quasi-stationary internal Rossby waves formed by resonant conditions within the lower layer of the atmosphere. The SST spectrum is similar to the air temperature spectrum. This means that wave constituents in the SST field are induced by air temperature influences