Perspectives on Ionosphere-Thermosphere Science Using Swarm: The GOCE-CHAMP-GRACE-DMSP

Mini-Constellation

Jeffrey M. Forbes1, Eelco Doornbos2, Mark Conde3, Sean L. Bruinsma4, Gang Lu5, Daniel Ober6

University of Colorado1; Delft University of Technology2; University of Alaska3; Centre National d’Etudes Spatiales4; National Center for Atmospheric

Research5; Air Force Research Laboratory6

How does the magnetic field mediate the interaction between the neutral atmosphere and ionosphere?

What have we learned from recent missions?

What will Swarm contribute?1

Thermosphere and Ionosphere Densities

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3

CHAMP neutral densities, 2005

• The highly variable IT system is relevant to satellite orbit and reentry prediction, and to the operation of communications and navigation systems.

• External drivers of the IT are solar EUV flux, solar wind energy reprocessed by the magnetosphere, and meteorological disturbances originating in the lower atmosphere.

• Interactions between the thermosphere and ionosphere, mediated by Earth’s magnetic field, translate the above drivers into IT “space weather”.

• Swarm, combined with other key assets (see later slides), will enable measurement of the IT system response to various drivers.

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IT System

0 km

90 km

800 km

Pole Equator

Mass Transport

Wave Generatio

n

Planetary Waves

ConvectiveGenerationof GravityWaves & Tides

Turbulence

CO2

CH4

CO2 Cooling

Solar Heating

The Ionosphere-Thermosphere (IT) System

Wind Dynamo

BEEnergetic Particles

B

Polar/AuroralDynamics

E

MagnetosphericCoupling

Joule Heating

H2O

solar-driven tides

O3NOTopographicGenerationof GravityWaves

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Several significant IT achievements made possible by CHAMP and other missions (e.g., GRACE, CLUSTER, DMSP, ACE, TIMED, etc.):

• Statistical relationships developed between interplanetary magnetic field (IMF) configuration and polar region neutral densities, winds, and plasma drifts, with significant hemispheric asymmetries.

• Lower atmosphere variability drives significant IT variability through the vertical propagation of waves, both directly and indirectly through the dynamo generation of electric fields.

• High-speed solar wind streams emanating from coronal holes impose periodicities on the IT system at subharmonics of the solar rotation period (27, 13.5, 9, 6.7 days).

• Regional and local structures at low latitudes discovered that likely have their origins in plasma-neutral coupling.

• Statistical relationships developed between interplanetary magnetic field (IMF) configuration and polar region neutral densities, winds, and plasma drifts, with significant hemispheric asymmetries.

• Lower atmosphere variability drives significant IT variability through the vertical propagation of waves, both directly and indirectly through the dynamo generation of electric fields.

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Forster et al., 2011

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3

4

56

78

ClassicGeoeffectiveSolar Wind-

Magnetosphere CouplingIMF Bz < 0

magnetic merging

IMFBz < 0

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electric field

E-region Hall currentsF-region plasma drifts

Pedersen currents

field

-alig

ned

curr

ents

opposite in direction to electrons, or feet of field lines

Dayside

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recovery depends on NO cooling

Occasional opportunities to study relation between evolution of plasma drifts (DMSP) during geoeffective

coupling periods (Bz < 0) when CHAMP is co-planar with dawn/dusk DMSP

On Swarm, this will be possible all the time, due to the coincident

measurement of plasma drifts and neutral winds.

co-vary over long time scales but not short time scales

In addition, the neutral and plasma densities, which determine the time scale of the neutral wind

response, will also be measured

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CHAMP, DMSP and ACE Measurements Reveal Consequences of Cusp Reconnection (Bz >0, By large)

Maezawa (1976)

Cusp or sidelobe reconnection occurs when Bz > 0 and By >> 0 Significant energy enters dayside

thermosphere without enhancements in traditional magnetic indices [Knipp et

al., 2011; Li et al., 2011]

Forster et al., 2011Luhr et al., 2004

FACs

CHAMP density enhancement

FACs accompany this reconnection process.

