UL220
[ Name  Synopsis  Arguments  Description  Diagnostics  Common Blocks  Dependencies  See Also  Reported Bugs  Examples ]
Name

Subroutine UL220  get information on a magnetic field line segment
Synopsis
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)
Arguments

mpos
 Geographic location (GEO) [in]

alpha
 Local pitch angles [in]

nfbm
 Number of pitch angles [in]

fbm
 Magnetic field intensity at the mirror points [out]

flm
 McIlwain's shell parameter [out]

fkm
 Kaufman parameter K [out]

fsm
 Arc length of the field line segment between the mirror points [out]

fbeq
 Lowest magnetic field intensity along the field line [out]

fs

Arc length of the field line segment from the northern mirror point to
mpos
[out] 
ifail
 Error flag (see diagnostics) [out]
Description

The subroutine UL220 computes magnetic coordinates such as B_{m}
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 flm  error 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**) 
10  Not documented 
References
 Heynderickx, D., Lemaire, J., and Daly, E.J., Historical review of the different procedures used to compute the L parameter, Aeronomica Acta ANb 380 (1994), J. Nuclear Tracks Radiat. Meas. (1995)
 McIlwain, C.E., Coordinates for mapping the distribution of magnetically trapped particles, JGR 66 (1961) 36813691
 Roederer, J.G., Dynamics of geomagnetically trapped radiation, SpringerVerlag (1970)
History

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

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
Dependencies
Called by

None
Calls

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

None