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Trapped Radiation ENvironment model Development


[ Name | Synopsis | Arguments | Description | Diagnostics | Common Blocks | Dependencies | See Also | Reported Bugs | Examples ]


    Subroutine UL220 - get information on a magnetic field line segment


      RECORD /zgeo/ mpos
      INTEGER*4     ifail, nfbm
      REAL*8        alpha(nfbm), fbm(nfbm), flm(nfbm)
      REAL*8        fkm(nfbm), fsm(nfbm), fbeq, fs(nfbm)
      CALL UL220 (mpos, alpha, nfbm, fbm, flm, fkm, fsm, fbeq, fs, ifail)


    Geographic location (GEO) [in]
    Local pitch angles [in]
    Number of pitch angles [in]
    Magnetic field intensity at the mirror points [out]
    McIlwain's shell parameter [out]
    Kaufman parameter K [out]
    Arc length of the field line segment between the mirror points [out]
    Lowest magnetic field intensity along the field line [out]
    Arc length of the field line segment from the northern mirror point to mpos [out]
    Error flag (see diagnostics) [out]


    The subroutine UL220 computes magnetic coordinates such as Bm and L associated to a magnetic field line segment passing through the geographic position mpos. The subroutine accepts as input a list of local pitch angles. Note that the values set in the argument alpha must be sorted by increasing order (from 0 to 90 degree). The magnetic field line passing through the position mpos is traced until all the mirror points are encountered. For each value of argument alpha, a pair of mirror points are determined and the corresponding arguments fbm, flm, fkm, fsm, fs are evaluated.

    Note that some errors may occur during the process for a subset of local pitch angles. As far as possible, the subroutine UL220 does not stop on these errors and continues the process for the other pitch angle values. As a trace of such an error, the corresponding value of argument flm is set to a negative value. The list of possible errors are given in the table below.

    Value of flmerror diagnostic
    -1 The magnetic field line reaches too high geomagnetic latitude (see diagnostic -53003)
    -2 The magnetic field crosses the magnetopause (see diagnostic -53301)
    -3 The reached magnetic field intensity is outside valid limits (see diagnostic -53002)
    -4 Maximum number of steps along the magnetic field line has been reached (see diagnostic -42009)
    -5 The magnetic field line goes too deep inside the Earth (see diagnostics -53001 and -53004)
    -6 Out of allocated memory (see diagnostics -42301 and -42401)
    -7 The magnetic field line pass through a local maximum
    -8 An error occurred in the interpolation routine (see diagnostics -428** and -426**)
    -9 An error occurred in the evaluation of I (see diagnostics -230** and -240**)
    -10Not documented


  • Heynderickx, D., Lemaire, J., and Daly, E.J., Historical review of the different procedures used to compute the L parameter, Aeronomica Acta A-Nb 380 (1994), J. Nuclear Tracks Radiat. Meas. (1995)
  • McIlwain, C.E., Coordinates for mapping the distribution of magnetically trapped particles, JGR 66 (1961) 3681-3691
  • Roederer, J.G., Dynamics of geomagnetically trapped radiation, Springer-Verlag (1970)


    In version 2.02 in earlier, some L values are not evaluated when more than one local pitch angle is requested.


    -22001, Invalid value of alpha
    -22002, Values of alpha are not increasing or invalid values
    -22003, Do not find a pair of mirror points
    -22004, Unable to trace correctly the field line segment

Common Blocks

    UC160, general constants
    UC170, temporary magnetic field line
    UC190, control parameters, set 1


Called by



    UM530, evaluate the magnetic field vector
    UF420, trace a magnetic field line segment passing through a given position
    UL230, evaluate the integral invariant coordinate I
    UL240, evaluate the Hilton's function

See also

    FAQ G.05 Which are the coordinates and units used ?

Reported Bugs



    #2, evaluation of the (B, L) coordinates
    #7, iso-contour of the shell parameter