NAME¶
mgd77magref - Evaluate the IGRF or CM4 magnetic field models
SYNOPSIS¶
mgd77magref [
inputfile ] [
-A[
+aalt+tdate+y] ] [
-Ccm4file ] [
-DDstfile ] [
-Ef107file ] [
-Fflags ] [
-G ] [
-H[
i][
nrec] ] [
-Sc|
llow/high ] [
-V ] [
-:[
i|
o] ] [
-b[
i|
o][
s|
S|
d|
D[
ncol]|
c[
var1/...]]
] [
-f[
i|
o]
colinfo ] [
-m[
i|
o][
flag] ]
DESCRIPTION¶
mgd77magref will evaluate the IGRF or the CM4 geomagnetic models at the
specified locations and times.
OPTIONS¶
No space between the option flag and the associated arguments.
- inputfile
- Contains the moments in space-time where we want to evaluate the magnetic
reference field. The first two columns must contain longitude and latitude
(however, see -: for latitude and longitude instead). Normally, the
third and fourth columns must contain altitude (in km) and time,
respectively, but if one or both of these are constant for all records
they can be supplied via the -A option instead and are thus not
expected in the input file. If no input file is given we read
stdin. A note about the CM4 validity domain. The core field of CM4
is valid from 1960-2002.5 but the ionospheric and magnetospheric fields
are computed after the Dst and F10.7 coefficient files. We
extended here those coefficient files up to 2007, which means that one can
compute external contributions up until 2007 but the Secular Variation
will be biased (non reliable). New indices files may be retrieved
from:ftp://ftp.ngdc.noaa.gov/STP/GEOMAGNETIC_DATA/INDICES/DST/ (the
Dst coefficients) and
ftp://ftp.ngdc.noaa.gov/STP/SOLAR_DATA/SOLAR_RADIO/FLUX/ (The F10.7
index file is a MONTHPLT.ABS). NOTE: since the Dst files in the
.../DST/ directory are still only up to 2007, for GMT4.5.3 we extended the
Dst until April 2010 by reformatting the data in the preliminary
file Est_Ist_index_0_mean.pli, which is at
ftp://ftp.ngdc.noaa.gov/STP/GEOMAGNETIC_DATA/INDICES/EST_IST/
- -A
- Adjusts how the input record is interpreted. Append +a to set a
fixed altitude (in km) that should apply to all data records
[Default expects altitude to be in the 3rd column of all records].
Append +t to set a fixed time that should apply to all data
records [Default expects time to be in the 4th column of all
records]. Finally, append +y to indicate that all times are
specified as decimal years [Default is ISO dateTcolck
format].
- -C
- Specify an alternate CM4 coefficient file [umdl.CM4].
- -D
- Specify an alternate file with hourly means of the Dst index for CM4
[Dst_all.wdc]. Alternatively, simply specify a single index to apply for
all records.
- -E
- Specify an alternate file with monthly means of absolute F10.7 solar radio
flux for CM4 [F107_mon.plt]. Alternatively, simply specify a single flux
to apply for all records.
- -F
- Selects output items; flags is a string made up of one or more of
these characters:
r means output all input columns before adding the items below
t means list total field (nT).
h means list horizontal field (nT).
x means list X component (nT, positive north).
y means list Y component (nT, positive east).
z means list Z component (nT, positive down).
d means list declination (deg, clockwise from north).
i means list inclination (deg, positive down).
Append one or more number to indicate the requested field contribution(s):
0 means IGRF field (no combinations allowed)
1 means CM4 Core field
2 means CM4 Lithospheric field
3 means CM4 Primary Magnetospheric field
4 means CM4 Induced Magnetospheric field
5 means CM4 Primary ionospheric field
6 means CM4 Induced ionospheric field
7 means CM4 Toroidal field
9 means Core field from IGRF and other contributions from CM4. DO
NOT USE BOTH 1 AND 9.
Appending several numbers (1-7) will add up the different contributions. For
example -Ft/12 computes the total field due to Core and
Lithospheric sources. Two special cases are allowed, which mix which Core
field from IGRF and other sources from CM4. -Ft/934 computes
Core field due to IGRF plus terms 3 and 4 from CM4 (but you can add
others). -Ft/934 the same as above but output the field
components. The data is written out in the order they appear in
flags [Default is -Frthxyzdi/1].