Closure of the FACs results in Joule heating and density increasesFirst principles models reveal physical processes

[Deng et al., 2011; Crowley et al., 2010]

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CHAMP and ACE Measurements Relate Different IMF Configurations to Cusp Density Anomalies and Neutral

Wind Circulations

Statistical distribution of cusp density anomalies during 2005 [Rentz and

Lühr, 2008].

Note the strong hemispheric differences.

S. Hemis. N. Hemis.

Statistical distributions of neutral wind vorticity for By < 0 (left) and By >

0 (right) over S. polar region [Förster et al.,

2011]

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e-

e-

O+B

O2+, NO+

Vn

equipotentiallineGlobal electrostatic

field set up by dynamo action

F-Region

E-Region

The Ionospheric Dynamo

Tidal structures at 110 km: An upper atmosphere signature of wave-4 land-sea differences

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Swarm will also measure the electric fields globally

CHAMP electron densitiesJuly, 2004

Pedatella et al., 2008

CHAMP revealed the longitude structures of tidal dynamo-induced Sq currents, electrojet currents and ionospheric plasma densities, but not the electric fields

that tie all of these together

Alken & Maus

Pedatella et al., 2011

CHAMP Sq currents

Electrojet currents

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CHAMP & GRACE also revealed that the tides propagate to orbital altitudes

CHAMP,Häusler & Lühr

SABER & theory, Oberheide

DE3 Zonal winds over the equator, 400 kmLongitude structures of exosphere temperature & density tides attributable to troposphere forcing

DE3 DE2

CHAMP-DE3 @ 390 km

SABER extrapolated by theory 100 390 km

Propagation of tides into the thermosphere exhibit a solar cycle dependence

due to the way that molecular diffusion dissipates the tides

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Ground-based measurements capture high spatio-temporal variability

Valuable for both validation and scientific studies.

Ground-based measurements of winds at satellite altitudes available from a number of locations

Neutral Wind Measurements from the Ground and Space

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First-Principles Models Provide the “Glue” that Links Measurements Together

Apr 5, 2010

First-Principles models • Place the measurements in

perspective (note that the satellite measurements only provide the cross-track wind component)

• Provide the context to better understand plasma-neutral interactions

Ionospheric Connections Explorer (ICON): A low-latitude (±30o) mission schedule for launch in 2017.

ICON’s science objectives are to understand:

• the sources of strong ionospheric variability;

• the transfer of energy and momentum from our atmosphere into space; and

• how solar wind and magnetospheric effects modify the internally-driven atmosphere-space system.

ICON will measure:

Temperatures, Winds, Plasma drifts, Neutral composition

Michelson Interferometer

Ion Velocity Meter

EUV Imager

UV Imager16

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The Swarm+ ConstellationFirst-Principles & Assimilative Models

Iridium/AMPERE

ACE

Ground-based Observations

GOCE

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Swarm Attributes for IT Science

• Swarm A/B will separate from Swarm C (530 km) in altitude and local time (460 km

to 300 km after 4 years; > 3 hours after 18 months)

• Swarm electric and magnetic field measurements will enable Poynting Flux to be determined

• Coincident plasma drift, neutral wind, and neutral and plasma densities will be made.

• High inclination, so all latitudes are covered.

Swarm Shortcomings With Respect to IT Science

• No neutral and plasma composition measurements

• Restricted local time coverage

• No in-track wind measurements.

• No measurements of upward-propagating waves in the lower IT region (100-150 km)

IT Science Questions that Can be Addressed by the Swarm+ Constellation

• Swarm+ will enable more of a “system-level” perspective.• Swarm+ measurements will not fully define the IT system, but it will significantly

constrain the system. • Defining the system will involve assimilation of Swarm+ data into first principles

models to guide the solutions of these models.

How are energy and momentum transferred from the plasma to neutrals in the polar regions over various temporal scales?• How is this exchange controlled by the interplanetary magnetic field (IMF)?• What are the hemispheric differences imposed by Earth’s B-field?

How do high-latitude energy and momentum inputs influence middle and low latitudes?• How does the magnetic field mediate this transfer and the plasma neutral

interactions that are involved?

What aspects of IT variability in electric fields, currents, neutral winds, neutral and plasma densities are attributable to influences from the lower atmosphere?• How does the magnetic field mediate the transfer of momentum and energy

between the atmosphere and ionosphere?19