Geomagnetic Indices

Menvielle, M.; Iwamoto, Toshihiko; Marchaudon, A.; Nosé, M.

doi:10.1007/978-90-481-9858-0_8

Cited by 70 publications

(65 citation statements)

References 112 publications

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“…Menvielle et al, 2011). The daily sum of the eight 3 h Ki values ( K) and monthly means of this sum (< K > monthly ) have been previously used as representative of the irregular geomagnetic activity observed at a certain station (see e.g.…”

Section: Data Descriptionmentioning

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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Section: Data Descriptionmentioning

confidence: 99%

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

2014

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“…activity during the period of interest. In addition, we have also used the αλ longitude sector indices of magnetic activity (Menvielle et al, 2011) because magnetic activity may display marked variations in longitude. Each sector position is defined by an average longitude and an index at an intermediate longitude is linearly interpolated.…”

Section: Methods Of Statistical Analysismentioning

confidence: 99%

Critical analysis of the electrostatic turbulence enhancements observed by DEMETER over the Sichuan region during the earthquake preparation

Onishi

Berthelier

Kamogawa

2011

Nat. Hazards Earth Syst. Sci.

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Abstract. In this paper, we report initial results from a detailed statistical study of the plasma waves observed by the DEMETER satellite over the Sichuan region during a period of 20 days encompassing the large earthquake of magnitude M = 7.9 that occurred on 12 May 2008. The main objective of this paper is to present a statistical method to process and analyze plasma wave data and assist in detecting possible earthquake precursors among larger irregular disturbances arising from the natural variability of the ionized environment of the Earth. This method, presently used for dayside observations, involves two stages. First, VLF wave spectra are processed to recognize the various types of plasma waves usually observed at mid and low latitudes and derive a reduced number of parameters that fully characterize these emissions and may be conveniently used for a detailed statistical study. In a second stage, we perform a statistical analysis of the results by taking into account two "reference zones" displaced respectively 30 • eastward and westward from the "epicentre zone". Plasma and wave disturbances possibly induced by earthquakes in preparation are likely to maximize close to the "epicentre" zone, while natural disturbances associated, in particular, with the varying magnetic activity are rather uniform over a wider longitude sector, thus enabling the use of observations over the reference zones as a base line. The initial results of this study show a deviation of the power spectrum of electrostatic turbulence in the epicentre zone about 6 days prior to the earthquake but no significant anomalous variations can Correspondence to: T. Onishi (tatsuo.onishi@latmos.ipsl.fr) be observed on other characteristics of plasma waves. From the analysis of the data over the two reference zones and using recently produced sector magnetic activity indices, we conclude that the enhancement of electrostatic turbulence is associated with magnetospheric processes rather than with pre-seismic activity.

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“…However, other indices have 15-minute values (PC) and even 1-minute values (the new 1-minute Dst). A detailed description of the numerous geomagnetic indices is out of the scope of this paper, but can be found, for instance, in Menvielle (2011).…”

Section: Long-term Evolution Of the Geomagnetic Responsementioning

confidence: 99%

Geomagnetic response to solar and interplanetary disturbances

Sáiz

Cerrato

Cid

et al. 2013

J. Space Weather Space Clim.

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The space weather discipline involves different physical scenarios, which are characterised by very different physical conditions, ranging from the Sun to the terrestrial magnetosphere and ionosphere. Thanks to the great modelling effort made during the last years, a few Sun-to-ionosphere/thermosphere physics-based numerical codes have been developed. However, the success of the prediction is still far from achieving the desirable results and much more progress is needed. Some aspects involved in this progress concern both the technical progress (developing and validating tools to forecast, selecting the optimal parameters as inputs for the tools, improving accuracy in prediction with short lead time, etc.) and the scientific development, i.e., deeper understanding of the energy transfer process from the solar wind to the coupled magnetosphere-ionosphere-thermosphere system. The purpose of this paper is to collect the most relevant results related to these topics obtained during the COST Action ES0803. In an end-to-end forecasting scheme that uses an artificial neural network, we show that the forecasting results improve when gathering certain parameters, such as X-ray solar flares, Type II and/or Type IV radio emission and solar energetic particles enhancements as inputs for the algorithm. Regarding the solar wind-magnetosphere-ionosphere interaction topic, the geomagnetic responses at high and low latitudes are considered separately. At low latitudes, we present new insights into temporal evolution of the ring current, as seen by Burton's equation, in both main and recovery phases of the storm. At high latitudes, the PCC index appears as an achievement in modelling the coupling between the upper atmosphere and the solar wind, with a great potential for forecasting purposes. We also address the important role of small-scale field-aligned currents in Joule heating of the ionosphere even under non-disturbed conditions. Our scientific results in the framework of the COST Action ES0803 cover the topics from the short-term solar-activity evolution, i.e., space weather, to the long-term evolution of relevant solar/heliospheric/magnetospheric parameters, i.e., space climate. On the timescales of the Hale and Gleissberg cycles (22-and 88-year cycle respectively) we can highlight that the trend of solar, heliospheric and geomagnetic parameters shows the solar origin of the widely discussed increase in geomagnetic activity in the last century.

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Geomagnetic Indices

Cited by 70 publications

References 112 publications

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

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

Critical analysis of the electrostatic turbulence enhancements observed by DEMETER over the Sichuan region during the earthquake preparation

Geomagnetic response to solar and interplanetary disturbances

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