Forecasting secular variation using core flows

Beggan, Ciarán; Whaler, Kathy

doi:10.5047/eps.2010.07.004

Cited by 21 publications

(20 citation statements)

References 24 publications

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“…These difficulties were further underlined by retrospective analysis of IGRF-10 SV candidates centered in 2007.5 which differed by 20 to 30 nT/yr from the retrospective IGRF-11 estimate for the same interval. It will be of considerable interest over the next 5 years to discover whether data assimilation methods utilizing approximations of core physics to forward propagate information (see Beggan and Whaler, 2010;Kuang et al, 2010, this issue) are yet at the stage where they can provide better forecasts than the traditional statistical extrapolation strategies.…”

Section: Resultsmentioning

confidence: 99%

“…In comparison, the IGRF-10 SV prediction differed from the IGRF-11 model by 21.5 nT/yr. Interestingly Beggan and Whaler (2010), also in this issue, demonstrate that by using a steady, tangentially geostrophic, core flow they are able to derive a predictive SV model that performs slightly better than any of the candidate models for IGRF-10, with a RMS vector field difference of ∼17 nT/yr.…”

Section: Evaluation Of Predictivementioning

confidence: 99%

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Evaluation of candidate geomagnetic field models for IGRF-11

et al. 2010

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Here, we report the evaluations of candidate models carried out by the IGRF-11 task force during October/November 2009 and describe the weightings used to derive the new IGRF-11 model. The evaluations include calculations of root mean square vector field differences between the candidates, comparisons of the power spectra, and degree correlations between the candidates and a mean model. Coefficient by coefficient analysis including determination of weighting factors used in a robust estimation of mean coefficients is also reported. Maps of differences in the vertical field intensity at Earth's surface between the candidates and weighted mean models are presented. Candidates with anomalous aspects are identified and efforts made to pinpoint both troublesome coefficients and geographical regions where large variations between candidates originate. A retrospective analysis of IGRF-10 main field candidates for epoch 2005.0 and predictive secular variation candidates for 2005.0-2010.0 using the new IGRF-11 models as a reference is also reported. The high quality and consistency of main field models derived using vector satellite data is demonstrated; based on internal consistency DGRF-2005 has a formal root mean square vector field error over Earth's surface of 1.0 nT. Difficulties nevertheless remain in accurately forecasting field evolution only five years into the future.

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Section: Resultsmentioning

confidence: 99%

Section: Evaluation Of Predictivementioning

confidence: 99%

Evaluation of candidate geomagnetic field models for IGRF-11

et al. 2010

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“…Mandea et al, 2010), whose occurrence has been impeding a more efficient prediction at decadal timescale (Maus et al, 2008;Beggan and Whaler, 2010).…”

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confidence: 99%

Correction of artificial jumps in the historical geomagnetic measurements of Coimbra Observatory, Portugal

2014

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Abstract. The Coimbra Magnetic Observatory (International Association of Geomagnetism and Aeronomy code COI) inPortugal has a long history of observation of the geomagnetic field, spanning almost 150 yr since the first geomagnetic measurements in 1866. These long instrumental geomagnetic records provide very important information about variability of geomagnetic elements and indices, their trends and cycles, and can be used to improve our knowledge on the sources that drive variations of the geomagnetic field: liquid core dynamics (internal) and solar forcing (external).However, during the long life of the Coimbra Observatory, some inevitable changes in station location, instrument's park and electromagnetic environment have taken place. These changes affected the quality of the data collected at COI causing breaks and jumps in the series of geomagnetic field components and local K index. Clearly, these inhomogeneities, typically shift-like (step-like) or trend-like, have to be corrected or, at least, minimized in order for the data to be used in scientific studies or to be submitted to international databases.In this study, the series of local K index and declination of the geomagnetic field are analysed: the former because it allows direct application of standard homogenization methods and the latter because it is the longest continuous series produced at COI. For the homogenization, visual and statistical tests (e.g. standard normal homogeneity test) have been applied directly to the local geomagnetic K index series (from 1951 to 2012). The homogenization of the monthly averages of declination (from 1867 to 2012) has been done using visual analysis and statistical tests applied to the time series of the first differences of declination values, as an approximation to the first time derivative. This allowed not only estimating the level of inhomogeneity of the studied series but also detecting the highly probable homogeneity break points. These points have been cross-checked with the metadata, and the COI series have been compared with reference series from the nearest geomagnetic stations and, in the case of declination series, from the recent geomagnetic field model COV-OBS to set up the required correction factors. As a result, the homogenized series measured in COI are considered to be essentially free of artificial shifts starting from the second half of the 20th century, and ready to be used by the scientific community.

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“…doi:10.5047/eps.2010.07.005 average of the main field time derivative over the previous five years is considered to approximate well the secular variation over the next five years (Beggan and Whaler, 2010). More instantaneous estimates may nevertheless be proposed.…”

Section: Introductionmentioning

confidence: 99%

On the possibility of extending the IGRF predictive secular variation model to a higher SH degree

Silva

Maus²,

Hulot

et al. 2010

Earth Planet Sp

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The International Geomagnetic Reference Field (IGRF) is an internationally agreed global spherical harmonic model of the Earth's magnetic field of internal origin. It is currently computed every five years in the form of a model describing this field up to degree 13 at a reference epoch, plus a secular variation model up to degree 8, best estimating the linear evolution of this field over the following five years. Such a simple description of the field evolution is thought to provide a good enough prediction of the field, both for navigational and internationally agreed reference purposes (the very purpose of IGRF models). In particular, it assumes that any change in the field described by spherical harmonic degrees between 9 and 13 may be neglected over five years, given the uncertainties already involved in the determination of all other coefficients, and the practical accuracy needed for most IGRF applications. Recent progress in global field modelling based on increasingly accurate and numerous satellite data however show that all field coefficients can now be computed with much higher accuracy than possible in the past, and that higher degree secular variation coefficients could therefore also be considered for inclusion in IGRF models. The present short note intends to investigate the potential benefit of extending the IGRF predictive secular variation model to degrees higher than 8, given our current knowledge of the way the field behaves over time periods of five years.

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Forecasting secular variation using core flows

Cited by 21 publications

References 24 publications

Evaluation of candidate geomagnetic field models for IGRF-11

Evaluation of candidate geomagnetic field models for IGRF-11

Correction of artificial jumps in the historical geomagnetic measurements of Coimbra Observatory, Portugal

On the possibility of extending the IGRF predictive secular variation model to a higher SH degree

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