GE SPACE

Geomagnetic Earth Observation

from SPAce

Fit to NERC’s Science Priorities

• Understanding the complex interactions and feedbacks within the Earth system over a range of space and time scales

Fit to NERC’s Science Priorities

• Understanding the complex interactions and feedbacks within the Earth system over a range of space and time scales

• climate change– magnetic field sensitive to some atmospheric

parameters, a measure of ocean circulation, and measures effect of solar cycle

Interaction of Magnetic Field with Atmosphere

Air drag at 450 km altitude as measured by CHAMP during geomagnetically disturbed and quiet periods

Crossings of the northern (southern) polar region are indicated by blue (red) line segments, accordingly

disturbed quiet

Measuring Oceanic Circulation

Elevation and transport due to M2 tide ... ... and magnetic field at 400 km altitude

Br [nT]h [m]

Measurement of oceanic transport (depth integrated velocity) ?Electric field: E = v x B0

Sheet current density: J = hE

B0 = 50000 nTv = 0.1 m/s = 3.2 Smh = 4 km

E = 5 V/mJ = 70 mA/mB = 14 nT (at surface)

results in

Fit to NERC’s Science Priorities• Understanding the complex interactions and

feedbacks within the Earth system over a range of space and time scales

• climate change– magnetic field sensitive to some atmospheric parameters, a

measure of ocean circulation, and measures effect of solar cycle

• sustainable economies– energy (ensuring security of electricity supply)– hazard mitigation (magnetic storms, radiation effects)

UK magnetic observatories

Measured GIC

Arrows denote measured ionospheric field variations during the July 2000 magnetic storm at various observatories and survey points

Circles denote size and polarity of measured GIC (red = positive current flow to ground)

Application of External Field Studies: Using Models of Surface Electric Fields in the UK for Study of GIC

Model GIC

Arrow head denotes direction of a simple model plane wave ionospheric field variation

(E-field scale = 1.6 V/km; max GIC = 40 A)

South Atlantic Anomaly radiation hazard

Sites of Topex anomalies 1992-98, at approximately 1000km.Red star is site of MODIS failure.

NERC’s other strategic priorities

• Skilled people - attracting mathematicians and physicists

NERC’s other strategic priorities

• Skilled people - attracting mathematicians and physicists

• Leadership - world class researchers have ensured access to satellite data without a UK financial contribution to the missions

NERC’s other strategic priorities• Skilled people - attracting mathematicians and

physicists

• Leadership - world class researchers have ensured access to satellite data without a UK financial contribution to the missions

• Using knowledge – directional drilling for hydrocarbons

– exploring for and exploiting natural resources

– predicting geomagnetically induced currents in power systems

Major Questions To Address:

• How to unscramble the combined source effects?• How does the dynamo work?• Can we predict changes in the Earth’s magnetic

field?• What is the core’s contribution to the Earth’s angular

momentum budget?• What is the 3D conductivity structure of the mantle?• What is the nature of lithospheric magnetization?• What is the signal associated with flow in the

oceans?

CoreMagnetic

FieldCoreFluid Flow

SpaceEnvironment

Crust &Lithosphere

No other measurable physical parameter can be used tosense so many diverse regions of the Earth

Geomagnetic DataEskdalemuir observatory

Ørsted

How does the geodynamo work?

The combination of progress in numerical modeling of the geodynamo and new satellite observations promises to greatly advance our understanding of the origin of the Earth’s magnetic field.

•What is the dominant mechanism of angular momentum exchange in the solid Earth-core-inner core system (at each timescale)?

•How do core-mantle interactions influence the geodynamo?

•What accounts for the time-averaged field morphology?

•What causes abrupt changes in the field (jerks)?

•Can we forecast the magnetic field using techniques of data assimilation?

•by nearly 10%. This is ten times faster than if the dynamo were switched off.

• The current decay rate is characteristic of magnetic reversals.

• Geographically, the dipole decay is largely due to changesin the field beneath the south Atlantic Ocean, connected to the growthof the South Atlantic Anomaly.

• Is the Earth’s magnetic field entering a reversal?

Over the last 150 years, the Earth’s axial dipole component has decayed

Can we explain the decay of the Earth’s dipole?

The map shows the contribution to changes in the dipole component. The map is dominated by changes beneath the south Atlantic Ocean.

How Will Changes in Earth’s Magnetic Field AffectSatellite Operations and Communications?

• In 2000, the field is about 35%weaker in this region than wouldbe expected.

• This weakness in the field hasserious implications for low-Earthorbit satellite operations since itimpacts the radiation dosage atthese altitudes.

• How much longer will the SouthAtlantic Magnetic Anomalycontinue to grow? How deep will itbecome?