- -G
- Specifies that coordinates are geocentric [geodetic].
- -H
- Input file(s) has header record(s). If used, the default number of header
records is N_HEADER_RECS. Use -Hi if only input data should
have header records [Default will write out header records if the input
data have them]. Blank lines and lines starting with # are always
skipped.
- -L
- Computes J field vectors from certain external sources.
r means output all input columns before adding the items below (all
in Ampers/m).
t means list magnitude field.
x means list X component.
y means list Y component.
z means list Z or current function Psi.
Append a number to indicate the requested J contribution:
1 means Induced Magnetospheric field.
2 means Primary ionospheric field.
3 means Induced ionospheric field.
4 means Poloidal field.
- -Sc
- Limits the wavelengths of the core field contribution to the band
indicated by the low and high spherical harmonic order [1/13].
- -Sl
- Limits the wavelengths of the lithosphere field contribution to the band
indicated by the low and high spherical harmonic order [14/65].
- -V
- Selects verbose mode, which will send progress reports to stderr [Default
runs "silently"].
- -:
- Toggles between (longitude,latitude) and (latitude,longitude) input and/or
output. [Default is (longitude,latitude)]. Append i to select input
only or o to select output only. [Default affects both].
- -bi
- Selects binary input. Append s for single precision [Default is
d (double)]. Uppercase S or D will force
byte-swapping. Optionally, append ncol, the number of columns in
your binary input file if it exceeds the columns needed by the program. Or
append c if the input file is netCDF. Optionally, append
var1 /var2/... to specify the variables
to be read. [Default is 4 input columns unless -A is used].
- -bo
- Selects binary output. Append s for single precision [Default is
d (double)]. Uppercase S or D will force
byte-swapping. Optionally, append ncol, the number of desired
columns in your binary output file. [Default is reflected by
-F].
- -m
- Multiple segment file(s). Segments are separated by a special record. For
ASCII files the first character must be flag [Default is '>'].
For binary files all fields must be NaN and -b must set the number
of output columns explicitly. By default the -m setting applies to
both input and output. Use -mi and -mo to give separate
settings to input and output.
TIME SETTINGS¶
If binary input files are used then absolute time are stored as time relative to
the selected epoch. However, since the epoch used is not stored in the data
files there can be problems decoding the correct time. The mgd77 supplement
uses the Unix time system as its default; thus you should make sure that
binary data files with time uses the same system (see the GMT default
TIME_SYSTEM).
EXAMPLES¶
To get the CM4 Total field, Declination and Inclination due to all but
lithospheric and toroidal field at a one point location and decimal time
2000.0, try
echo -28 38 0 2000.0 |
mgd77magref -A+y
-F tdi/13456
To do the same as above but at noon (Universal Time) of first May 2001, try
echo -28 38 0 2001-05-01T12:00:00 |
mgd77magref -F tdi/13456
SEE ALSO¶
GMT(1) mgd77info(1) mgd77list(1) mgd77manage(1)
mgd77track(1)
REFERENCES¶
Wessel, P., and W. H. F. Smith, 2014, The Generic Mapping Tools (GMT) version
4.5.12 Technical Reference & Cookbook, SOEST/NOAA.
Wessel, P., and W. H. F. Smith, 1998, New, Improved Version of Generic Mapping
Tools Released, EOS Trans., AGU, 79 (47), p. 579.
Wessel, P., and W. H. F. Smith, 1995, New Version of the Generic Mapping Tools
Released, EOS Trans., AGU, 76 (33), p. 329.
Wessel, P., and W. H. F. Smith, 1995, New Version of the Generic Mapping Tools
Released,
http://www.agu.org/eos_elec/95154e.html, Copyright 1995 by the
American Geophysical Union.
Wessel, P., and W. H. F. Smith, 1991, Free Software Helps Map and Display Data,
EOS Trans., AGU, 72 (41), p. 441.
"Comprehensive Modeling of the Geomagnetic Field", see
http://denali.gsfc.nasa.gov/cm/.
"The International Geomagnetic Reference Field (IGRF)", see
http://www.iugg.org/IAGA/iaga_pages/pubs_prods/igrf.htm.