TY  - STD
AU  - A. Bernard, M. Menvielle
PY  - 2010//
TI  - K GEOMAGNETIC INDICES INFLUENCED BY DATA SAMPLING
N2  - XIVth IAGA WORKSHOP ON GEOMAGNETIC OBSERVATORY INSTRUMENTS, DATA ACQUISITION AND PROCESSING; September 13 – 23, 2010; Changchun, Jilin Province, China.The K index was devised by Bartels et al. (1939) to provide an objective monitoring of the irregular geomagnetic activity, namely the magnetic signature of the solar wind and IMF effects on the Earth's magnetic field. It was then routinely used to monitor the magnetic activity at permanent magnetic observatories, as well as at temporary stations. The increasing number of digital and sometimes unmanned observatories and the creation of INTERMAGNET put the question of computer production of K at the centre of the debate. Four algorithms were selected during the Vienna meeting (1991), and endorsed by IAGA for computer production of K indices To start with, we recall how geomagnetic data sampling may impact on computer-derived values of K-indices, and lead to underestimated values resulting in a statistical bias. We use one of the algorithms endorsed by IAGA, the so-called FMI algorithm developed by the Finnish Meteorological Institute, to investigate the impact of the geomagnetic data sampling interval on computer produced K values. We use this algorithm since it gives results that are fairly comparable to those hand-scaled on analogue magnetograms by an experienced observer.The impact of the sampling interval on computer-produced K values is investigated through the comparison of the computer derived K values for the period 2009, January 1st to 2010, May 31 at the Port aux Français magnetic observatory using magnetic data series with different sampling rate (the smaller: 1 second; the larger 1 minute). The impact is investigated on both 3-hour range values and K indices data series, as a function of the activity level, for low and moderate geomagnetic activity (there was no intense magnetic storm during 2009, and very few during the first months of 2010).
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ID  - A.Bernard2010
ER  -