Testing ocean tide models in the Nordic seas with tidal gravity observations

Abstract

Summary Tidal gravity observations at Ny‐Ålesund on Spitzbergen, made with a LaCoste & Romberg gravimeter with electrostatic feedback, have been used to assess the accuracy of ocean tide models in the Nordic seas. Eight ocean tide models have been used to compute the ocean tide loading at Ny‐Ålesund. The station is very close to the coast and therefore experiences a significant direct gravitational attraction of the nearby tidal water mass. For the bay adjacent to the station, the model values have been replaced by the tide gauge values and a special effort has been made to fit the models correctly to the coastline. The ocean tide models for M2 and O1 have also been compared with observations made over 30 years ago at Longyearbyen, Spitzbergen, with Askania gravimeters. The comparisons of the tidal gravity observations with computed ocean tide loading show that for the harmonic M2 the phase lag of the ocean tide model of Schwiderski and the local tide model of Gjevik et al. are wrong by +15° and −5° in the Norwegian Basin. For the harmonic S2, the models FES94.1, GOT00.2 and Schwiderski give a poor fit to the observed tidal loading at Ny‐Ålesund because of phase lags that are too large in the Norwegian Basin by ∼10°. FES94.1 and GOT00.2 also have S2 amplitudes that are ∼5 cm too large in the Norwegian Basin. For N2, FES94.1, FES95.2, GOT00.2 and Schwiderski have phase lags that are ∼10° too large in the Norwegian Basin and FES94.1 and 95.2 also have N2 amplitudes that are 2–4 cm too large in that region. Overall, for these three harmonics the global model FES99 gives the best fit to the tidal gravity observations at Ny‐Ålesund and this agreement is even closer than that obtained using regional Arctic Ocean tide models.

Gravity tide and seasonal gravity variation at Ny-Ålesund, Svalbard in Arctic

“…covering area of T/P: less than ±66 • in the latitude). Sato et al (2003) compared the results for three waves of Mf, O1 and M2 computed by GOTIC2 with those of Bos et al (2002), which were based on the FES98 global ocean tide model (Lefevre et al, 2000) and a local ocean tide model. The two independent results are consistent with each other within the difference of 0.05 Gal in amplitude and 30 • in phase for any of the three waves, even though the ocean tide models are different in the respective computations.…”

Earth tides observed by gravity and GPS in southeastern Alaska

“…Presumably, this may contribute to the better agreement in the comparison of phase in SE-AK, although, as indicated by the previous works shown in Section 1 (e.g. Bos et al, 2002;Sato et al, 2004;Neumeyer et al, 2005) and described in Section 5.1, it is known that the recent tide models based on the satellite altimeter data should give the amplitude and phase better than those of Schwiderski model in the open seas.…”

“…Bos et al, 2002;Sato et al, 2004;Neumeyer et al, 2005). On the other hand, they pointed out importance to take into account tide gauge measurements for the ocean loading correction for the gravity stations near the coasts.…”

A historical review of gravimetric observations in Norway

“…In collaboration with international partners the Norwegian Mapping Authority were also engaged in the temporal variations of the gravity field and monitoring of various kinds of surface loads as measured by relative gravimeters. Long time series for the analysis of tidal effects at Spitzbergen (80 • N) were collected in 1969 (Melchior et al, 1970) and again in 1996, the latter with a LaCoste & Romberg gravimeter equipped with an electronic feedback system (Bos et al, 2002).…”