Geomagnetism

Ocean tidal dynamo seen in CHAMP satellite magnetic data

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
	Type	Format	Mbyte	Date	Contents
	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
		ASCII			AMS
		ASCII			CZT
		ASCII			GNA
		ASCII			HER
		ASCII			LRM
		ASCII			TAN
	Listing	ASCII	5.5	Jun 2004	Power spectra of CHAMP total intensity measurements over the Indian Ocean.
	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).
		ASCII			K2
		ASCII			M2
		ASCII			N2
		ASCII			O1
		ASCII			P1
		ASCII			Q1
		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
	Type	Format	Mbyte	Date	Contents
	Poster	PDF	1.8	Dec 2007	Where do we stand on identifying motional induction in the oceans?, presented at AGU Fall Meeting 2007
	Poster Handout	PDF	1.4	Dec 2002	Tide Poster DIN A4 handout, Page 1
		PDF	0.4		Tide Poster DIN A4 handout, Page 2
	Animation	mov	4.4	Dec 2002	Final comparison of M2 magnetic field signal - observed against predicted
		swf	4.4
	Animation	mov	3.6	Dec 2002	Observed M2 magnetic field signal against TPXO sea surface height
		swf	4.4
	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.
		swf	4.4

Stefan Maus