University of Colorado 1 ; Delft University of Technology 2 ; University of Alaska 3 ; Centre National d’Etudes Spatiales 4 ; National Center for Atmospheric Research 5 ; Air Force Research Laboratory 6 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 2

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. 3

IT System 0 km 90 km 800 km PoleEquator Mass Transport Wave Generation Planetary Waves Convective Generation of Gravity Waves & Tides Turbulence CO 2 CH 4 CO 2 Cooling Solar Heating The Ionosphere-Thermosphere The Ionosphere-Thermosphere (IT) System Wind Dynamo B E Energetic Particles B Polar/Auroral Dynamics E Magnetospheric Coupling Joule Heating H2O solar-driven tides O3 NO Topographic Generation of Gravity Waves 4

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. 5

Forster et al., Classic Geoeffective Solar Wind- Magnetosphere Coupling IMF B z < 0 magnetic merging IMF B z < 0 6

electric field E-region Hall currents F-region plasma drifts Pedersen currents field-aligned currents 7 opposite in direction to electrons, or feet of field lines

recovery depends on NO cooling 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 8

Maezawa (1976) Cusp or sidelobe reconnection occurs when B z > 0 and B y >> 0 Significant energy enters dayside thermosphere without enhancements in traditional magnetic indices [Knipp et al., 2011; Li et al., 2011] 9 Forster et al., 2011 Luhr et al., 2004 FACs CHAMP density enhancement FACs accompany this reconnection process. Closure of the FACs results in Joule heating and density increases First principles models reveal physical processes [Deng et al., 2011; Crowley et al., 2010]

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 (right) over S. polar region [Förster et al., 2011] 10

e-e- e-e- O+O+ B O 2 +, NO + VnVn equipotential line Global electrostatic field set up by dynamo action F-Region E-Region Tidal structures at 110 km: An upper atmosphere signature of wave-4 land-sea differences 11

Swarm will also measure the electric fields globally CHAMP electron densities July, 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 12

CHAMP & GRACE also revealed that the tides propagate to orbital altitudes CHAMP, Häusler & Lühr SABER & theory, Oberheide DE3 Zonal winds over the equator, 400 km Longitude structures of exosphere temperature & density tides attributable to troposphere forcing DE3 DE2 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 13

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 14

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 15

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 Imager 16

First-Principles & Assimilative Models Iridium/AMPERE ACE Ground-based Observations GOCE 17

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. 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 ( km) 18

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