A global ground truth view of the lunar air pressure tide L₂

Abstract

A comprehensive model of the lunar air pressure tide L 2 is developed on the basis of 2315 ground truth estimates from land barometers and moored buoys. Regional-scale features of the tide and its seasonal modulations are well resolved by the in situ scatter and gridded to a 2 ∘ mesh through multiquadric interpolation. The resulting climatologies serve as an independent standard to validate the lunar semidiurnal tidal signal that is present in ERA-Interim reanalysis products despite the absence of L 2 -related gravitational forcing mechanisms in the prescribed model physics. Inconsistencies between the reanalysis solution of the barometric lunar tide and its empirical account are generally small, yet when averaged over the period 1979-2010, ERA-Interim underestimates the 100 μbar open ocean tidal amplitude in the Tropics by up to 20 μbar and produces times of peak pressure that are too early by 10 lunar minutes. Large-amplitude features of the reanalysis tide off the coast of Alaska, the eastern U.S., and Great Britain are evidently spurious, introduced to the analysis system by assimilating marine pressure data at an invariant reference surface instead of properly accounting for vertical sensor movements associated with the M 2 ocean tide. Additionally, a credible L 2 signal is documented for the ERA-20C pilot reanalysis of the twentieth century. The fact that this model rests upon input data from mere surface observations provides an unambiguous indication that the lunar tidal oscillation in atmospheric analysis systems is closely tied to the assimilation of conventional pressure measurements from stations and marine objects.

Rainfall variations induced by the lunar gravitational atmospheric tide and their implications for the relationship between tropical rainfall and humidity

“…That the tropospheric signal is almost pure barotropic (KW14, Figure ) confirms that it is a passive response to diabatic heating at much higher levels of the atmosphere. In contrast to the L 2 pressure signature, which may be distorted by irregular features of the oceanic tide [ Schindelegger and Dobslaw , ], the S 2 pressure signature is much closer to a pure, equatorially symmetric, zonal wave number 2 pattern.…”

Using barometric time series of the IMS infrasound network for a global analysis of thermally induced atmospheric tides

“…In 5 contrast, we have even found a significant lunar semidiurnal tide at the Antarctic IMS station, thus far beyond the tropics. We have pointed out that it can be of spurious nature as indirect sensor lifting effect of the ocean tide (Schindelegger and Dobslaw, 2016). …”

“…Dai and Wang, 1999;Schindelegger and Ray, 2014) and lunar tides (e.g. Kohyama and Wallace, 2014;Schindelegger and Dobslaw, 2016) at ground level would be a valuable application of the IMS infrasound data. By now, the focus of such empirical models is often limited to the diurnal and the semidiurnal tide.…”

“…20 A study of Chapman and Westfold (1956) indicated that the global distribution of the lunar semidiurnal tide is similar to that of the solar counterpart. Hence, the mean annual amplitude is maximum in equatorial regions and decreases with increasing latitude (Haurwitz and Cowley, 1969;Schindelegger and Dobslaw, 2016). Combined with its generally small amplitude (Lindzen and Chapman, 1969), this explains why distinct signatures of the lunar semidiurnal tide (Fig.…”

“…Near IS27, these excitations amount to about 4 Pa (Schindelegger and Dobslaw, 2016). The open-ocean tide amounts to 0.5 m (Kohyama and Wallace, 2014).…”