TERRAIN EFFECTS IN THE ATMOSPHERIC GRAVITY AND GEOID CORRECTIONS

In view of the smallness of the atmospheric mass compared to the mass variations within the Earth, it is generally assumed in physical geode sy that the terrain effects are negligible. Subsequently most models a ssume a spherical or ellipsoidal layering of the atmosphere. The remov al and restoring of the atmosphere in solving the exterior boundary va lue problems thus correspond to gravity and geoid corrections or the o rder of 0.9 mGal and -0.7 cm, respectively. We demonstrate that the gr avity terrain correction for the removal of the atmosphere is of the o rder of 50 muGal/km of elevation with a maximum close to 0.5 mGal at t he top of Mount Everest. The corresponding effect on the geoid may rea ch several centimetres in mountainous regions. Also the total effect o n geoid determination for removal and restoring the atmosphere may con tribute significantly, in particular by long wavelengths. This is not the case for the quasi geoid in mountainous regions.