Michael Schindelegger

GPT2: Empirical slant delay model for radio space geodetic techniques

Up to now, state-of-the-art empirical slant delay modeling for processing observations from radio space geodetic techniques has been provided by a combination of two empirical models. These are GPT (Global Pressure and Temperature) and GMF (Global Mapping Function), both operating on the basis of long-term averages of surface values from numerical weather models. Weaknesses in GPT/GMF, specifically their limited spatial and temporal variability, are largely eradicated by a new, combined model GPT2, which provides pressure, temperature, lapse rate, water vapor pressure, and mapping function coefficients at any site, resting upon a global 5° grid of mean values, annual, and semi-annual variations in all parameters. Built on ERA-Interim data, GPT2 brings forth improved empirical slant delays for geophysical studies. Compared to GPT/GMF, GPT2 yields a 40% reduction of annual and semi-annual amplitude differences in station heights with respect to a solution based on instantaneous local pressure values and the Vienna mapping functions 1, as shown with a series of global VLBI (Very Long Baseline Interferometry) solutions.

Surface Pressure Tide Climatologies Deduced from a Quality-Controlled Network of Barometric Observations*

AbstractGlobal “ground truth” knowledge of solar diurnal S1 and semidiurnal S2 surface pressure tides as furnished by barometric in situ observations represents a valuable standard for wide-ranging geophysical and meteorological applications. This study attempts to aid validations of the air pressure tide signature in current climate or atmospheric analysis models by developing a new global assembly of nearly 6900 mean annual S1 and S2 estimates on the basis of station and marine barometric reports from the International Surface Pressure Databank, version 2 (ISPDv2), for a principal time span of 1990–2010. Previously published tidal compilations have been limited by inadequate spatial coverage or by internal inconsistencies and outliers from suspect tidal analyses; here, these problems are mostly overcome through 1) automated data filtering under ISPDv2’s quality-control framework and 2) a meticulously conducted visual inspection of station harmonic decompositions. The quality of the resulting compilation...

Atmospheric Effects on Earth Rotation

One of the pivotal sources for fluctuations in all three components of the Earth’s rotation vector is the set of dynamical processes in the atmosphere, perceptible as motion and mass redistribution effects on a multitude of temporal and spatial scales. This review outlines the underlying theoretical framework for studying the impact of such geophysical excitation mechanisms on nutation, polar motion, and changes in length of day. It primarily addresses the so-called angular momentum approach with regard to its physical meaning and the application of data from numerical weather models. Emphasis is placed on the different transfer functions that are required for the frequency-dependent intercomparison of Earth rotation values from space geodetic techniques and the excitations from the output of atmospheric circulation models. The geophysical discussion of the review assesses the deficiencies of present excitation formalisms and acknowledges the oceans as other important driving agents for observed Earth rotation variations. A comparison of the angular momentum approach for the atmosphere to an alternative but equivalent modeling method involving Earth-atmosphere interaction torques is provided as well.

Detection of the Atmospheric S 1 Tide in VLBI Polar Motion Time Series

The contribution of the diurnal atmospheric S1 tide to Earth’s wobble is assessed by tidally analyzing hourly polar motion (PM) estimates from approximately 25 years of geodetic Very Long Baseline Interferometry (VLBI) observations. Special emphasis is placed on the dependency of S1 estimates on various settings in the a priori delay model and on the method of time series analysis in post-processing. The considered VLBI solutions differ with regard to the inclusion/exclusion of weak network geometries and the choice of a priori geophysical corrections such as thermal antenna deformation. Prograde PM coefficients \(\text{A}^{+} + i\text{B}^{+}\) of S1 are on the level of 9 + i10 μas (microarcseconds) for all solutions and none of the changes in the processing strategies perturbs this estimate beyond the twofold S1 standard deviation (\(\sim\) 2.6 μas). An independent validation of the deduced harmonics against excitation estimates from atmosphere-ocean models shows that space geodetic and geophysical accounts of the S1 effect in PM are still inconsistent by about 10 μas.