S1/S2 Surface Pressure Tides

IAP Data and Documentation

Atmospheric surface pressure exhibits small but ubiquitous oscillations of magnitudes < 200 Pa at diurnal (S1) and semidiurnal (S2) periods. These well-known manifestations of solar tides are forced primarily by cyclic tropospheric water vapor and stratospheric ozone absorption as well as radiative and convective heating of the atmosphere from the Earth's surface. S2 tidal signals, dominated by Sun-locked, westward-travelling waves, appear with a marked zonal symmetry, whereas the diurnal pressure tide S1 has more obvious geographical modulations; cf. the figure below.

Mean annual diurnal (left panel) and semidiurnal (right panel) surface pressure tide amplitudes in units of (Pa) as deduced from globally distributed S1/S2 station tide estimates (updated version of Schindelegger and Ray, 2014).

Tidal pressure waves load the oceans and land and impact Earth's rotational and gravitational field via the redistribution of air masses. These geophysical effects must be precisely modeled when analyzing sea level or determining stable reference frames from the observations of modern space geodetic techniques (Ray and Ponte, 2003). Seemingly credible definitions of surface pressure tides based on atmospheric analysis and assimilation systems have been used for such purposes with varying degrees of success. Valuable alternative S1/S2 information, used to validate or possibly even to replace the solutions from global analysis models, is furnished by barometric in situ observations.

Schindelegger and Ray (2014) recently developed a new global assembly of more than 7100 mean annual S1/S2 in situ estimates from 20 years of station and marine pressure observations as archived and quality-controlled within version 2 of the International Surface Pressure Databank (Compo et al., 2010). The interpolation of this ground truth scatter to a global 1-degree grid was accomplished by multiquadric radial basis functions. The key results of this study include:

Tidal estimates at land and oceanic points as well as the interpolated S1/S2 climatologies are summarized under the generic term IAP (In situ air pressure tides) and can be found here. The usability of these products, e.g. for studies of short period Earth rotation excitation signals or atmosphere loading, will be investigated in future publications.


M. Schindelegger, R.D. Ray. Surface pressure tide climatologies deduced from a quality-controlled network of barometric observations, Mon. Wea. Rev., 142(12), 48724889, doi: 10.1175/MWR-D14-00217.1, 2014.
» Full article (Open Access)

R.D. Ray, R.M. Ponte. Barometric tides from ECMWF operational analyses. Ann. Geophys., 21, 1897-1910, 2003.

Compo, G. and Coauthors. International Surface Pressure Databank (ISPDv2) 1768 to 2010. Research Data Archive at the National Center for Atmospheric Research, Computational and Information Systems Laboratory, Boulder, CO. http://dx.doi.org/10.5065/D6SQ8XDW, 2010.

IAP Data and Documentation