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Gravimetric effects induced by vertical air mass shifts at Medicina

Dietrich Simon

1998
unpublished

The gravimetric effects of vertical air mass displacements were computed at the locations of six European stations, where superconducting gravimeters are recording. The modelling was made based on radiosonde data using the AMACON software of SIMON (2003). The length of the g c (t) model curves is 8 years (1998/01/01-2005/12/31) for Medicina station / Italy and 7 years (1998/01/01-2004/12/30), respectively, for the five other stations Bad Hom-burg/Germany, Wettzell/Germany, Moxa/Germany,
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... ech Republic and at Vi-enna/Austria. As before the modelling was made with a general sampling rate of 24 hours (12 h of any day). Some examples of g c (t) model curves are given where the sampling rates are shorter. 1. Background of the modelling Four years ago the existence of a gravimetrical component g c (t) induced by vertical air mass shifts in the case of a constant ground air pressure was firstly shown by SIMON (2002). The effect is caused by an unaccelerated rising of warmed (lighter) and the sinking of colder (heavier) air particles, respectively. The air mass attraction varies due to these vertical air mass shifts according to A c (t) = A(t)-A p (t) = A(t)-r AP * P(t) (1) A(t): air mass attraction at the measuring point G, P(t): surface pressure at the measuring point G A p (t), A c (t): surface pressure-dependent and independent component of A(t) r AP = 0.40 µGal/hPa: regression coefficient (SIMON, 2003). The corresponding component g c (t) of the gravity variation has the opposite sign. It is obtained from g c (t) =-A c (t) + C, C = constant (2) The seasonal warming /cooling of air masses is an effect of low regional variability. As a consequence the data of a network of eight radiosonde stations located in Germany, Austria, Po-land and Italy were enough for the calculation of the g c (t)-variations at the mentioned six European gravimeter stations. The radiosonde stations were seldom situated in the direct vicinity of a gravimeter location, as for instance at Medicina and Vienna. Therefore the g c (t) modelling was made in most cases according the so-called 3 stations method (SIMON, 2003).

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