GCM: NSSDC vs SWIM

[Robert Wagner]

Hallo,

entschuldigt den kryptischen Betreff. Hier mein Problem, vielleicht ist das jemandem ja schon mal aufgefallen:

Mit dem IGRF/DGRF-Konverter berechne ich meine CGM-Latitude (Standort: N48.3100E011.5600) zu 43.56.

Andererseits berechnet der Geomagnetic Latitude Calculator von SWIM die CGM-Latitude für die gegebenen Koordinaten zu N48.7440.

Welche Angabe ist korrekt? Die vom IGRF/DGRF-Konverter, nehme ich an. Aber warum weicht die SWIM-Berechnung so stark ab? Weil Näherungen an das Modell benutzt werden, die nur für Nordamerika gelten?

Viele Grüsse,
Robert

[Ulrich Rieth]

Hallo Robert!

Deswegen hatten Peter Kuklok und ich im Oktober 2002 schonmal Kontakt mit Cary Oler.
Hier ein Auszug aus seiner Antwort.
Gruß

Ulrich

Code: Alles auswählen

> I have a question about the geomag. lat. calculator in SWIM.
> If I use it, my latitude is give as 50.98N.
> On the other hand there are several calculators on the net which give a
> value arround 45N.
> Here is one of them: http://nssdc.gsfc.nasa.gov/space/cgm/cgm.html
> If you have time, could you please explain me the difference between your
> code and the code these calculators use. And above all, what is the better
> modell to use for getting comparable values to check the advantage or
> disadvantage of an individual place?

The CGM code is more accurate at calculating the geomagnetic coordinates of
an observer. The code in our software is based on a simpler dipole model
(not the simplest model - an intermediate model). However, you can't look at
the CGM coordinates and relate them to our definitions of "high", "middle"
and "low" latitudes because those definitions are based on a dipole model.
I'm not exactly certain why we did this - it was done many years ago (almost
a decade ago). It works well enough for purposes of defining latitude
boundaries for auroral observers, but it wouldn't work well enough if you
wanted precise geomagnetic coordinates based on geographic coordinates.

Most people would probably lean towards referring you to the CGM-related
models for determining the advantages or disadvantages of individual places
since it is a more accurate method of computing coordinates.