Magnetic Field 4

1. Magnetic Field 4

2. Geochronology based on paired magnetic anomalies across mid-ocean ridges Fowler

3. Geochronology based on paired magnetic anomalies across mid-ocean ridges Fowler

4. Paleomagnetic stratigraphy Useful technique if parts of the section can be tied to isotopic dating of interbedded volcanic ash Samples analysed have shown that there are correlations with positive and negative epochs of the Geomagnetic Polarity Time Scale  parts of the Nagri and Dhok Pathan formations were deposited at the same time. Lillie

5. Paleolatitude studies 1. Measure the magnetic inclination (i) of the remanent magnetization from the time the rocks was formed. 2. Calculate the magnetic latitude () of the rock at the time it formed: tan i = 2 tan   = tan-1((tan i)/2) Assumptions: The magnetic poles coincided with the geographic poles; the rock was not tilted. Lillie

6. Paleomagnetic pole positions studies Polar-wander curves for North America and Europe (coinciding) The two continents did not move relative to each other during the time shown. Virtual pole position – direction toward a magnetic pole, together with a magnetic latitude Fowler

7. Source of the geomagnetic field - dynamo By moving through the existing magnetic field, the molten metal in the outer core creates a system of electric currents, spread out through the core, somewhat like disk dynamo. Currents create a magnetic field--a distribution of magnetic forces--and the essence of the self-sustaining dynamo problem is to find solutions such that the resulting magnetic field is also the input field required for generating the current in the first place.     Actually, that is only the lowest level of the problem, in which one is free to prescribe the motions. To solve the full problem, we also need information about the heat sources (the energy sources for these processes), and these sources must be able to drive motions which also solve the dynamo problem. Campbell, 2003; http://en.wikipedia.org/wiki/Dynamo_theory

8. Source of the geomagnetic field - dynamo Dynamo theory describes the process through which motion of a conductive body in the presence of a magnetic field acts to regenerate that magnetic field. This theory is used to explain the presence of anomalously long-lived magnetic fields in astrophysical bodies. Campbell, 2003; http://www.phy6.org/earthmag/dynamos2.htm

9. Simulation of the Earth’s dynamo http://www.psc.edu/science/Glatzmaier.html

10. Reversal of the Earth’s dynamo For that matter, why is it that instead of quietly fading away, as magnetic fields do when left to their own devices, Earth's magnetic field is still going strong after billions of years? Einstein is said to have considered it one of the most important unsolved problems in physics. With a year of computing on Pittsburgh's CRAY C90, 2,000 hours of processing, Glatzmaier and collaborator Paul Roberts of UCLA took a big step toward some answers. http://www.psc.edu/science/Glatzmaier.html

11. Reversal of the Earth’s dynamo 500 years before in the middle 500 years after the middle the middle of the reversal of the reversal of the reversal At about 36,000 years into the simulation the magnetic field reversed its dipole polarity over a period of only 1200 years. The image here is from an animated sequence showing how the field's structure changed. http://www.psc.edu/research/graphics/gallery/CORRECTno_earth.mpg

12. Other applications of the geomagnetic field Pipe corrosion Power failure during the magnetic storms Spacecraft anomalies due to solar storms (satellite failure) Telecommunication cables damage Modeling of atmosphere weather and climate Human impacts (MRI – different proton density) Earthquake prediction???

13. Other applications of the geomagnetic field Pipe lines corrosion Pipelines, particularly those that are buried under water, are often protected from corrosion by maintaining them under at a negative electrical potential with respect to the ground. During a magnetic storm a electric field induced along the pipeline may counteract the applied potential, removing the corrosion and possibly even accelerating corrosion. Reliable forecasts of geomagnetic activity may be useful in planning service schedules when testing may be disrupted by the geomagnetic activity.

14. Other applications of the geomagnetic field Power failure during the magnetic storms The problem in high voltage transformers was the cause of widespread failure of the Hydro-Quebec power grid resulting from the geomagnetic storm on 13/14 March 1989 – geomagnetically induced currents flow between the high voltage lines and the earth through transformer windings. Power systems in areas of igneous rock (gray) are the most vulnerable to the effects of intense geomagnetic activity because the high resistance of the igneous rock encourages geomagnetically induced currents (GICs) to flow in the power transmission lines situated above the rock. http://www.agu.org/sci_soc/eiskappenman.html

15. Telecommunication cables damage The operation of a transtlantic cable was severally affected during the magnetic storm 13/14 March 1989 (not a fiber optic cable) Other applications of the geomagnetic field

16. Other applications of the geomagnetic field Human impacts Geomagnetic disturbance effects upon man – correlation with disturbed mental behaviour – correlation with deaths due to miocardial infarction – correlation with convulsive seazures – etc. Magnetic Resonance Imaging – each group of human body has its own particular density of protons, with their characteristic responses to different processing signals Magnetic fields of the human body compared to geomagnetic field levels and sensitivity of SQUID magnetometer