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evert in sign. The reason for this is that due to the Earth’s curvature, the
attraction effect around the zone of 3° - 5° is nearly at the same height level as
the gravity meter. The attraction from the zone which is more than 5° from the
gravity station is already below the height level of the gravity meter. Thus, the
direction of the attraction effect changes in sign. These characteristics are also
visible in the tabulated Green’s functions in Merriam (1992).
In order to estimate for which area the attraction effect using 3D data should
be computed, a reduction based on 2D surface data (pressure and temperature)
from ECMWF and a standard atmosphere is calculated for comparison (Fig.5).
Figure 5
Attraction effect from the zones indicated in Fig.2 computed with 2D with
temperature data from 2007/01/01 to 2007/12/31 (different scaling)