Ocean tidal dynamo seen in CHAMP satellite magnetic data

Image: Visualisation of Magnetic Signature

The monitoring of ocean currents is of primary importance for understanding sea water quality, climate change and the global CO2 budget. Currently, global monitoring of ocean currents relies mainly on satellite radar measurements of the dynamic sea surface height.

From two years of high precision CHAMP satellite magnetic measurements it has now been found possible to map the magnetic signal of ocean tidal flow. Movement of the highly conductive sea water through the Earth's magnetic field induces electric fields and currents, similar to a dynamo. The electric currents generate secondary magnetic fields which have been identified in the CHAMP satellite data. See

Science, January 10, 2003, Volume 299, pp. 239-241.

Apart from opening new opportunities in the monitoring of ocean flow, the inclusion of ocean flow magnetic fields in our geomagnetic field modeling will raise the detectability of small scale crustal magnetisation.

Spectra and grids are given in the following table:

Tide Downloads
Download Listing ASCII 0.116 Jun 2004 ABG Power spectra of the Z component
of the magnetic field at
observatories in and around the Indian Ocean
Download ASCII AMS
Download ASCII CZT
Download ASCII GNA
Download ASCII HER
Download ASCII LRM
Download ASCII TAN
Download Listing ASCII 5.5 Jun 2004 Power spectra of CHAMP total intensity measurements over the Indian Ocean.
Download Listing ASCII 7.3 Jun 2004 K1 1x1 degree grids of the predicted global magnetic field
for each major tidal constituent, computed by Alexei Kuvshinov.
The columns are phi (longitude), theta (co-latitude),
Br_re, Br_im, Btheta_re, Btheta_im, Bphi_re, Bphi_im,
where B = B_re cos(phase) + B_im sin(phase).
Download ASCII K2
Download ASCII M2
Download ASCII N2
Download ASCII O1
Download ASCII P1
Download ASCII Q1
Download ASCII M2 Same as above with the effect of variable salinity on conductivity taken into account. Salinities taken from the ECCO ocean model.

Handouts and movies are given in the following table:

Ocean/Tide Downloads
Download Poster PDF 1.8 Dec 2007 Where do we stand on identifying motional induction in the oceans?, presented at AGU Fall Meeting 2007
Download Poster
PDF 1.4 Dec 2002 Tide Poster DIN A4 handout, Page 1
Download PDF 0.4 Tide Poster DIN A4 handout, Page 2
Download Animation mov 4.4 Dec 2002 Final comparison of M2 magnetic field signal -
observed against predicted
Download swf 4.4
Download Animation mov 3.6 Dec 2002 Observed M2 magnetic field signal against TPXO sea surface height
Download swf 4.4
Download Animation mov 3.6 Dec 2002 Observed M2 magnetic field signal against TPXO sea surface height. In this case, however, the field lost in filtering has been added back on to the observation. This lost field was obtained from the difference between the unfiltered and filtered prediction. This comparison has to be taken with a pinch of salt since a prediction from the TPXO model was actually added onto the observations. Hence, the two images are not derived independently as in the above 2 movies.
Download swf 4.4