SIO 229 Part II Geomagnetism. Lecture 1 Introduction to the geomagnetic field

Transcription

1 SIO 229 Part II Geomagnetism Lecture 1 Introduction to the geomagnetic field

2 Why study Earth's magnetic field Schematic picture of Earth's magnetic field interacting with the solar wind (credit: NASA) Anomaly mapping, Air traffic control, Mobile phones

3 Fundamental science: the geodynamo The geodynamo operating in Earth's core (credit: J. Aubert, IPGP) Long standing scientific quest to understand how the dynamo in Earth's core is operating and the mechanisms by which it evolves.

4 A little bit of history 1st century AD Earliest known magnetic compass invented by the Chinese Petrus Peregrinus describes a floating compass and writes about the polarity of magnets. William Gilbert concludes Earth is magnetic, Henry Gelibrand documents the magnetic field changes with time, Edmund Halley and Alexander von Humboldt carry out magnetic surveys. Danish physicist Hans Christian Ørsted discovers the relationship between electricity and magnetism. Michael Faraday establishes the first basis for the magnetic field concept in physics. Carl Friedrich Gauss publishes the first geomagnetic field model demonstrating the dipolar nature of Earth's magnetic field. (credit: ESA)

5 Front page of the 1628 edition of De Magnete [Gilbert, 1600].

6 Halley s 1702 AD map of declination He knew that the field was not static. Edmond Halley, Wednesday, May 9, 2012

7 A little bit of history The Carnegie, a yacht made almost entirely of wood and other non-magnetic materials, sets sail to gather oceanic magnetic data. Joseph Larmor suggests that dynamos could naturally sustain themselves in conducting fluids, explaining how the geomagnetic field originates deep inside Earth. Nasa launches Magsat to map Earth's magnetic field. Denmark launches the Ørsted to measure Earth's magnetic field. Scientists conclude that the magnetic poles wander. ESA launches Cluster mission to study interaction of solar wind with the magnetosphere. Germany launches CHAMP satellite to study variations in magnetic and gravity fields. (credit: ESA)

8 November 2013: SWARM (credit: ESA)

9 'South Atlantic Anomaly' The white dots indicate positions where the TOPEX/Poseidon satellite experienced single event upsets. (credit: ESA)

10 Pole reversals imprinted in the seafloor (credit: ESA)

11 Components of the geomagnetic field

12 Data types Magnetic Observatory Intermagnet network

13 Magnetic Observatory Data types Hartland in the UK ( Huancayo in Peru ( Boulder (

14 Magnetic Observatory Data types The number of data holdings at the World Data Center (Edinburgh) for various time resolutions. (Credit: BGS/NERC)

15 Geomagnetic repeat stations Data types Repeat stations positions (Positions of all repeat stations that have been occupied at least twice since 1975 and have submitted their data to the World Data Centers) (credit: Geomagnetic Observations and Models, eds. M. Mandea and M. Korte, 2011)

16 Data types Historical observations of the geomagnetic field Reconstruction of Cook s Endeavour (left) and extract from logbook of King George from 2nd July (right) (Jonkers et al., 2003)

17 Data types Historical observations of the geomagnetic field Geographical data distribution of declination observations made in (n =68,076) (Jonkers et al., 2003)

18 Data types Lava flows and archaeological artifacts: Thermal Remanent Magnetisation (TRM) a) Picture of lava flow. b) While the lava is still well above the Curie temperature, crystals start to form, but are non-magnetic. c) Below the Curie temperature but above the blocking temperature, certain minerals become magnetic, but their moments continually flip among the easy axes with a statistical preference for the applied magnetic field. As the lava cools down, the moments become fixed, preserving a thermal remanence. (Figure from Tauxe and Yamazaki,

19 Data types Lake/Marine/Ocean Sediments : Depositional Remanent Magnetisation (DRM) a) Schematic drawing of traditional view of the journey of magnetic particles from the water column to burial in a non-flocculating (freshwater) environment. Magnetic particles are black. b) View of depositional remanence in a flocculating (marine) environment. (Figure from Tauxe and Yamazaki, 2007)

20 Geometry of the geomagnetic field (credit: INGV)

21 Magnetic poles (credit:

22 Geomagnetic field at Earth's surface Figure 1.2 notes: (a) Radial component of the magnetic field at Earths' surface in µt (b) its rate of change in µt/yr for the year 2000.

23 Geomagnetic field at Earth's surface Figure 1.3 notes: (a) Scalar magnetic field at Earths' surface in µt and (c) its rate of change in nt/yr for the year (b) and (d) are the same with the dipole part of the field subtracted out.