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Icebase: A proposed suborbital Icebase: A proposed suborbital survey to map geothermal heat survey to map geothermal heat
flux under an ice sheetflux under an ice sheet
Michael Purucker
SGT at Planetary Geodynamics Lab, Goddard Space Flight Center/NASA, Greenbelt, USA
Team members include: Connerney, Blakely, Bracken, Nowicki, Le, Sabaka, Bonalsky, Kuang, Ravat, Ritz, Bouligand, Vaughan, Gaina, McEnroe, Tyler, Nelson + Danish team
Taipei: 19 Nov 2012
OutlineOutline Motivation: Magnetic fields as ‘tracers’ of processes active in the
lithosphere of a planet or moon. Rheology, tectonics, subduction, igneous processes and impact (Earth, Moon, Mars, Mercury)
Primary science goal: map geothermal heat flux under an ice sheet.
Relevance: response of ice sheet to climate forcing, search for oldest ice.
Isolating the geothermal heat flux:– Unmodeled external fields– Induced vs remanent magnetism– Varying magnetic susceptibility and thickness– Magnetizations below Moho– Heat production within the crust, mantle, thermal conductivity
Designing the survey and instrument suite. Why Global Hawk? What else could the survey accomplish?
Focus and PhysicsFocus and Physics
Taipei: 19 Nov 2012
This talk will examine Earth’s magnetic field complex, concentrating on fields of internal origin.
NASA
The Earth: a satellite view of its magnetic lithosphereThe Earth: a satellite view of its magnetic lithosphere
Taipei: 19 Nov 2012
Maus et al., 2010
Integrated satellite and ground views of Integrated satellite and ground views of Earth’s magnetic lithosphereEarth’s magnetic lithosphere
Taipei: 19 Nov 2012
WDMAM
Why sub-orbital?Why sub-orbital?
Sub-orbital missions at altitudes comparable to crustal thickness ‘image’ the upper and lower crust with comparable sensitivity. In contrast, aeromagnetic surveys are overwhelmingly dominated by the upper crust, and satellite surveys are unable to distinguish between the upper and lower crust.
Sub-orbital missions at higher, mesospheric (80-90 km) altitudes, ‘image’ a poorly understood region important for an understanding of space climate, and it’s impact on atmospheric climate.
Taipei: 19 Nov 2012
Survey and Instrument suiteSurvey and Instrument suite
12 km flight line separations, 200 km tie lines, base stations, compensation maneuvers
Vector & total field magnetometers, dual frequency GPS, star camera
Team: GSFC, USGS, DTU, Grenoble, Trondheim
Taipei: 19 Nov 2012
Isolating the geothermal heat fluxIsolating the geothermal heat flux Starting point: 3SMAC starting thermal and compositional
model.
3SMAC modified in an iterative fashion with magnetic observations until the magnetic field predicted by the model matches the observed magnetic field to some Delta.
Thermal model: 1-D, heat conducttion, steady state, constant thermal conductivity, simple model for radioactive heat production in the crust.
Input: CHAMP high degree crustal field solution (Deg 120) Validation: Western North America, India, Australia, High
Antarctic heat flux corresponds to active volcanism Other processes in action:
– Unmodeled external fields– Induced vs remanent magnetism– Varying magnetic susceptibility and thickness– Magnetizations below Moho– Heat production within the crust, mantle, thermal conductivity
Taipei: 19 Nov 2012
What else could the survey What else could the survey accomplish-1?accomplish-1?
Mapping of time variable magnetic fields associated with oceanic, core, crustal, ionospheric, and magnetospheric sources through the use of exact repeat surveys under Swarm.
Taipei: 19 Nov 2012
Motional InductionMotional Induction
Taipei: 19 Nov 2012
Magnetic field range produced by ocean flow estimated from monthly averages (Jan-Dec, 2001).
Serpent, 2009
What else could the survey What else could the survey accomplish-2?accomplish-2?
In areas where heat flux can not be isolated, the magnetic maps could be used for– Tectonics– Igneous processes– Identification of impacts– Resource assessment
Taipei: 19 Nov 2012
Taipei: 19 Nov 2012
Earth: igneous processesEarth: igneous processes
Western Australia
Purucker and Whaler, 2006
Taipei: 19 Nov 2012
Earth: impactEarth: impact
Purucker and Whaler, 2006
Spray et al. 2004
2013 IAGA MtgOn outer ring
SummarySummary
A knowledge of magnetic fields at suborbital (20 km) altitudes would help answer questions about the lithosphere, and specifically heat flux under ice sheets. It is also expected to add to our knowledge of the global hydrologic cycle, and the processes producing time-variable magnetic fields of core, crustal, ionospheric, and magnetospheric sources.
Taipei: 19 Nov 2012
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