Davis, James L. and Wernicke, Brian P. and Tamisiea, Mark E. (2012) On seasonal signals in geodetic time series. Journal of Geophysical Research B, 117 . Art. No. B01403 . ISSN 0148-0227 http://resolver.caltech.edu/CaltechAUTHORS:20120210-114355340
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We explore implications for modeling and noise analysis of stochastic seasonal processes of climatic origin in geodetic time series. Seasonal signals are generally modeled as sinusoids with annual periods (and harmonics thereof), each with constant amplitude and phase. However, environmental noise that underlies the seasonal signal in geodetic time series has a reddened power spectral density (PSD). We investigate the form of the PSD of a time series having a stochastic seasonal component and find that for frequencies greater than the nominal seasonal frequency, the PSD of the time series reflects the PSD of the seasonal amplitudes. For example, if the PSD of the seasonal amplitudes can be expressed as an inverse power law, then the PSD of the time series will behave as an inverse power law for high frequencies. Stochastic seasonal variability will also induce a peak near the nominal seasonal frequency in addition to that of the mean seasonal signal and will be relatively flat below this frequency. It is therefore possible that some of the noise in Global Navigation Satellite Systems (GNSS) time series reported by others may be associated with neglecting the stochastic component of the seasonal signal. We use a GNSS time series from site ZIMM as an example to demonstrate the existence of a variable seasonal signal (without attributing its cause), and we use an example Gravity Recovery and Climate Experiment (GRACE) time series from Alaska to demonstrate that use of a nonstochastic seasonal model can have a significant impact on the value and uncertainty of time-variable rates estimated from the time series.
|Additional Information:||© 2012 by the American Geophysical Union. Received 19 July 2011; revised 1 November 2011; accepted 21 November 2011; published 11 January 2012. This work was supported in part by NSF grants EAR-0809195 and EAR-0810328 and NASA grants NNX08AJ79 and NNX11AB97G. The ZIMM (Zimmerwald) GNSS site is operated by the Swiss Federal Office of Topography. The time series of ZIMM coordinates was obtained from the Scripps Orbit and Permanent Array Center (SOPAC). We thank Y. Bock and P. Feng for providing details concerning the SOPAC analysis and R. King for information regarding the impact of firmware changes. The GRACE Level-2 data (Stokes coefficients) used in our study were provided by the University of Texas Center for Space Research (CSR) analysis and were retrieved from ftp://podaac.jpl.nasa.gov/allData/grace/. GRACE is a joint partnership between the National Aeronautics and Space Administration (NASA) in the United States and Deutsches Zentrum für Luft- und Raumfahrt (DLR) in Germany. Generic Mapping Tools (GMT) [Wessel and Smith, 1998] were used to make the figures. We thank M. Kogan and W. Menke for comments on the manuscript. T. Parsons (Associate Editor), C. Watson, and an anonymous reviewer provided valuable reviews.|
|Subject Keywords:||GNSS; GRACE; power spectrum; seasonal signals; stochastic seasonal processes; time series analysis|
|Official Citation:||Davis, J. L., B. P. Wernicke, and M. E. Tamisiea (2012), On seasonal signals in geodetic time series, J. Geophys. Res., 117, B01403, doi:10.1029/2011JB008690.|
|Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Tony Diaz|
|Deposited On:||13 Mar 2012 19:34|
|Last Modified:||26 Dec 2012 14:49|
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