Lecture 19: Geomagnetic hazards

Question 1

what is magneto telluric sounding

Answer 1

• prospecting technique
• record for a few hours to a few days
• earth’s magnetic field - magnetometers
• telluric currents - electrodes
• estimate the electrical conductivity in the subsurface (regional scale)

Question 2

electromagnetic surveying

Answer 2

• instrument composed of coiled wire to artificially create a magnetic field (primary field)
• controlled experiment: the primary magnetic field includes currents in the subsurface ore bodies. these currents generate a secondary magnetic field which is recorded
• estimate the depth, shape and electrical conductivity of subsurface ore bodies
• metallic ore bodies are more conductive than the surrounding rocks

Question 3

geomagnetic hazards

Answer 3

• extreme variations of the earth’s magnetic field can have a significant impact of technological systems
  first observed on telegraph machines approximately 150 years ago

Question 4

earth’s internal geomagnetic field

Answer 4

• internal geomagnetic field due to movement of liquid iron in outer core
• earth’s rotation
• heat transfer by convection at the outer-inner core boundary
• out of south into north
• magnetic poles wander a little bit and every few hundred thousand years the magnetic poles flip

Question 5

earth’s external geomagnetic field

Answer 5

• disturbances affecting technological systems are caused by variations of the external geomagnetic field
• driven by solar activity
• only a few hours or days

Question 6

gusts of solar wind (two causes)

Answer 6

• caused by:
• coronal hole explosions: occur in small localized areas of the sun’s surface. violent explosions heat up material and shoot it in outer space
• coronal mass ejections: star scale events. charged particles and radiation are released from the sun’s corona in the vicinity of sunspots

Question 7

solar cycle

Answer 7

• 11 year cycle
• a higher number of sunsports is indivative of a more energetic sun

Question 8

magnetic storm

Answer 8

• temporary (few hours/days) large-scale perturbation of the external geomagnetic field due to strong gusts of solar wind
• most frequent: peak of solar cycle and declining phase of solar cycle

Question 9

earth’s magnetosphere

Answer 9

• region around the earth shielded from the solar wind by the internal geomagnetic field
• extends several 1000s km above earth’s surface, beyond the atmosphere
• solar wind compresses magnetosphere sunward

Question 10

interaction between the solar wind and the earth’s magnetosphere

Answer 10

• charged particles from the solar wind are guided by the magnetic field lines towards the poles
• excite atoms in the upper atmosphere
• charged particles from the solar wind create currents int he ionosphere. that causes variations in the external geomagnetic field and induces telluric currents

Question 11

impact of magnetic storms: bombardment by charged particles

Answer 11

• affecting satellites
• pressure from solar wind affects satellite orbit
• charged particles can interfere with circuitry
• charged particles can lead to violent discharge

Question 12

ionospheric disturbances

Answer 12

• problems affecting the global positioning system (GPS)
• GPS signal delayed between ground and satellite
  error in distance determination

Question 13

electromagnetic induction effects

Answer 13

• extreme variations in the external geomagnetic field induce telluric currents along electrically conducting networks
• telegraph
• power transmission lines
• pipelines
• coronal mass ejection
• space weather

Question 14

mitigation

Answer 14

• Ottawa geomagnetic laboratory has developed space weather forecasts specifically designed for utility companies
• sensitive equipment to be taken off line during magnetic storms