MIRACLE data analysis tools

3) 1D-field separation of the X component of a north-south IMAGE magnetometer chain into its internal and external parts:

- Short description of the analysis method:

The X component data of a 1D north-south chain is separated into the parts caused by internal (i.e., flowing below the ground, mainly geomagnetically induced currents) and external (i.e., flowing above the ground, mainly ionospheric currents).
Two different algorithms have been developed: Both methods can be carried out for a whole range of time quickly.

- Input data requirements:

IMAGE magnetometer data of the chain NUR-NAL (X and Z components; see MIRACLE map for stations overview).

- Output quantities:

Internal and external parts of the X component on the ground. (Fourier method: Equally spaced on a north-south profile; Spatial integral transform method: On the original magnetic data points)

- Literature:

- Example plots:

This is the input data: measured X components of MIRACLE magnetometers on January 17, 1998, between 1630 UT and 1800 UT, for the approximately north-south aligned chain of stations reaching from NUR to NAL (see MIRACLE map). The colour bar indicates the value of the X component in nT for the respective times and latitudes.


The plot below shows the separated external part of the X component (on the ground) during the same interval as for the input data.  Note that the general structure of the external part is similar to that of the total measured field (see input). For this example, the Fourier space method was used.


The separated internal part of the X component (on the ground). This part is usually somewhat smaller than the external part, and shows less structure.


Finally, below is the ratio between the minimum/ maximum of the internal part and the same value of the total X component. This quantity describes how much of a "chain AL or AU index" would be caused by the internal part of the currents. Note that the value increases clearly after 1730 UT when the westward electrojet intensifies at about 75 degrees of latitude (over the ice sea). After that time, the ratio values come mostly from this westjet, before they come from the eastjet over the land flowing at about 70 degrees latitude. The westjet over the sea seems to cause relatively larger internal currents, probably due to high sea water conductance.


For further questions contact Olaf Amm (regarding the Fourier space method), or Ari Viljanen (regarding the spatial integral transform method).

Maintained by: Olaf Amm
Latest update: 14. 2. 2000