The barotropic vorticity equation is the simplest way for forecasting the movement of Rossby waves ( that is, the hPa geopotential height ) over a limited amount of time ( a few days ).
32.
The geopotential height of this point was calculated in 1986 as part of the United European Levelling Network ( UELN ), based on the Amsterdam Ordnance Datum, which represents the average level of the North Sea.
33.
A geopotential field U is constructed, being the sum of a gravitational potential \ Psi and the known centrifugal potential \ Phi, that " has the GRS80 reference ellipsoid as one of its equipotential surfaces ".
34.
"' Geopotential function "'is a function that at each point is equal to a constant minus the energy that would be acquired by a unit mass in falling from rest at infinity to the point in question.
35.
Since the atmosphere at a height of approximately is mostly divergence-free, the barotropic model best approximates the state of the atmosphere at a geopotential height corresponding to that altitude, which corresponds to the atmosphere's pressure surface.
36.
Where the \ phi _ x are geopotential height fields with \ phi _ 1 > \ phi _ 0, f is the Coriolis parameter, and \ mathbf { k } is the upward-pointing unit vector in the vertical direction.
37.
In the above table, " geopotential altitude " is calculated from a mathematical model that adjusts the altitude to include the variation of gravity with height, while " geometric altitude " is the standard direct vertical distance above mean sea level.
38.
One can construct a simple model geopotential U that has as one of its equipotential surfaces this reference ellipsoid, with the same model potential U _ 0 as the true potential W _ 0 of the geoid; this model is called a " normal potential ".
39.
Once a clean, smooth geopotential field U has been constructed matching the known GRS80 reference ellipsoid with an equipotential surface ( we call such a field a " normal potential " ) we can subtract it from the true ( measured ) potential W of the real Earth.
40.
As part of this work, he introduced normal heights, which can be calculated from geopotential numbers ( obtained from precise levelling ) without needing the uncertain value of gravity along the plumbline of a point, i . e ., inside the continental crustal rock under the point.
