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GEG 1220 Compass Navigation and Magnetic Declination

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Title: GEG 1220 Compass Navigation and Magnetic Declination


1
GEG 1220Compass Navigation and Magnetic
Declination
  • Dr. Walter Goedecke
  • Fall 2007

2
Compass NavigationTopics
  • Basic Compass
  • Geomagnetism and the Earths Dynamo
  • Earth-Sun Interactions
  • Aurora
  • Magnetic Declination True vs. Magnetic North

3
Compass NavigationBasic Compass
  • A compass, when level, has a floating, balanced
    magnetic needle that pivots in the Earths
    magnetic field.
  • This is also referred to as the geomagnetic
    field.
  • Source The Mountaineers Online

4
Compass Navigation Terrestrial Geomagnetism
  • The geomagnetic field can be approximated by a
    simple dipole magnet in the middle of the Earth
  • The magnets south end actually points to the
    North Pole, and the north end points to the South
    Pole.

5
Compass Navigation The Earths Dynamo
CIRES
6
Compass Navigation Magnetic Multipole Moments
  • The Earth actually has additional magnetic
    moments beyond a simple dipole - these are
  • Quadrapole moment
  • Octapole moment
  • 16-uple moment
  • Etc.
  • Although each successive moment is more complex,
    it is weaker than the previous one

CIRES
7
Compass Navigation The Source the Earths
Dynamo
  • The source of the geomagnetic field is a poorly
    understood self-sustaining dynamo, probably due
    to currents within the liquid core
  • All the other terrestrial planets within this
    solar system do not have a planetary magnetic
    field, although some may have in the distant past
  • Most of the gas giant planets have a powerful
    magnetic field surrounding them, as does the Sun

The Earths Structure http//www.lhs.sad49.k12.me.
us/ljhs/Website20Resources/earth's_structure.htm
8
Compass Navigation Sun - Earth Interaction
  • The geomagnetic field is pushed by the solar wind
    and interplanetary magnetic field, so solar
    storms can affect magnetic readings.
  • Solar-terrestrial diagram, showing Earths bow
    shock IMF, and magnetosphere. Source Space
    Environment Center, NOAA, http//www.sec.noaa.gov/
    info/SolarEffects.html

9
OVERVIEW OF SPACE ENVIRONMENT - Aurora
  • Aurora is due to the bombardment of solar wind
    charged particles along magnetic field lines into
    the polar geomagnetic footprint.
  • These particles then can interact with the upper
    atmosphere where the magnetic field enters the
    Earth, in the polar regions.
  • These charged particles strike the molecules and
    atoms of the thin, high atmosphere, causing
    energized atomic states.
  • When the atoms then relax to its lower ground
    state, energy is released as a photon, or light.

Source Exploratorium, San Francisco, CA,
http//www.exploratorium.edu/learning_studio/auror
as/difcolors.html
10
OVERVIEW OF SPACE ENVIRONMENTAurora
Aurora highlights conjunction planets from photo
by Keith Cooley in Athens Alabama on April 6,
2000, at 830 p.m. CDT. Source Space Science
News, NASA, http//www.spacescience.com/headlines/
y2000/ast25apr_1m.htm
11
OVERVIEW OF SPACE ENVIRONMENTCoronal Mass
Ejection Effect - Aurora
Juergen Rendtel snapped this photo from Marquardt
(near Potsdam), Germany, from April CME
event. Source Space Science News, NASA,
http//www.spacescience.com/headlines/y2000/ast25a
pr_1m.htm
12
  • Five magnetometer stations in the Western US

13
Magnetic Declination
  • Since the magnetic poles are not coincident with
    the true poles, compass readings need correction.
  • This correction is the magnetic declination.
  • The magnetic north appears east of true north in
    the western US, and west of true north in the
    eastern US.
  • The dividing line is approximately the
    Mississippi River.
  • The magnetic poles also drift with respect to
    time.
  • The north magnetic pole is drifting
    north-northwest.

14
Compass NavigationReferences
  • The Mountaineers Onling, http//www.mountaineers.o
    rg/navigation/
  • National Geophysics Data Center, NOAA,
    http//www.ngdc.noaa.gov/seg/geomag/icons/us_d_con
    tour.jpg
  • Shawhan, S.D., Solar System Plasma Physics III
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