Lunar Air Pressure Tide L2

L2 Data and Documentation

Gravitationally driven tides dominate the short period dynamics in the oceans but are much smaller in the atmosphere due to the comperatively low density of air. Yet, determinations of surface pressure variations at lunar periods have received wide attention, particularly the semidiurnal L2 band, which represents the only wave in the atmosphere for which the forcing is, in principle, perfectly known. Hence, the tide has the potential to reveal details about the structure of the atmosphere itself, by comparing theory with observations as well as by numerical modeling (Vial and Forbes, 1994). Semidiurnal signals in air pressure are also of interest for the processing of satellite gravimetry observations from the GRACE mission. A proper reduction of L2 can avoid temporal aliasing of short period mass variability into global gravity fields that are typically derived from data accumlated over several days.

Cotidal chart of the annual mean barometric L2 tide as deduced from multiquadric interpolation of 2315 in situ estimates (Schindelegger and Dobslaw, 2015). Color-filled contours are amplitudes in microbar and white isolines show Greenwich phase lag every 30 degree.

The global distribution of barometric L2 tide, including its annual variation, has traditionally been inferred by spherical harmonic analysis of some 100 widely distributed station tide estimates. The classic study in this regard is that of Haurwitz and Cowley (1969). Numerical simulations (Vial and Forbes, 1994) have led to a more refined picture of the tide, and in a recent paper, Kohyama and Wallace (2014) have documented a surprisingly accurate lunar semi-diurnal tide in the data-assimilative ERA-Interim reanalysis as operated by the ECMWF. To validate this L2 oscillation at ground level, Schindelegger and Dobslaw (2015) have tackled an update of the Haurwitz and Cowley data, by an automated tidal analysis of barometer time series at several thousand stations as contained in various international archives. A final compilation of 2315 ground truth estimates has been mapped to a global domain through multiquadric interpolation. The data, comprising both the individual station tide determinations as well as their interpolated variants, can be found here.


B. Haurwitz, A.D. Cowley. The lunar barometric tide, its global distribution and annual variation, Pure Appl. Geophys., 77, 122-150, 1969.

T. Kohyama, J.M. Wallace. Lunar gravitational atmospheric tide, surface to 50 km in a global, gridded dataset, Geophys. Res. Lett., 41, 8660-8665, 2014.

M. Schindelegger, H. Dobslaw. A global ground truth view of the lunar air pressure tide L2, J. Geophys. Res. Atmos., 121, 95-110, doi: 10.1002/2015JD024243, 2016.
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F. Vial, J.M. Forbes. Monthly simulations of the lunar semi-diurnal tide, J. Atmos. Terr. Phys., 56, 1591-1607, 1994.

L2 Data and Documentation