European Space Agency

Royal Belgian Institute for Aeronomy

uf420 - trace a magnetic field line segment passing through a given position

subroutine  uf420(mpos, fbm, nfbm, falt, ifail)

Parameters:

• mpos [zgeo,in] :: The geographic position (GEO) through which the searched magnetic field line is passing

• fbm (nfbm) [real8,in] :: Boundary conditions on the magnetic field intensity

• nfbm [integer4,in] :: Number of boundary conditions on the magnetic field intensity

• falt [real8,in] :: Boundary condition on the altitude.

• ifail [integer4,out] :: error flag (see Diagnostics)

Description

The subroutine uf420() traces a magnetic field line segment passing through the geographic position mpos. The magnetic field line segment is limited by one of the following boundary conditions :

• the altitude falt has to be reached;

• the magnetic field intensity fbm(1) has to be reached.

The condition on the altitude can be avoided by setting falt to a value lower than -500. The different points along the field line segment are stored in the common block uc170. It includes the points corresponding to the boundary conditions, as well as, the points corresponding to the magnetic field intensities fbm(2), …, fbm(nfbm). Note that the intensities set in the array fbm have to be strictely decreasing : fbm(1) > fbm(2) > fbm(nfbm).

History

• From version 1.13 to version 2.00, the algorithm has been improved for the case where the first boundary condition on the magnetic field intensity is close to the minimum value of the magnetic field intensity along the field line segment.

Diagnostics

• -42001, incorrect boundary conditions

• -42002 or -42004, strange behaviour of the field line near the altitude boundary condition

• -42003 or -42006, strange behaviour of B along the field line

• -42005, problem with the boundary condition on the altitude

• -42007, problem with the boundary conditions on B

• -42008 or -42010, find the minimum of B before any one of the boundary conditions

• -42009, too many points along the field line segment

• -42011, error in UF428 detected a posteriori

Common Blocks

• uc160 - general constants

• uc170 - temporary magnetic field line

• uc190 - control parameters, set 1

Dependencies

Called by

• ul220 - get information on a magnetic field line segment

• uf410 - search the geographic position of a magnetic field line

• uf417 - search the geographic position of a magnetic field line

• uf411 - search a local magnetic equator

Calls

• uf421 - initialize and close a field line segment

• uf422 - follow a field line until a boundary condition is reached

• uf424 - search the lowest B value

• uf429 - transpose a field line segment

See also

• G.05 - What are the coordinates and units used ?

Reported Bugs

None

Examples

• Ex. #6. visualisation of a drift shell

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UNILIB/tags/v3.02