The hourly monthly mean atmospheric pressure variation has a semidiurnal oscillation of few hectoPascals (between approximately 4 and 2 hPa), an effect known as barometric tide. The existence of this oscillation is well known but not well documented, so this work describes the monthly barometric tide for some synoptic stations from Argentina.

The semidiurnal variation of pressure is more important during the warm months. The principal maximum and minimum take place between 12 and 14 UTC and 20 and 21 UTC and presents three types of behaviors. The Central and East regions, where the amplitude decreases as the latitude increase and show an important seasonal cycle. The Patagonia region, with smaller amplitude but showing a greater difference between summer and winter than the previous region. And the West region, which has the largest wave amplitude and also the largest difference between summer and winter. The wavelength is 5 hours greater in summer than in winter for the whole synoptic stations studied. The amplitude of these oscillations would modulated not only by the effect of heat from the sun but also for other local effects.

Depending of the time of the day, the barometric tide affects in a different way the depth of pressure systems. So this result should be taken into account when defining and characterizing the depth of cyclones / anticyclones for the analyses and weather forecast.