Determination of the Earth's pole tide Love number k₂ from observations of polar motion using an adaptive Kalman filter approach

Abstract

[1] The geophysical interpretation of observed time series of Earth rotation parameters (ERP) is commonly based on numerical models that describe and balance variations of angular momentum in various subsystems of the Earth. Naturally, models are dependent on geometrical, rheological and physical parameters. Many of these are weakly determined from other models or observations. In our study we present an adaptive Kalman filter approach for the improvement of parameters of the dynamic Earth system model DyMEG which acts as a simulator of ERP. In particular we focus on the improvement of the pole tide Love number k 2 . In the frame of a sensitivity analysis k 2 has been identified as one of the most crucial parameters of DyMEG since it directly influences the modeled Chandler oscillation. At the same time k 2 is one of the most uncertain parameters in the model. Our simulations with DyMEG cover a period of 60 years after which a steady state of k 2 is reached. The estimate for k 2 , accounting for the anelastic response of the Earth's mantle and the ocean, is 0.3531 + 0.0030i. We demonstrate that the application of the improved parameter k 2 in DyMEG leads to significantly better results for polar motion than the original value taken from the Conventions of the International Earth Rotation and Reference Systems Service (IERS).

Polar motion excitations for an Earth model with frequency‐dependent responses: 1. A refined theory with insight into the Earth's rheology and core‐mantle coupling

“…Despite that, by numerically simulating atmospheric and oceanic excitations with an adaptive Kalman filter, Seitz et al . [] got their best estimates T CW = 432.98 days and Q CW = 97.…”

“…At the end of this section, we would like to emphasize that our estimate of Love number k 21 = 0.35184 + 0.00293i (for the Chandler period; see Table and equation ) agrees quite well with the best simulation result 0.3531 + 0.0030i of Seitz et al . [].…”

“…On the other hand, the Chandler wobble, a free wobble undergoing continuous decay, must be excited by some geophysical processes. Only in the most recent two or three decades have fluctuations in the atmospheric, oceanic, and hydrological angular momenta been recognized as potential major sources of Chandler wobble excitation [e.g., Gross , ; Brzeziński et al ., ; Gross et al ., ; Wilson and Chen , ; Seitz et al ., ]. Previously, stochastic excitations were usually assumed [e.g., Jeffreys , ; Wilson and Haubrich , ; Ooe , ; Wilson and Vicente , ; Vicente and Wilson , ].…”

Erdrotation

“…Dieser Rückkopplungseffekt wird als Rotationsdeformation bezeichnet. Daraus resultiert eine Verlagerung der Hauptträgheitsachse gegenüber dem Erdkörper, die sich unmittelbar auf die Chandler-Schwingung auswirkt [80].…”

“…Auf Zeitskalen von wenigen Stunden bis zu mehreren Jahren werden Schwankungen der Erdrotation vor allem durch Massenverlagerungen in Atmosphäre, Ozean und fester Erde verursacht. Letztere entstehen durch Deformationen des Erdkörpers aufgrund von Gezeiten [62] und Auflasten [79] sowie durch die Rotationsdeformation [80].…”