• Long-term satellite observationsallow us to model future evolutionof this anomaly.

-15000nT

1900

1980

2000

+15000nT

Field in 1990 at core surface

South Atlantic reverse flux patch is responsible forradiation doses experienced by satellites

“Jerks”: Rapid changes in secular variation:Proxies for core fluid velocity

Niemegk observatory, Germany.

What is the contribution of the core to the Earth’s angular momentum balance?

•On inter-annual and decadal timescales the core, solid Earth, oceans and atmosphere are coupled.

•Length-of-day observations give the rotation rate of the solid Earth

- dataset extends back ~150 years

•Geomagnetic observations give the rotation rate of the core

- dataset extends back ~300 years

• Meteorological observations give the mean rotation rate of the atmosphere

-dataset extends back a few decades

•Can we estimate the mean rotation of atmosphere before direct observations from core and mantle rotation?

•Can we detect short-term variations in core circulation on inter-annual timescales?

Decadal angular momentum exchanges between core and mantle

•Electrical conductivity varies by orders of magnitude within the Earth and provides a source of information complementary to that obtained from seismology.

•Conductivity studies have relied largely on ground based magnetic observatories with poor spatial distribution.

•Satellite-based magnetic induction promises to open a new era in mapping the electrical structure of the crust and mantle.

The Electrical Structure of the Crust and Mantle

Induced magnetic field, expressed as a fraction of the inducing field as found by analysing Magsat data

There is a strong correlation between smaller induced fields (blue) and equatorial landmasses, implying lower conductivity under the

continents than in the oceans.

The Lithospheric Magnetic Field

Magnetic fields of lithospheric origin at

satellite altitude (400km)

Lithospheric magnetization addresses:

•Origin of magnetization of the upper continental crust

•Lithospheric tectonics and hazards

•Influence of large impacts on Earth’s early tectonic development

•Regional and global distribution of energy and mineral resources

CHAMP

CHAMP & South Atlantic

CHAMP TMI

CHAMP Vert. Der.

Trans BrasilianLineament

Aeromagnetic Data

CHAMP

CHAMP & Brazil

CHAMP TMI

Cret. Alkaline Volcanics REDCret. Kimberlites BLUE

Trans BrasilianLineament

Analytic Signal (Suscep.)

Craton

Craton

Trans BrasilianLineament Kimberlite

Trend

Core Field and Secular VariationUnmodelled large-scale external

(magnetospheric) sources are at present the major limitation in field modelling

This improvement was partly possible because data from Ørsted-2 were used to determine (and to correct for) magnetospheric contributions

Power spectrum shows improvement from Magsat to CHAMP/Ørsted/Ørsted-2 field modelsSecular variation is now resolvable up to n=12; higher terms still masked by contributions from external sources

mean SV 1980-2000

External field signal remains after selection on basis of LT and indices

Important Magnetospheric Current Systems

Symmetric ring current, usually parameterised by Dst index or even the ‘pressure corrected’ Dst (i.e. removing CF contribution)

Partial ring current, which strengthens on dusk side with increasing magnetospheric activity and is connected to Region 2 system

Cross-tail current, which moves Earthward with increasing magnetospheric activity

Region 1 and 2 Birkeland (field aligned) currents, Region 1 system closing on magnetopause

Chapman-Ferraro (magnetopause) currents, shielding the internal (dipole) field

Not modelled or less well understood: polar latitude currents - the ‘Region 0’ and ‘North Bz’ (NBZ) systems

Courtesy of Igor Alexeev (MSU)

Sun

An Example of an Existing External Field

Model:

The Tsyganenko Model (2001 Version)

Mean External Field at Ørsted Satellite Orbit (1999-2000) Under Quiet External Field

Conditions (e.g. Kp<1+)

Current Main Field Modelling Methodologies Typically Only

Represent the Symmetric Ring Current (in Yellow) from

Night-side Measurements

Averaged External Field in 1 Degree Bins; Averaged Over Dipole Longitude; BGS Main

Field Model (D&O 13) Subtracted

Comparison of Tsyganenko Model with Ørsted Data

Shown is mean external field in 1 degree colatitude bins

Model appears best at low to mid latitudes.

Poorer model, compared with real data, at high latitudes

Low latitude field is similar to the P1

0 potential often assumed in main field modelling

Fine scale detail, especially at high latitudes, needs further study/modelling

Fit to q20 with cos(local time) cos(time of year)

Summary

• Geomagnetism can play a significant role in answering fundamental questions about the core, mantle, oceans, lithosphere and the near-Earth environment

• Requires interdisciplinary collaboration (space physics, geodesy, oceanography, numerical simulation)

• GEOSPACE can play a leading role; members are sizable and high-profile part of international community

• Technology and missions for collecting new datasets are in place